672 Journal of Leukocyte Biology Volume 56, December 1994
Neutrophils, host defense, and inflammation: a double-edged
swordJohn A. SmithDivision of Biochemistry & Molecular Biology, School of Life Sciences, Faculty of Science, Australian National University,
Canberra, Australia
Abstract: Neutrophils play important roles in host
defense against all classes of infectious agents but, para-
doxically, they are also involved in the pathology of van-
ous inflammatory conditions. Their microbicidal armory
consists of oxidative and nonoxidative processes that are
activated simultaneously upon phagocytosis. Althoughdestruction of infectious agents occurs intracellulanly,
release of cytotoxic molecules into the extracellulan milieu
can damage body tissues. Neutrophils are heterogeneous.
Subpopulations exist in various stages from dormant toprimed to fully activated. The activities of neutrophils
are regulated locally in microenvironments and systemi-
cally by a plethora of mediators including cytokines,
“classical” neuroendocrine hormones, and bioactive
lipids. The net response depends on a complex balance of
stimulatory and inhibitory pathways that are regulated
by these mediators. Although some effector and regula-
tory pathways are vital, considerable redundancy is alsoevident. Identification of the essential mediators and the
unraveling of any interactions may be the keys to under-standing the neutrophil paradox and developing then-
apeutic strategies that optimize microbial killing and
minimize host tissue damage. Finally, reports that neu-trophils can act as drug delivery vectors and that their
function is influenced by stress and other lifestyle factors
suggest that new homeostatic functions for these cells,
outside their traditional roles in host defense and inflam-mation, remain to be identified: some are speculated onhere.J. Leukoc. Biol. 56: 672-686; 1994.
Key Words: cytokines free radicals hormones . infection. immunoregulation . inflammation . phagocytes
INTRODUCTION
The human immune system consists of a complex network
of interacting cells and humoral factors. The intricate coun-
terregulation and apparent redundancies ofthe immune sys-
tern also apply to the functions of neutnophils, which are also
known as polymorphonuclear leukocytes [1]. Because neu-
trophils are abundant in the circulation, they are readily ac-
cessible to experimental investigation. Indeed, the cytokine
revolution, the emergence of neuroimmunoendocrinology,
and the discovery that phagocytes produce reactive nitrogen
species (RNS) show that although our understanding of neu-
trophil function has increased substantially, we still have a
long way to go. One paradoxical aspect of leukocyte biology
is that while neutrophils are essential for host defense, they
are also involved in the pathology of various inflammatory
conditions. The aim of this brief review is to examine this
neutrophil paradox. Where possible, human studies are exa-
mined. Emphasis is placed on analyzing the microbicidal ar-
mory of these cells and the mechanisms that counterregulate
various neutnophil functions and can potentially contribute
to dysnegulation. The influence of stress and other lifestyle
factors is also mentioned. The review concludes with some
speculation on novel homeostatic functions for neutrophils,
outside their traditional roles in host defense and inflamma-
tion, and suggestions for future work.Neutnophils represent 50 to 60% of the total circulating
leukocytes and constitute the “first line ofdefense” against in-
fectious agents or “nonself” substances that penetrate the
body’s physical barriers. Once an inflammatory response is
initiated, neutrophils are the first cells to be recruited to sites
of infection or injury [2]. Their targets include bacteria,
fungi, protozoa, viruses, virally infected cells, and tumor
cells [3]. Evasion of neutnophil defenses may provide a “win-
dow of opportunity” for local infections to be established un-
less the infectious agent is rendered harmless by interaction
with memory components such as neutralizing antibodies
(e.g., immunoglobulin A or G) already present.
Neutnophil microbicidal processes consist ofthe formation
of a combination of reactive oxygen (and, possibly, nitrogen)
species and various hydrolytic enzymes and antimicrobial
polypeptides. This broad-spectrum arsenal can be
influenced-both positively and negatively-by a wide van-
ety of mediators, which include cytokines, neuroendocrine
factors, and bioactive lipids. Subpopulations of neutrophils
have been identified by various criteria [4]. These cells exist
not only in dormant (nesting) or activated states but also invarious intermediate stages. For example, priming is a
mechanism whereby dormant neutrophils acquire a state of
preactivation that enables a more powerful response to be
generated once microbicidal activity is initiated (activated).
Neutrophils also interact reciprocally with other cells (e.g., T
cells, endothelial cells, and platelets) through either direct
cell-to-cell contact or humoral mediators; they even cooper-ate in the synthesis of eicosaniods [5, 6]. Although neu-
trophils are thought, classically, to be effector cells, they also
synthesize and secrete humoral mediators such as cytokines
that may play a role in regulating the afferent limb of im-
mune or inflammatory responses [7�.
Abbreviations: AIDS, acquired immunodeficiency syndrome; G-CSF,
granulocyte colony-stimulating factor; GM-CSF, granulocyte-macrophage
colony-stimulating factor; HIV, human immunodeficiency virus; H202,
hydrogen peroxide; HOd, hypochlorous acid; IL, interleukin; MPO, my-
eloperoxidase; NO, nitric oxide; PAF, platelet-activating factor; RNS, reac-
tive nitrogen species; ROS, reactive oxygen species; SERPIN, serine pro-
tease inhibitor; SOD, superoxide dismutase; TNF, tumor necrosis factor.
Reprint requests: John A. Smith, National Quality of Life Foundation,
Department of Physiology and Applied Nutrition, Australian Institute of
Sport, P0 Box 176, Belconnen, ACT, 2616, Australia.
Received July 27, 1994; accepted July 27, 1994.
Smith Neutrophils, host defense, and inflammation 673
BIOLOGY OF NEUTROPHILS
Neutrophils are terminally differentiated cells rich in
cytoplasmic granules and contain a lobulated chromatin-
dense nucleus with no nucleolus. Four types of cytosolic
granules have been characterized; these granules contain
various receptors, enzyme components, and antimicrobial
proteins [8]. Neutrophils mature in the bone marrow before
being released into the circulation, where they spend only 4
to 10 h before marginating and entering tissue pools, where
they survive for 1 to 2 days. Cells of the circulating and mar-
ginated pools can exchange with each other, but little is
known about the size or fate of the individual tissue pools
[9]. Senescent neutrophils are thought to undergo apoptosis
( programmed cell death) prior to removal by macrophages
[10]. This stops disintegration in vivo, which would other-
wise expel their cytotoxic contents into the extracellular
milieu; this process may also play a role in terminating
inflammatory responses [10].
Neutrophils are produced in human bone marrow at the
rate of 10” cells per day [11]. This is controlled by two
colony-stimulating factors (CSFs) [i.e., granulocyte (G-CSF)
and granulocyte-macrophage (GM-CSF)] that direct the
production and differentiation of bone marrow progenitorcells. The rate of neutrophil differentiation can increase as
much as 10-fold during states of stress and infection [11].
CSFs also amplify the activities of various neutrophil func-
tions in vitro [12]. It is unclear why neutrophils are turned
over so rapidly in healthy subjects, but it may be related to
their role in immunosurveillance and/or nonimmunological
roles in maintaining homeostasis.
During the inflammatory response, chemotactic factors
generated by infectious agents themselves, as well as those
released as a result of their initial contact with phagocytes
and other components of the immune system, signal the
recruitment of additional neutrophils to sites of infectionand/or injury. Under normal conditions, neutrophils roll
along microvascular walls via low-affinity interactions of
selectins with specific endothelial carbohydrate ligands. Acti-vation of neutrophil /32-integnins and subsequent high-
affinity binding to intracellular adhesion molecules on the
surfaces ofactivated endothelial cells in postcapillary venules
is the first step in transmigration to sites of infection [13).
Under the influence of a chemotactic gradient, generated lo-
cally and by diffusion of chemoattractants from the infection
site, neutrophils penetrate the endothelial layer and migrate
through connective tissue to sites of infection (diapedesis),
where they finally congregate and adhere to extracellular
matrix components such as laminin and fibronectin [13, 14].
A wide variety of adhesion molecules have been character-
ized on the surface of phagocytic cells [13].
NEUTROPHILS AND HOST DEFENSE
Humans are exposed to thousands of microorganisms and
harbor many potential pathogens on the skin and mucosal
surfaces, but healthy people seldom develop serious infec-
tions. Neutrophils are essential for host defense. These cells
form part of the natural (nonspecific) immune system. Their
major role is to phagocytose and destroy infectious agents
but they also limit the growth of some microbes, thereby
buying time for adaptive (specific) immunological responses
to develop [15]. With many microbes, however, neutrophil
defenses are ineffective in the absence of opsonins and vari-
ous agents that amplify the cytotoxic response. This empha-
sizes the cooperative interaction between natural and adap-tive components of the immune system.
During phagocytosis of most microorganisms, cytosolic
granules fuse with the invaginating plasma membrane to
form a phagolysosome into which they release their contents,
thereby creating a highly toxic microenvironment (Fig. 1).
This normally prevents release of the components of theirmicrobicidal armoury into the extracellular milieu.
However, some targets may be too large to be fully phagocy-
tosed or they avoid engulfment, resulting in “frustrated”
phagocytosis in which no phagosome is formed. These may
be killed extracellularly [16]. However, tissue damage occurs
when neutrophil microbicidal products are released extracel-lulanly to such an extent that host defenses (antioxidant and
antiprotease screens) in the immediate vicinity are over-
whelmed [17].
The importance of neutrophils in host defense is illus-
trated by deficiencies in number and/or function. Neutrope-
nia induced by chemotherapy or rare inherited defects in
neutrophil function such as deficiencies in cytotoxic oxida-
tive metabolism (e.g. , chronic granulomatous disease),
specific granules, and adhesion molecules are substantial risk
factors for developing potentially fatal bacterial and fungal
infections [18]. Gram-negative bacilli and Staphylococcus infec-
tions are the most common bacterial infections in neutro-
penic people [19]. Neutrophils also determine susceptibilityto opportunistic fungi and pathogenesis may be related to
their resistance to the neutrophil’s microbicidal armory [20].
Commensal microorganisms such as Candida albicans become
pathogenic in people with neutrophil dysfunction. Bacterial
virulence can be influenced by the ability of bacteria to resist
phagocytosis (e.g., mucoid cell wall, formation ofcolonies) or
secrete agents that inhibit neutrophil cytotoxicity [21]. Other
immune processes may counter this, but chronic infections
do occur (e.g., Pseudomonas aeruginosa in people with cystic
fibrosis [21]). However, neutrophil killing capacity against
some bacterial, protozoan, and fungal pathogens can be
boosted substantially by cytokines and other humoral media-tons [22-24). This is discussed in greater detail under regula-
tion of neutrophil function. This type of therapy is the sub-
ject of ongoing clinical trials.
Although the importance of neutrophils in fighting bac-
tenial and fungal infections is well recognized, only limited
attention has been paid to their involvement in viral infec-
lions. This is surprising considering that neutrophils are
found in abundance in virally induced lesions [3, 25]. Neu-
trophils appear to be the primary cells responsible for protec-
tion against the influenza virus during the initial stage of in-
fection in mice [26], and they appear to play an important
role in diminishing the severity of vaccinia and herpes infec-tions [27]. Neutrophils bind to opsonized viruses and virally
infected cells via antibody (Fc) and complement (C3b) recep-
tors [3]. The rate of vinion uptake is increased following
cytokine-induced priming [25]. Viruses such as influenza
can be inactivated by neutrophils through damage to viral
proteins (e.g., hemagglutinin and neuraminidase) mediated
by the myeloperoxidase (MPO) released during degranula-
tion [28]. In contrast to these acute diseases, chronic
influenza infections can diminish or exhaust the microbicidal
potency of neutrophils [29). The systemic depression of neu-
trophil activity could lead to secondary bacterial infections
but the presence of priming agents such as cytokines (actingeither locally or systemically) may prevent this [30].
The rapid changes that occur in the antigenic deter-
minants of some viruses such as influenza suggest that
nonspecific defenses (e.g., neutrophils and natural killer
674 Journal of Leukocyte Biology Volume 56, December 1994
NEUTROPHIL
1 MICROBE
PHAGOCYTOSIS
KILLING
Fig. 1. l’hagocvtosis and bacterial killing. This diagram shows that binding of an opsonized microbe to the neutrophil membrane initiates the phagocytic
� lnvagination of the portion of the membrane containing the microbe leads to the formation of the phagosome. Fusion and release of granule con-tents into the phagosome create a highly microbicidal environment (phagolysosome) where killing and degradation takes place via a combination of oxida-
live ansi flOflOXi(lat se processes. See text for full details.
cells) may, out of necessity, play an essential role in combat-
ing these inkctions [29]. The ability ofneutrophils to destroy
human immunodeficiency virus (HIV) [31] may explain why
many HIV-inf#{232}cted people do not develop symptoms of ac-
quired immunodeficiency syndrome (AIDS) lbr many years.
Compared to healthy controls, neutrophil phagocytic and
oxidative burst activities are higher in people with stage 1
(asymptomatic) HIV infection 1321. Suppressed neutrophil
functions are Ibund in patients with AIDS or AIDS-related
complications [33]. Interferon--)’ �34] or GM-CSF/G-CSF
[35] treatment primes the antibody-dependent cytotoxicity
of neutrophils against HIV-infccted lymphocytes in vitro.
NEUTROPHILS AND HOST TISSUE DAMAGE
Although neutrophils arc essential to host defense, they have
also been implicated in the pathology of many chronic
inflammatory conditions 1171 and ischemia-reperfusion in-
jury [361. Hydrolytic enzymes of’ neutrophil origin and ox-idatively inactivated protease inhibitors can be detected in
fluids isolated from inflammatory sites [17]. Under normal
conditions, neutrophils can migrate to sites of’ infection
without damaging host tissues. Some neutrophil secretory
processes are activated during this process (e.g. , to enable the
expression of adherence molecules and to activate signaling
responses to chemoattractants) [8]. However, the same secre-tory responses are also connected with the activation of
microbicidal activity.Host tissue damage may occur through several indepen-
dent mechanisms. These include premature activation dur-
ing migration, extracellular release of microbicidal products
during the killing of some microbes, removal of infected or
damaged host cells and debris as a first step in tissue
remodeling, or failure to terminate acute inflammatory
responses. Ischemia-reperfusion injury is associated with an
influx of neutrophils into the affected tissue and subsequent
activation; this may be triggered by substances released fromdamaged host cells or as a consequence of superoxide gener-
at ion through xanthine oxidase [36, 37]. Superoxide also sig-
nals recruitment of additional neutrophils to the affected site
and ischemia may be sustained by plugging of capillaries
with aggregates of activated neutrophils [36, 37].
Neutrophils have been implicated in the pathology of
many diseases. Chronic Pseudomonas infection in the lung
leads to the destruction of protease inhibitors through oxida-
tive inactivation; the large release of neutrophil proteases(activated by bacterial phenazine pigments) destroys lung
Smith Neutrophils, host defense, and inflammation 675
tissue [38]. Activation of neutrophils by immune complexes
in synovial fluid contributes to the pathology of rheumatoid
arthritis [39]. Chronic activation of neutrophils may also in-
itiate tumor development because some reactive oxygen spe-
cies (ROS) generated by neutrophils damage DNA in vitro[40] and proteases promote tumor cell migration [41]. Chlo-
rinated oxidants, in particular, have been shown to cause tis-
sue damage [17]. Oxidants of neutrophil origin have also
been shown to cause red blood cell damage and destruction
in vivo [42] and to oxidize low-density lipoproteins in vitro;
uptake of these damaged lipoproteins by macrophages isthought to initiate atherosclerosis [43].
A good example ofthe neutrophil paradox is found in peo-ple with the adult respiratory distress syndrome. Neutrophils
have been implicated in the pathology of this condition be-
cause of the large influx of these cells into the lung and the
associated tissue damage caused by oxidants and hydrolyticenzymes released from activated neutrophils. The impair-
ment of neutrophil microbicidal activity that occurs as this
condition worsens may be a protective response on the part
of the host, which is induced locally by inflammatory
products [44]. This “down-regulation” of neutrophil function
may explain why many of these patients eventually die fromoverwhelming pulmonary infections [44]. The acute phase of
thermal injury is also associated with neutrophil activation,
and this is followed by a general impairment in various neu-
trophil functions [45].
NEUTROPHIL SUBPOPULATIONS
Peripheral blood neutrophils have been shown by many
criteria to be heterogeneous. The majority of these so-called
subpopulations have been identified on the basis of cell sur-
face markers, but there are reported examples of functional
heterogeneity within the neutrophil population [4]. The
physiological significance of neutrophil heterogeneity is not
understood, but exercise, infection, and stress alter the distri-
butions of subpopulations in the circulation. Under normal
conditions, blood may contain a mixture of normal, primed,
activated, and spent neutrophils. In fact, not all neutrophilsare phagocytically and oxidatively active. Single-cell assess-
ment of chemiluminescence in neutrophils isolated from
healthy human subjects showed that although 80%
responded to phorbol myristate acetate, an activator of pro-
tein kinase C, only 30% were activated by the particulate
stimulus opsonized zymosan [46]. GM-CSF treatment invitro also increases the percentage of neutrophils responsive
to stimulation with chemotactic N-formylated peptides [47].
A subpopulation of neutrophils with an enhanced oxidative
burst has been detected in the blood of people with an acute
bacterial infection [48] and patients with the adult respira-
tory distress syndrome [49]. Our recent work showed that
moderate exercise increased the percentage of circulating
neutrophils in men that were highly responsive to phorbol
myristate acetate stimulation in vitro U.A. Smith et al., un-
published data). Neutrophils isolated from patients with
blunt trauma show reduced binding of the 31D8 antibody,
which correlates with the increased susceptibility of these
people to infection [50]. These “dull 31D8” neutrophils that
dilute out the circulating population are normally located in
the bone marrow and are probably immature and function-
ally inactive [51]. In patients suffering from severe burns, a
strong correlation has been established between the onset of
bacteremic infection and reductions in the proportion andabsolute numbers of neutrophils positive for antibody and
complement receptors [52].
NEUTROPHIL MICROBICIDAL MECHANISMS
Neutrophil microbicidal mechanisms consist of a combina-
tion of oxidative and enzymatic (oxygen-independent)
processes that appear to be activated simultaneously upon
initiation of phagocytosis (Fig. 1). Phagocytosis is triggered
upon the binding of opsonized microorganisms through op-
sonin receptors (for complement fragments and antibodies)
or through nonspecific glycoslyated receptors that recognize
certain lectins on target microorganisms. Two microbicidal
processes are activated concomitantly with phagocytosis: (1)
the oxidative burst, so called because of the 50- to 100-fold
increase in 02 consumption, which results in the production
of cytotoxic reactive oxygen species (ROS) and, possibly,
through a different mechanism, reactive nitrogen species
(RNS), and (2) degranulation, which corresponds to the
release of contents of azurophilic (primary) and specific
(secondary) granules into the phagosome to form a
phagolysosome. These processes involve rearrangement of
contractile proteins, triggered by Ca2�, which leads to inter-
nalization of the portion of plasma membrane that contains
the receptor-target complex [53]. The following discussion
also illustrates the apparent redundancy of the neutrophil
microbicidal arsenal.
Oxidative mechanisms
Reactive oxygen species
The oxidative or respiratory burst in neutrophils is triggered
upon phagocytosis or when the pathway is activated by an
appropriate synthetic stimulus in vitro. The oxidative burst
results in the sequential production of a variety of microbio-
static and microbicidal ROS (Fig. 1). Superoxide (02) is
formed, initially, by the reduction of molecular oxygen by
single electrons that originate from NADPH generated via
the oxidative segment of the pentose phosphate pathway.
This process is catalyzed by the combined action ofa plasma
membrane NADPH oxidase and cytochrome b558 (with an
redox potential of - 245 mV), which appears to be the termi-
nal electron acceptor of a short electron transport chain thatconveys single electrons from NADPH to oxygen [54]. Two
cytosolic proteins (p47P�i0X, �fi7Phox), a quinone, and an Rac-
related GTP-binding protein are thought to be the other
functional components ofthis electron transport system [55].
The NADPH oxidase system is dissociated and thus inactive
in dormant neutrophils. While some components are mem-
brane bound, others are stored in the cytosolic granules.
Upon activation, the cytosolic components translocate to the
plasma membrane to assemble the active oxidase [54]. The
importance of the oxidative burst in the microbicidal activity
of neutrophils is shown in people with severe impairments in
this pathway (e.g., chronic granulomatous disease). They
suffer from repeated infections that respond poorly to con-
ventional therapy and almost invariably lead to early death;
treatment with interferon-y shows promise [56].
Although 02 may contribute to microbial killing, other
more potent ROS are generated rapidly from this precursor.
Hydrogen peroxide (H202), is formed by spontaneous dis-
mutation and/or the catalytic action of superoxide dismutase(SOD). MPO-dependent oxyhalides such as hypochlorous
acid (HOC1) are generated by the reaction of H202 with the
abundant C1 ions taken up from extracellular fluid; secon-
dary chlorinated amines are generated by the reaction of
HOC1 with nitrogen-containing compounds [17]. The per-
centage of H202 converted to HOC1 varies from 30 to 70%,
depending on the experimental system used 1161. Various
676 Journal of Leukocyte Biology Volume 56, December 1994
groups have claimed that the hydroxyl radical (OH.),
formed by the Fe2�-catalyzed decomposition of H202, and
singlet oxygen (102) are also generated by neutrophils.
There is considerable debate, however, as to whether these
ROS are produced under physiological conditions. Lactofer-rin may, in fact, prevent Fe3� from being used as a Fenton
catalyst and the bulk ofthe H202 may be converted to HOCI
[17]. The importance of MPO oxyhalides in neutrophil
microbicidal activity, however, is poorly understood, because
MPO deficiency has been reported to have little clinical
significance, although some affected people may suffer fromsevere Candida infections [16]. Although neutrophils deficient
in MPO can kill most microbes, they do so at a greater meta-
bolic cost than MPO-rich cells by prolonging H202 produc-
tion, possibly because HOCI is 100 to 1000 times more effec-
tive than H202 [57]. Furthermore, HOC1-induced cell death
occurs very rapidly in comparison to that mediated by H202[58]. However, sustained H202 production could also in-
crease the risk of host tissue damage and perhaps activate
inflammatory cascades, particularly if the generation of
OH . compensates for MPO deficiency. Thus, NADPH oxi-dase is essential for neutrophil microbicidal activity, but the
MPO arm is probably reinforced by other microbicidal
molecules or redundant processes.
Although critical to neutrophil antimicrobial function, the
exact mechanisms by which different oxidants contribute to
microbial killing have not yet been elucidated [59]. Bacterial
growth may be arrested by the inhibition of DNA synthesis
[59], but killing may involve multiple hits on essential
microbial constituents with unprotected functional groups
and/or fatal disruption of metabolic homeostasis [16]. The
exact targets, which include proteins, lipids, and nucleic
acids, may vary considerably between different species of
microorganisms. The nonoxidative processes also contribute
to varying degrees (see nonoxid#{225}tive mechanisms). Chiori-
nated oxidants are thought to be an important component of
defense against protozoa, fungi [23], and some viruses [28].
Microbial virulence may be related to the capacity to detox-
ify neutrophil ROS. Many microorganisms can catalytically
detoxify 02 and H2O2 but not HOCI [57].
Neutrophil-generated ROS also influence some cellular
functions. Superoxide and H2O2 may augment phagocytosis
independently of the MPO-halide system, whereas chlori-nated oxidants may limit this process by oxidatively mac-
tivating opsonin receptors [60]. Oxidants also promote the
margination of neutrophils by triggering the expression of
adhesion molecules on endothelial cells [61]. The mechan-
isms by which the oxidative burst is terminated are not
known, but inactivation of the oxidase may occur when acti-vation factors are consumed or when the enzyme is macti-
vated by oxidants and hydrolytic enzymes released by the
neutrophil or as a result of specific dephosphorylation reac-
tions [62].
Neutrophils contain large reserves of endogenous antioxi-
dants such as glutathione and ascorbate [57, 63]. Their abil-
ity to maintain these antioxidants in the reduced state during
phagocytosis [63] may prevent death from oxidative suicide.A substantial proportion of activated neutrophils are not des-
troyed during the killing process, but a significant refractory
period must elapse before these cells can be reactivated with
a secondary stimulus [64]. The antioxidant protection of
host tissues and fluids also plays a role in preventing
neutrophil-mediated destruction.
Reactive nitrogen species
Like macrophages, neutrophils appear to produce reactive
nitrogen species (RNS). The pathway is an oxidative process
in which short-lived nitric oxide (NO ) is derived from the
guanidino nitrogen in the conversion of L-arginine to L-
citrulline. This reaction is catalysed by N0 synthase and-
like the oxidative burst-it involves 02 uptake [65]. The con-
stitutive form of N0 synthase has been purified from hu-
man neutrophils [66]. Caution is needed in interpreting
many of these studies, as the measurements may not reflect
RNS generation through the N0 synthase pathway. Most
reports of phagocyte production of RNS involve indirect or
nonspecific methods for measuring the presence of N0
such as nitrite and L-citrulline accumulation or
chemiluminescence. Nitrosylation reactions with thiol-
containing compounds and proteins, particularly
glutathione, or heme iron also consume N0 [67]. Further-
more, doubt has been cast on the authenticity of RNS
production assessed by arginine analogues because these in-
hibitors of NO synthase have also been reported to block the
activities of heme-containing enzymes [68]. Nonspecificityhas also been a problem in the measurement of ROS in neu-
trophils [69]. In both cases, controversy may be avoided if
two or more independent techniques are used.
Independent pathways are involved in the synthesis of
ROS and RNS [65]. Dormant neutrophils incubated at
37#{176}Cproduce N0 continuously but activation arrests this
pathway in favor of the oxidative burst [70]. Neutrophil
migration is mediated by N0 because N0 synthase inhi-
bitors attenuate neutrophil responses to chemotactic gra-
dients in vitro [71], and it also interferes with assembly of
NADPH oxidase in activated neutrophils [72]. Thus,
although the ROS and RNS pathways are independent, they
may compete for common substrates such as NADPH and
02 and exert other modulating effects on each other. Thesteady-state production of these species may dictate the anti-
/proinflammatory balance. This may be controlled by the
level of neutrophil degranulation because heme enzymes
such as MPO scavenge N0 [68]. Various pathways deter-
mine the ultimate fate of N0 , which appears to be anti-
inflammatory itself.
Nitric oxide may contribute to the microbicidal activity of
neutrophils by reacting with ROS to form secondary cyto-
toxic species such as peroxynitrite (O0N02) [73]. For ex-ample, RNS appear to contribute to the killing of
Staphylococcus aureus by neutrophil cytoplasts, but not intact
cells, in vitro because the process is attenuated by M�-monomethyl arginine; this was reversed by adding L-
arginine [74]. At acidic pH, HNO3/NO2 either alone or
combined with H202, or H202 and MPO, in vitro is toxic
to Escherichia coli [75]. Therefore, microbial killing appears to
ROS dependent in normal neutrophils but RNS may play arole in cells with deficiencies in the NADPH oxidase/MPO
pathways. It would be interesting to determine whether RNS
production is greater in neutrophils isolated from people
with chronic granulomatous disease or MPO deficiency.
The main role of neutrophil-derived N0 may be to facili-
tate the migration of neutrophils from blood vessels to sur-
rounding tissues by causing vasodilation [69]. N0 facili-
tates relaxation of vascular smooth muscle, and ROS initiate
vasoconstriction through the production of O2, which re-
moves N0. Activated neutrophils have been implicated in
the development of inflammatory injury to the microvascula-
ture through the release of ROS and hydrolytic enzymes but
a shift in the balance in favor of RNS production may pre-
vent this. For example, N0 inhibits neutrophil adhesion to
vascular endothelium and this may prevent inflammatory
and ischemia-reperfusion injuries [76].
Hypertensive patients have circulating neutrophils that
are more oxidatively active than those of their normotensive
Smith Neutrophils, host defense, and inflammation 677
counterparts [77]. This suggests that some types of hyperten-
sion may be mediated by the collective failure of neutrophils
and endothelial cells to produce sufficient RNS to maintain
optimal vascular tone. Further support for this hypothesis
comes from a report suggesting that excessive formation ofNO may mediate the hypotensive effects of tumor necrosis
factor (TNF) [78]. Much more work, however, is required to
unravel the interactions between these pathways and the
physiological consequences of their cooperative and recipro-
cal activities.
Non-oxidative mechanismsNeutrophils contain an abundance of hydrolytic enzymes
and antimicrobial polypeptides. Acid hydrolases and an-
timicrobial defensins are contained within the intracellular
granules [8]. The azurophilic granules contain many proteo-
lytic and saccharolytic enzymes capable of digesting
microbial structural proteins and mucopolysaccharides,
whereas the contents of the specific granules include binding
proteins such as lactoferrin, which deprive microorganisms
of essential nutrients, and lysozyme and collagenase, which
destroy cell envelope components. Most of these proteins arepositively charged, which enhances their binding to cell surfaces.
Neutrophil hydrolytic enzymes augment microbial damage
initiated by ROS and participate in the digestion ofdead mi-
crobes and damaged host cells. Serine proteases such as
elastase and cathepsin G hydrolyze proteins in bacterial cell
envelopes and lysozyme degrades the polysaccharide compo-nents. The enzymes may also limit the spread of inflamma-
tion within local microenvironments by degrading priming
agents such as TNF-a and lymphotoxin [79]. Cathepsin G
also contributes to bacterial killing through a mechanism in-
dependent of its enzyme activity [80]. Neutrophils also acti-
vate platelets through cathepsin G [6]. Bactericidal/permeability-
increasing protein, a factor that is highly toxic to gram-
negative bacteria but not to gram-positive bacteria or fungi,
can also neutralize endotoxin, the toxic lipopolysaccharide
component of gram-negative bacterial cell walls [81].
Azurocidin is also active against gram-negative bacteria and,
to a lesser extent, gram-positive bacteria and fungi; its
microbicidal mechanism is unknown but proteolysis is not
involved [82]. Lactoferrin sequesters free iron, thereby
preventing the growth of ingested microorganisms that sur-
vive the killing process [83]. Lactoferrin also increases bac-
terial permeability to lysozyme [84]. The candidastatic ac-
tivity of neutrophils may be due to binding of Zn2� and Ca2�by the calprotectin complex of proteins [85]. Thus neu-
trophil microbiostatic and microbicidal mechanisms may be
independent to some extent.
Defensins, which constitute 30-50% of azurophilic gran-
ule protein, are small (molecular weight < 4000) potent an-
timicrobial peptides that are cytotoxic to a broad range of
bacteria, fungi, and some viruses. Their toxicity may be due
to membrane permeabilization of the target cell [86].
Limited attention has been paid to microbial DNA damage
by neutrophils, but endonuclease activity in human neu-
trophils has been reported [87]. Although neutrophils do not
degrade the DNA of phagocytosed E. colt, monocytes, in con-trast, degrade chromosomal DNA but not plasmid DNA;
this could have important implications in antibiotic
resistance [88].
Interactions between oxygen-dependent and oxygen-independent mechanisms
The oxidative and non-oxidative processes may kill some mi-
crobes independently, but the combination of the two in-
creases the microbial killing potential ofneutrophils substan-
daily. Unfortunately, the potential for host tissue damage is
also increased. In fact, cooperative interaction is vital in
many cases. Gram-negative bacteria, for example, are resis-
tant to lysozyme unless they are subjected simultaneously to
oxidants and/or complement factors [86]. Defensins and ox-
idants interact synergistically to lyse tumor cells in vitro[89]. Chlorinated oxidants also sustain the activity of some
proteases [17]. Serine proteases such as elastase constitute
part of a regulatory circuit that modulates the oxidative and
phagocytic functions of neutrophils, the activation of lym-
phocytes, and the activities of complement factors [90].
These proteases can prime the responsiveness of NADPH
oxidase to N-formylated peptides and phorbol esters by
modifying proteins present on the outer surface of the
plasma membrane, thereby increasing the lateral mobility ofmembrane lipids [90].
Hydrolytic damage to host tissue and therefore chronic
inflammatory conditions may occur only when antioxidant
and antiprotease screens are overwhelmed. Antiprotease
deficiency is thought to be responsible for the pathology ofemphysema [91]. Many antiproteases are members of the
serine protease inhibitor (SERPIN) family. Although the cir-
culation is rich in antiproteases, these large proteins may be
selectively excluded at sites of inflammation because neu-
trophils adhere tightly to their targets. Oxidative stress may
initiate tissue damage by reducing the concentration of ex-
tracellular antiproteases to below the level required to inhibit
released proteases [17]. Chlorinated oxidants and H2O2 can
inactivate antiproteases such as cr3-protease inhibitor and
a2-macroglobulin (which are endogenous inhibitors of
elastase) but, surprisingly, simultaneously activate latent
metalloproteases such as collagenases and gelatinase [17, 92],which contribute to the further inactivation of antiproteases
[93]. Many antiproteases are susceptible to oxidative attack,
probably because of exposed thiol groups. These destructive
processes may prolong the inflammatory response by trans-
forming the immediate nonspecific effects mediated by ROS
into more prolonged effects that depend on the activation ofa complex array of endogenous, and perhaps more specific,
proteolytic activities. These reactions may be regulated by
negative feedback because SERPINs such as a1-protease in-
hibitor, for example, block O2 production by activated neu-
trophils [94], possibly by inhibiting the synthesis of cytokines
and bioactive lipids [95] and/or by inhibiting NADPH oxi-dase activity by mechanisms not linked directly to their an-
tiprotease activities [94].
Priming and activation
Neutrophils exist in various states of activation, which varyfrom dormant to primed to fully activated. While activation
triggers the immediate expression of neutrophil microbicidal
activity, priming stimuli amplify the magnitude of the
response when it is activated subsequently and/or switch
cells from a nonresponsive to a responsive state. Althoughpriming and activation appear to be distinct processes, they
are biochemically integrated and require at least two events
(initiation and prolongation), which may be mediated by
separate mechanisms [96]. For example, subactivating con-
centrations of stimuli such as N-formylated peptides and
phorbol esters induce priming of the oxidative burst [90].
Stimuli at priming concentrations also regulate other neu-trophil activities; for example, N-formylated peptides at
nanomolar concentrations activate chemotaxis, whereas
micromolar concentrations arrest cell movement and trigger
microbicidal activity directly [97]. Although the distinct
678 Journal of Leukocyte Biology Volume 56, December 1994
multistep mechanisms responsible fbr the induction of’ prim-
ing and activation (and the interaction between them) arepoorly understood, several levels of involvement have been
identified. The transmembrane signaling processes involved
share salient features with those that occur in other cell
types. They begin with the binding of soluble or particulate
mediators to a complementary cell surface receptor and the
transduction of this initial signal to the effector machinery.The signal transduction processes involved in coupling
receptor-ligand binding vary according to the nature of the
stimulus.
Cell surface markers
Priming and activation are associated with changes in the ex-
pression of a variety of molecules on the cell surface. Up-
regulation of complement receptors occurs in vitro in
response to many neutrophil priming and activating agents
including cytokines, eicosanoids, and bacterial chemoattrac-
tants [98, 99] as well as in vivo in patients with thermal in-jury [45] and in response to exercise U.A. Smith et al., un-
published data). Dormant neutrophils do not express Fc�yRI
under normal conditions, but its expression can be induced
by treatment with interferon-’y [1]. In contrast, Fc�yRII and
Fc�yRIII expression decreases by 50 to 80% in activated neu-
trophils [99] and this may coincide with an increase in cir-culating forms of these receptors [100]. Selectins are also
shed from the surface of activated neutrophils [13].
Several novel neutrophil activation markers have been
described. The lymphocyte activation marker CD69 has
been reported to be expressed on the surface of the plasma
membrane of activated (but not dormant) neutrophils [101].Furthermore, CD66 and CD67, which are stored in the
specific granules, and CD63, a marker of azurophilic
degranulation, have also been reported to be neutrophil acti-
vation markers; the functions ofthese proteins are not known
[102, 103]. No marker that is exclusive to primed neutrophils
has been described yet, although expression of CD1O andbinding of the monoclonal antibody 7D5 have been reported
to be early activation markers in circulating neutrophils [104].
Signal transduction
Multiple signal transduction processes are involved in prim-
ing and activation of neutrophil microbicidal activity. Theactivation of NADPH oxidase activity has received the most
experimental attention [105]. This subject is discussed only
briefly here. At present priming and activation appear to be
biochemically inseparable. For example, primed neutrophil
oxygenation activity may be the result of an alteration to one
or more of the components of the transduction system. Thiscould include fluxes of free cations (Nat, K� and Ca2�),
changes in membrane potential, activation of intracellular
proteases, changes in arachidonic acid and phospholipid
metabolism, phosphorylation of specific proteins (i.e., oxi-
dase components), and changes in the intracellular concen-
trations of cyclic nucleotides. Small changes may triggerpriming and large changes lead to full activation including
degranulation. Furthermore, these signaling processes may
be involved in other neutrophil functions such as expression
of adhesion molecules and chemotaxis inter alia. Thus it is
difficult to characterize signaling mechanisms of a single
neutrophil function in intact cells.At present, two distinct signaling pathways of NADPH ox-
idase activation have been identified: one is Ca2� dependent
and leads to the activation of the Ca2�/phospholipid-
dependent protein kinase C; the other is Ca2� independent
and does not involve phospholipase C or protein kinase C;
both pathways must be functional, however, for activation ofthe oxidative burst [106]. Distinct pathways of activation of
a common NADPH oxidase appear to be triggered by differ-
ent classes of intracellular messengers, suggesting that the
activation pathways converge at a common intermediate
[107]. Interactions between protein kinase C, cAMP- and
cGMP-dependent protein kinases may combine to regulate
NADPH oxidase activity [107]. Some of the proximal steps
of the Ca2�-protein kinase C pathways may be bypassed in
vitro by using Ca� ionophores and/or protein kinase C activators.
Physiological examples of neutrophil priming andactivation
Various infectious and inflammatory conditions trigger the
priming response or neutrophil activation. Neutrophils iso-
lated from patients with acute bacterial infections show
primed oxidative responsiveness [48] and enhanced
antibody-mediated phagocytosis [108]. Primed neutrophils
have been found in people with essential hypertension [77],Hodgkin’s disease [109], inflammatory bowel disease [110],
psoriasis [111], sarcoidosis [112], and septicemia, where prim-
ing correlates with high concentrations of circulating TNF-a
I113]. In most cases, the mechanisms involved are not known.
Our group has shown that moderate exercise also triggers the
priming response in both trained and untrained men [114].In contrast to priming, activation is indicated by the in-
creased concentration of neutrophil granule contents found
in plasma, for example, from people with septicemia or bac-
terial meningitis [115], or after strenuous exercise [116, 117].
Elevated plasma concentrations of autoantibodies against
some neutrophil cytoplasmic components are associated withsome autoimmune diseases; as these antibodies can activate
neutrophils, they may play a role in the pathology [118],
although some may, possibly, neutralize cytotoxic neutrophil
components.
REGULATION OF NEUTROPHIL FUNCTION
The activities of immune cells such as neutrophils are or-
chestrated by a complex balance of counterregulatory (and
somewhat redundant) pathways. The immune system is not
autonomous: cellular and humoral immune activities areinfluenced by a plethora of soluble mediators secreted from
the endocrine, nervous, and cardiovascular systems as well as
by those produced by other immune cells. These mediators
include cytokines, hormones, and bioactive lipids, many of
which are secreted in response to stress. As immune cells
synthesize and release small amounts of most of these fac-tors, they have the potential to function in autocrine and
paracrine amplification networks [119, 120]. A large number
of mediators have been reported to modulate neutrophil
functions in vitro and some in vivo (Fig. 2). This list is ex-
panding rapidly. Activation of the complement cascade also
generates fragments that enhance phagocytosis (C3b),
chemotaxis, and microbicidal activity (C5a) [98, 105].
Cytokines
Many cytokines including hematopoietic growth factors and
pyrogens have been shown to be potent neutrophil primingagents in vitro [12]. Cytokines are immunoregulatory pro-
teins produced and secreted in different combinations, and
at different rates, by most immune cells, including macro-
phages, neutrophils, and lymphocytes [7, 121]. They have
powerful and multiple overlapping (pleiotropic) actions on
target cells; they can, in a concentration-dependent manner,
PAF(+) A�ATP(+)
Adenosine (-)
1�
GM-CSF (+)
G-CSF (+)
r
Interleukins 4 (+1-), 6 (+), 10 (-)
Interferon-i (+)
GM-CSF (+)
Growth Hormone (+)
TNF(+)
PAF (+)
PGE2 �
TNF (+)
PAF (+)
GM-CSF (+)
Leukotriene B4 (+) Interleukins 1,6,8 (+)
Adrenalin (-)
<SGlucocorticoids (-)
IAdenosine () Prostacyclin (-)
PAF(+)�11 GM-CSF(+)
Leukotriene B4 (+) Interleukins 6,8 (+)
Atrial Natriuretic Peptide (+)
Substance-P (+)
Interleukins 1,6,8 (+)
Smith Neutrophils, host defense, and inflammation 679
Fig. 2. Regulation of neutrophil function. This diagram illustrates the plethora of mediators that modulate various neutrophil functions and the potential
cellular sources (compiled from refs. 2, 6, 7, 12, 121, 189, 190). See text for full explanation.
amplify or diminish all responses of the immune system.
Some cytokines also interact to produce additive or synergis-
tic amplification. Neutrophils also synthesize and secrete
small amounts ofsome cytokines including interleukins (ILs)
1, 6, and 8, TNF-a, and GM-CSF; they may act in an auto-
crine or paracrine manner [7]. In fact, under normal condi-
tions, most cytokines act locally in microenvironments. They
are virtually undetectable in the circulation except under
pathological conditions.
The pyrogenic cytokines, IL-i [122], TNF-a [123], and
IL-6 [124] all prime various pathways that contribute to the
activation of NADPH oxidase. TNF-a also primes HOC1
production in these cells both in vitro and in vivo [125].
MPO release is also primed by IL-1j3 [122]. High concentra-
tions of circulating TNF-a have been detected in patients
with bacterial infections, cancer, and thermal injury [126].
IL-8, which is also known as neutrophil-activating factor, is
a potent chemoattractant and activating agent; it synergizes
with interferon-y, TNF-a, GM-CSF, and G-CSF to amplifyvarious neutrophil cytotoxic functions in vitro [127].
Cytokines also increase the microbiostatic and killing ca-
pacities of neutrophils against bacteria [22], protozoa [23],
and fungi [24]. G-CSF and interferon-rny prime the neu-
trophil oxidative burst to soluble stimuli and ingestible and
noningestible fungal forms [24]. Administration of G-CSF tohuman subjects increases neutrophil complement receptor
expression and enhances superoxide generation in stimu-
lated cells in vitro [128]. Interferon-’y and GM-CSF indepen-
dently amplify neutrophil antibody-dependent cytotoxicity
[33, 35]. These observations have physiological implications
because priming of neutrophils by nontoxic doses of TNF-aand IL-i appears to be responsible for the increased
resistance ofmice to bacterial infection [129] and for the en-
hanced candidicidal activity of human neutrophils that ac-
companies the priming of the oxidative burst [130]. Further-
more, administration of IL-i to neutropenic mice protects
them from lethal Candida albicans infection [131].The effect of the anti-inflammatory (type II) cytokines,
IL-4 and IL-lO, on neutrophils has received little experimen-
tal attention. Although IL-4 diminishes #{176}2 production in
monocytes [132], one group has reported that it increases the
neutrophil oxidative burst and bacterial killing in vitro [133].
However, IL-4 inhibits the production of IL-8 in lipopoly-saccharide-stimulated neutrophils [134] and blocks the ac-
tion of IL-i by increasing the expression of apparently non-
functional IL-i (type II) receptors [135] on the cell surface.
IL-lO inhibits the release of TNF-a, IL-1f3, and IL-8 [136]
and blocks IL-1/3 transcription [137] from lipopolysaccharide-
stimulated neutrophils.Like neutrophils, cytokines have been implicated in the
pathology of inflammatory disease. Synovial inflammation
and other manifestations of rheumatoid arthritis may be
caused by cytokines [i38]. However, although plasma TNF
is elevated in the majority of people with the adult respira-
tory distress syndrome, a direct cause-and-effect relationshipwas not established [49]. Furthermore, some cytokines
prolong neutrophil survival [139]. The acute inflammatory
response may be terminated by the secretion of macrophage
inflammatory protein-la from neutrophils; this protein may
signal mononuclear cell recruitment and clear neutrophils
from the affected tissue site [140]. Cytokine effects can be
blocked by endogenous inhibitors or carrier proteins; this in-
cludes soluble receptors shed from neutrophils and cytokine
autoantibodies that have been isolated in plasma 1141, 142].
680 Journal of Leukocyte Biology Volume 56, December i994
Pyrogenic cytokines also mediate septic shock; clinical trials
are in progress to examine the therapeutic potential of
cytokine neutralizing antibodies and soluble receptors [143].Although most neutrophil priming studies in vitro have in-
volved cell suspensions, some cytokines can stimulate the ox-
idative burst directly in adherent cells but not in cell suspen-
sions [144]. Neutrophils must adhere to matrix proteins for
cytokines to activate the oxidative burst directly; this may
prevent premature or “accidental” activation of circulating
neutrophils by cytokines [144] but without preventin.g prim-
ing. Adherence may also lower the steady-state concentration
of cytosolic cAMP, which could prepare neutrophils for the
onset of the oxidative burst by driving the concentration of
this potent inhibitor below its effective threshold [14]. Bac-
terial endotoxin (lipopolysaccharide), a potent stimulus ofpyrogenic cytokine secretion, may prime neutrophils directly
in vitro. This does not occur with cells in suspension, possi-
bly because additional serum factors are required [145]. The
stimulatory effect of lipopolysaccharide is enhanced when it
is complexed to the lipopolysaccharide-binding protein
found in the plasma of healthy humans in trace concentra-
tions [146].
Bioactive lipids
Arachidonic acid and its metabolites also modulate various
neutrophil functions. Neutrophil membranes are rich in
arachidonic acid and neutrophils are potent producers of bi-
oactive lipids. Leukotriene B4 is a strong neutrophil
chemoattractant that may play a role in the priming process
[76]. Vasoactive leukotrienes produced by neutrophils and
platelets (C4, D4, E4) increase microvascular permeability
and may contribute to ischemia-reperfusion injury [36, 76].
In contrast to leukotrienes, prostaglandins suppress most
neutrophil functions, possibly through their ability to elevate
intracellular cAMP [147].
Platelet-activating factor (PAF) is the most extensively
studied neutrophil lipid mediator. In many inflammatory
conditions, the levels of PAF rise in the affected tissues, but
injury can be attenuated by PAF antagonists [76]. PAFdirectly primes superoxide generation and elastase release
[i48]. The mechanisms by which cytokines prime neu-
trophils are not known, but PAF appears to mimic many of
the roles ascribed to TNF-a and IL-i [149, 150]. It may be
a direct second messenger for some cytokines because they
induce PAF accumulation in neutrophils and this increasesfurther upon activation [151]. The synthesis and release of
IL-I are triggered by PAF in a positive feedback manner; this
may be an important factor in the amplification of some im-
mune and inflammatory responses [149, 150]. GM-CSF also
primes PAF, arachidonic acid, and leukotriene B4 synthesis
in response to secondary stimuli [152, 153].
Neuroendocrine hormones
The major “stress hormones” are involved in immunoregula-
tion at both the systemic and, perhaps, local levels. The bi-
directional interactions of cytokines and neu rotransmitters
with neurons and immune cells, respectively, provide ameans of indirect chemical communication between the neu-
roendocrine and immune systems. The plasma concentra-
tions of these hormones fluctuate throughout the day be-
cause of pulsatile secretion and rapid metabolic clearance,
both of which are partially regulated by negative feedback
[154]. This may explain diurnal variations in various T cellsubset numbers in the circulation [155]. It is not known
whether neutrophil activities fluctuate throughout the day
under normal conditions. This may be an important variable
in many studies.
Growth hormone deficiency, which reduces the potency of
virtually all immune mechanisms, increases vulnerability to
infection [156]. Growth hormone also primes the oxidative
burst ofhuman neutrophils [157]. This is initiated by growth
hormone binding to the prolactin (and not the growth hor-
mone) receptor on neutrophils in a zinc-dependent process
[157]. The mechanisms underlying growth hormone-induced
priming have not been identified, but protein synthesis ap-
pears to be involved [157]. The growth-promoting effects of
growth hormone are mediated through insulin-like growth
factor 1, which is also a strong neutrophil-priming agent
[157]. Growth hormone synergizes with interferon-’y to re-
store the suppressed neutrophil oxidative burst and bacteri-
cidal activity in cells isolated from senescent rats; interferon-,y alone did not have any priming effect [158].
Other neuroendocrine factors have been reported to be
potent neutrophil priming agents. Prolactin-which shares
considerable functional and structural similarities with
growth hormone - is also a strong immunopotentiating
agent [i56]. Prolactin primes the oxidative burst of macro-
phages and neutrophils to the same intensity as that induced
by growth hormone [157]. Atrial natriuretic peptide has also
been reported to be a potent neutrophil-priming agent [159].
This hormone may play a role in neutrophil activation in
heart tissue during ischemia-reperfusion injury [159].
Although glucocorticoids and opioids may enhance someimmune responses at very low concentrations, they are
generally considered to be immunosuppressive [154]. These
contrasting responses may be controlled by the presence of
multiple receptors for the same mediator that are coupled to
stimulatory and inhibitory pathways. Saturation of the
stimulatory receptor may eventually trigger expression and
activity of the inhibitory receptor-linked pathway. In fact,
containment of the stress response may be the principal role
of glucocorticoids [160]. Glucocorticoids severely impair the
phagocytic and cytotoxic activities of neutrophils [161] and
their capacity to produce ROS and secrete lysozyme in
response to stimulation with chemotactic peptides in vitro[162]. Treatment of cattle with glucocorticoids inhibits the
oxidative burst, chemotaxis, and antibody-dependent
cytotoxicity [163]. Some cytokines protect against
glucocorticoid-induced impairment of neutrophil responses
to certain fungi [24]. However, glucocorticoids increase the
expression of the nonfunctional type II receptor for IL-i,
which may down-regulate the effect of this cytokine on neu-
trophils [135]. The physiological relevance of many studies is
questionable, however, because of the very high concentra-
tions of glucocorticoids used [2].
Catecholamines and opioids also suppress a variety of im-
mune activities. Epinephrine treatment of isolated cells invitro inhibits the oxidative burst of macrophages and neu-
trophils [164] and the tumoricidal and antiviral activities of
macrophages [165]. Opioid addiction increases susceptibility
to a variety of infections. This may be due to suppressed T
cell proliferation and neutrophil microbicidal activity [166].
Oxidant production by neutrophils is also inhibited by f3-
endorphin activity mediated via nonopioid receptors [167].
Other mediators
Histamine, [168], lipoxins A4 and B4 [169], and some
unidentified products from platelet lysates [170] are potent
inhibitors of neutrophil microbicidal activity. However,
platelets are immunomodulatory because activated cells can
bind to neutrophils and stimulate the oxidative burst [171],
Smith Neutrophils, host defense, and inflammation 681
possibly through the release of ATP [i72]. The interactions
between platelets and neutrophils are essential for platelets
to synthesize vasoconstrictive leukotrienes [6]. Likeprostaglandins, many immunosuppressive mediators use
cAMP as a second messenger [173]. Increased intracellular
cAMP in neutrophils is associated with decreases in a num-
ber of microbicidal functions [53]. Phagocyte priming and
activation may, in fact, be controlled by shifts in the intracel-
lular ratio ofcGMP to cAMP [173], since cGMP is stimula-
tory [174].
Adenosine provides an interesting example ofhow a single
mediator may play dual roles. Adenosine, a vasodilator, is a
potent anti-inflammatory agent released from damaged host
cells. Neutrophil chemotaxis is activated by adenosine oc-
cupancy ofA1 receptors and inhibition ofthe oxidative burst
triggered through A2 receptors [175]. Adenosine suppresses
the oxidative burst only if it is added before the triggering
agent [176], but it has no effect on the initiation or progress
ofdegranulation [175]. Circulating adenosine, at physiologi-
cal concentrations, may prevent the premature activation of
peripheral blood neutrophils by cytokines without prevent-
ing priming [176].
This discussion highlights the complexity and apparent
redundancy of the humoral mediators that regulate neu-
trophil function. Identification of people with deficiencies
will verify which mediators serve crucial roles that cannot be
replaced by substitutes. The plethora of humoral mediatorsthat influence neutrophil function means that therapeutic
strategies that are employed to correct neutrophil deficien-
cies must be carefully examined in animal models before
proceeding to human trials.
Interactions between the immune and neuroendocrinesystems
The communication between the neuroendocrine and im-
mune systems and its mediation by hormones and cytokines
is one the most active areas of current biological research
[119, 120]. Pyrogenic cytokines stimulate the hypothalamus
to secrete corticotropin-releasing factor which, in turn, acti-
yates the immunosuppressive arm of the pituitary-adrenal
axis by stimulating the secretion of adrenocorticotropic hor-
mone [119, 120, 154]. Immune cells also synthesize and
release hypothalamic regulatory factors such as somatosta-
tin, which may modulate hormone secretion from immune
cells in a manner analogous to the regulation of pituitary
hormone secretion by hypothalamic hormones [177]. The
physiological significance of cell communication at this level
is not known, but hormone secretion by immune cells may
participate in the paracrine amplification of afferent
pituitary signals in microenvironments such as infection
sites. Immune cells in these regions may secrete cytokines
and other mediators that feed back to the pituitary gland and
the brain [178]. In contrast to hormones of neuroendocrine
origin, hormones secreted by leukocytes are not stored and
must be synthesized de novo; the quantities produced by leu-kocytes are much smaller than those produced by neuroen-
docrine cells, but immune cells are mobile and can concen-
trate the hormone at distant targets [119]. Although antigenic
stimuli are not recognized directly by the central nervous or
endocrine systems, leukocytes may convey information deli-
vered by antigens, via humoral mediators, to these systems [178].
STRESS AND OTHER LIFESTYLE FACTORS
Cells of the immune system, including neutrophils, are
influenced by age, diet, psychological stress, health status,
and physical activity. Advancing age is associated with im-
paired cell-mediated immunity, but studies of neutrophils
have been conflicting. Aging, when combined with malnutri-
tion, does produce significant impairments in neutrophil
function [179]. Dietary deficiency or excessive intake of some
vitamins and minerals may impair immune responses [180].
Low neutrophil oxidative activity is associated with a poor
prognosis in some cancer patients [181]. Neutrophils isolated
from cancer patients not receiving any therapy have defec-
tive cytotoxic responses to antibody-coated tumor cells in
vitro [182]. Psychological stress has been shown by many
groups to suppress cell-mediated immunity and increase sus-
ceptibility to infection [183], but neutrophil responses have
not been examined.Exercise has intensity-dependent effects on the immune
system [116, 184]. We have shown that the neutrophil oxida-tive burst is deficient in athletes compared with untrained
men; in contrast, moderate episodes of exercise prime these
cells [114]. Differential secretion of neuroendocrine hor-
mones into the circulation may be responsible for theintensity-dependent effects ofexercise on the immune system
[184]. Priming of neutrophil microbicidal activity may cx-
plain, partially, why moderate exercise programs appear to
reduce the susceptibility of humans to infection and some
cancers, while overtraining is a high-risk factor for infectious
disease [185, 186]. In fact, the immunological and endocrineresponses to psychological stress and intensive physical train-
ing are remarkably similar [i84]. Further work is required to
link the immunological and clinical evidence directly and to
investigate the regulatory mechanisms involved. Circadian
and seasonal variation must also be taken into account.
NOVEL ROLES FOR NEUTROPHILS
As well as their functions in immunity and inflammation,
neutrophils may play other roles in the maintenance ofhomeostasis. This may explain why neutrophil function is
affected by stress and other lifestyle factors and why neu-
trophils are turned over so rapidly in healthy people. Neu-
trophils scavenge and degrade toxic molecules [81] and assist
in platelet removal [6]. Because of their motility and ability
to gain access to most body tissues, neutrophils are ideal car-
riers ofchemical signaling molecules and enzymes inter alia.
Containment and transport of regulatory factors in neu-
trophils may prevent their degradation or nonspecific inter-
actions during transit. For example, under normal condi-
tions, neutrophils may act as “vectors” to deliver essential
molecules such as proteases directly to sites of tissueremodeling (e.g., muscle adaptation to physical training).
This would prevent indiscriminate activation of proteolytic
inflammatory cascades by circulating free proteases or inhi-
bition by circulating antiproteases. Free elastase can activate
some proteolytic cascades including those of the comple-
ment, coagulation, and fibrinolytic systems [i87]. Because of
their accumulation in sites of infection and inflammation,neutrophils cells provide a convenient vehicle for delivering
drugs and reducing the potential for debilitating side effects
[188]. Packaging of cytotoxic molecules in cytosolic granules
with differential sensitivity to neutrophil activating agents
confers additional safety [17]. However, these safety meas-
ures break down during sustained inflammatory responses.
FUTURE DIRECTIONS
The greatest challenge to workers in this field is to determine
how optimal neutrophil function can be maintained and
682 Journal of Leukocyte Biology Volume 56, December 1994
what the essential regulatory factors are, given the apparent
high level of redundancy. The key to solving the neutrophil
paradox at the cellular level may lie in unraveling the
balance between secretory responses involved in the
chemotactic and cytotoxic pathways, and priming and acti-vation. The significance of neutrophil heterogeneity has still
not been solved [4] but this may provide further clues. For
example, ifneutrophils do produce RNS, are there subpopu-
lations that can be divided into ROS and RNS dominant?
Mutants or transgenic manipulation of animal cells may
solve some of these issues.Although many functional assays of neutrophil activity
have been described, we still do not know what constitutes a
normal response. For example, there is great variability in
the magnitude of the oxidative burst in neutrophils isolated
from healthy human subjects and stimulated in vitro [69]. As
a starting point, a reference range for the major neutrophil
functions should be determined in healthy subjects under
standard conditions. This information would aid therapeutic
strategies aimed at boosting specific neutrophil functions in
immunocompromised people or preventing inflammatory
conditions mediated by activated neutrophils.
CONCLUSIONS
Neutrophils are highly destructive cells that are essential for
host defense but also contribute to various inflammatory dis-
eases. This brief review has highlighted the complex path-
ways involved in regulating the diverse and somewhat redun-
dant array of neutrophil functions at the cellular and
humoral levels. Uncoupling of any essential part of the se-
quence may lead to neutrophil dysfunction. This balance is
controlled by the interaction of multiple regulatory cascades.
Unraveling these interactions is one of the greatest
challenges in leukocyte biology, but it is probably the key to
resolving the neutrophil paradox.
ACKNOWLEDGEMENTS
I am grateful to Dr. Maurice Weidemann and Dr. David
Pyne of the Division of Biochemistry and Molecular Biology,
Australian National University for their critical evaluation of
the manuscript. I also thank Prof. Chris Bryant of the Divi-
sion of Biochemistry and Molecular Biology, Australian Na-
tional University for continued support. My work has been
supported by an Australian Postgraduate Research Award,
grants from the Faculties Research Fund of the Australian
National University, and the National Quality of Life Foun-
dation.
REFERENCES
1. Huizinga, T.W.J., Roos, D., Kr. von dem Borne, A.E.G. (1990)
Neutrophil Fc1 receptors: a two-way bridge in the immune sys-
tem. Blood 75, 1211-1214.
2. Schlcimer, R.P., Freeland, H.S., Peters, S.P., Brown, K.E.,Derse, C.P. (1989) An assessment of the effects of glucocorti-
coids on degranulation, chemotaxis, binding to vascular en-dothelium and formation of leukotrienc B4 by purified human
neutrophils. J. Pharmacol. Exp. Ther. 250, 598-605.3. Ratcliffe, D.R., Nolin, S.L., Cramer, E.B. (1988) Neutrophil
interaction with influenza-infected epithelial cells. Blood 72,142-149.
4. Gallin, J.I. (1984) Human neutrophil heterogeneity exists, but
is it meaningful? Blood 63, 977-983.
5. Zhang, J.-H., Ferrante, A., Appigo, A-P., Dayer, J.-M. (1992)
Neutrophil stimulation and priming by direct contact with ac-tivated human T-lymphocytes. j Immunol. 148, 177-181.
6. Henson, P.M. (1990) Interactions between neutrophils and
platelets. Lab. Invest. 62, 391-393.7. Lloyd, AR., Oppenheim, J.J. (1992) Poly’s lament: the
neglected role of the polymorphonuclear neutrophil in theafferent limb of the immune response. Immunol. Today 13,169-172.
8. Borregaard, N., Lollike, K., Kjeldsen, L., Sengeldw, H.,
Bastholm, L., Nielsen, M.H., Bainton, D.F. (1993) Humanneutrophil granules and secretory vesicles. Eur. J. Haematol. 51,187-198.
9. MacNec, W., Selby, C. (1990) Neutrophil kinetics in the lungs.
Gun. Sci. 79, 97-107.
10. Savill, J., Fadok, V., Henson, P., Haslett, C. (i993) Phagocyterecognition of cells undergoing apotosis. Immunol. Today 14,131-136.
11. Cannistra, S.A., Griffin, J.D. (1988) Regulation of the produc-tion and function of granulocytes and monocytes. Semin.
Hematol. 25, 173-188.12. Steinbeck, M.J., Roth, J.A. (1989) Neutrophil activation by
recombinant cytokines. Rev. Infrct. Dis. 11, 549-568.13. Cronstein, B.N., Weissmann, G. (i993) The adhesion
molecules of inflammation. Arthritis Rheum. 36, i47-i57.14. Nathan, C. , Sanchez, E. (1990) Tumor necrosis factor and
CD11/CD18 (j32) integrins act synergistically to lower cAMP inhuman neutrophils. J. Cell Biol. 111, 217i-2i8i.
15. Mannion, BA., Weiss, J., Elsbach, P. (1990) Separation of
sublethal and lethal effects of polymorphonuclear teukocyteson Escherichia coli. j C/in. invest. 86, 631-641.
16. Klebanoff, S.J. (1992) Oxygen metabolites from phagocytes. In
Inflammation: Basic Principles and Clinical Correlates, 2nd ed. UIGallin, M. Goldstein, and R. Snyderman, eds) Raven Press,
New York, 541-588.
17. Weiss, S.J. (1989) Tissue destruction by neutrophils. N Engi.
j Med. 320, 365-376.
18. Malech, H.L., Gallin, J.I. (1987) Neutrophils in human dis-
eases. N Engl. J. Med. 317, 687-694.
19. Verhoef, J. (1993) Prevention of infections in the neutropenic
patient. C/in. infect. Dis. 17(Suppl. 2), S359-S367.20. Schaffner, A., Davis, CE., Schaffner, T., Markert, M.,
Douglas, H., Braude, A.!. (1986) In vitro susceptibility tofungi to killing by neutrophil granulocytes discriminates be-
tween primary pathogenicity and opportunism. j C/in. invest.78, 511-524.
21. Pedersen, S.S., Kharazmi, A., Espersen, F., H�iby (1990) Pseu-domonas aeruginosa alginate in cystic fibrosis sputum and theinflammatory response. infect. immun. 58, 3363-3368.
22. Ferrante, A., Martin, A.J., Bates, E.J., Goh, D.H.B., Harvey,
D.P., Parsons, D., Rathjen, D.A., Russ, G., Dayer,J.-M. (1993)
Killing of Staphylococcus aureus by tumor necrosis factor-a-acti-
sated neutrophils. j Immunol. 151, 4821-4828.23. Ferrante, A., Hill, N.L., Abell, T.J., Pruul, H. (i989) Augmen-
tation of the neutrophil response to Naegleriafowleri by tumor
necrosis factor alpha. Infect. Immun. 57, 3110-3115.24. Roilides, E., Uhlig, K., Venzon, D., Pizzo, PA., Walsh, T.J.
(1993) Prevention of corticosteroid-induced suppression of hu-
man polymorphonuclear leukocyte-induced damage of Asper-
gillusfumigatus hyphae by granulocyte colony-stimulating factorand gamma interferon. infect. immun. 61, 4870-4877.
25. Van Strijp, JAG., Van Kessel, K.P.M., van der Tol, ME.,
Verhoef, J. (1989) Complement-mediated phagocytosis of
herpes simplex virus by granulocytes.j C/in, invest. 84, 107-112.
26. Tsuro, S., Fujisawa, H., Taniguchi, M., Zinnaka, Y., Nomoto,
K. (1987) Mechanism of protection during the early phase ofa generalised viral infection: contribution of polymor-
phonuclear leukocytes to protection against intravenous infec-
tion with influenza virus. j Cen. Virol. 68, 419-424.27. West, B.C., Eschete, ML., Cox, ME., King, J.W. (1987) Neu-
trophil uptake of vaccinia virus in vitro. J. infect. Dis. 156,597-606.
28. Yamamoto, K., Miyoshi-Koshio, T., Utsuki, Y., Mizuno, S.,
Smith Neutrophils, host defense, and inflammation 683
Suzuki, K. (1991) Viricidal activity and viral protein modifica-
tion by myeloperoxidase: a candidate for defense factor of hu-man polymorphonuclear leukocytes against virus infection. J.Infect. Dis. 164, 8-14.
29. Harthshorn, K.L., Collamer, M., White, MR., Schwartz,
J.H., Tauber, Al. (i990) Characterization of influenza A virusactivation of the human neutrophil. Blood 75, 218-226.
30. Abramson, J.S., Wagner, M.P., Ralston, E.P., Wei, Y.,Wheeler, J.G. (1991) The ability of polymorphonuclear leuko-
cyte priming agents to overcome influenza virus-induced cell
dysfunction. j Leukoc. Biol. 50, 160-166.31. Klebanoff, S.J., Coombs, R.W. (1992) Viricidal effect of poly-
morphonuclear leukocytes on human immunodeficiencyvirus-i. j C/in. Invest. 89, 2014-2017.
32. Bandres,J.C., Trial,J., Musher, D.M., Rossen, RD. (1993) In-
creased phagocytosis and generation of reactive oxygenproducts by neutrophils and monocytes of men with stage 1
human immunodeficiency virus infection. j Infect. D#{252}.168, 75-83.
33. Ellis, M., Gupta, S., Galant, S., Hakim, S., VandeVen, C., Toy,C., Cairo, MS. (i988) Impaired neutrophil function in pa-tients with AIDS or AIDS-related complex: a comprehensive
evaluation. J. infect. Dis. 158, i268-i276.
34. Howell, AL., Guyre, P.M., You, K-S., Fanger, MW. (1994)Targeting HIV-1 to FcyR on human phagocytes via bispecific
antibodies reduces infectivity of HIV-l to T-cells. j Leukoc.Bio/. 55, 385-391.
35. Baldwin, G.C., Fuller, ND., Roberts, R.L., Ho, D.H., Golde,
D.W. (1989) Granulocyte- and granulocyte-macrophage colonystimulating factors enhance neutrophil cytotoxicity towardHIV-infected cells. Blood 74, 1673-1677.
36. Ricevetti, G. , Mazzone, A. , Pasotti, D. , de Servi, S. , Specchia,G. (199i) Role ofgranulocytes in endothelial injury in coronary
heart disease in humans. Atherosclerosis 91, 1-14.37. McCord, J.M. (1987) Oxygen-derived radicals: a link between
reperfusion injury and inflammation. Fed. Proc. 46, 2402-2406.38. Ras, G.J., Theron, A.J., Andersen, R., Taylor, G.W., Wilson,
R., Cole, P.J., van der Merwe, CA. (1992) Enhanced releaseof elastase and oxidative inactivation of a-i-protease inhibitorby stimulated neutrophils exposed to Pseudornonas aeruginosa pig-
ment 1-hydroxyphenazine. j infect. Dis. 166, 568-573.39. Robinson,J., Watson, F., Bucknall, R.C., Edwards, SW. (1992)
Activation of neutrophil reactive oxidant production by syn-ovial fluid from patients with inflammatory joint disease: solu-
ble and insoluble immunoglobulin aggregates activate differentpathways in primed and unprimed cells. Biochem. j 286, 345-351.
40. Weitzman, S.A., Gordon, LI. (1990) Inflammation and
cancer: role ofphagocyte-generated oxidants in carcinogenesis.Blood 76, 655-663.
41. Opdenakker, G., Van Damme, J. (i992) Cytokines and pro-
teases in invasive processes: molecular similarities betweeninflammation and cancer. Cytokine 4, 251-258.
42. Hatherill,J.R., Till, GO., Bruner, L.H., Ward, P. (1986) Ther-mal injury, intravascular hemolysis, and toxic oxygenproducts. j C/in. invest. 78, 629-636.
43. Scaccini, C., Jialah, I. (1994) LDL modification by activatedpolymorphonuclear leukocytes: a cellular model of mild oxida-
tive stress. Free Radicals Bio/. Med. 16, 49-55.44. Martin, T.R., Pistorese, B.P., Hudson, L.D., Maunder, R.J.
(1991) The function of lung and blood neutrophils in patientswith the adult respiratory distress syndrome. Am. Rev. Respir.
Dis. 144, 254-262.
45. Bjerknes, R., Vindenes, H., Laerum, O.D. (1990) Altered neu-trophil functions in patients with large burns. Blood Ce//s 16,127-143.
46. Fritzsche, R., Dc Weck, AL. (1988) Chemiluminescencemicroscopy reveals functional heterogeneity in single neu-trophils undergoing oxygen burst. Eur J. immuno/. 18, 817-820.
47. Fletcher, M.P., Gasson, J.C. (1988) Enhancement of neutrophilfunction by granulocyte-macrophage colony-stimulating factor
involves recruitment of a less responsive subpopulation. Blood71, 652-658.
48. Bass, D.A., Olbrantz, P., Szejda, P., Seeds, MC., McCall,
CE. (1986) Subpopulations of neutrophils with increased ox-
idative product formation in blood of patients with infection.
I. immuno/. 136, 860-866.49. Chollet-Martin, S., Montravers, P., Gibert, C., Elbim, C.,
Desmonts, J.M., Fagon, J.Y., Gougerot-Pocidalo, MA. (1992)
Subpopulation of hyperresponsive polymorphonuclear neu-trophils in patients with adult respiratory distress syndrome.Am. Rev. Respir. Dis. 146, 990-996.
50. Krause, P.J., Maderazo, E.G., Bannon, P., Kosciol, K.,
Malech, H.M. (i988) Neutrophil heterogeneity in patientswith blunt trauma. j Lab. C/in. Med. 112, 208-215.
51. Krause, P.J., Todd, MB., Hancock, W.W., Pastuszak, W.T.,
Maderazo, E.G., Hild, D.H., Kosciol, CM. (1990) The role ofcell maturation in neutrophil heterogeneity. Blood 76, i639-i646.
52. Babcock, GE, Alexander, J.W., Warden, GD. (1990) Flow
cytometric analysis of neutrophil subsets in thermally-injured
patients developing infection. C/in. immuno/. immunopathol. 54,117-125.
53. Krause, K-H., Lew, D.P. (1988) Bacterial toxins and neu-
trophil activation. Semin. Hematol. 25, 112-124.54. Babior, B.M. (1992) The respiratory burst oxidase. Adv. En-
zymol. 65, 49-95.55. Rotrosen, D., Yeung, CL., Leto, T.L., Malech, H.L., Kwong,
C.H. (1992) Cytochrome b558: the flavin-binding component ofthe phagocyte NADPH oxidase. Science 256, 1459-1462.
56. Curnutte,J.T. (1993) Chronic granulomatous disease: the solv-
ing of a clinical riddle at the molecular level. C/in. immunol. im-
munopathol. 67, 52-515.57. Eaton, J.W. (1993) Defenses against hypochlorous acid: parry-
ing the neutrophil’s rapier thrust. J. Lab. C/in. Med. 121,197-198.
58. Schraufstatter, lU., Browne, K., Harris, A., Hyslop, PA.,
Jackson, J.H., Quehenberger, 0., Cochrane, C.G. (1990)Mechanisms of hypochlorite injury of target cells. J. C/in. in-
vest. 85, 554-562.
59. McKenna, SM., Davies, K.J.A. (i988) The inhibition of bac-
terial growth by hypochlorous acid. Biochem. J. 254, 685-962.60. Gresham, H.D., McGarr, J.A., Shackelford, PG., Brown, E.J.
( 1988) Studies on the molecular mechanisms of human Fereceptor-mediated phagocytosis. J. C/in. invest. 82, li92-i2Oi.
61. Patel, PD., Zimmerman, GA., Prescott, SM., McEver, R.P.,
McIntyre, TM. (1991) Oxygen radicals induce human en-dothelial cells to express GMP-140 and bind neutrophils. J.Ce/I Biol. 112, 749-759.
62. Ding, J., Badwey, J.A. (1992) Effects of antagonists of protein
phosphatases on superoxide release by neutrophils. J. BioLChem. 267, 6442-6448.
63. Voetman, A.A., Loos, J.A., Roos, D. (1980) Changes in the
levels of glutathione in phagocytosing neutrophils. Blood 55,741-747.
64. Prasad, K., Chaudhary, AK., Kalra, J. (1991) Oxygen-derived
free radicals producing activity and survival of activated poly-
morphonuclear leukocytes. Mol. Ce/I. Biochem. 103, 51-62.65. Kwon, N.S., Nathan, CF., Gilker, C., Griffith, OW., Mat-
thews, D.E., Stuehr, D.J. (1992) 1.-Citrulline production fromL-arginine by macrophage nitric oxide synthase. j Biol. Chem.265, 13442-13445.
66. Bryant, J.L., Jr., Mehta, P., Von der Porten, A., Mehta, J.L.
(1992) Co-purification of 130 kD nitric oxide synthase and a 22
kD link protein from human neutrophils. Biochem. Biophys. Res.
Commun. 189, 558-564.67. Clancy, R.M., Levartovsky, D., Leszczynska-Piziak, J.,
Yegudin,J., Abramson, SB. (1994) Nitric oxide reacts with in-tracellular glutathione and activates the hexose monophosphateshunt in human neutrophils. Evidence for S-nitroglutathione
as a bioactive intermediatiary. Proc. Nat/. Acad. Sci. USA 91,3680-3684.
68. Peterson, D.A., Peterson, D.C., Archer, S., Weir, E.K. (1992)
The non-specificity of specific nitric oxide synthase inhibitors.Biochem. Biophys. Res. Commun. 187, 797-801.
69. Smith, J.A., Weidemann, M.J. (1993) Further characterization
of the neutrophil oxidative burst by flow cytometry.J. immunol.Methods 162, 261-268.
70. Wright, CD., Mulsch, A., Busse, R., Osswald, H. (1989)
684 Journal of Leukocyte Biology Volume 56, December 1994
Generation of nitric oxide by human neutrophils. Biochem. Bio-
phys. Res. Commun. 160, 813-819.71. Belenky, SN., Robbins, R.A., Rennard, SI., Gossman, G.L.,
Nelson, K.J., Rubinstein, I. (i993) Inhibitors of nitric oxide
synthase attenuate human neutrophil chemotaxis in vitro. j
Lab. C/in. Med. 122, 388-394.72. Clancy, R.M., Leszczynska-Piziak, J., Abramson, SB. (1992)
Nitric oxide, an endothelial relaxation factor, inhibits superox-
ide anion production via a direct action on the NADPH oxi-
dase. j C/in. Invest. 90, 1116-1121.73. McCall, TB., Boughton-Smith, N.K., Palmer, R.M.J., Whit-
tle, B.J.R., Moncada, S. (1989) Synthesis of nitric oxide fromL-arginine by neutrophils: release and interaction with su-
peroxide. Biochem. j 261, 293-296.74. Malawista, SE., Montgomery, R.R., Van Blaricom, G. (1992)
Evidence for reactive nitrogen intermediates in killing ofstaphylococci by human neutrophil cytoplasts. j C/in. Invest.
90, 631-636.75. Klebanoff, S.J. (1993) Reactive nitrogen intermediates and an-
timicrobial activity: role of nitrite. Free Radicals Bio/. Med. 14,351-360.
76. Kubes, P. (1993) Polymorphonuclear leukocyte-endotheliuminteractions: a role for proinflammatory and anti-inflamma-tory molecules. Can. J. Physio/. PharmacoL 71, 88-97.
77. Pontremoli, S., Salamino, F., Sparatore, B., De Tullio, R., Pa-
trone, M., Tizianello, A., Melloni, E. (i989) Enhanced activa-tion ofthe respiratory burst oxidase in neutrophils from hyper-
tensive patients. Biochem. Biophys. Res. Commun. 158, 966-972.78. Kilbourn, R.G., Gross, S.S., Jubran, A., Adams, J., Griffith,
O.W., Levi, R., Lodato, R.F. (1990) M-Methyl-L-arginine in-
hibits tumor necrosis factor-induced hypotension: implications
for the involvement of nitric oxide. Proc. Nat/. Acad. Sci. USA
87, 3629-3632.79. Scuderi, P., Nez, PA., Duerr, ML., Wong, B.J., Valdez, CM.
(i99i) Cathepsin-G and leukocyte elastase inactivate tumornecrosis factor and lymphotoxin. CelL Immunol. 135, 299-3i3.
80. Miyasaki, K.T., Bodeau, AL. (1991) In vitro killing of Ac-
tinobacillus actinomycetemcomitans and Capnocytophaga spp. by hu-man neutrophil cathepsin G and elastase. Infect. Immun. 59,3015-3020.
81. Marra, MN., Wilde, C.G., Collins, MS., Snable,J.L., Thorn-ton, MB., Scott, R.W. (i992) The role of bacterial/permeability-increasing protein a natural inhibitor ofbacteriai endotoxin.jImmunol. 148, 532-537.
82. Gabay, J.E., Almeida, R.P. (1993) Antibiotic peptides and ser-
me protease homologs in human polymorphonuclear leuko-
cytes: defensins and azurocidin. Curt. Opin. immuno/. 5, 97-102.83. Molloy, AL., Winerbourn, CC. (1990) Release of iron from
phagocytosed Escherichia co/i and uptake by neutrophil lactofer-rin. Blood 75, 984-989.
84. Ellison, R.T., III, Geihl, T.J. (i99l) Killing of gram-negative
bacteria by lactoferrin and lysozyme. J. C/in. Invest. 88,1080-1091.
85. Murthy, ARK., Lehrer, RI., Harwig, S.S.L., Miyasaki, K.T.(1993) In vitro Candidastatic properties of the human neu-
trophil calprotectin complex. J. Immuno/. 151, 6291-6301.86. Lehrer, RI., Ganz, T. (1990) Antimicrobial polypeptides of
human neutrophils. Blood 76, 2169-2181.87. Chung, M.-H., Kim, H-S., Ohtsuka, E., Kasai, H.,
Yamamoto, F, Nishimura, S. (1991) An endonuclease activityin human polymorphonuclear neutrophils that removes
8-hydroxyguanine residues from DNA. Biochem. Biophys. Res.
Commun. 178, 1472-1478.88. Rozenberg-Arska, M., van Strijp, W.P., Hoekstra, M.,
Verhoef, J. (i984) Effect of human polymorphonuclear andmononuclear leucocytes on chromosomal and plasmid DNA ofEscherichia co/i. j C/in. Invest. 73, 1254-1262.
89. Lichtenstein, AK., Ganz, T., Selsted, ME., Lehrer, RI.(1988) Synergistic cytolysis mediated by hydrogen peroxidecombined with peptide defensions. Cell. immunol. 114, i04-i16.
90. Kusner, D.J., Aucott, J.N., Franceschi, D., Sarasua, MN.,Spagnuolo, P.J., King, C.H. (1991) Protease priming of neu-trophil superoxide production.j Biol. Chem. 266, i6465-1647i.
91. Gadek, J.E. (1992) Adverse effects of neutrophils on the lung.
Am. j Med. 92(Suppl. 6A), 275-315.92. Saari, H., Suomalainen, K., Lindy, 0., Konttinen, Y.T., Sorsa,
T. (1990) Activation oflatent human neutrophil collagenase byreactive oxygen species and serine proteases. Biochem. Biophys.
Res. Commun. 171, 979-987.93. Vissors, M.C.M., George, P.M., Bathurst, IC., Brennan, 5.0.,
Winterbourn, CC. (1988) Cleavage and inactivation ofai-antitrypsin by metalloproteinases released from neu-
trophils. J. C/in. Invest. 82, 706-710.94. Kilpatrick, L., McCawley, L., Nachiappan, V., Greer, W.,
Majumdar, S., Korchak, H.M., Douglas, S.D. (1992)a-1-Antichymotrypsin inhibits the NADPH oxidase-enzyme
complex in phorbol ester-stimulated neutrophil membranes.jImmuno/. 149, 3059-3065.
95. Camussi, G., Tetta, C., Bussolino, F., Baglioni, C. (1988) Syn-
thesis and release of platelet activating factor is inhibited by
plasma ai-proteinase inhibitor or a1-antichymotrypsin and isstimulated by proteinases. j Exp. Med. 168, 1293-i306.
96. Bass, D.A., McPhail, L.C., Schmidt, J.D., Morris-Natschke,
S., McCall, CE., Wykle, R.L. (i989) Selective priming of rateand duration of the respiratory burst of neutrophils by1,2-diacyl and i-O-alkyl-2-acyl diglycerides.j BiOL Chem. 264,19610-19617.
97. Lew, D.P. (1989) Receptor signaling and intracellular calcium
in neutrophil activation. Eur. j C/in. Invest. 19, 338-346.98. Berger, M., Wetzler, EM., Wallis, R.S. (1988) Tumor necrosis
factor is the major monocyte product that increases comple-ment receptor expression on mature human neutrophils. Blood
71, i5i-i58.99. Leino, L., Lilius, E.-M. (1992) The up- and down-modulation
of immunoglobulin G Fe receptors and complement receptorson activated neutrophils depends on the nature of the activa-
tor.J. Leukoc. Biol. 51, 157-163.100. Fleit, H.B., Kobasiuk, CD., Daly, C., Furie, R., Levy, P.C.,
Webster, R.0. (1992) A soluble form of FcyIII is present in hu-
man serum and other body fluids and is elevated at sites ofinflammation. Blood 79, 2721-2728.
101. Gavioli, G., Risso, A., Smilovich, D., Baldissarro, I., Capra,
MC., Bargellesi, A., Cosulich, ME. (1992) CD69 molecule inhuman neutrophils: its expression and role in signal-transducing mechanisms. Ce/I. Immunol. 142, i86-l96.
102. Ducker, T.P., Skubitz, KM. (1992) Subcellular localization of
CD66, CD67, and NCA in human neutrophils. j Leukoc. BioL
52, il-i6.103. Niessen, H.W.M., Verhoeven, A.J. (1992) Differential up-
regulation of specific and azurophilic granule membrane mar-
kers in electropermeabilized neutrophils. Cell SignaL 4,501-509.
104. Kuijpers, T.W., Tool, A.TJ., van der Schoot, CE., Ginsel,
L.A., Onderwater, J.J.M., Roos, D., Verhoeven, A.J. (1991)
Membrane surface antigen expression on neutrophils: a reap-praisal and use of surface markers for neutrophil activation.Blood 78, 1105-1111.
105. Thelen, M., Dewald, B., Baggiolini, M. (1993) Neutrophil sig-
nal transduction and activation of the respiratory burst. Phys-
ioL Rev. 73, 797-821.106. Dewald, B., Thelen, M., Baggiolini, M. (1988) Two transduc-
tion sequences are necessary for neutrophil activation byreceptor agonists. j BioL Chem. 263, 16179-16184.
107. McPhail, L.C., Shirley, P.S., Clayton, CC., Snyderman, R.
(1985) Activation of the respiratory burst enzyme from human
neutrophils in a cell-free system. J. C/in. Invest. 75, 1735-1739.
108. Simms, H.H., Frank, MM., Quinn, T.C., Holland, S.,
Gaither, T.A. (1989) Studies on phagocytosis in patients with
acute bacterial infections. j C/in. Invest. 83, 252-260.109. Tullgren, 0., Giscombe, R., HoIm, G., Johansson, B., Mdl-
stedt, H., Bjorkholm, M. (1991) Increased lummol-enhancedchemiluminescence of blood monocytes and granulocytes inHodgkin’s disease. C/in. Exp. immunol. 85, 436-440.
110. Suematsu, M., Suzuki, M., Kitahora, T., Miura, T., Suzuki,K., Hibi, T., Watanabe, T., Nagata, H., Asakura, H.,Tsuchiya, M. (1987) Increased respiratory burst of leukocytes
Smith Neutrophils, host defense, and inflammation 683
in inflammatory bowel diseases - the analysis of free radical
generation using chemiluminescence probe. j C/in. Lab. Im-
munol. 24, 125-128.iii. Bloomfield, F.J., Young, MM. (1988) Enhanced chemilumi-
nescence production by phagocytosing neutrophils in psoriasis.inflammation 12, 153-159.
112. Barth, J. , Entzian, P. , Petermann, W. (1988) Increased releaseof free oxygen radicals by phagocytosing and nonphagocytos-ing cells from patients with active pulmonary sarcoidosis as
revealed by luminol-dependent chemiluminescence. K/in.
Wochenschr. 66, 292-297.113. Trautinger, F., Hammerie, A.F., Poschi, G., Micksche, M.
(1991) Respiratory burst capability of polymorphonuclear neu-
trophils and TNF-a serum levels in relationship to the develop-ment ofseptic syndrome in critically ill patients.j Leukoc. Biol.
49, 449-454.114. Smith, J.A., Telford, RD., Mason, lB., Weidemann, M.J.
(1990) Exercise, training and neutrophil microbicidal activity.Int. j Sports Med. 11, 179-187.
115. Panyutich, A.V., Panyutich, E.A., Krapivin, E.A., Ganz, T.
(1993) Plasma defensin concentrations are elevated in patientswith septicemia or bacterial meningitis.]. Lab. C/in. Med. 122,202-207.
116. Pyne, D.B. (1994) Regulation of neutrophil function during ex-
ercise. Sports Med. 17, 245-258.1i7. Dufaux, B., Order, U. (1989) Plasma elastase-ai-antitrypsin,
neopterin, tumor necrosis factor and soluble interleukin-2receptor after prolonged exercise. In!. j Sports Med. 10,434-438.
118. Kallenberg, C.G.M., Mulder, A.H.L., Tervaert, J.W.C. (1992)Antineutrophil cytoplasmic antibodies: a still-growing class ofautoantibodies in inflammatory disorders. Am. j Med. 93,675-682.
119. Blalock, J.E. (1989) A molecular basis for the bidirectionalcommunication between the immune and neuroendocrine sys-tems. Physiol. Rev. 69, 1-32.
120. Reichlin, S. (1993) Neuroendocrine-immune interactions. N
EngL ]. Med. 329, 1246-1253.
121. Nicola, NA. (1989) Hemopoietic cell growth factors and theirreceptors. Annu. Rev. Biochem. 58, 45-77.
122. Dularay, B., Elson, C.J., Clements-Jewery, S., Damais, C.,
Lando, D. (1990) Recombinant human interleukin-I betaprimes human polymorphonuclear leukocytes for stimulus-induced myeloperoxidase release. ]. Leukoc. Biol. 47, 158-163.
123. Shalaby, MR., Palladino, MA., Hirabayashi, SE., Eessalu,
T.E., Lewis, GD., Shephard, H.M., Aggarwal, B.B. (1987)Receptor binding and activation of polymorphonuclear neu-trophils by tumor necrosis factor-alpha. j Leukoc. Biol. 41,196-204.
124. Kharazmi, A., Nielsen, H., Rechnitzer, C., Bendtzen, K.(1989) Interleukin-6 primes human neutrophil and monocyteoxidative burst response. Immunol. Lett. 21, 117-184.
125. Wewers, M.D., Rinehart,J.J., She, Z.-W., Herzyk, D.J., Hum-
mel, MM., Kinney, PA., Davis, W.B. (1990) Tumor necrosis
factor infusions in humans prime neutrophils for hypochlorousacid production. Am. ]. Physiol. 259, L276-L282.
126. Fong, Y., Lowry, S.F. (1990) Tumor necrosis factor in the
pathophysiology of infection and sepsis. C/in. immunol. Im-
munopathol. 55, 157-170.127. Yuo, A., Kitagawa, S., Kasahara, T., Matsushima, K., Saito,
M., Takaku, F. (1991) Stimulation and priming of human neu-
trophils by interleukin-8: cooperation with tumor necrosis fac-tor and colony-stimulating factors. Blood 78, 2708-27i4.
128. Ohsaka, A., Kitagawa, S., Sakamoto, S., Miura, Y., Takanashi,N., Takaku, F., Siato, M. (1989) In vivo activation of humanneutrophil functions by administration of recombinant human
granulocyte-colony stimulating factor in patients with malig-
nant lymphoma. Blood 74, 2743-2748.129. Cross, AS., Sadoff, J.C., Kelly, N., Bernton, E., Gemski, P.
(1989) Pretreatment with recombinant murine tumor necrosisfactor-a/cachectin and murine interleukin-la protects micefrom lethal bacterial infection.]. Exp. Med. 169, 2021-2027.
130. jupin, C., Parant, M., Chedid, L. (1989) Involvement of reac-
tive oxygen metabolites in the candidacidal activity of human
neutrophils stimulated by muramyl dipeptide and tumornecrosis factor. Immunobiology 180, 68-79.
131. Van’t Wout, j.W., Van der Meer, J.W.M., Barza, M., Dinarello,CA. (1988) Protection ofneutropenic mice from lethal Candida
albicans infection by recombinant interleukin 1. Eur. ]. Immunol.
18, 1143-1146.
132. Abramson, S.L., Gallin, J.I. (1990) IL-4 inhibits superoxide
production by human mononuclear phagocytes. j Immunol.
144, 625-630.
133. Boey, H., Rosenbaum, R., Castracane, j., Borish, L. (1989)
Interleukin-4 is a neutrophil activator. j C/in. Allergy immunol.
83, 978-984.
134. Wertheim, WA., Kunkel, S.L., Standiford, T.J., Burdick,
M.D., Becker, F.S., Wilke, CA., Gilbert, AR., Strieter, R.M.(1993) Regulation of neutrophil-derived IL-8: the role of
prostaglandin E2, dexamethasone, and IL-4. j Immuno/. 151,2166-2i75.
135. Collotta, F., Re, F., Muzio, M., Bertini, R., Polentarutti, N.,
Sironi, M., Gin, J.G., Dower, 5K., Sims, j.E., Mantovani, A.
(1993) Interleukin-i type II receptor: a decoy target for IL-i
that is regulated by IL-4. Science 261, 472-475.
136. Castatella, MA., Meda, L., Bonora, S., Ceska, M., Constan-
tin, G. (1993) Interleukin-iO (IL-b) inhibits the release of
proinflammatory cytokines from human polymorphonuclear
leukocytes.j Exp. Med. 178, 2207-2211.137. jenkins, j.K., Malyak, M., Arend, W.P. (1994) The effects of
interleukin-lO on interleukin-i receptor antagonist andinterleukin-if3 production in human monocytes and neu-
trophils. Lymphokine Cytokine Res. 13, 47-54.
138. Gosset, P., Perez, T., Lassalle, P., Duquesnoy, B., Farre, J.M.,Tonnel, A.B., Capron, A. (1991) Increased TNF-a secretion byalveolar macrophages from patients with rheumatoid arthritis.Am. Rev. Respir. Dis. 143, 593-597.
139. Collotta, F , Re, F. , Polentarutti, N. , Sozzani, S. , Mantovani,A. (1992) Modulation of granulocyte survival and programmed
cell death by cytokines and bacterial products. Blood 80,2012-2020.
140. Kasama, T., Strieter, R.M., Standiford, T.j., Burdick, M.D.,
Kunkel, S.L. (1993) Expression and regulation of humanneutrophil-derived macrophage inflammatory protein icr. jExp. Med 178, 63-72.
141. jeffes, E.W.B., III, Ininns, E.K., Schmitz, K.L., Yamamoto,R.S., Dett, CA., Granger, GA. (1989) The presence of anti-bodies to lymphotoxin and tumor necrosis factor in normal se-
rum. Arthritis Rheum. 32, 1148-1152.142. Porteu, F., Nathan, C. (1990) Shedding of tumor necrosis fac-
tor receptors by activated neutrophils.j Exp. Med. 172, 599-607.143. Dinarello, CA., Gelfand, j.A., Wolff, SM. (1993) Anticytokine
strategies in the treatment of the systemic inflammatory
response syndrome. JAMA 269, 1829-1835.144. Nathan, CF. (1989) Respiratory burst in adherent human neu-
trophils: triggering by colony-stimulating factors CSF-GM and
CSF-G. Blood 73, 301-306.145. Aida, Y., Pabst, M.j. (1991) Neutrophil responses to
lipopolysaccharide: effect ofadherence on triggering and prim-
ing of the respiratory burst. ]. immuno/. 146, 1271-1276.146. Schumann, R.R., Leong, SR., Flaggs, G.W., Gray, P.W.,
Wright, S.D., Mathison, j.C., Tobias, P.S., Ulevitch, R.j.(i990) Structure and function of lipopolysaccharide binding
protein. Science 249, 1429-1433.147. Sedgewick, J.B., Berube, ML., Zurier, RB. (1985) Stimulus-
dependent inhibition of superoxide generation by prostaglan-dins. C/in. Immunol. Immunopathol. 34, 205-215.
148. Vercellotti, G.M., Yin, H.Q, Gustafson, KS., Nelson, R.D.,jacob, H.S. (1988) Platelet-activating factor primes neutrophilresponses to agonists: role in promoting neutrophil-mediatedendothelial damage. Blood 71, 1100-1107.
149. Braquet, P., Touqui, L., Shen, T.Y., Vargaftig, B.B. (1987) Per-spectives in platelet-activating factor research. PharmacoL Rev.
39, 98-145.150. Poubelle, P.E., Gingras, D., Demers, C., Dubois, C., Harbour,
D., Grassii, j., Rola-Pleszczynski, M. (1991) Platelet-activating
686 Journal of Leukocyte Biology Volume 56, December 1994
factor (PAF-acether) enhances the concomitant production of
tumor necrosis factor-alpha and interleukin-l by subsets of hu-man monocytes. immunology 72, i81-i87.
151. Stewart, AG., Harris, T., De Nichilo, M., Lopez, A.F. (1991)
Involvement of leukotriene B4 and platelet-activating factor incytokine priming of human polymorphonuclear leucocytes.
immunology 72, 206-212.
152. Wirthmueller, U., de Weck, AL., Dahinden, CA. (1990)
Studies on the mechanism of platelet-activating factor produc-
tion in GM-CSF primed neutrophils: involvement of protein
synthesis and phospholipase A2 activation. Biochem. Biophys.
Res. Commun. 170, 556-562.153. DiPersio, j.F., Billing, P., Williams, R., Gasson, J.C. (1988)
Human granulocyte-macrophage colony-stimulating factorand other cytokines prime human neutrophils for enhancedarachidonic acid release and leukootriene B4 synthesis. ]. Im-
munol. 140, 4315-4322.154. Ader, R., Felten, D., Cohen, N. (1990) Interactions between
the brain and the immune system. Annu. Rev. Pharmacol. Toxicol.
30, 561-602.155. Levi, F.A., Canon, C., Touitou, Y., Sulon, j., Mechkouri, M.,
Ponsart, E., Touboul, j.P., Vannetzel, j.M., Mowzowicz, I.,
Reinberg, A., Mathe, G. (1988) Circadian rhythms in circulat-ing T lymphocyte subsets and plasma testosterone, total and
free cortisol in five healthy men. C/in. Exp. Immunol. 71,329-335.
156. Gala, R.R. (1991) Prolactin and growth hormone in the regula-
tion of the immune system. Proc. Soc. Exp. Bwl. Med. 198,513-526.
157. Fu, Y.K., Arkins, S., Fuh, G., Cunningham, B.C., Wells, j.A.,
Fong, S., Cronin, M.j., Dantzer, R., Kelley, K.W. (1992)Growth hormone augments superoxide anion secretion of hu-
man neutrophils by binding to the prolactin receptor. j C/in.
Invest. 89, 451-457.158. Fu, Y.K., Arkins, S., Li, Y.M., Dantzer, R., Kelley, K.W.
(1994) Reduction in superoxide secretion and bactericidal ac-
tivity of neutrophils from aged rats: reversal by the combina-
tion of gamma interferon and growth hormone. inject. immun.
62, 1-8.159. Wiedermann, C.j., Niedermuhlbichlcr, M., Braunstiner, H.
(1992) Priming of polymorphonuclear neutrophils by atrialnatriuretic peptide in vitro. ]. C/in. Invest. 89, 1580-1586.
160. Munck, A., Guyre, P.M. (1986) Glucocorticoid hormones in
stress: physiological and pharmacological actions. News PhysioL
Sci. 1, 69-72.161. Petroni, K.C., Shen, L., Guyre, P.M. (1988) Modulation of hu-
man polymorphonuclear leukocyte IgG Fc receptors and Fe
receptor-mediated functions by IFN-gamma and glucocorti-coids. j Immunol. 140, 3467-3472.
162. Coates, T.D., Wolach, B., Tzeng, DY., Higgins, C., Baehner,
R.L., Boxer, L.A. (1983) The mechanism of action of the an-
tiinflammatory agents dexamethasone and auranofin in hu-
man polymorphonuclear leukocytes. Blood 62, 1070-1077.163. Webb, D.S.A., Roth, J.A. (1987) Relationship of glucocorticoid
suppression of arachidonic acid metabolism to alteration of
neutrophil function. j Leukoc. Biol. 41, 156-164.164. Bazzoni, G., Dejana, E., Del Maschio, A. (1991) Adrenergic
modulation of human polymorphonuclear leukocyte activa-
tion. Potentiating effect of adenosine. Blood 77, 2042-2048.
165. Dantzer, R., Kelley, K.W. (1989) Stress and immunity: an in-
tegrated view of relationships between the brain and the immune
system. Life Sci. 44, 1995-2008.166. Morley,j.E., Kay, N.E., Solomon, GE, Plotnikoff, NP. (1987)
Neuropeptides: conductors of the immune orchestra. LjJe Sci.
41, 527-544.167. Diamant, M., Henricks, P.A.J., Nijkamp, F.P., de Wied, D.
(1989) 13-Endorphin and related peptides suppress phorbol-
myristate acetate-induced respiratory burst in human poly-
morphonuclear leucocytes. Life Sci. 45, 1537-1545.168. Fantozzi, R., Brunlleschi, S., Guiliattini, L., Blandina, P.,
Masini, E., Cavallo, G., Mannaioni, P.F. (1985) Mast cell andneutrophil interactions: a role for superoxide anion and hista-
mine. At�ent Actions 16, 260-264.
169. Conte, P., Reale, M., Barbacane, R.C., Bongrazio, M.,
Panara, MR. (1990) Lipoxins A4 and B4 inhibit leukotriene B4generation from human neutrophil leukocyte suspensions. Im-
munol. Lett. 24, 237-242.170. McGarrity, ST., Hyers, TM., Webster, R.O. (i988) Inhibition
of neutrophil functions by platelets and platelet-derivedproducts: description of multiple inhibitory properties. ]. Leu-
koc. Biol. 44, 93-100.171. Nagata, K., Tsuji, T., Todoroki, N., Katagiri, Y., Tanoue, K.,
Yamazaki, H., Hanai, N., Irimura, T. (1993) Activated plate-lets induce superoxide anion release by monocytes and neu-
trophils through P-selectin (CD62).j ImmunoL 151, 3267-3273.
172. Boxer, L.A., Axtell, R., Suchard, S. (1990) The role ofthe neu-
trophil in inflammatory diseases of the lung. Blood Ce//s 16,25-42.
173. Renz, H., Gong, j.-H., Schmidt, A., Nain, M., Gemsa, D.
( 1988) Release of tumor necrosis factor-a from macrophages;enhancement and suppression are dose-dependently regulated
by prostaglandin E2 and cyclic nucleotides. ]. Immunol. 141,2388-2393.
174. Coffey, R.G., Davis, J.S., Djeu, J.Y. (1988) Stimulation of
guanylate cyclase activity and reduction of adenylate cyclase
activity by granulocyte-macrophage colony-stimulating factor
in human blood neutrophils. ]. ImmunoL 140, 2695-2701.175. Cronstein, B.N. (1994) Adenosine, an endogenous anti-inflam-
matory agent. ]. AppI. Physio/. 76, 5-13.176. de la Harpe, Nathan, CF. (1989) Adenosine regulates the
respiratory burst of cytokine-triggered human neutrophils ad-
herent to biological surfaces. j Immunol. 143, 596-602.
177. Aguila, MC., Dees, W.L., Haensly, WE., McCann, ,S.M.
(1991) Evidence that somatostatin is localized and synthesizedin lymphoid organs. Proc. NatI. Acad. Sci. USA 88, 11485-11489.
178. Blalock, j.E. (1992) Production of peptide hormones and neu-
rotransmitters by the immune system. In Neuroimmunoendocri-
nology, 2nd ed. U.E. Blalock, ed) Basel, Karger, 1-24.179. Lipschitz, D.A., Udupa, KB. (1986) Influence of aging and
protein deficiency on neutrophil function. j GerontoL 41,690-694.
180. Chandra, R.K. (1992) Effect ofvitamin and trace-element sup-
plementation on immune responses and infection in elderly
subjects. Lancet 340, 1124-1127.
181. Kaffenberger, W., Clasen, B.P.E., Van Beuningen, D. (1992)
The respiratory burst of neutrophils: a prognostic parameterin head and neck cancer? C/in. ImmunoL immunopathoL 64,57-62.
182. Dallegri, F., Ballestrero, A., Ottonello, L., Patrone, F. (1989)
Defective antibody-dependent tumour cell lysis by neutrophils
from cancer patients. C/in. Exp. immunol. 77, 58-61.183. Irwin, M. (1993) Stress-induced immune suppression. Ann.
N}’ Acad Sci. 697, 203-218.
184. Smith, j.A., Weidemann, M.j. (1990) The exercise and immu-
nity paradox: a neuroendocrine/cytokine hypothesis. Med. Sci.
Res. 18, 749-753.185. Mackinnon, L.T. (1992) Exercise and Immunology. Curr. Issues
Exercise Sci. 2, 1-90.
186. Shephard, Rj. (1990) Physical activity and cancer. Int. ]. Sports
Med. 11, 413-420.187. Dufaux, B., Order, U., Liesen, H. (1991) Effect of short max-
imal physical exercise on coagulation, fibrinolysis, and comple-
ment system. mt. j Sports Med. 12(Suppl. 1), 538-542.188. Sixou, S., Teissie, J. (i992) In vivo targeting of inflammed
areas by electroloaded neutrophils. Biochem. Biophys. Res. Com-
mun. 186, 860-866.189. Das, U.N. (1991) Interaction(s) between essential fatty acids,
eicosanoids, cytokines, growth factors and free radicals:
relevance to new therapeutic strategies in rheumatoid arthritisand other collagen vascular diseases. Prostaglandins Leukoir. Es-
sent. Fatty Acids 44, 201-210.190. Lehmmann, V., Benninghoff, B., Droge, W. (1988) Tumor
necrosis factor-induced activation of peritoneal macrophagesis regulated by prostaglandin E2 and cAMP.]. Immunol. 141,587-591.
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