Neuropathology and Applied Neurobiology 1997, 23, 83–92

Astrocytic adhesion molecules are increased in

HIV-1-associated cognitive/motor complex

D. Seilhean, A. Dzia-Lepfoundzou*, V. Sazdovitch, B. Cannella†, C. S. Raine†, C. Katlama*, F. Bricaire*,C. Duyckaerts and J.-J. Hauw

Raymond Escourolle Laboratory of Neuropathology and *Department of Infectious Diseases, La Salpêtrière Hospital, Paris, France,and †Department of Pathology, Division of Neuropathology, Albert Einstein College of Medicine, Bronx, NY, USA

D. Seilhean, A. Dzia-Lepfoundzou, V. Sazdovitch, B. Cannella, C. S. Raine, C. Katlama, F. Bricaire, C. Duyckaertsand J.-J. Hauw (1997) Neuropathology and Applied Neurobiology 23, 83–92Astrocytic adhesion molecules are increased in HIV-1-associated cognitive/motor complex

Half of AIDS dementia cases are associated with HIV-encephalitis or myelin pallor. Another half die with noHIV-related neuropathological changes. Previous obser-vations suggest that cerebral dysfunction may resultfrom more subtle cellular interactions, and that some ofthem may be mediated by cell adhesion molecules. In thepresent study the expression by astrocytes and endo-thelial cells of intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) wasanalysed as a function of the neuropathological diag-nosis, the density of astrogliosis and of HIV-1 positivecells, and of the mental status. Twelve AIDS cases,without focal brain lesion, eight of whom weredemented, were selected from a prospective study. Theywere compared with six control cases with multiple

sclerosis, and with six control patients without neuro-logical disease. ICAM-1 and VCAM-1 expression waslocalized by immunofluorescence and confocal mi-croscopy. HIV protein gp41 was detected by immuno-histochemistry on adjacent sections. Endothelialexpression of ICAM-1 and VCAM-1 was significantlyup-regulated in all AIDS patients. VCAM-1 only wasrelated to myelin pallor. The density of VCAM-1 orICAM-1 positive astrocytes increased in demented AIDSpatients, independently of the neuropathological findingsor the density of gp41 positive cells. Expression of celladhesion molecules, together with other secondarymechanisms such as secretion of cytokines may play arole in the pathogenesis of white matter lesions leadingto HIV-1-associated cognitive changes.

Keywords: VCAM-1, ICAM-1, AIDS dementia complex, prospective study, confocal microscopy

Introduction

AIDS dementia complex [27] or HIV-1-associatedcognitive/motor complex [58] occurs in about 15–20%of AIDS cases, mainly in the late stages of the disease[25]. This cognitive decline typically presents as a sub-cortical dementia [27, 58], the mechanism of which isstill obscure. Morphometric studies measuring neuronaldensities in the neocortex of AIDS patients concludedthat there was no correlation between dementia andneuronal loss, suggesting that the substrate of cognitive

impairment was more likely to be related to dysfunctionthan to death of neurons [11, 44]. Prospective studieshave estimated that only 50% of AIDS dementia caseswere associated with HIV-encephalitis, diagnosed on thepresence of multinucleated giant cells or myelin pallor[15]. Cerebral white matter is indeed one of the brainareas with the highest density of gp-41 positive cells[21]. Demyelination [20, 28] and alteration of the blood–brain-barrier [32, 33, 34] or microvasculature [50] havebeen proposed as possible mechanisms contributing tocognitive impairment. Nevertheless 50% of patientswith AIDS dementia die with no HIV-related neuro-pathological changes [15], suggesting that more subtle

Correspondence: Dr D. Seilhean, Laboratoire de NeuropathologieRaymond Escourolle, Association Claude Bernard, Hôpital de LaSalpêtrière, 47 boulevard de l’Hôpital, 75651 Paris cedex 13, France.

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neuropathological correlates for AIDS dementia exist.Recent studies have stressed a role for cytokines, inparticular tumour necrosis factor (TNF)-á. Higher levelsof TNF-á mRNAs have been found in the frontal subcor-tical white matter of patients with AIDS dementia [15,56]. In vitro this molecule is toxic for myelin [46, 57],stimulates astrocyte proliferation [47] and inducesexpression of adhesion molecules on endothelial cells,astrocytes, and microglial cells [35, 41, 43].Cell adhesion molecules are probably involved at dif-

ferent stages of HIV infection of the nervous system, frominvasion of the nervous system by infected macrophages[31, 38, 39] to cellular interactions leading to neuronaldysfunction [18, 53]. The process of cerebral dysfunctionis presumed to be initiated by penetration of the blood–brain barrier, followed by extravascular spread ofinfected macrophages. Nevertheless, considering the lownumber of infected microglial cells in AIDS brains, it wassuggested that neurotoxicity, initiated by HIV-1 infectedmacrophages, was amplified by cell–to–cell interactionswith astrocytes [10]. In vitro models of HIV infectionhave shown that astrocytes regulate the activity ofmacrophages and neurons [7, 14, 26, 30], and thatneuronal toxicity was highly dependent on the presenceof astrocytes and microglia [23].Intercellular adhesion molecule-1 (ICAM-1) and

vascular cell adhesion molecule-1 (VCAM-1) are bothinducible on the surface of endothelial cells and astro-cytes by cytokines such as tumour necrosis factor(TNF)-á and interferon-ã, released by activated microglia[13, 36, 41, 43]. They belong to the same superfamily ofimmunoglobulins and recognize different types of ligandsof the integrin family. All types of leucocytes tend toadhere to ICAM-1, which is constitutively expressed byendothelial cells, with a significant increase after acti-vation by cytokines [52], whereas VCAM-1 supports theadhesion of lymphocytes and monocytes [9]. In thesimian immunodeficiency virus (SIV) encephalitis model,VCAM-1, unlike ICAM-1, is highly expressed on whitematter blood vessels and mediates the entry into thebrain of circulating HIV-infected blood macrophages[38, 39]. Elevated levels of soluble ICAM-1 have beenfound in the serum and cerebrospinal fluid of dementedHIV-infected patients [17].The purpose of this study was to test the hypothesis

that higher expression of ICAM-1 and VCAM-1 onastrocytes and endothelial cells in the brain of AIDSpatients was a correlate of both viral spread into the CNS

and cognitive impairment. ICAM-1, VCAM-1 and cellu-lar markers were detected by immunohistochemistry inthe frontal white matter of selected AIDS patients takenfrom a prospective study. This expression was analysedas a function of various parameters: (i) the neuropatho-logical diagnosis; (ii) the density of associated astro-gliosis; (iii) the density of gp-41-positive cells; (iv) theseverity of the cognitive decline measured by the MiniMental State evaluation [14]. The results were comparedwith those obtained in patients with multiple sclerosisand in normal controls.

Patients and methods

AIDS patients

Twelve AIDS patients, whose intellectual status had beenprospectively assessed (Table 1) were selected from aseries of 382 HIV-positive cases whose brain had beenexamined in the Raymond Escourolle laboratory at LaSalpêtrière from 1981 to 1993 [45]. The selectedpatients were men who did not have focal lesions oncomputerized tomography (CT) scan, magnetic reso-nance imaging (MRI), or macroscopic examination of thebrain. The diagnosis of dementia was made in eight of 12cases, following the DSM-IV criteria [2]. In addition, innine cases, the cognitive performances were measuredwith the Mini Mental Status (MMS) psychometric evalu-ation [12]. MMS scores superior to 24/30 (n=4) wereconsidered normal [3]. Three other patients (1, 2, 3),already included in a previous study, had undergone anextensive battery of psychometric tests, recommendedfor the evaluation of HIV-1-associated cognitive/motorcomplex [58], which had shown moderate to severeintellectual deterioration [44]. Cognitive decline wasneither related to age (Table 1), nor to immunosuppres-sion level (CD4 lymphocytes=30&11/mm3).

Controls

Six patients with multiple sclerosis (MS) were included inthe study as controls exhibiting an inflammatory diseaseof the central nervous system (CNS). All MS cases had achronic relapsing form of the disease (duration of thedisease: 18&1.3 years). Six controls without knownneurological disease died of miscellaneous causes. Agesdid not differ significantly between AIDS (41&3 years),MS (48&3 years) and normal control patients (48&6years).

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Tissues

Post-mortem was performed 29&4 h after death. Thebrain and spinal cord were removed. The brain weightwas not significantly different in AIDS (1380&30 g), inMS (1320&90 g), and in controls (1380&50 g), anddid not vary according to the mental status in AIDS cases(Table 1). One hemisphere, left or right at random, wasfixed in 4% formalin for conventional histopathology.Seven micron-thick paraffin sections from the midfrontal,superior temporal and cingulate gyri, hippocampus,occipital cortex, nucleus basalis of Meynert, head of thecaudate nucleus, pallidum, white matter of the centrumovale, dentate nucleus, spinal cord at cervical, thoracicand lumbar levels were studied.On the other cerebral hemisphere, a frontal coronal

section through the mamillary bodies was sampled forcryopreservation. Eleven regions were frozen in iso-pentane cooled by liquid nitrogen, and were stored at"80 )C. White matter from the centrum semi-ovale wasstudied by immunohistochemistry. In MS cases, plaquesand peri-plaques were sampled from the same region asfor AIDS cases. Frozen sections were obtained with acryostat (nominal thickness: 10 ìm).

Immunohistochemistry for HIV and CMV proteins

HIV proteins were sought in frozen sections of thefrontal white matter from all AIDS and MS cases,

using a monoclonal antibody directed against thegp41 antigen (Dako: 1:100). Immunohistochemistry forCMV early and late antigens was performed with amonoclonal antibody (Dako: 1:600) on paraffin sec-tions in AIDS cases. A biotinylated anti-mouse IgG(Amersham: 1:200), detected with streptavidin-peroxidase (Amersham: 1:400), was used as secondaryantibody.

Immunohistochemistry of adhesion molecules

MS plaque areas were used as positive controls. Adhesionmolecules were detected in frozen sections with mono-clonal antibodies (Immunotech): anti-ICAM-1 (1:25)and anti-VCAM-1 (1:20). The secondary antibodywas an anti-mouse IgG either labelled with FITC(Cappel: 1:200) or biotinylated (Amersham: 1:200) anddetected with steptavidin-peroxidase (Amersham:1:400). Cell adhesion molecules were localized by doublelabelling with polyclonal anti-GFAP (Dako: 1:200) forastrocytes, and lectin Ulex europaeus (Dako: 1:500)detected with an anti-Ulex polyclonal antibody (Dako:1:250) for endothelial cells. The secondary antibodywas a biotinylated anti-rabbit IgG (Amersham: 1:200)detected with a streptavidin-Texas-red complex(Amersham: 1:300) or with a streptavidin/alkalinephosphatase system (Vectastain Kit, Vector: 1:100).

Table 1. Clinical and neuropathological data for AIDS patients

CasesAge(years)

Riskfactor MMS

Brainweight (g) MNGCs

Microglialnodules

Myelinpallor Additional findings

gp41+cells

1 32 D ** 1200 + + ++ — 47.6&62 45 ? * 1410 " + + CMV encephalitis 10.8&13 47 H *** 1550 " " + — 16.3&14 32 D 0 1340 + + ++ — 48.1&75 67 H 13 1370 + + +++ — 16.3&26 49 D 20 1330 " " " — 32.6&27 26 D 22 1300 " + " Chronic toxoplasmosis 30.3&48 26 D 23 1500 " " " — 12.2&49 47 H 26 1450 " + " Chronic toxoplasmosis 26.4&410 37 H 28 1450 " + " CMV encephalitis+Cryptococcosis 16.0&311 38 H 29 1350 " " " Central pontine myelinolysis 3.9&112 47 H 30 1300 " + " CMV encephalitis 4.1&1

D, Drug addict. H, Homosexual. ?, Unknown. MMS, The last score obtained with Mini Mental Status (MMS) examination (score/30) [12].Patients 1, 2, 3 underwent a battery of psychometric tests other than MMS (cf. patients 3, 4, 5 in [44]). For those three patients,deterioration is quoted as moderate (*) to severe (***). MNGCs: Mononucleated giant cells. Myelin pallor, In the frontal lobe white matter:quoted mild (+) to severe (+++). gp41 positive cells, Mean&1 standard error of the mean (SEM)mm2 in the frontal white matter.

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Confocal microscopy

Co-localization of adhesion molecules and cellular mark-ers (GFAP and Ulex europaeus) was qualitativelyassessed in confocal microscopy (Biorad MRC-600; CSLMPhoibos 1000).

Quantitative assessment

Cell densities and all Ulex-positive vascular profiles,whatever their orientation, were counted at #100magnification (#10 objective) within fields of0.735 mm2. The mean and standard error of the mean(SEM) of 12 fields/case were calculated. The results wereexpressed in n/mm2.

Statistical analysis

VCAM-1 and ICAM-1 expression on astrocytes andendothelial cells was analysed as a function of: (i) consen-sual neuropathological criteria [5]; (ii) density of HIV-positive cells; (iii) astrogliosis; and (iv) cognitive abilitiesmeasured by the MMS score. Non-parametric tests wereused for statistical analysis. Groups were compared withthe Mann–Whitney U-test and interrelationships of quan-titative variables were analysed with the Kendall rankcorrelation coefficient, on Statview 4.02 software. Valuesof P¦0.05 were considered significant. Bonferroni’s cor-rection was used for multiple comparisons. The meanvalues are given &1 standard error of the mean (SEM).

Results

Neuropathological diagnosis

In AIDS cases, the neuropathological diagnosis wasbased on the criteria proposed in a consensus report [5].Histology combined with gp-41 immunoreactivity led tothe detection of HIV-1-induced cellular changes (HIV-encephalitis) (Table 1).

HIV-encephalitisThree patients (1, 4 and 5) had characteristic features ofHIV-encephalitis including multinucleated giant cells(MNGCs), microglial nodules and myelin pallor (Table 1).Six others had various degrees of cortical and subcorticalastrogliosis associated with frontal and temporal corticalspongiosis. Myelin pallor associated or not with MNGCsand microglial nodules was found in five of eight demented

patients (Table 1). Perivascular macrophages were foundin all AIDS cases. Gp41 intracytoplasmic positivity (Figure1a) was detected either in some perivascular macrophages(12/12 cases), in multinucleated giant cells (three of 12cases) or in rod-shaped microglia (five of 12 cases), con-firming the morphological heterogeneity of infectedcells found by other authors [21]. For densities above16.3/mm2, most gp41 positive cells were rod-shapedmicroglia (Figure 1a), spread throughout the whitematter. The highest densities were observed in cases 1 and4, which both had multinucleated giant cell encephalitis.

Additional brain pathology (Table 1)In six of 12 cases, additional neuropathological featureswere found at a distance from the frontal white matter,which was sampled for immunohistochemical study.Three patients (2, 10 and 12) had CMV encephalitis withcytomegalic inclusions and CMV-positive cells. CMVpositivity was found in the ependymal and subependy-mal areas of the lateral ventricles (case 2 and 12), in thedorsal part of the medulla (case 12) and in the cerebel-lum (case 10). Cytoplasmic and nuclear positivity wasfound in cytomegalic cells with owl’s eye inclusions,whereas positivity was limited to the nucleus in somesubependymal cells without inclusion.Two cases had small foci of cystic microabcesses with

mineral deposits limited to the pallidum (case 7) and tothe pons (case 9) corresponding to chronic toxoplasmosis[8, 42]. Case 11, who was treated for Hodgkin’s disease,had recent central pontine myelinolysis.

MS and control cases

In MS cases, demyelinated and gliotic plaques werenumerous. Two cases presented with scattered perivas-cular lymphocytic infiltrates, in areas at a distance fromplaques, including those used for immunohistochemistry.In control cases, no lesion was observed, except for someanoxic-ischaemic neurons in three cases, and scatteredperivascular cuffs of mononucleated cells in two cases.No gp41 positivity was detected in MS and control cases.

Astrogliosis

The density of GFAP positive astrocytes in the white mat-ter of the frontal lobe was higher in AIDS (U=4,P=0.0027) and MS cases (U=4, P=0.025) than in con-trols (Table 2; Figure 2a). AIDS and MS cases did not differ

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significantly. In AIDS patients, the densities of GFAP andgp41 positive cells were related (ô=0.615, P=0.0054).CMV encephalitis (n=3) was not statistically associatedwith marked astrogliosis in the frontal white matter.

Cell adhesion molecules

Qualitative assessmentThe cellular pattern of labelling was similar for ICAM-1and VCAM-1. Endothelial cells showed a diffuse cyto-plasmic labelling (Figure 1b). In astrocytes, focal posi-

tivity was observed in the cell body, close to themembrane, and extended usually to one or more pro-cesses (Figure 1c). In microglial cells, the cytoplasmicmembrane and most processes were labelled.In some control cases, cell adhesion molecules were

detected on endothelial cells (VCAM-1: two of six cases;ICAM-1: four of six cases), whereas neither VCAM-1 norICAM-1 were detectable on GFAP positive astrocytes. Inevery AIDS and MS case, VCAM-1 and ICAM-1 weredetected on endothelial cells and astrocytes. Some GFAPnegative cells were also labelled, including perivascular

Figure 1. Immunohistochemistry ofgp41 and cell adhesion molecules. a,gp-41 positive cell with elongatedcytoplasm and fine processesconsistent with a rod-shapedmicroglial cell. b,c, Co-localization ofcell adhesion molecules in confocalmicroscopy, showing (b) endothelialcells (Ulex+) labelled with FITC andICAM-1 detected with Texas Red (c)an astrocyte (GFAP+) labelled withTexas Red and VCAM-1 labelled withFITC. Co-localization FITC/Texas-redresults in yellow fluorescence.a#500. b#500. c#1000. Bars,20 ìm.

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macrophages and ramified microglial cells. In MS,VCAM-1 and ICAM-1 expression was not confined to thelesions, being present on blood vessels and some astro-cytes in apparently normal white matter beyond thelesion edge.

Quantitative assessment: endothelial vs astrocyticexpressionThe expressions of VCAM-1 and ICAM-1 were linked inmost cases. This was true for astrocytes (n=24; ô=0.74,P<0.0001) as for endothelial cells (n=24; ô=0.67,P<0.0001). Nevertheless the pattern of cell adhesionmolecules on astrocytes was different from that foundon endothelial cells. Endothelial expression of the celladhesion molecules was higher in AIDS patients than inMS (U=5, P=0.0037 for VCAM-1; U=3, P=0.002 forICAM-1) and in controls (U=0, P=0.0007 for VCAM-1and ICAM-1), whereas MS and control cases did notdiffer significantly from each other (Table 2; Figure 2c).Astrocytic expression of cell adhesion molecules paral-

leled GFAP positive astrogliosis (n=24; ô=0.516,P=0.0005 for VCAM-1; ô=0.547, P=0.0003 forICAM-1). As for astrogliosis, higher levels of adhesionmolecules were found in both AIDS (U=0, P=0.0006for VCAM-1 and ICAM-1) and MS patients (U=0,P=0.0021 for VCAM-1 and ICAM-1) compared withcontrols (Table 2; Figure 2b). The difference betweenAIDS and MS was significant for ICAM-1 (U=12,P=0.025) but not for VCAM-1.

Correlations with the neuropathological findingsVCAM-1 expression was higher on both astrocytes andendothelial cells in cases with myelin pallor (U=2,P=0.0117 for astrocytes; U=4, P=0.0284 for endo-thelial cells), whereas ICAM-1 did not vary significantly.Astrocytic expression of VCAM-1 and ICAM-1 wasrelated to the density of gp41 cells (ô=0.49, P=0.026 forVCAM-1; ô=0.52, P=0.018 for ICAM-1). In contrast no

correlation was found with CMV encephalitis or otheradditional pathology.

Correlations with the mental statusAIDS patients suffering from cognitive disorders (n=8)showed higher expression of astrocytic VCAM-1 (U=3.5,P=0.034) and ICAM-1 (U=1, P=0.011) than AIDSpatients without cognitive disorder (n=4). In addition, acorrelation was found between the astrocytic expressionof the two cell adhesion molecules and the MMS score(n=9; ô=–0.54, P=0.044 for VCAM-1; ô=–0.67,P=0.012 for ICAM-1) (Figure 3). Although MMS scoreswere significantly lower in the three patients with multi-nucleated giant cells encephalitis (U=1, P=0.0275),AIDS patients with cognitive disorders did not differsignificantly from others for gp41, GFAP and endothelialVCAM-1 and ICAM-1.

Discussion

The present results confirmed the hypothesis thatICAM-1 and VCAM-1 were up-regulated in the frontalwhite matter of AIDS patients, and that astrocytic andendothelial expression of VCAM-1 was increased in caseswith myelin pallor. In addition, the expression of the twoadhesion molecules exhibit patterns which suggest thatthey could mediate cellular interactions associated withcognitive dysfunction. They were differently expressed byastrocytes and endothelial cells. Endothelial expressionwas uniformly up-regulated in AIDS patients, whereashigh astrocytic expression of VCAM-1 and ICAM-1 wasonly observed in the most demented patients, even in theabsence of specific neuropathological finding. Inductionof cell adhesion molecules in AIDS brains could simplyattest the high production of TNF-á observed in frontalwhite matter [15, 56]. Based, however, on the differentpatterns of expression on the two cell types, and fol-lowing the delineation between neuroinvasion and

Astrocytes GFAP VCAM-1 ICAM-1AIDS 107.5&4.3 13.3&2.2 15.0&2.0MS 104.5&6.8 8.0&2.2 7.4&0.7Controls 64.9&5.3 0.0&0.0 0.0&0.0

Endothelial cells Ulex VCAM-1 ICAM-1AIDS 17.5&0.9 12.9&1.3 14.8&1.2MS 13.0&2.8 4.1&1.5 5.1&1.6Controls 11.9&2.0 0.9&0.6 2.2&0.9

Table 2. Quantitation of astrocytes andendothelial cells in the frontal whitematter (mean&SEM/mm2)

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neurovirulence stressed by R. T. Johnson [22], we pro-pose that endothelial cells and astrocytes may playspecific roles in the processes leading to cerebral damage:

the former participating in invasion into perivascularspaces and the latter being involved in cellular inter-actions leading to neuronal dysfunction.Constant up-regulation of endothelial VCAM-1 and

ICAM-1 was consistent with the presence of perivasculargp41 positive cells in all the cases. This finding argues fora role of both adhesion molecules in penetration byinfected macrophages into the cerebral perivascularspaces. Invasion of the nervous system has been claimedto be an early event in the course of HIV infection, sinceabnormalities including the ability to recover viruswere detected in the cerebrospinal fluid of asymptomatic

Figure 2. Quantification of astrogliosis and of the expression ofcell adhesion molecule in the frontal white matter from AIDS, MSand control patients. AIDS: n=12; MS: n=6; controls: n=6.Results are expressed as the mean density/mm2. Bars, 2 standarderrors of the mean (SEM). The Mann–Whitney U-test was used forcomparison. Significant differences are indicated: *P<0.05;**P<0.01; ***P<0.001. Significant differences with controls areindicated above the error bars, and differences between AIDS andMS are indicated by lines above the graphs (**). a, Density ofGFAP positive astrocytes. b, Density of VCAM-1 and ICAM-1positive astrocytes. c, Density of VCAM-1 and ICAM-1 positiveblood vessels. ., AIDS. , MS. , Controls.

Figure 3. Density of positive cells for adhesion molecules in thewhite matter of AIDS patients as a function of the cognitivedecline. MMS: n=9 (cf. Table 1). ,, ICAM-1. -, ICAM-2.

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HIV-positive patients [24]. However, other studies ofasymptomatic patients showed that HIV-antigens werenot detected by immunohistochemistry [16, 49], andthat PCR amplification of proviral sequences gave vary-ing results [4, 48, 49]. In Rhesus monkeys, cerebralendothelial cells express VCAM-1 as early as 2 weekspost-inoculation with pathogenic SIV [40]. The presentseries was not selected to analyse early stages of HIV-infection, but to evaluate the role of adhesion moleculesin the development of brain damage at late stages of thedisease, when it commonly occurs. The results suggestthat there is continuous endothelial activation, andrecruitment of macrophages in full blown AIDS. Incontrast with the SIV encephalitis model [38] we did notfind dramatic differences between endothelial ICAM-1and VCAM-1 expression, except in association withmyelin pallor which seemed more closely related toVCAM-1.Higher expression of VCAM-1 and ICAM-1 by astro-

cytes in the brain of demented patients, with or without aneuropathological lesion, suggests that they may play arole during the development of cerebral dysfunction. Theexpression of cell adhesion molecules might be a compo-nent of non-specific reactive astrogliosis. In fact, astro-cytic expression of VCAM-1 or ICAM-1 has been reportedin a variety of disorders in the human central nervoussystem, such as MS [6, 51], tumours [19, 36], andAlzheimer’s disease [1]. However, their up regulation inour series was more closely related to the cognitive statusthan was GFAP positive astrogliosis. VCAM-1 andICAM-1 positive astrocytes could play a specific role incerebral dysfunction by facilitating the spread of thevirus. Nevertheless, the density of gp41 cells was notsignificantly related to the cognitive decline, suggestingthat adhesion molecules could be better markers of sec-ondary processes, such as secretion of cytokines, whichamplify the toxicity of infected microglia. Direct infectionof astrocytes, restricted to the production of early regu-latory proteins, has been recently demonstrated in childencephalopathy [37, 54]. Its existence and influence onastrocytic behaviour remains to be evaluated in adults.In addition, molecular changes in frontal white matter

astrocytes could by themselves interfere with cognitiveprocessing. The central nervous system is composed ofintimately associated networks of neurons and astro-cytes, and astrocytic functions, including not only struc-tural and trophic support, but also propagation of electricactivity, are essential to neurons [29, 55].

The correlation of AIDS associated dementia with highlevels of astrocytic VCAM-1 and ICAM-1 expressionopens many questions about the cellular and molecularmechanisms of neuronal dysfunction. Expression of celladhesion molecules, together with other secondarymechanisms such as secretion of cytokines may play arole in white matter lesions leading to HIV-1-associatedcognitive changes.

Acknowledgements

We thank Michael Cammer (Albert Einstein College ofMedicine, Bronx, NY, USA) and Antoine Triller (PasteurInstitute, Paris, France) for providing the use of a con-focal microscope. We are also grateful to Claudine Berr(INSERM U360, Epidemiologic Research in Neurologyand Psychopathology, La Salpêtrière, Paris, France) forskilful advice in statistical analysis; to Leslie Conquy,Ouriel Rosenblum and Sandra Suarez for discussion ofneuropsychological data; to Christelle Py and OdileRussaouen for technical assistance; and to DawnRushton for reviewing the manuscript. This work wassupported by grants from the Agence Nationale deRecherches sur le SIDA (ANRS) and Association pour laRecherche sur la Sclérose en Plaques (ARSEP).

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