IMUNITAS SELULER DAN HUMORAL

a. Mekanisme Imunitas Seluler

b. Mekanisme Imunitas Humoral

Kuliah 7

Kriana Efendi, M.Farm., Apt.

Tipe Respon Imunitas Spesifik/didapat

Limfosit B/ sel B Humor cairan tubuh Maturasi sumsum

tulang Menyerang patogen

ekstraseluler Plasma cell Antibodies

/immunoglobulins Memory B cells

Limfosit T / sel T Maturasi Thymus Pertahanan thd patogen

intraseluler, sel kanker dan jaringan transplantasi

CD8 –cytotoxic T cells CD 4 cells –Helper T Memory T

Humoral immunity Cell Mediated immunity

Humoral Immunity Antibody-mediated Immunity

Antibody-mediated Immunity Response of B cells Secrete antibodies which circulate in

lymphatic fluid and blood• Activation:

– Antigen binds to B-cell receptor– antigen-MHC complex-Recognized by helper T cells– T cells produce interleukins that activate B cells

• Differentiation: – B cells differentiate into plasma cells & memory cells – Plasma cells release antibodies

Activation & Differentiation of B Cells

Antibody-secreting plasma cells Secrete antibodies for 4 or 5 days Cells die

Some remain as memory B cells Each particular clone able to secrete only

one type of antibody

Antibodies Also known as immunoglobulins Globular glycoproteins The heavy and light chains are polypeptides The chains are held together by disulphide

bridges Each ab has 2 identical ag binding sites –

variable regions. The order of amino acids in the variable region

determines the shape of the binding site

Antibodies Effective against extracellular antigens including

bacteria, viruses, protozoans, fungi, parasites, and toxins when they are outside cells.

combine specifically with antigen - serves as trigger

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Variable regions differ in the a.a. sequences at the antigen-binding site & are responsible for the diversity of Ab specificity

BivalentAntibodies / Immunoglobins

Fc

Antibody / Immumoglobulin• Product of B cell (plasma cell) activation

– Immunoglobulin (Ig) or antibody• Structure

– Four polypeptides – Connected by disulfide bonds– Antigen binding fragment (Fabs)– Crystallizable fragment (Fc)

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Fab

Variable (N-terminal of the heavy and light chains)

Binds to the antigenic determinant Swiveling enables more efficient Held together by disulfide bonds

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Fc

Constant (C-terminal of heavy chain) Binds to macrophages Anchors Ig to lymphocyte Held together by disulfide bonds Responsible for class identification

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Classes

Isotypes – based on the Fc fragment Immunoglobulin (Ig)

IgG IgA IgM IgD IgE

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IgG

Monomer Primary response Memory cell response Most prevalent in tissue fluid and blood

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IgA

Monomer or dimer (secretory IgA) Dimer – held together by a J chain Secretory IgA (mucous and serous

secretions)Local immunitySalivary glands, intestine, nasal membrane,

breast, lung, genitourinary tract Protection for newborns

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IgM

Five monomers Held together by a J chain First to be synthesized during primary

immune response Associated with complement fixation Receptor for antigens on B cells Circulates in the blood

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IgD

Monomer Small amounts in the serum Receptor for antigens on B cells

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IgE

Allergies Parasite infections Fc portion binds to mast cells and

basophilsrelease chemical mediators that aid

inflammation

Different Immunoglobulins

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How Abs work Some act as labels to identify

antigens for phagocytes Some work as antitoxins i.e. they block toxins

for e.g. those causing diphtheria and tetanus Some attach to bacterial flagella making them

less active and easier for phagocytes to engulf Some cause agglutination (clumping together)

of bacteria making them less likely to spread

Antibody Actions

Neutralizes antigen Immobilizes bacteria Agglutinates and precipitates antigen Activates complement proteins Enhances phagocytosis

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Consequences of Antibody Binding

Cellular Immunity Cell-mediated Immunity

Cell-mediated Immunity

Activation of T cells by specific antigen Eliminate intracellular pathogens and cancer cells First signal TCRs – T cell receptors(CD4 and CD8 proteins)

recognize antigen –MHC complexes Second signal- costimulation

cytokins- Interlukins -2 –produced by helper T cells

Proliferation and differentiation of the T cell to acquire effector function

(Mature naive T cell)

The two signal model for lymphocyte activation(antigen alone is insufficient)

(Mature dendritic cell)

Signal 1 comes from recognition of antigenSignal 2 comes from another (activated) cells

Antigen+MHC TCRTH2 activation,

for example

Proliferation and differentiation of the B cell to acquire effector function

(Armed effector T cell)

B cell activation,

for example

Plas

ma

cell

Mem

ory

B ce

ll

Cell-mediated Immunity - T cells Functions: most effective against intracellular

microorganisms: viruses, fungi, intracellular bacteria, parasites

Types : Cytotoxic T cells: Helper T cells Memory T cells

Cytotoxic T cells CD8 Release cytotoxic

substancesGranzymes – cell apoptosis Perforins –cytolysisLymphotoxins- destroys

DNA of the target cell Recognize foreign antigen-

MHC complex on:Virus infected cellsTissue transplant cellsCancer/ tumor cells

Helper-T cells

Called CD4 Secrete cytokines Interlukin-2 activates

T cells , B cells NK cells

Tumor necrosis factor (TNF)- inflammation

Positive feedback loop

Table 21.4

TERIMA

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