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The antigen receptors on the surface of B and T cellsThe antigen receptors on the surface of B and T cells

B cells have about 100,000 molecules

of a single antibody receptor per cell,

which has specificity for one antigen

epitope.

T cells bearing the surface membraneprotein CD4 always recognize

peptides bound to MHC class II

proteins and function as Th cells.

T cells bearing the surface membraneprotein CD8 always recognize peptide

antigens bound to MHC class I

proteins and function as cytotoxic T

cells.

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Endocytosis Phagocytosis Phagocytosis Receptor-

mediatedphagocytosis

Receptor-mediated

phagocytosis

MHC

expression

Constitutive (+++) Inducible

(-)

Inducible

(++)

Constitutive (++) Constitutive

(+++)

Constitutive

(CD80/86)

Inducible

CD80/86

(-)

Inducible

(CD80/86)

(++)

Inducible

CD80/86

(-)

Inducible

(++)

T-cell

activation

Nave cells

Effector T cells

Memory T cells

-- Effector T

cells

Memory T

cells

Effector T cells

Memory T cells

Nave cells

Effector T cells

Memory T cells

Ag capture

Co-

stimulation

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Endogenous antigen processing: MHC class I peptideEndogenous antigen processing: MHC class I peptide

presentationpresentation

Intracellular proteins of host and virus are marked for

degradation by ubiquitination and are degraded by theProteasome.

The resulting viral peptides are transported into the ER

lumen by the Tap1-Tap2 heterodimeric transporter.

In the ER lumen, viral peptides associate with newly

synthesized MHC class I molecules.

MHC class I-peptide complex is transported to the cellsurface via the golgi compartments.

On the cell surface, the MHC class I-peptide complex

interacts with the T- cell receptor of a Tc cell carrying the

CD8 coreceptor.

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Endogenous antigen processing: MHC class I peptide presentationEndogenous antigen processing: MHC class I peptide presentation

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Exogenous antigen processing: MHC class II peptideExogenous antigen processing: MHC class II peptide

presentationpresentation

MHC class II complex is prevented form binding to viral

peptides in the ER by association with the invariant chain.

The complex is transported through golgi where the

invariant chain is removed, activating the MHC class II

complex.

The peptides are derived from extracellular proteins

that enter the cell by endocytosis.

Viral proteins are degraded in the lysosomes by

proteases that are activated by low pH. Endosomes fuse with vesicles containing MHC class II.

On the surface of the cell the MHC class II complex

interacts with the T cell receptor of a Th cell carrying the

CD4 coreceptor.

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Exogenous antigen processing: MHC class II peptideExogenous antigen processing: MHC class II peptide

presentationpresentation

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Dendritic cell

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Interaction between APC and lymphocyte

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INTERACTION BETWEEN APC AND T-LYMPHOCYTE

IMMUNE SYNAPSE

APC-cell

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