Antigen Processing and Presentation 09

8/13/2019 Antigen Processing and Presentation 09

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Antigen processing and

presentation

Dr Jacinta Kelly


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presentation

Why is it needed?

How does it happen?

How are the pathways of endogenous andexogenous antigen kept apart?

What are the consequences?


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T cell receptor: antigen receptor of T cells

Cannot recognise antigen in solution

Must have the antigen processedand presented to it

Specialised molecules present

antigens to T cells:

MHC molecules


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Antigen presentation cells required


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1.

3.

2


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TCR

MHC


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Antigen presentation by MHC

molecules

Two types of MHC molecules MHC class I

MHC class II

Two types of T cells CD4 T helper cells

CD8 T cytotoxic cells

Two types of antigen Endogenous (from within the cell)

Exogenous (from outside the cell)


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Type of T cell activated

MHC class I activate CD8 T cytotoxic cells

Present endogenous (eg viral) antigens

Target cell is killed by CD8 cell

Any cell can become virallyinfected/neoplastic

Therefore: MHC class I is on all nucleated

cells


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Cell expressing MHC class I

Ag

CD8+ T cell

CD 8 binds 3 domain

Stabilises interaction

MHC class I Ag presentation to CD8 T cell

Death of target

cell


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CD8 CTL

Tumour cell


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T cytotoxic cell

Endogenous antigenTCR MHC I

Death of target cell


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Type of T cell activated

MHC class II activate CD4 T helper cells

Present exogenous (eg bacteria) antigens

CD4 T cells upregulate all immunefunctions

MHC class II found only on cells thatsample the extracellular environment


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MHC class II-CD4 T cell

activation CD4 T helper cells up regulate immune

function

Stimulate Mactivation and phagocytosis,

B cell antibody production

Help to clear exogenous antigen


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CD4+ T cell

CD 4 binds mainly 2 domain

Stabilises interaction

Cell expressing MHC class II

MHC class II Ag presentation to CD4 T cell

Upreglation of

Immune responses


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T helper cell macrophage

cytokines

Bcell

antibodies

phagocytes

Exogenous antigenTCR MHC

II


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Antigen: linearProtein fragments

How does antigen getInto MHC binding cleft

How does endogenousAg bind MHC class I?

How does exogenous ag

Bind MHC class II?


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A question of language

Cells that express MHC class I, present

endogenous ag

Are killed by CD8+ cells

Are called Target cells

Cells that express MHC class II, present

exogenous ag

Activate the CD4 T cell response

Are called Antigen presenting cells


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Target cells:

All nucleated cells express MHC class I

Can be a target cell if virally

infected/neoplastic

Antigen presenting cells

Limited number of cells express MHC class II

Must sample extracellular environment

Monocytes, M, B cells


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presentation Separate pathways for endogenous and

exogenous pathways


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Endogenous antigen presentation

1

2

3


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Exogenous antigen presentation

1

2

34


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Loading of antigen to MHC

class I


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Loading of antigen to MHC

class II


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Useful textbooks

Kuby Immunology

Cellular and molecular immunology

(Abbas and Lichtman)

Janeways Immunobiology (Murphy,

Travers, Walport)

Antigen Processing and Presentation 09

Documents

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