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8/13/2019 Antigen Processing and Presentation 09
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Antigen processing and
presentation
Dr Jacinta Kelly
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Antigen processing and
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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Antigen processing and
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)