2 Immuno: Adaptive Immunity: Antigen Processing And Presentation

Front 1

exogenous Ag

Back 1

exogenous Ag:
- MHC II process this phagocytized material and present its Ag to Th cells
- Th cells can only recognize foreign Ag if bound to an MHC II on an APC

Front 2

exogenous Ag processing

Back 2

exogenous Ag processing:
1. foreign material phagocytized and taken into phagosome
2. phagosome fuses with lysosomes= endosome
3. inside endosome: proteins broken down into peptide fragments
4. endosome fuses with other endosomes carrying newly synthesized MHC II

Front 3

exogenous Ag presentation

Back 3

exogenous Ag presentation:
1. MHC II loaded with peptide (12-24 aa long) fragment and transported to the cell surface
- MHC II specifically bind only some peptides created in processing= select epitopes presented to T cells
- APC can express about 200K different MHC II so can present many Ag silmultaneously

Front 4

endogenous Ag

Back 4

endogenous Ag:
- mediated by MHC I
- present Ag originating from body's own cells ( NOT phagocytized): foreign proteins are in cytoplasm not the phagosome
- eg proteins made by virus-infected cells

Front 5

endogenous Ag processing

Back 5

endogenous Ag processing:
1. infected cell chops up microbial proteins into fragments
2. fragments 9 aa long (only!!) bind to MHC I

Front 6

endogenous Ag presentation

Back 6

endogenous Ag presentation:
1. protein fragments bound to MHC I are carried to the cell surface
2. CTLs respond to Ag stimulation by destroying infected cells
- not only includes microbial infection, but neoplastic cells

Front 7

APCs and MHC

Back 7

APCs are:
- nucleated: can make and express both MHC I and II
- able to present both exogenous and endogenous Ag at the same time
- MHC I: becomes infected
- MHC II: engulf and present foreign material

Front 8

Cross-presentation/ priming

Back 8

cross-presentation/ priming:
- not fully understood
- under some circumstances, exogenous Ag may enter the endogenous Ag pathway and be presented by MHC I to CTLs

Front 9

example of cross-priming

Back 9

cross- priming:
- macrophage or dendritic cell endocytoses viral Ag (eg killed virion) which are transported from the phagosomes into the cytoplasm
- enters endogenous Ag pathway: CTL response
- important in viral immunity

Front 10

heat shock proteins gen

Back 10

heat shock proteins:
- induced in cells by stress: change in T, stavation, toxins
- in all organisms at low levels
- molecular chaperones of proteins through the cell

Front 11

heat shock proteins fx

Back 11

heat shock proteins:
1. binds endocytozed viral (exogenous) Ag and channels into endogenous pathway
- eg killed virus vaccines shuttled into endogenous pathway to be presented by MHC I to CTLs
2. likewise, tumor Ag from exogenous to endogenous pathway
- important as these Ag can then stimulate a CTL and Th cell response