Antigen Processing and presentation

Question 1

understand the structure and function of MHC 1 and MHC 2

Answer 1

necessary to present Ag to T cells
MHC 1 - present on any cells that has a nucleus (basically everything besides RBC), displays endogenous (self) peptides , always presents to a CD8+ T cell (killer T cells)
MHC 2 - only expressed on professional antigen presenting cells (B cells, dendritic cells, and macrophages) , display exogenous (outside of cell) peptides (so they have to ingest it first), presents to CD4+ T cells, ingests larger sized peptides 13-18 AA’s long

Question 2

Describe each of the 4 diff pathways of antigen processing and presentation

Answer 2

antigen processing - breaking down macromolecules in order to present them to a T cell

1) exogenous - internalizing an outside molecule to present with MHC 2
2) endogenous - anything inside of the cell the can be chewed up and presented on the outside of the cell
3) cross-presentation - displaying an exogenous Ag and present it to a Cd8+ T cell
4) autophagic - where an internal antigen (endogenous)_ presents to a CD4+ T cell through MCH 2

Question 3

Differentiation diff pathways of antigen processing: exogenous pathway

Answer 3

only Ag presenting cells can do this - macrophages, dendritic, and B cells. internalize external Ag’s then expose it to lysosome to break the Ag up into fragment to be displayed by MHC. while in ER, MCH 2 components, alpha and beta, clamp onto and the invariant chain (important because it prevents self peptides from being displayed like an Ag). It’s a placeholder for the real fragments that will eventually get displayed. once the complex goes through the Golgi and into a phagolysosome, enzymes (HLA_DM) pop out the invariant chain and also the MHC 2 to grab a real Ag fragment. IT then goes to cell wall to display for a CD4+ T cell.

Question 4

Differentiation diff pathways of antigen processing: endogenous

Answer 4

presenting internal or self peptides. An Ag inside a cell will be marked by ubiquitin. A PROTEASOME then comes and chops it up into lots of peptides. These are shuttled to ER (like exogenous path) through TAP (a shuttle) transmembrane proteins. TAPs are linked to MHC1 in the ER so when short chunks of peptides (8-10 AAs long) come in, they can grab them (she made a point to know that MCH1’s are LOADED in the ER). It then goes through golgi and then to surface to present for a CD8+ T cell

Question 5

Differentiation diff pathways of antigen processing: cross presentation

Answer 5

basically the same as endogenous except it escapes the lysosome that first degrades it and enters the cytosol. Then the proteasome just chops it up instead and it continues on the endogenous pathway from there (because the proteasome chops it up it enters the endogenous pathway rather than staying in the lysosome for the exogenous)

Question 6

Differentiation diff pathways of antigen processing: autophagic

Answer 6

recycling old cell components. Autosome merges with lysosome- autolysosome. The old cell parts are degraded and then displayed to by a MCH2 to a CD8+ T cell on surface

Question 7

anything presented by MHC2 has to be degraded by a lysosome Anything presented by MCH1 has to be degraded by a proteasome

Answer 7

anything presented by MHC2 has to be degraded by a lysosome

Anything presented by MCH1 has to be degraded by a proteasome

Question 8

Know the antigen presenting cells and their capabilities of activating T cells

Answer 8

Dendritic cells- the best at presentation b/c they express high levels of MHC2 and co-stimulatory molecules, the only ones that can ACTIVATE a naive T cell
Macrophages- good act activating effector T cells and memory T cells. Have MHC1 and 2
B cells- good act activating effector T cells and memory T cells. Have MHC1 and 2