MHC and Antigen Presentation Flashcards
what types of antigens are presented via MHC 1
intracellular antigens, cytosolic
what types of cells express MHC 1?
all cells
what else is necessary for T cell activation besides MHC recognition
costimulation- usually provided by APCs in tandem with antigen
describe the MHC class 1 pathway
protein antigens are targeted for proteasome degradation. under inflammatory conditions or in APCs, subunits of the proteasome are switched to form a immunoproteasome, which generates MHC compatable peptides. Transporter associated with processing (TAP) transports peptides to the ER where they are loaded onto new MHC class 1 complexes and sent to the cell surface
what does transporter associated with processing do?
TAP is the protein that moves peptides from the immunoprotesome to the ER in MHC 1 creation
what cells are activated by MHC class 1 complexes?
CD8 T cells
MHC 2 molecules are activated by what types of antigens?
extracellular protein antigens
MHC 2 molecules complex with what cells?
CD4 T cells
describe the MHC 2 pathway
extracellular antigens are phagocytosed and digested in the endosome/lysosome pathway. the acidic conditions in the lysosomes fragments the protein into small peptides. these lysosomes fuse with vesicles containing MHC 2 molecules.
The MHC 2 molecules are created in the ER, but are very unstable without a peptide bound. thus, an invariant chain binds their temporarily, and is eventually removed, leaving only a CLIP protein in the binding pocket.
when the lysosome fuses with the vesicle, the protein DM exchanges CLIP with an appropriate peptide.
describe cross-presentation of peptides by MHC 1
DCs are capable of shuttling peptides in the extracellular pathway into the MHC 1 pathway
how do MHC complexes accommodate the variety of antigens
they contain variable polymorphisms on the floor of their binding cleft
describe the MHC 1 structure
contains a single polymorphic chain called beta-microglobulin, the binding cleft is closed on either end and can only accommodate peptides 8-10 AAs
describe the MHC 2 structure
comprised of alpha and beta chains, with open ended binding cleft so that it can accommodate peptides 8-30 AAs in size
what is the HLA
the MHC locus in humans. it contains 3 MHC 1 and 3 MHC 2 genes (x2 because one from each parent), giving humans 6 of each type of MHC complex. their expression is codominant
what is the difference between the antigens the spleen and lymph nodes encounter
as a general rule, the spleen primes T cells for antigens what were encountered in the blood, whereas the lymph nodes get primed from antigens in the tissue
