MHC and Antigen Presentation Flashcards
(16 cards)
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
describe how DCs present antigens
they exist in an immature state in tissue, where they phagocytose indiscriminately. when their pattern recognition receptors are activated, they stop phagocytosing, upregulate MHC receptors, and enter the lymphatics
