Adaptive Immunity - T cells (part 1) Flashcards
What are the requirements for activating a T cell?
Acquire and process antigen by antigen presenting cells (MHC pathways), locate appropriate T cells, adhere to T cells, present MHC associated peptides to T cells, provide co-stimulation for T cells
What is the structure of the T cell receptor?
heterodimer, alpha and beta chains, variable and constant regions, antigen binds at variable region
Do T cell receptors undergo somatic hypermutation?
No - because T cell receptors only bind a small part of the antigen - if they had high affinity they would be self reactive
What are the two major types of T cells?
CD8 - cytotoxic (kills cells that are infected intracellularly) and CD4 - helper (produces cytokines to augment immune response)
What are the two types of MHC molecules?
Class I and Class II
Where do you find class I and class II molecules?
Class I are on all nucleated cels, class II are only on professional APCs
What is the structure of the MHC class I receptor?
Three alpha subunits plus a beta2 microglobulin. The binding site is formed by two alpha helices around a beta sheet (hot dog bun)
What is the structure of the MHC class II receptor?
Two alpha subunits and two beta subunits. The binding site is formed by two alpha helices around a beta sheet
What are the genes for class II MHC molecules?
DP, DQ, DR
What are the genes for class I MHC molecules?
B, C, A
What is the expression of MHC alleles?
Co-dominant expression - gives diversity
Why are genetic poylmorphisms in MHC important?
It affects ability to generate an adaptive response, resistance or susceptibility to infectious disease, resistance or susceptibility to allergic disease, resistance or susceptibility to autoimmune diseases and transplantation responses
What are the two ways that antigens are processed before being presented to MHC molecules?
cytosolic access (for class I) or endosomal access (for class II)
Describe the cytosolic access pathway for class I MHC
Antigens are degraded into peptides in the cytosol and then transported to the ER by TAP. Class I MHC are synthesised in the ER. Without a peptide bound, MHC is unstable. If a peptide binds, then it can be processed through the golgi apparatus and go through to being expressed at the cell surface.
Describe the endosomal access pathway for class II MHC
Antigens are taken up by endosomes and degraded into peptides. MHC in the ER is stabilised with an invariant chain. MHC is transported through golgi to a vesicle. The endosome and the MHC vesicle intersect. The invariant chain degrades and the peptide binds to the MHC. The MHC is expressed at the cell surface.
