22 - T cell recognition Flashcards
what is T cell recognition involved in?
cell mediated specific immunity
T cell antigen recognition
don’t recognise native or ‘free’ extracellular antigens
recognise antigens on body surfaces that have been processes and presented to them
processed antigens presented via the MHC
2 types of T cells
cytotoxic T cells - go and kill other cells
helper T cells - enhance other cell responses: produce cytokines which promote other cells
T cells express a T cell receptor (TCR), where is it found and whats its structure?
anchored on their cell surface • similarity to an antibody • have immunoglobulin domain • alpha and beta chains • variable region at the top • constant region at the bottom • alpha and beta have transmembrane regions - have small cytoplasmic tails • joined by disulphide bond • have carbohydrates attached
what does the variable region of TCR do?
binds to the antigen
what does the constant region of TCR do?
doesn’t activate immune cells
always remains bound to the cell so not accessible
what does the TCR do?
recognises a peptide fragment (epitope) of Ag on surfaces of other cells in a complex with a MHC
what does antigen recognition by T cells work?
1) antigen gets processed and cleaved into shorter fragments
2) fragments presented by MHC
3) TCR will search all cells
4) T cell will bind and produce cytokines and other immune cells
what are the 2 classes of MHC?
class I class II
class I MHC
not in cells without a nucleus - RBCs
peptide binding cleft made of alpha 1 and alpha 2 domains
has only 1 transmembrane domain
class II MHC
expressed by APCs
peptide binding cleft made of alpha 1 and beta 1 domains
has 2 transmembrane domains
T cell recognition of MHC/peptide complex enables T cells to perform what 3 functions:
to act against extracellular antigens
to act against intracellular infections
to regulate activities of other cells
extracellular antigen presentation by MHC class II
1) extracellular antigens engulfed by cells into endoscope
2) in the endoscope they begin to acidify due to influx of H+
3) this cleaves antigens into smaller fragments
4) small peptides bind to MHC class II molecule
5) take to cell surface and presented on outside
6) T cell receptors bind and activate T helper cells
cytotoxic T cells
- CD8+
- recognise and kill infected cells
- recognise viral antigens presented by MHC class I molecules on infected cells
- kill by a mechanism involving perforin and granzymes
- can go wrong - autoimmunity
what does perforin do?
perforating enzyme
punches holes in cell surface
