T and B cells: MHC Flashcards
where do T cells spend their time
they arrive in the thymus from the bone marrow after a short period in the blood stream, they spend between 7 and 21 days undergoing differentiation and proliferation into a mature, but antigen naive, phenotype. some of these never leave the thymus but the others go on to populate lymph nodes
how do T cells become educated
- they begin as x2 -ve thymocytes which then turn into small double positive thymocytes known as CD4 and CD8
- these initially express low levels of the receptor they use to recognise the antigen, the TcR
- most of the TcRs won’t recognise your own MHC molecules so the T cells die because of a lack of positive selection
- the ones that do then mature and express high levels of TcR, losing either cd4 or CD8 and become single positive cells
- however at a latter stage they undergo negative selection to eliminate t cells that recognise your own MHC cells with high affinity as these can lead to autoreactive T cells causing autoimmune disease
what cells mediate T cell education POSITIVE selection
cortical epithelial cell
what cells mediate T cell education NEGATIVE selection
dendritic cell
what region does binding occur in a T cell receptor
the alpha beta chain binding site (two polypeptide chains, membrane bound, each with a V and C domain) with the variable and constant regions
what attaches the T cell receptor to the cell
the transmembrane region with the cytoplasmic tails
describe the relationship between T cells and antibodies
antibodies can bind to the antigen free in solution or maybe in a membrane however the TcR only ever recognises an antigen when it is bound by an MHC molecule therefore it is MHC RESTRICTED !!!
Class one MHC molecules
they are composed of two chains, a heavy chain and a small beta2-microglobulin
the upper surface forms a groove into which small 8-10 amino acid peptides sit
CNS expresses low levels of these
MHC class 2
two chains, alpha and beta which are both membrane bound
- upper surface forms groove into which longer peptides, over 20 amino acids sits.
- expression more limited to specialised antigen presenting cells and immune cells like macrophages and b and T cells
what cells recognise MHC Class 1
CD8 T cells
what cells recognise MHC class 2
CD4 T cells
where do MHC 1 molecules pick up peptides from
mostly derived fro internal contents of your cells (cytoplasm and nucleus) (meeting most of their peptides in the ER)
where do MHC 2 molecules pick up peptides from
peptides derived from external sources like outside your cells (meeting their peptides mostly in endosomes)
Ankylosing spondylitis
HLA-B27
Multiple sclerosis
HLA-DR2
