Development Cytotoxic T cell

development of single positive t cells in thymus

the immune system must recognize millions of potential antigens. there fewer 30,000 genes in human body, impossible have 1 gene every antigen. instead, dna in millions of white blood cells in bone marrow shuffled create cells unique receptors, each of can bind different antigen. receptors bind tissues in human body itself, prevent body attacking itself, self-reactive white blood cells destroyed during further development in thymus, in iodine necessary development , activity .

tcrs have 2 parts, alpha , beta chain. (some tcrs have gamma , delta chain.) hematopoietic stem cells in bone marrow migrate thymus, undergo vdj recombination of beta-chain tcr dna form developmental form of tcr protein, known pre-tcr. if rearrangement successful, cells rearrange alpha-chain tcr dna create functional alpha-beta tcr complex. highly-variable genetic rearrangement product in tcr genes helps create millions of different t cells different tcrs, helping body s immune system respond virtually protein of invader. vast majority of t cells express alpha-beta tcrs (αβ t cells), t cells in epithelial tissues (like gut) express gamma-delta tcrs (γδ t cells), recognize non-protein antigens.

t cells functionally stable tcrs express both cd4 , cd8 co-receptors , therefore termed double-positive (dp) t cells (cd4+cd8+). double-positive t cells exposed wide variety of self-antigens in thymus , undergo 2 selection criteria:

only t cells bind mhc-self-antigen complexes weakly positively selected. cells survive positive , negative selection differentiate single-positive t cells (either cd4+ or cd8+), depending on whether tcr recognizes mhc class i-presented antigen (cd8) or mhc class ii-presented antigen (cd4). cd8+ t-cells mature , go on become cytotoxic t cells following activation class i-restricted antigen.