T cell receptor. The clonally distributed antigen receptor on CD4 and CD8 T lymphocytes that recognizes complexes of foreign peptides bound to self MHC molecules on the surface of APCs. The most common form of TCR is composed of a heterodimer of disulfide-linked transmembrane polypeptide chains, designated a and ß, each containing one terminal Ig -like variable (v) domain, one Ig-like constant (c) domain , a hydrophobic transmembrane region, and a short cytoplasmatic region. (Another less common type of TCR , composed of ? and d chains, is found on a small subset of T cells and recognizes different forms of antigens )