Interaction of the major histocompatibility complex and the T cell antigen receptor complex

The TCR is composed of an alpha and a beta chain (or gamma and delta), which are linked by disulfide bonds (S-S) forming a heterodimer. The CD3 complex consists of five polypeptides, one each of gamma and delta, two of epsilon, and a disulfide-linked homodimer of two zeta chains (or a heterodimer of zeta and eta). Signaling cascades are activated upon engagement of the TCR/CD3 complex. The TCR recognizes and interacts with processed peptide antigen presented in the context of the MHC (HLA class I, which binds to CD8, or HLA class II, which binds to CD4). CD3 is important in transducing the signal that initiates a T cell activation and differentiation pathway.

APC: antigen-presenting cell; MHC: major histocompatibility complex; HLA: human leukocyte antigen; TCR: T cell antigen receptor; P: phosphate.

Adapted from: Krensky AM, Weiss A, Crabtree G, et al. T-lymphocyte-antigen interactions in transplant rejection. N Engl J Med 1990; 322:510.

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Interaction of the major histocompatibility complex and the T cell antigen receptor complex