A review of the structure and function of the T-cell receptor-T3 complex

Of fundamental importance in understanding the events involved in T cell activation is the identification and characterization of the relevant cell surface molecules. Antigen-induced stimulation and subsequent activation of the T cell are initiated through interactions with the T cell antigen receptor. Several lines of evidence have demonstrated the intimate association between the T cell antigen receptor and T3, thus forming the so-called T3-T cell receptor complex. First, in immunoprecipitates with either anti-T3 monoclonal antibodies, or with anti-T cell receptor antibodies, five polypeptide chains have been detected. These are two disulfide bridged variable glycoproteins (alpha and beta chains) and three invariable structures the T3-gamma, delta, and epsilon chains with molecular weights of 25, 20, and 20 kdaltons, respectively. Second, mutants of a T leukemic cell line which were selected for the loss of the T3 complex from their surface by treatment with an anti-T3 antibody and complement concomitantly lost expression of the clonotypic heterodimer. Third, monoclonal antibodies directed at either the T cell receptor alpha and beta chains or at the T3 chains affect T cell functions in an identical fashion. Thus, we see that the complex formed between the T cell receptor and the T3 molecules is functionally as well as structurally central to the immune response. The structure, biosynthesis, and regulation of gene expression of the T3-T cell receptor complex will be discussed. An attempt will be made to relate the structural information to the function of the T3-T cell receptor complex.