Structure and Expression of Genes Involved in T Lymphocyte Recognition and Activation

Abstract

Human T lymphocytes can be activated by two apparently distinct pathways. The first pathway is mediated through the T cell receptor (TcR) complex following corecognition of antigen and major histocompatibility complex (MHC) gene products (Reinherz et. al., 1982). The TcR complex comprises an αβ heterodimer (Ti) which is linked non-covalently to a non-polymorphic glycoprotein, the CD3 antigen (see Kronenberg et al., 1986 for a review). The CD3 antigen in turn comprises at least three polypeptide chains, γ, δ and ε (Borst et al., 1983; Kanellopoulos et al., 1983). The αβ heterodimer is sufficient to confer clonal variability in the recognition of antigen/MHC to a T cell (Dembic et al., 1986). The CD3 antigen, which is obligatorily expressed with the αβ heterodimer (or with TcR γ chains: see Brenner et al., 1986; Bank et al., 1986) has been implicated in the signal transfer process consequent to specific binding of a T cell to a target cell or antigen presenting cell. Several events have been implicated in the signal transfer process, including phosphorylation of the CD3 γ chain, increased phosphatidyl inositol bis phosphate turnover and downregulation of the TcR complex from the cell surface (Weiss et al., 1984; Cantrell et al., 1985; Davies et al., 1985; Imboden et al., 1985).