The δ- and ε-chains of the human T3/T-cell receptor complex are distinct polypeptides

Abstract

The T3/T-cell receptor complex on the surface of human thymus-derived lymphocytes consists of four glycoproteins: the α-chain of relative molecular mass (M_r) 40,000–50,000 (40–50K), the β-chain (37–45K); the γ-chain (25K) and the δ-chain (20K)^1–3. The T3 α- and β-chains have been identified as clonotypic T-cell receptors^3–7, but functionally the T3/T-cell receptor chains seem to form a single complex: monoclonal antibodies directed at the 20K T3 components are mitogenic for normal human T lymphocytes^8,9 and, at higher concentrations, anti-clonotypic and anti-20K reagents block T-cell function^4,10. Recently, Zanders et al.¹¹ showed that incubation of human T-helper clones with high concentrations of antigen abolishes antigen-specific proliferation and induces disappearance of T3 from the cell surface. Thus, the T3/T-cell receptor complex consists of two variable subunits, the T3 α- and β-chains, which interact with antigen and the monomorphic 20K/25K T3 chains. Recently, the existence of a fifth polypeptide chain, the unglycosylated T3 ε-chain, has been postulated^12,13. Here we confirm that a 20K ε-chain does exist. The T3 ε-chain differs from the T3 δ-chain in primary structure as judged by N-terminal amino acid sequencing, peptide mapping and immuno-blotting with anti-T3-δ and anti-T3-ε antibodies. Treatment with endoglycosidase F revealed two nonglycosylated T3 δ polypeptide backbone chains (16K and 14K) with identical amino termini. Together with previous pulse-chase experiments² this observation suggests that the 14K T3 polypeptide is derived from the 16K T3 precursor by proteolytic processing near the C-terminus of the molecule.