Peptide sequences of T-cell receptor δ and γ chains are identical to predicted X and γ proteins

Abstract

Although most mature peripheral T lymphocytes express a major histocompatibility complex restricted, CD3-associated, antigen receptor (TCR) which has been well characterized^1–16, some T cells carry a different CD3-associated heterodimer on their surface^17–22. One of the two disulphide-linked chains of this putative second receptor, which in mice has relative molecular mass (M_r) 35,000 (35K), has been identified as a product of the group of γ genes¹⁸. The other chain, termed δ (M_r 45K in mice), is not as well characterized. Although γ/δ-bearing cells are a minor subset among peripheral T lymphocytes, they are the only CD3⁺ cells in the thymus early in ontogeny¹⁹. Taking advantage of these kinetics, we have generated γ/δ-bearing hybridomas, using a new TCR α chain-negative variant of the AKR thymoma BW5147 as tumour parent, fetal thymocytes as normal cell partners, and an anti-CD3 monoclonal antibody (mAb) as screening reagent²³. Gamma and δ chains from one of these hybrids have been purified and partially sequenced. The sequences obtained indicate that δ is indeed identical to the polypeptide encoded by the recently described gene X, as suggested by Chien et al.²⁴.