A novel γδ T cell receptor for antigen adds limited diversity to the γδ repertoire in adult thymus

The surface expression of CD3-associated TCR chains on hybridoma cell lines derived from adult γδ thymocytes was analyzed. These cell lines were unusual, in that a) they expressed a surface heterodimer consisting of a 40- and a 42-kDa chain, i.e., comprised of chains different from any previously reported γδ-TCR all of which express Cγ1- or Cγ2-encoded γ-chains; b) their CD3-associated TCR could not be categorized as αβ-TCR dimers, despite the similarities in m.w. of the TCR chains, because full size 1.3-kb β-chain mRNA capable of encoding a functional β-chain could not be detected in these cells; c) neither of the receptor chains could be precipitated with anti-Cγ1Cγ2-peptide antisera. Biochemical analysis demonstrated that the 42-kDa δ-chain is a novel chain, which differs from any reported δ-chains in size, charge and number of glycosylation sites. Collectively, the data on analysis of the 40-kDa chain strongly suggest that it represents a γ-chain encoded for by the Cγ4 locus, protein products of which have not yet been reported in the thymus. This γ-chain was also unique, in that its isoelectric point was much lower than that of other γ-chains. The γ- and δ-chains on these Cγ4-expressing hybridomas were indistinguishable from one another in size and charge (as determined by nonequivalent pH gradient electrophoresis/SDS-PAGE analysis and analysis after endoglycosidase treatment). Because the cell lines were randomly chosen from large panels of hybridomas, these results may well imply strikingly nonrandom pairing of thymocyte-derived Cγ4 chains and the δ-chains reported here. Thus, only limited additional γδ repertoire diversity may be generated by availability of this γδ-TCR in the thymus.