δ-chains of dendritic epidermal T cell receptors are diverse but pair with γ-chains in a restricted manner

To assess the diversity of TCR δ-gene expression in dendritic epidermal T cells (DETC), we characterized the δ-gene used by a panel of cell lines that express the γδ TCR on the cell surface. Northern hybridization analyses with a panel of Vδ probes representing each of the six known Vδ families showed that each of these lines expressed either Vδ1 or Vδ6 containing transcripts. Southern hybridization analysis with the Vδ probes gave rearrangement patterns consistent with Northern hybridization results. The correlation of Vδ expression with Vγ expression revealed that not only may Vδ usage be restricted in DETC cells, but that the pairing of γ- and δ-chains may not be random. In the DETC cells examined, Vδ1 chains paired exclusively with Vγ3Cγ1 chains and Vδ6 chains paired with Cγ2 and Cγ4 chains. Sequence analysis of δ-cDNA clones corresponding to the expressed δ-chains from one of the Vδ1 expressing cell lines and two of the Vδ6 expressing cell lines revealed that, although the Vδ1 gene segment sequence and one of the Vδ6 gene segment sequences were identical to previously published Vδ sequences, considerable variable region diversity was generated by complex V-D-J rearrangement patterns that utilized various combinations of N-additions, Dδ2 and possibly Dδ1 segments, and Jδ1 or Jδ2 segments. These complex rearrangement patterns distinguish these DETC lines from early thymocytes and suggest that, if DETC are thymic derived, they originate from relatively mature thymic cells.