Genomic sequence encoding diversity segments of the pig TCR δ chain gene demonstrates productivity of highly diversified repertoire

To better understand the function and diversity of γδ T cells, we determined the genomic sequence encoding diversity (D) segments of the porcine TCR δ chain and its upstream regions, because pigs and other artiodactyls have relatively high proportions of γδ T cells. The revealed sequence contained 28 variable (V) α/δ segments, including 4 TRDV1 and at least 6 Dδ segments, a much higher number than in humans and mice. All 6 of the Dδ segments that had canonical recombination signal sequences were functionally utilized in expressed TCR δ chain genes. The multiplicity of Dδ segments enabled the use of more than 3 Dδ segments in a single functional TCR δ chain. The increased number of TCR δ segments was acquired by the duplication of the germline sequence, which occurred after the divergence of artiodactyls from primates and rodents. These data demonstrate that the pig is able to generate a highly diversified repertoire of TCR δ chain molecules.