Vb6 T-cell receptor elements in artiodactyls: conservation and germline polymorphisms.

By use of primers specific for human T-cell receptor (Tcr) Vb6 gene elements, a typing system for Tcr Vb variability in several artiodactyl species has been established. The amplified polymorphic locus is homologous to the human Vb6 gene element. Like the human counterpart, the artiodactyl Vb6 element contains a polymorphic intronic simple (gt)n repeat stretch. Extensive length polymorphism of this simple repeat sequence in some artiodactyls should allow efficient association studies in a multiplex approach, especially including MHC class II genes. On the protein level the Vb regions display little variability in the inter-species comparison among artiodactyls. The amino acid substitutions are not concentrated in the putative complementarity determining regions, suggesting evolutionary conservation. In addition, the simple repetitive element has been preserved in the same genomic location for more than 7 x 10(7) years. Similar evolutionary persistence has already been demonstrated for a (gt)n(ga)m repeat stretch in the second intron of the MHC-DRB locus. The reasons for these parallel developments in evolution are so far not clear, but they may point to a biological meaning if not function of the intronic simple repeat element.