Influence of coding region polymorphism on the peripheral expression of a human TCR V beta gene

A number of human TCR V beta gene segments are reported to be polymorphic, with alleles differing by one or a small number of amino acid substitutions. In the absence of detailed structural information regarding the interaction of specific positions in the TCR with Ag or MHC, the significance of such variation is difficult to assess. In this report the relative use of the two common alleles of the human V beta 6.7 gene, 6.7a and 6.7b, which differ by two non-conservative amino acid substitutions, and the use of two common alleles of the V beta 12.2 gene, which differ by only silent substitutions, were measured in PBL derived from individuals heterozygous for these alleles. Equal use of V beta 12.2 alleles was observed, consistent with the inability of selection mechanisms to discriminate between the products of these alleles that are indistinguishable at the amino acid level. However, statistically significant skewing in the use of V beta 6.7 alleles was observed in 15 of 16 individuals studied. Expression levels for each allele ranged from 16 to 84% of the total V beta 6.7 signal in heterozygous individuals, with either the 6.7a or the 6.7b allele predominant in different individuals. Based on segregation studies in families, it seems unlikely that other unidentified polymorphism in the TCR beta locus, such as in the V beta 6.7 promoter, was responsible for the differential allele expression. Family studies provided no evidence for an association between specific HLA haplotypes and V beta 6.7 allele use. These results indicate that even modest allelic variation in human TCR V beta coding regions can have a significant impact on the expression of human V beta genes in the peripheral repertoire.