Human T-cell receptor BV6 gene polymorphism in relation to expression level and CD4/CD8 skewness

Using 50 samples of umbilical cord blood lymphocytes from Japanese donors, we analysed two human T-cell receptor beta variable (TCRBV) genes, BV6S4 an d BV6S5, for their polymorphism, usage frequencies and CD4/CD8 skewness. Th ey showed contrasting CD4/CD8 skewness, BV6S4 to CD8(+) T cells and BV6S5 t o CD4(+) T cells. Genotyping of the BV6S4 alleles (A1, A2 and A3) revealed two of the six possible BV6S4 genotypes, A1/A2 and A2/A2. Among the two BV6 S4 genotypes, no significant difference was detected in usage frequency or CD4/CD8 skewness. On the other hand, genotyping of the BV6S5 alleles (A1 an d A2) revealed all three possible BV6S5 genotypes, A1/A1, A1/A2 and A2/A2, and the gene usage frequency was high, in the order A1/A1 > A1/A2 > A2/A2. These results indicate that the amino acid substitutions in BV6S5 (S36R and G70E) are in some way associated with the expression level of this gene. I n the analysis of CD4/CD8 skewness, the three BV6S5 genotypes had similar s kewness, indicating that A1 alleles are expressed more frequently than A2 a lleles in both CD4(+) and CD8(+) T-cell populations. Although BV6S5 exhibit s marked skewness to CD4(+) T cells, our results indicate that the higher e xpression of A1 alleles is not associated with the increased ratio of CD4() T cells.