Polymorphism of the T-cell receptor gamma variable and constant region genes in a Chinese population.

The human T-cell receptor gamma gene region spans 160 kb genomic DNA. Restriction fragment length polymorphisms (RFLPs) have been previously documented for the constant region (TRGC) genes, the joining (TRGJ) segments and the variable (TRGV) genes. We have recently defined the alleles of the T-cell receptor gamma V, J and C genes and we have described seven haplotypes of the V gamma subgroup I genes characterized either by RFLPs or by deletion or insertion of V gamma genes. The number of V gamma I genes may vary from 7 to 10 per haploid genome, the 9-gene haplotype being the most frequent. Allelic fragments can unambiguously characterize the TRGC2 gene with duplication or triplication of the exon 2. These alleles and haplotypes have been analyzed in four different populations (French, Lebanese, Tunisian and Black African). In this paper, we compare these allele and haplotype frequencies with those found in a Chinese population and we describe new TRGV allelic restriction fragments found only in the Chinese samples. These results and the previous data demonstrate the flexibility of the human T cell receptor gamma locus and the importance of unequal crossing-overs in the evolution of that locus. Moreover, they underline the importance of studying these polymorphisms in population genetics.