HLA-G genetic polymorphism in 57 Portuguese white families studied by PCR-RFLP and PCR-SSOP.

FROM STUDIES on tissue-specific expression and interaction with T and NK cells, it was suggested that HLA-G may have an important role in immunologic tolerance. The recognition of HLA-G polymorphism, its association with other classical HLA class I loci, and eventual variation among different populations may prove to be useful in understanding its immunologic functions and evolution of human populations. Although the level of polymorphism in HLA-G has been considered low, it was hypothesised that large differences concerning the nature, site, and frequency of HLA-G polymorphisms do exist in different ethnic groups. In whites, the limited and conservative nature of nucleotide and amino acid substitutions, seems to diverge significantly from the changes found at the antigen-binding domain of black samples. The HLA-G locus also shows a strong and selective linkage disequilibria with most (but not all) HLA-A alleles. This nonrandom association is due to the presence of a highly polymorphic region between the two genes, producing a true variation in physical distance of the A–G segment carried by different haplotypes. The most common association found in all studied populations, A*2-G*01011, is probably the oldest A/G linkage disequilibrium present in human genome that is shared with other nonhuman primates. On the basis of this theoretical background, we studied