Gene polymorphism of HLA-DPB1 and DPA1 loci in caucasoid population: frequencies and DPB1-DPA1 associations.

The genetic polymorphism of the HLA-DPB1 and DPA1 loci was studied in 60 unrelated caucasoid individuals by PCR-RFLP. The polymorphic second exon of DPB1, the third exon of DPA1, and the transmembrane DPA1 exon were specifically amplified in vitro by polymerase chain reaction (PCR). Amplified DNAs were digested with selected enzymes. Twenty patterns were obtained with DPB1 defining 20 DPB1 alleles. Thirty-nine homozygous cell lines were used as HLA-DP reference cells. The results obtained with these cell lines were compared to those obtained by PLT, RFLP, and SSO. Although three subdivisions of the allele DPA101 were reported, DPA10103 was the only represented one in the caucasoid population. In the studied population, it was the most frequent DPA1 allele (76.6%), whereas DPA10201 frequency is 23.3%. DPB10401 and DPB10402 are the most frequent among the DPB1 alleles (40.0% and 13.3%, respectively). This may lead to a lower HLA-DPB1 diversity among caucasoids. Certain HLA-DPB1 alleles associate exclusively with one DPA1 allele (DPB10401, 0402, and 0301 with DPA101 and DPB10101, 0501, and 1701 with DPA1*0201) whereas the others can associate with both DPA1 alleles. This by itself can create another kind of polymorphism, indicating the importance of HLA-DPA1 typing. Thus, PCR-RFLP seems to be one of the best DNA typing methods: it represents direct, accurate, fast, and nonradioactive typing for both HLA-DPA1 and HLA-DPB1 alleles.