Definition of a new HLA-B7 subtype (B*0704) by isoelectric focusing, family studies and DNA sequence analysis.

During screening of potential bone marrow donors, a previously undescribed banding position for the serologically defined HLA-B7 antigen was identified in three unrelated families using one dimensional isoelectric focusing and class I specific Western blot analysis. The isoelectric point of the new variant is more acidic than the two HLA-B7 variants that had been defined before. In each family the new B7 variant was found linked to HLA-A2 and -Cw7. Cloning and sequencing of full-length clones of complementary DNA showed that the new allele (B*0704) differs from B*0702, the common allele encoding HLA-B7, by three nucleotide substitutions within the codon for residue 156 of the mature heavy chain. As a result of these differences amino acid 156 is changed from arginine to aspartic acid, a difference consistent with the isoelectric points. The group of three nucleotide substitutions that distinguish B*0704 from B*0702 is present in other HLA-B alleles.