DEFINITION OF A NEW HLA-B7 SUBTYPE (B-ASTERISK-0704) BY ISOELECTRIC-FOCUSING, FAMILY STUDIES AND DNA-SEQUENCE ANALYSIS

During screening of potential bone marrow donors, a previously undescr ibed banding position for the serologically defined HLA-B7 antigen was identified in three unrelated families using one dimensional isoelect ric focusing and class I specific Western blot analysis. The isoelectr ic point of the new variant is more acidic than the two HLA-B7 variant s 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 (B0704) diffe rs from B0702, the common allele encoding HLA-B7, by three nucleotide substitutions within the codon for residue 156 of the mature heavy ch ain. As a result of these differences amino acid 156 is changed from a rginine to aspartic acid, a difference consistent with the isoelectric points. The group of three nucleotide substitutions that distinguish B0704 from B*0702 is present in other HLA-B alleles.