The relationship between HLA-B45 and B*5002 in the five major US population groups

The antigen encoded by B*5002 differs in sequence from that encoded by B*50 01 only at amino acid residue 167 (consensus tryptophan vs, serine) which r esults in B45 serologic reactivity. To search for B*5002, the frequencies o f alleles encoding the serologically defined B45 antigen were determined by sequence-based typing in 5 major U.S. populations: Caucasians, African Ame ricans, Asians/Pacific Islanders, Hispanics, and Native Americans, The perc ent of serologically defined B45-positive individuals in the 5 populations ranged from 0.7-9.0%. Thirty-two B45-positive individuals were randomly cho sen, when available, for sequence-based typing from each ethnic group from a database of 82,979 consecutively typed unrelated individuals. The B*5002 allele was most prevalent in Hispanic (22%) and Caucasian (9%) individuals, while conspicuously absent in African Americans. In addition, a new allele associated with the B45 antigenic specificity, B*4502, has been identified from an African American individual of Middle Eastern descent. In light of the continuing need to reconcile differences between relationships determi ned by the sequence homologies among alleles and relationships based on the serologic determinants carried by allelic products when determining the le vel of HLA match for hematopoietic stem cell transplantation, it is suggest ed that B*5002 be recognized individually from other B*50 alleles when repo rting HLA-B typings for clinical purposes.