A new HLA-B44 variant (B44BO [B*4408]) identified by serology.

Using HLA serology, we detected a new variant of HLA-B44- B44BO- in two families. This antigen reacts with B44 antisera and is negative with over one-third of B12 (B44, B45) sera but reacts with 50% antisera with a B62 component, especially if they contain anti-B57. The variant, B4408, differs from the common B4402 by 4 nucleotide substitutions in exon 2: 193, 206 and 209, which produce changes in the the alpha 1 domain at positions 41, 45 and 46 (TKE in B4402 and AMA in B44BO); and nucleotide 213, a silent substitution. At each of these positions, B4408 is identical to B46 B57 and may B15 alleles. As anticipated from its predicted iso-electric point (5.71), one-dimensional isoelectric focusing studies showed that B44BO focuses at the same position as B4402. The sequence and serological reactivity of this rare antigen allowed the identification of two likely epitopes shared by two different groups of HLA-B antigens.