Alloantibody to a Bw4 epitope in a Bw4⁺ B∗27:05 patient

Background. Alloantibodies to the Bw4 epitope are known to be heterogeneous, but it is widely assumed that anti-Bw4 alloantibodies arise only in individuals who do not express a Bw4 epitope. Methods. Bw4 expression was confirmed by DNA sequence analysis. Anti-Bw4 reactivity was confirmed by absorption with transfected cells. Results. A Bw4⁺ (B∗27:05 or B∗27:13) patient expressed antibody that bound all Bw4⁺ human leukocyte antigen-A and human leukocyte antigen-B antigens tested, except B∗27:05 and B∗44:02. Serum absorbed with B∗51:01-transfected HYM2.C1R cells left only reactivity to B17 (B57, B58), but not to any other Bw4⁺ antigens. Conclusion. A Bw4⁺ patient made antibody to a Bw4 epitope. This finding indicates that apparent anti-Bw4 or anti-Bw6 antibody should not be ignored even in patients who express a common Bw4⁺ or Bw6⁺ antigen, respectively.