Alloantibody to a Bw4 Epitope in a Bw4+ B*27

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.