The First Example of an HLA‐Bw45 Antiserum Produced in a HLA‐Bw44 Positive Woman

An HLA-Bw45 serum (Mu46), which was produced by pregnancy in a Bw44 positive woman, is described. The serum was unable to be absorbed by Bw44 positive cells. Blocking tests employing broad B12 (Bw44 + Bw45) antisera, stimulated by either Bw44 or Bw45, showed that only F(ab)'2 from Bw45-stimulated B12 sera would completely block the cytotoxicity of this serum. It was concluded that Bw44 and Bw45 are distinct specificities which share common determinants. These findings are briefly discussed in relation to a recent report on the HLA-B antigen and supertypic Bw4, Bw6 antigen relationship.