A monoclonal antibody against an epitope common to HLA-b locus antigens.

A monoclonal antibody G4 that appears to be directed against a determinant common to all HLA-B locus antigens is described. This antibody reacted with a large panel of B and T lymphocyte and cell lines, but it did not react with two lines that do not serologically express HLA antigens (Daudi and K562) and two lines that expressed A-locus but not B-locus antigens (8402 and HPBMLT). The F(ab')2 fragment of G4 blocked B-locus but not A-locus HLA alloantisera. By immunoprecipitation and SDS-polyacrylamide gel electrophoresis G4 reacted with a dimer consisting of a heavy chain of 44,000 daltons and a light chain of 12,7000 daltons.