A monoclonal antibody that recognizes the alpha chain of HLA-DR antigens.

A monoclonal antibody, HC2.1, has been generated that specifically reacts with both the denatured and the in vitro translated alpha chain of the DR antigen. Although HC2.1 antibody reacted with the alpha chain of protein immunoprecipitated by two DR-specific monoclonal antibodies, L227 and LB3.1, it did not react with the alpha chain of the DQ1 antigen immunoprecipitated by the monoclonal antibody, Genox 3.53. The isoelectric focusing pattern of the alpha chain precipitated by HC2.1 antibody was invariant across a range of DR specificities within a panel of lymphoblastoid cells. The alpha chain of DR antigen from a B cell line was purified by HC2.1-Sepharose immunoaffinity chromatography and limited amino acid sequence analysis was carried out with Staphylococcus aureus SV8 protease fragments purified by high-pressure liquid chromatography. The sequence analysis confirmed that the antigen reactive with HD2.1 antibody is encoded by the DR alpha chain gene.