Cross-reacting xenoantibodies to the heavy chain of H-2 and HLA-A,B antigens: serologic and immunochemical characterization.

H-2 cross-reactive antibodies present in HLA xenoantisera were purified by absorption on and elution from murine cells. Antibodies isolated from one of these antisera, 78-E48, were found to mediate complement-dependent lysis of both human and murine lymphoid cells but not of Daudi cells or of human lymphoid cells coated with Fab2 fragments from a cow anti-human beta 2-microglobulin (beta 2 m) antiserum. In indirect immunoprecipitation analyses 78-E48 reacted only with proteins of approximately 45,000 and 12,000 MW present in NP-40 extracts of both human and murine lymphoid cells. Sequential precipitation experiments with rabbit anti-human beta 2 m and allo-anti-H-2Kk, Iak sera established that these proteins were in fact H-2 and HLA-A,B antigens. It was also found that 78-E48 reacted only with the heavy chain of HLA-A,b and H-2 antigens, since this eluate was unreactive with beta 2 m in a radioimmunoassay, and its capacity to immunoprecipitate the 45,000 and 12,000 MW proteins from human cell extracts was unaffected by prior reaction with purified human beta 2 m. These data show for the first time that H-2 and HLA-A,B antigens share properties that probably depend upon their teritary structure.