Identification of a second class I antigen controlled by the K end of the H-2 complex and its selective cellular expression.

Immunoprecipitates obtained from [35S]methionine-labeled spleen cells by using monoclonal antibodies specific for H-2Kd and H-2Dd have been separated by two-dimensional polyacrylamide gel electrophoresis. Analysis of these gel patterns revealed the presence of an additional product of the K end of the H-2d complex, designated here as H-2K'. To determine whether H-2K' is a unique protein or a differentially glycosylated form of the previously characterized H-2Kd histocompatibility antigen, nonglycosylated molecules labeled in the presence of tunicamycin were examined. The results showed that both H-2K and H-2K' have distinct nonglycosylated polypeptide precursor forms. The approximate molecular weight differences between the fully glycosylated and nonglycosylated molecules also indicated the presence of three oligosaccharide side chains on H-2K', as is the case with H-2Kd, whereas H-2Dd has only two oligosaccharide units. The cellular expression of H-2K' was also investigated. Comparison of H-2 antigens immunoprecipitated from normal spleen cells and from thioglycollate-induced adherent peritoneal exudate cells cultured in the presence or absence of supernatant fluids from concanavalin A-stimulated spleen cells revealed that H-2K' was not expressed on the adherent peritoneal cells. This indicates that H-2K' is expressed in a tissue-specific manner, unlike the classical histocompatibility antigens H-2K and H-2D.