Small subunit of I-A subregion antigens determines the allospecificity recognized by a monoclonal antibody.

The murine major histocompatibility complex (MHC) codes for three groups of identifiable cell-surface proteins, the K, D molecules, the I-A subregion antigens and the I-E subregion antigens. All three groups of molecules display a high degree of serologically detectable polymorphism and consist of two noncovalently associated polypeptides. Amino acid sequence and peptide comparisons among allotypes of K, D and I-E molecules reveals that one polypeptide is relatively constant, whereas the other is highly variable. Thus, it is likely that only one of the two polypeptides, the variable component, determines the antigenic specificities recognized by alloantisera. In contrast to the K, D anad I-E molecules, both subunits of I-A molecules display substantial structural differences when comparisons among allotypes are made. Therefore, we have investigated whether one or both subunits of I-A molecules determine their alloantigenic specificities. Our results, presented here, indicate that only one of the two subunits determines a particular allospecificity recognized by a monoclonal antibody.