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

Abstract

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 polymorphism¹ and consist of two noncovalently associated polypeptides^2–8. 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^9–13. 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 and I–E molecules, both subunits of I–A molecules display substantial structural differences when comparisons among allotypes are made^4,14–16. 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.