Detergent-solubilised H-2 alloantigen is associated with a small molecular weight polypeptide

Abstract

THERE have been several reports that purified papain-solubilised HL-A alloantigens contains two polypeptides with molecular weights of approximately 31,000 and 11,500 (refs 1–3). The combined molecular weights of these two polypeptides (42,500) is similar to the molecular weight reported for detergent-solubilised HL-A alloantigens (43,000) (ref. 4). The smaller fragment seems to resemble β₂ microglobulin^3,5, which has an amino acid sequence homologous to that of an immunoglobulin heavy chain constant region domain⁶. This smaller fragment does not seem to contain any alloantigenic activity⁵ and is found in association with several different HL-A alloantigenic molecules^1,3. Further evidence of the close association of these two polypeptides is based on observations that capping or immunoprecipitation of β₂ microglobulin using antisera directed against β₂ microglobulin results in the cocapping⁷ or coprecipitation⁸ of HL-A molecules. One critical question is whether the HL-A alloantigens and β₂ microglobulin are covalently⁵ or noncovalently joined to one another. Our studies on a homologous system, the H-2 complex of the mouse, suggest that mouse H-2 alloantigens are noncovalently associated with a small polypeptide.