Epitope sites on human beta 2-microglobulin identified by xenogeneic polyclonal and monoclonal antisera

The relationship between the ability to produce insoluble antigen--antibody complexes from a polypeptide antigen, beta 2-microglobulin and specific antisera from several different species has been examined. The size of complexes was determined by gel-filtration chromatography using serum, immunoglobulin, and divalent F(ab')2 or monovalent Fab fragments therefrom. Non-precipitating primate antihuman beta 2-microglobulin sera recognized two epitopes on the antigen and monoclonal antibody only one epitope, whereas precipitating antisera recognized three or more epitopes, as lattice theory predicts. The paucity of epitope sites reaffirms the unusual immunogenicity of human beta 2-microglobulin when presented to certain primates in the form of an HLA antigen.