Isolation of I–A subregion-like molecules from subhuman primates and man

Abstract

Immune response-associated (Ia) molecules play a major part in cellular interactions that initiate an immune response. Two families of Ia molecules, determined by the I–A and I–E subregions of the murine major histocompatibility complex (MHC), have been isolated and characterized in mice¹. I–A and I–E molecules each consist of two polypeptide chains (molecular weights (M_rs) of 26,000 and 35,000 for I–A and 24,000 and 32,000 for I–E) that are noncovalently associated². Their large subunits are designated A_α and E_α, respectively, and their small subunits A_β and E_β. Despite the similarity in their subunit composition, the I–A and I–E molecules are structurally distinct according to peptide mapping and partial N-terminal sequence analysis^3,4. Although the structural homologue of murine I–E molecules has been identified in man and is known as HLA-DR⁵, the I–A equivalent has never been described. In an attempt to identify the human analogue of the murine I–A molecule, murine monoclonal antibodies were produced after immunization with a mixture of three putative human cell lines. We report here that one of these antibodies reacts with I–A-like molecules from two cell lines, GM3158, which after karyotype analysis was shown to have originated not from man but from a marmoset, and GM3163, a cell line of human origin.