HLA-DR products are a subset of human Ia antigens

Abstract

Human Ia antigens are polymorphic cell-surface sialoglycoproteins which have restricted tissue distribution^1,2. They are bimolecular complexes of 34,000 (α) and 28,000 (β) molecular weight and most of the polymorphism is found in the smaller polypeptides^3–5. They are involved in the initiation of immune responses⁶ and particular Ia antigens are associated with increased susceptibility to certain diseases⁷. They are also the major barrier to human allogeneic tissue transplantation⁸. Whereas serological analysis and mixed lymphocyte typing have defined three polymorphic families of Ia antigens, HLA-DR, -DC and -SB^9–17, protein sequencing results¹⁸ and studies with monoclonal antibodies indicate that the complexity is much greater^19–23. Thus the HLA-DR and DC specificities as defined by alloantisera, could represent groups of antigens which are controlled by HLA genes in linkage disequilibrium. Here, we have used a monoclonal antibody specific for HLA-DR2 to show that this determinant is carried by molecules which are distinct from those of the DC series and which represent 30% of the Ia antigens expressed on the cell surface of an HLA homozygous line PGF.