Heavy HLA-DR (Ia) antigen chain is controlled by the MHC region

Abstract

THE major histocompatibility complex (MHC), called the HLA-region in man and the H–2 region in the mouse, contains many genes controlling an array of immunobiological phenomena. Thus certain parts of the immune response and various cell–cell interactions in normal immune processes are under genetic control from the MHC². Two structurally distinct groups of cell surface glycoproteins have so far been identified as products of genes localised to the MHC. The HLA-A, B and C loci control the expression of dimeric molecules composed of dissimilar subunits^3,4. The small subunit, β₂-microglobulin, is invariant and its structural gene resides on chromosome 15⁵. The large subunit carries the alloantigenic determinants which show that the A, B and C loci most probably harbour the structural genes for these polypeptide chains. The HLA-D locus also controls expression of cell surface antigens which are composed of two types of dissimilar subunits, and seem to be the human counterparts to murine Ia antigens^6–9. Neither in man nor in the mouse have unambiguous data been provided demonstrating whether only one or both HLA-D (Ia) antigen subunits express the particular allotypic determinants. However, Barnstable et al.¹⁰ approached this problem by using the somatic cell hybridisation technique and provided evidence suggesting that at least the large, 35,000 molecular weight HLA-D antigen subunit is controlled by the MHC. In this note we demonstrate that by serological analyses and peptide mapping experiments the 35,000 MW HLA-D antigen chain is a product of the HLA-D locus.