Dimeric and Monomeric Forms of HL-A Antigens Solubilized by Detergent

Abstract

Abstract HL-A antigens solubilized by papain contain two non-covalently linked subunits, a 34,000 m.w. glycoprotein and an 11,000 m.w. protein (1–3), estimated by sodium dodecyl sulfate (SDS)2 gel electrophoresis. The glycoprotein exhibits differences in electrophoretic mobility depending on HL-A specificity (3) and probably bears the antigenic determinant (4). The small protein, when assessed by immunologic and electrophoretic techniques, is identical to β2-microglobulin (4–7), a protein found in serum and in elevated amounts in nephrotic urine, which is significantly homologous to the constant region domains of IgG (8, 9). Numerous studies with immunofluorescent techniques have recently shown that β2-microglobulin is also associated with HL-A antigens on the lymphocyte membrane (10–13), and partially purified HL-A antigens solubilized by detergents contain β2-microglobulin (7) together with a glycoprotein of molecular weight 43,000 to 44,000 (14). In this report, we present evidence that the detergent-solubilized HL-A-β2-microglobulin complex, both labeled with radioactive precursors and in large-scale unlabeled preparations, exists in part in a dimeric form.