Molecular variants of human Ia-like antigens

Abstract

THE Ia antigens, a group of plasma membrane proteins predominately expressed on B lymphocytes and thought to be products of the ‘immune response (Ir) region’ of the major histocompatibility complex^1–4, are believed to play a part in the mechanism of T–B cell cooperation^1,5, stimulation in mixed lymphocyte culture¹, graft-versus-host reactions¹ and T-cell suppression⁶. They have been demonstrated on the surface of a variety of cells which take part in intercellular interactions, such as B lymphocytes, macrophages, suppressor T cells, sperm⁷ and Langerhans cells of the skin⁸. In several species these glycoproteins exist in a complex containing 33,000 and 27,000 molecular weight (MW) moieties^9,10. Although Snary et al.¹¹ have shown that the human alloantigens may reside predominantly on the 33,000 MW chain, alloantisera are able to precipitate both components. Attempts to show molecular variants within either chain by immune precipitation with alloantisera have given inconsistent and varying proportions of the light and heavy chains¹². Springer et al.¹³ used two-dimensional gel electrophoresis of human B-cell alloantigens to show the association of the two chains, but observed smearing in the isoelectric focusing dimension which they attributed in part to aggregation. We describe here the preliminary successful subfractionation of the 33,000 MW chain of human Ia-like antigens by a modification of the two-dimensional electrophoresis system which combines isoelectric focusing and discontinuous sodium dodecyl sulphate (SDS) electrophoresis.