Two‐dimensional gel analysis of the polypeptides precipitated by a polymorphic HLA‐DR1,2,w6 monoclonal antibody: Evidence for a third locus

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Abstract
The SDR1 monoclonal antibody reacts only with cells which express the HLA‐DR1, 2,w6 or w8 allogeneic specificities. Two‐dimensional nonequilibrium pH gradient/ sodium dodecyl sulfate polyacrylamide gel electrophoretic analyses of SDR1 im‐munoprecipitates from [35S]methionine biosynthetically labeled cells revealed the typical pattern of la antigens, namely two polypeptides of about 34kDa and 29kDa (designated ϵ and β−3) as well as the “basic invariant spot” of about 31 kDa. The ϵ and β‐3 polypeptides were only weakly represented in similar analyses of immunoprecipitates performed using a monomorphic HLA‐DR monoclonal antibody, TDR31.1. The ϵ and β−3 polypeptides of B lymphoblastoid cell lines homozygous for HLA‐DR2 and w6 were structurally polymorphic as judged by two‐dimensional gel analyses. This polymorphism was independent of the HLA‐DR specificity. It is concluded that the SDR1 antibody recognizes a polymorphic set of la antigens that are coded by a locus other than HLA‐DR. These antigens probably also express the MT1 (DC1, LB12) alloantigenic specificity and are most likely the human equivalent of the murine I‐A subregion antigens.