Structural analysis of a new B-cell-differentiation antigen associated with products of the I-A subregion of the H-2 complex.

Ia.W39 is a private specificity of the I-Ab subregion of the H-2 complex. It is selectively expressed on a subset of B lymphocytes that is absent in newborn normal and adult mutant mice carrying the xid gene. Immunoprecipitation and one-dimensional NaDodSO4/polyacrylamide gel electrophoresis showed that the molecule bearing Ia.W39 consists of two noncovalently linked glycoproteins of apparent Mr 33,000 and 28,000. Anti-Ia.W39 serum did not preclear the Iab molecule; however, the conventional allo-anti-I-Ab serum cleared Ia.W39 completely. In view of the identical two-dimensional gel pattern generated by the Ia.W39 and the conventional Iab immunoprecipitates, we believe that all Ia molecules bear the conventional specificities and only a subset would in addition express Ia.W39. Ia.W39 is probably not a carbohydrate antigen, because the antibiotic tunicamycin had no influence on its expression. It may be a conformational determinant on the A alpha and A beta complex induced by the association of an unknown molecule with these chains.