Enhancement of antibody responses by IgD-binding factors induced by anti-IgD treatment of spleen cells.

Treatment of normal BALB/c splenocytes with anti-mouse IgD antibodies at 0 degrees C followed by incubation of the cells at 37 degrees C resulted in the formation of soluble factors that selectively inhibit rosette formation of lymphocytes bearing Fc delta receptors with IgD-coated erythrocytes (i.e., IgD-binding factors). Treatment of the same cells with anti-IgM antibodies failed to induce the formation of the factors. Analysis of cellular mechanisms indicated that polymerized surface IgD on B cells, as well as surface IgD-anti-IgD complexes shed from the B cells, induced T cells bearing Fc delta receptors to form IgD-binding factors. The factors formed by the anti-IgD treatment of splenic lymphocytes are composed of molecular mass species of 70 and 34 kDa, as estimated by gel filtration. Both the 70- and 34-kDa IgD-binding factors enhanced IgM and IgG1 plaque-forming cell responses of sheep erythrocyte-primed mouse spleen cells to the antigen.