Role of the Bp35 cell surface polypeptide in human B-cell activation.
A 35-kDa polypeptide, Bp35, expressed on the surface of all B cells, plays a role in B-cell activation. Monoclonal antibodies to Bp35 stimulate human tonsillar B cells to proliferate. The activation induced by anti-Bp35 is similar to anti-Ig-mediated in several ways: the activation does not require T cells but is augmented by T-cell-derived allogeneic factors; monovalent Fab fragments to Bp35 do not trigger proliferation but instead block activation by whole antibody, indicating that cross-linking is required; and induction by anti-Bp35, like the induction by anti-Ig, is inhibited by monoclonal anti-IgM via an Fc domain-dependent mechanism. However, several features of anti-Bp35-mediated proliferation are clearly different from activation by anti-Ig: anti-Bp35 monoclonal antibodies do not require attachment to beads to function, the proliferation induced by anti-Bp35 and anti-Ig is additive, and Fab fragments of anti-Bp35 augment proliferation induced by anti-Ig. Models for the possible function of the Bp35 polypeptide as either a "bridge" or a "second signal" with surface Ig in B-cell activation are discussed.
D000888:Antibodies, Anti-Idiotypic / Q000276:immunology; D000911:Antibodies, Monoclonal / Q000276:immunology; D000954:Antigens, Surface / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology*; D006801:Humans; D066298:In Vitro Techniques; D008213:Lymphocyte Activation; D011947:Receptors, Antigen, B-Cell / Q000276:immunology; D011971:Receptors, Immunologic; D013601:T-Lymphocytes / Q000276:immunology
D000888:Antibodies, Anti-Idiotypic; D000911:Antibodies, Monoclonal; D000954:Antigens, Surface; D011947:Receptors, Antigen, B-Cell; D011971:Receptors, Immunologic