title: The B cell surface molecule B1 is functionally linked with B cell activation and differentiation.
abstract: The B1 molecule is a 32,000 m.w. phosphorylated cell surface protein expressed exclusively by B cells from the mid pre-B until the plasma cell stage of differentiation. Two monoclonal antibodies (gamma 2a and mu) reactive with this molecule were used to assess the role of B1 in B cell activation, proliferation, and differentiation. The anti-B1 antibodies at concentrations ranging from 0.1 to 100 micrograms/ml significantly inhibited B cell proliferation induced by anti-mu antibodies, Staphylococcus aureus Cowan strain 1, activated T cells, and Epstein Barr virus. Although capable of inhibiting proliferation, anti-B1 antibody in soluble form or coupled to beads did not activate B cells or induce proliferation. Antibodies of comparable isotypes or against other B cell-restricted antigens, including B2, B4, B5, and HB-5, did not inhibit activation. Pretreatment of B cells with anti-B1 antibody did not inhibit activation, indicating that B cells had to be cultured with anti-B1 antibody for anti-B1-mediated inhibition to occur. Maximum inhibition was obtained when anti-B1 antibody was added at the initiation of culture. In agreement with this, growth factor-dependent proliferation of preactivated B cells was not inhibited by anti-B1 antibodies. Comparable inhibition of B cell activation was noted with antibodies reactive with class II antigens of the major histocompatibility complex with the exception that anti-B1 antibody inhibited immunoglobulin secretion in pokeweed mitogen assays, whereas anti-DR antibody did not. These results suggest that the B1 molecule may serve a central role in the regulation of B cell activation and differentiation.
mesh_terms: D000328:Adult; D000911:Antibodies, Monoclonal / Q000502:physiology; D000944:Antigens, Differentiation, B-Lymphocyte; D000954:Antigens, Surface / Q000276:immunology*; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology*; D001667:Binding, Competitive; D002454:Cell Differentiation; D006133:Growth Substances / Q000494:pharmacology; D006801:Humans; D007399:Interphase; D008213:Lymphocyte Activation; D008863:Microspheres; D013997:Time Factors
chemical_list: D000911:Antibodies, Monoclonal; D000944:Antigens, Differentiation, B-Lymphocyte; D000954:Antigens, Surface; D006133:Growth Substances