title: Immunoglobulin production by human peripheral lymphocytes induced by anti-C3 receptor antibodies.
abstract: The exact function of receptors for C3b (CR1), which are present on B lymphocytes, is not clear. The present studies were performed to determine the influence of heterologous anti-CR1 on the production of IgM, IgG, and IgA by human peripheral B lymphocytes in vitro. Anti-CR1, raised in rabbits by immunization with purified erythrocyte CR1, was rendered immunospecific and was converted to F(ab')2 and Fab' by enzyme digestion. Pre-immune F(ab')2 and Fab' served as controls. Normal human blood T lymphocytes and T cell-depleted mononuclear cells were cultured for 6 days in RPMI medium and 10% heated fetal calf serum with a low dose (7 micrograms/ml) of pokeweed mitogen (PWM) alone or with PWM and F(ab')2-anti-CR1. In control experiments the effects of F(ab')2-anti-CR1 without PWM and of pre-immune F(ab')2, Fab'-anti-CR1 and pre-immune Fab' in combination with PWM were also tested. When PWM and F(ab')2-anti-CR1 were present simultaneously, 4.3 X 10(3), 2.5 X 10(3), and 1.8 X 10(3) ng/ml of IgM, IgG, and IgA were synthesized, respectively, in cultures containing 4.5 X 10(5) mononuclear blood cells. All other combinations resulted in synthesis of less than 250 ng/ml of each class of Ig. The presence of purified CR1 in the cultures containing PWM and F(ab')2-anti-CR1 caused a dose-dependent decrease of Ig synthesis. By culturing B cells isolated by E-C3b rosetting with T cells and monocytes, the anti-CR1 responding population was demonstrated to be mainly in the CR1-rich B cell fraction. Fab'-anti-CR1 at high doses was also able to stimulate Ig production in the presence of low concentrations of PWM. These data suggest that triggering of CR1 on B cells results in modulation of antibody production and that triggering of CR1 with more than one antibody is required for an optimal response.
mesh_terms: D000818:Animals; D000918:Antibody Specificity; D000921:Antibody-Producing Cells / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D004306:Dose-Response Relationship, Immunologic; D006801:Humans; D007106:Immune Sera / Q000276:immunology / Q000494:pharmacology*; D007140:Immunoglobulin Fab Fragments / Q000276:immunology; D007136:Immunoglobulins / Q000032:analysis / Q000096:biosynthesis; D008213:Lymphocyte Activation; D011817:Rabbits; D011951:Receptors, Complement / Q000276:immunology*; D017463:Receptors, Complement 3b
chemical_list: D007106:Immune Sera; D007140:Immunoglobulin Fab Fragments; D007136:Immunoglobulins; D011951:Receptors, Complement; D017463:Receptors, Complement 3b