title: Modulation of human B cell immunoglobulin secretion by the C3b component of complement.
abstract: The human C3b component of complement was found to inhibit the differentiation of human B lymphocytes into immunoglobulin-secreting cells in vitro. Pokeweed mitogen (PWM)-induced plaque-forming cell (PFC) responses were inhibited by C3-coated zymosan particles and by purified human C3b. C3b inhibited the PWM-driven responses in a dose-dependent fashion, and it was necessary for C3b to be present in the early phases of the cultures. C3b acted directly on B cells rather than on helper T cells because it inhibited the PFC responses of MNC depleted of T cells and subsequently stimulated with a T cell-independent Epstein Barr virus mitogen. Furthermore, C3b failed to stimulate the generation of suppressor lymphocytes and/or monocytes that might have been responsible for the inhibition of B cell responses. Our results indicate that C3b or its fragments exert negative modulatory effects on human B lymphocyte responses.
mesh_terms: D000906:Antibodies / Q000502:physiology; D000921:Antibody-Producing Cells / Q000166:cytology / Q000276:immunology*; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology*; D001667:Binding, Competitive; D002454:Cell Differentiation; D003179:Complement C3b / Q000276:immunology / Q000502:physiology*; D006462:Hemolytic Plaque Technique; D006801:Humans; D008213:Lymphocyte Activation; D011043:Pokeweed Mitogens / Q000494:pharmacology; D050378:T-Lymphocytes, Regulatory / Q000276:immunology; D015054:Zymosan
chemical_list: D000906:Antibodies; D011043:Pokeweed Mitogens; D003179:Complement C3b; D015054:Zymosan