title: Role of complement in the immune response.
abstract: Evidence has accumulated that shows that fragments of C3 are potent inhibitors of immune responses. A low-molecular-weight fragment of C3 and fragments possessing leukocyte-mobilizing activity have been shown to block both antigen- and mitogen-induced human T cell proliferation, and to block mixed lymphocyte culture responses and the generation of cytotoxic lymphocytes. The same fragments inhibit the development of secondary in vitro antibody responses of rat lymphocytes. C3b can be shown to inhibit the polyclonal activation of human lymphocytes by pokeweed mitogen, but it has no effect on T cell proliferation or on the generation of cytotoxic T cells. We now propose that different C3 fragments selectively act on various lymphocyte subsets and thus play a profound role in regulating both immune effector functions and the intensity of the immune response.
mesh_terms: D000818:Animals; D000917:Antibody Formation; D001402:B-Lymphocytes / Q000276:immunology*; D003176:Complement C3 / Q000276:immunology*; D015926:Complement C3a; D003182:Complement C5 / Q000276:immunology; D015936:Complement C5a; D003165:Complement System Proteins / Q000276:immunology*; D006801:Humans; D007111:Immunity, Cellular; D007694:Killer Cells, Natural / Q000276:immunology; D008213:Lymphocyte Activation; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D003176:Complement C3; D003182:Complement C5; D015926:Complement C3a; D015936:Complement C5a; D003165:Complement System Proteins