title: Anaphylatoxin-mediated regulation of the immune response. I. C3a-mediated suppression of human and murine humoral immune responses.
abstract: The C3a fragment of the third component of complement was found to have immunosuppressive properties. C3a is capable of suppressing both specific and polyclonal antibody responses. In contrast, C3a had no effect on antigen- or mitogen-induced B or T cell proliferative responses. The carboxy-terminal arginine is essential for C3a to exhibit its immunosuppressive properties. The serum carboxypeptidase inhibitor 2-mercaptomethyl-5-guanodinopentanoic acid, which prevents cleavage of the terminal arginine that would produce C3ades Arg-77, allowed us to assay the effects of C3a on in vitro immune response systems where serum is required. When  the terminal arginine is removed from C3a, the resulting C3ades Arg-77 molecule is nonsuppressive. Helper T lymphocytes are the target of C3a-mediated suppression of the immune response. Substitution of T cells by soluble T cell factors was found to abrogate the C3a suppressive activity.
mesh_terms: D000706:Anaphylatoxins / Q000378:metabolism*; D000818:Animals; D000917:Antibody Formation; D000921:Antibody-Producing Cells / Q000276:immunology; D002268:Carboxypeptidases / Q000037:antagonists & inhibitors; D003176:Complement C3 / Q000378:metabolism*; D015926:Complement C3a; D005260:Female; D006801:Humans; D007111:Immunity, Cellular; D007165:Immunosuppression Therapy; D007700:Kinetics; D008213:Lymphocyte Activation; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D010455:Peptides / Q000378:metabolism*
chemical_list: D000706:Anaphylatoxins; D003176:Complement C3; D010455:Peptides; D015926:Complement C3a; D002268:Carboxypeptidases