Morgan E L, Weigle W O, Hugli T E
J Exp Med. 1982 May 1;155(5):1412-26. doi: 10.1084/jem.155.5.1412.
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.
补体第三成分的C3a片段被发现具有免疫抑制特性。C3a能够抑制特异性和多克隆抗体反应。相比之下，C3a对抗原或丝裂原诱导的B细胞或T细胞增殖反应没有影响。C3a的羧基末端精氨酸对于其发挥免疫抑制特性至关重要。血清羧肽酶抑制剂2-巯基甲基-5-胍基戊酸可阻止末端精氨酸的裂解，而末端精氨酸裂解会产生C3ades Arg-77，这使我们能够在需要血清的体外免疫反应系统中检测C3a的作用。当从C3a上去除末端精氨酸时，产生的C3ades Arg-77分子没有抑制作用。辅助性T淋巴细胞是C3a介导的免疫反应抑制的靶点。发现用可溶性T细胞因子替代T细胞可消除C3a的抑制活性。
