目的:探讨脓毒症发病机制中补体C5a参与免疫调节的机制。方法:选择SPF级雄性C57BL/6J小鼠，按照随机数字表法分为假手术组（Sham组）、盲肠结扎穿孔术（CLP）模型组（CLP组）和CLP+抗C5a单克隆抗体干预组（CLP+anti-C5a组），每组20只。构建CLP诱发脓毒症模型；Sham组只开腹不进行结扎穿孔。CLP+anti-C5a组于制模后立即腹腔注射抗C5a单克隆抗体0.15 mg干预；Sham组和CLP组给予等量生理盐水。采用Kaplan-Meier法对各组小鼠进行累积生存分析；采用酶联免疫吸附试验（ELISA）检测术后24、48、72 h外周血血清肿瘤坏死因子-α（TNF-α）、白细胞介素（IL-12、IL-4）及γ-干扰素（IFN-γ）水平；采用免疫组化法观察术后48 h肺组织及肾组织C5a受体（C5aR）表达；采用流式细胞仪检测术后48 h脾脏单个核细胞中树突细胞（DC）、调节性T细胞（Treg）和辅助性T细胞17（Th17）的比例。结果:CLP组小鼠7 d累积生存率较Sham组明显下降（30.00%比100.00%；Log-Rank检验：n χ2＝47.470，n P<0.001）；血清炎性因子TNF-α、IL-12及IL-4水平于术后24 h先反应性升高，48 h明显下降，随后于72 h逐渐升高，而IFN-γ水平于术后24 h开始持续升高至72 h；免疫组化显示，CLP组术后48 h肺组织和肾组织内皮细胞中均有大量C5aR表达；与Sham组比较，脾脏单个核细胞中DC比例〔（1.80±0.30）%比（6.90±1.20）%，n P<0.05〕及Treg比例〔（0.38±0.02）%比（4.00±0.50）%，n P<0.05〕均明显下降，Th17比例明显升高〔（0.83±0.08）%比（0.32±0.03）%，n P<0.05〕，提示免疫细胞比例失衡，免疫功能紊乱。给予抗C5a单克隆抗体干预后，小鼠7 d累积生存率较CLP组明显升高（54.54%比30.00%；Log-Rank检验：n χ2＝28.090，n P<0.001）；血清TNF-α、IL-12和IFN-γ水平进一步升高，而IL-4水平明显下降；肺组织及肾组织C5aR表达较CLP组显著减少；脾脏中成熟DC比例〔（5.10±1.20）%比（1.80±0.30）%，n P<0.05〕和Treg比例〔（2.58±0.05）%比（0.38±0.02）%，n P<0.05〕较CLP组明显升高，Th17比例较CLP组明显降低〔（0.54±0.05）%比（0.83±0.08）%，n P<0.05〕。n 结论:初步判断抗C5a单克隆抗体可能通过改善脾脏中成熟DC及T细胞极化状态进而改善脓毒症预后，C5a在脓毒症细胞免疫调节中发挥重要作用。“,”Objective:To explore the mechanism of complement 5a (C5a) in the pathogenesis of sepsis.Methods:SPF male C57BL/6J mice were selected and divided into sham operation group (Sham group), cecal ligation and puncture (CLP) group and CLP+anti-C5A monoclonal antibody intervention group (CLP+anti-C5a group) according to random number table with 20 mice in each group. A CLP model was reproduced to induce sepsis, and those in the Sham group only underwent laparotomy without ligation and perforation. In the CLP+anti-C5a group, 0.15 mg of anti-C5a monoclonal antibody was injected intraperitoneally immediately after CLP, and in the Sham group and CLP group were given equal amount of normal saline. The cumulative survival rate was analyzed by Kaplan-Meier method. Serum levels of tumor necrosis factor-α (TNF-α), interleukins (IL-12, IL-4), and interferon-γ (IFN-γ) were measured 24, 48 and 72 hours after operation by enzyme linked immunosorbent assay (ELISA). Immunohistochemical staining was used to observe the expression of C5a receptor (C5aR) in lung and kidney tissues 48 hours after operation. The proportions of dendritic cell (DC), regulatory T cell (Treg) and helper T cell 17 (Th17) in splenic mononuclear cells 48 hours after operation were analyzed by flow cytometry.Results:The 7-day cumulative survival rate of mice in the CLP group was significantly lower than that in the Sham group (30.00% vs. 100.00%; Log-Rank test: χ n 2 = 47.470, n P < 0.001), and the peripheral blood inflammatory mediators TNF-α, IL-12 and IL-4 were increased 24 hours after operation, followed by a significant decreasing at 48 hours, and then gradually increased at 72 hours. IFN-γ gradually increased 24 hours after operation and lasted for 72 hours. Immunohistochemistry showed that a large number of C5aR was expressed in pulmonary and renal endothelial cells 48 hours after operation in the CLP group. Compared with the Sham group, the proportion of DC [(1.80±0.30)% vs. (6.90±1.20)%, n P < 0.05] and Treg [(0.38±0.02)% vs. (4.00±0.50)%, n P < 0.05] in splenic mononuclear cells was down-regulated in the CLP group, the proportion of Th17 was up-regulated [(0.83±0.08)% vs. (0.32±0.03)%, n P < 0.05], and disorder of immune function was found. After anti-C5A monoclonal antibody intervention, the 7-day cumulative survival rate increased significantly compared with the CLP group (54.54% vs. 30.00%; Log-Rank test: χ n 2 = 28.090, n P < 0.001); TNF-α, IL-12 and IFN-γ were further increased, while IL-4 was significantly decreased; the expression of C5aR in lung and kidney tissues were significantly decreased, and the expression of mature DC cells [(5.10±1.20)% vs. (1.80±0.30)%, n P < 0.05] and Treg [(2.58±0.05)% vs. (0.38±0.02)%, n P < 0.05] in spleen were significantly increased compared with the CLP group, and Th17 was significantly decreased [(0.54±0.05)% vs. (0.83±0.08)%, n P < 0.05].n Conclusion:It is preliminarily concluded that anti-C5A monoclonal antibody may improve the prognosis of sepsis by improving the polarization of mature DC and T cells in the spleen, and C5a plays an important role in the immune regulation of sepsis cells.