Dept. of Nephrology, Odense University Hospital, Kløvervænget 6, 5000 Odense, Denmark; Dept. of Clinical Research, University of Southern Denmark, J.B. Winsløwsvej 19, 5000 Odense, Denmark.
Dept. of Nephrology, Odense University Hospital, Kløvervænget 6, 5000 Odense, Denmark; Dept. of Molecular Medicine, Cardiovascular and Renal Research, University of Southern Denmark, J.B. Winsløwsvej 19, 5000 Odense, Denmark.
Immunobiology. 2023 Jul;228(4):152462. doi: 10.1016/j.imbio.2023.152462. Epub 2023 Jun 24.
The complement system, consisting of more than thirty different soluble and cell-bound proteins, exerts essential functions both in the innate and adaptive immune systems and is believed to be an important contributor to allograft injury in kidney transplantation. The anaphylatoxins C3a and C5a are powerful chemoattractants, recruiting immune effector cells toward the site of complement activation and enhance T-cell response, while C3dg binding to CR2 on B-cells, enhances B-cell immunity at several stages of the B-cell differentiation. Complement split products in plasma and urine could reflect ongoing inflammation and tissue injury. We, therefore, investigated if complement split products increase in plasma and urine in kidney transplant recipients with rejection.
In this case-control feasibility study, complement factors C3a, C3dg, C4a, and C5a were measured in plasma and C3dg and sC5b-9 associated C9 neoantigen in urine in 15 kidney transplant recipients with rejection (cases) and 15 kidney transplant recipients without (controls). The groups were matched on the type of transplantation and the time from transplantation to sampling. The complement split products were compared (i) between cases and controls and (ii) within the rejection group over time, comparing the measurements at rejection with measurements where the kidney transplant recipients were clinically stable. Possible moderators were explored, and results adjusted accordingly. P values < 0.05 were considered significant. Plasma C3dg was analyzed by immune-electrophoresis, plasma C3a, plasma C4a, and plasma C5a by flow cytometry, and urine C3dg and urine C9neo by ELISA.
In plasma, there were no significant differences between the rejection and the control group. However, steroids and pretransplant C3dg levels significantly influenced C3dg. Within the rejection group, plasma C3a and C3dg were significantly higher at the time of rejection compared to the stable phase (p < 0.01). In urine, C3dg/creatinine and C9 neoantigen/creatinine ratios were not different between the rejection and the control group. Urine C3dg/creatinine and urine C9 neoantigen/creatinine ratios correlated to urine albumin and significantly increased after the transplantation (p < 0.001).
This study shows increased plasma C3a and C3dg in kidney transplant recipients, primarily with T cell mediated rejection. This finding suggests that consecutive measurements of C3a and C3dg in plasma could be applicable to monitor alloreactivity in kidney transplant recipients. Urine complement split products are unsuitable as rejection biomarkers since the permeability of the glomerular filtration barrier strongly influences them. Prospective longitudinal studies on plasma C3a and C3dg dynamics will be needed to validate present findings.
补体系统由三十多种可溶性和细胞结合蛋白组成，在先天和适应性免疫系统中发挥着重要功能，被认为是肾移植中同种异体移植物损伤的重要因素。过敏毒素 C3a 和 C5a 是强有力的趋化因子，将免疫效应细胞募集到补体激活部位，并增强 T 细胞反应，而 C3dg 与 B 细胞上的 CR2 结合，增强 B 细胞在 B 细胞分化的几个阶段的免疫。血浆和尿液中的补体片段产物可反映持续的炎症和组织损伤。因此，我们研究了排斥反应的肾移植受者血浆和尿液中的补体片段产物是否增加。
在这项病例对照可行性研究中，我们测量了 15 例排斥反应的肾移植受者（病例）和 15 例无排斥反应的肾移植受者（对照组）的血浆补体因子 C3a、C3dg、C4a 和 C5a，以及尿液中 C3dg 和与 sC5b-9 相关的 C9 新抗原。两组在移植类型和从移植到采样的时间上相匹配。比较了（i）病例和对照组之间以及（ii）排斥组内随着时间的推移的补体片段产物，比较了在排斥时的测量值与在肾移植受者临床稳定时的测量值。探索了可能的调节剂，并相应地进行了调整。p 值<0.05 被认为具有统计学意义。血浆 C3dg 通过免疫电泳分析，血浆 C3a、血浆 C4a 和血浆 C5a 通过流式细胞术分析，尿液 C3dg 和尿液 C9neo 通过 ELISA 分析。
在血浆中，排斥组和对照组之间没有显著差异。然而，类固醇和移植前 C3dg 水平显著影响 C3dg。在排斥组中，与稳定期相比，排斥时血浆 C3a 和 C3dg 显著升高（p<0.01）。在尿液中，排斥组和对照组的尿液 C3dg/肌酐和 C9 neoantigen/肌酐比值无差异。尿液 C3dg/肌酐和尿液 C9 neoantigen/肌酐比值与尿液白蛋白相关，在移植后显著增加（p<0.001）。
本研究表明肾移植受者血浆 C3a 和 C3dg 升高，主要与 T 细胞介导的排斥反应有关。这一发现表明，连续测量血浆 C3a 和 C3dg 可能适用于监测肾移植受者的同种异体反应性。尿液补体片段产物不适合作为排斥反应的生物标志物，因为肾小球滤过屏障的通透性对其有很大影响。需要进行前瞻性纵向研究，以验证血浆 C3a 和 C3dg 动力学的现有发现。
