Molecular Parasitology Section, Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, United States.
Department of Microbiology and Immunology, Georgetown University Medical Centre, Georgetown University, Washington, DC, United States.
Front Immunol. 2020 Jan 17;10:3105. doi: 10.3389/fimmu.2019.03105. eCollection 2019.
Regulating complement is an important step in the establishment of infection by microbial pathogens. actively resists complement-mediated killing in non-immune human serum (NHS) by inactivating C3b, however the precise molecular basis is unknown. Here, a flow cytometry-based C3b binding assay demonstrated that Type II strains had significantly higher levels of surface-bound C3b than Type I strains. However, both strains efficiently inactivated C3b and were equally resistant to serum killing, suggesting that resistance is not strain-dependent. activated both the lectin (LP) and alternative (AP) pathways, and the deposition of C3b was both strain and lectin-dependent. A flow cytometry-based lectin binding assay identified strain-specific differences in the level and heterogeneity of surface glycans detected. Specifically, increased lectin-binding by Type II strains correlated with higher levels of the LP recognition receptor mannose binding lectin (MBL). Western blot analyses demonstrated that recruits both classical pathway (CP) and LP regulator C4b-binding proteins (C4BP) and AP regulator Factor H (FH) to the parasite surface to inactivate bound C3b-iC3b and C3dg and limit formation of the C5b-9 attack complex. Blocking FH and C4BP contributed to increased C5b-9 formation . However, parasite susceptibility was only impacted when FH was blocked, indicating that down regulation of the alternative pathway by FH may be more critical for parasite resistance. Infection of C3 deficient mice led to uncontrolled parasite growth, acute mortality, and reduced antibody production, indicating that both the presence of C3, and the ability of the parasite to inactivate C3, was protective. Taken together, our results establish that regulation of the complement system renders mice resistant to acute infection by limiting parasite proliferation , but susceptible to chronic infection, with all mice developing transmissible cysts to maintain its life cycle.
补体调节是微生物病原体感染建立的重要步骤。 通过使 C3b 失活，在非免疫人血清 (NHS) 中积极抵抗补体介导的杀伤，但其确切的分子基础尚不清楚。 在这里，基于流式细胞术的 C3b 结合测定表明，II 型菌株表面结合的 C3b 水平明显高于 I 型菌株。 然而，两种菌株都有效地使 C3b 失活，并且对血清杀伤具有同等抗性，表明抗性与菌株无关。 激活凝集素 (LP) 和替代 (AP) 途径，并且 C3b 的沉积既与菌株有关，也与凝集素有关。 基于流式细胞术的凝集素结合测定鉴定了表面糖基的水平和异质性存在菌株特异性差异。 具体而言，II 型菌株的凝集素结合增加与 LP 识别受体甘露糖结合凝集素 (MBL)的水平增加相关。 Western blot 分析表明，招募经典途径 (CP) 和 LP 调节剂 C4b 结合蛋白 (C4BP) 和 AP 调节剂因子 H (FH) 到寄生虫表面，以失活结合的 C3b-iC3b 和 C3dg 并限制 C5b-9 攻击复合物的形成。 阻断 FH 和 C4BP 有助于增加 C5b-9 的形成。 然而，只有当阻断 FH 时才会影响寄生虫的易感性，这表明 FH 对替代途径的下调可能对寄生虫的抗性更为关键。 C3 缺陷型小鼠的感染导致寄生虫不受控制的生长、急性死亡和抗体产生减少，表明 C3 的存在以及寄生虫失活 C3 的能力均具有保护作用。 总之，我们的结果表明，补体系统的调节通过限制寄生虫的增殖使小鼠对急性感染具有抵抗力，但易感染慢性感染，所有小鼠都会产生可传播的囊肿以维持其生命周期。
