Department of Immunology, Leiden University Medical Center, Leiden, the Netherlands.
Department of Nephrology, Leiden University Medical Center, Leiden, the Netherlands.
Mol Immunol. 2021 Dec;140:206-216. doi: 10.1016/j.molimm.2021.10.010. Epub 2021 Nov 2.
C1q is the recognition molecule of the classical pathway of the complement system. By binding to its targets, such as antigen-bound immunoglobulins or C-reactive protein, C1q contributes to the innate defense against infections. However, C1q also plays several other roles beyond its traditional role in complement activation. Circulating levels of C1q are determined in routine diagnostics as biomarker in several diseases. Decreased C1q levels are present in several autoimmune conditions. The decreased levels reflect the consumption of C1q by complement activation and serves as a biomarker for disease activity. In contrast, increased C1q levels are present in infectious and inflammatory diseases and may serve as a diagnostic biomarker. The increased levels of C1q are still incompletely understood but are suggested to modulate the adaptive immune response as C1q is known to impact on the maturation status of antigen-presenting cells and C1q impacts directly on T cells leading to decreased T-cell activity in high C1q conditions. In this review, we provide a comprehensive overview of the current literature on circulating levels of C1q in health and disease, and discuss how C1q can both protect against infections as well as maintain tolerance by regulating adaptive immunity.
C1q 是补体系统经典途径的识别分子。通过与自身抗体结合的免疫球蛋白或 C 反应蛋白等靶标结合，C1q 有助于先天防御感染。然而，C1q 在补体激活之外的其他几个角色中也发挥作用。在几种疾病的常规诊断中，循环 C1q 水平被确定为生物标志物。在几种自身免疫性疾病中存在 C1q 水平降低。降低的水平反映了补体激活对 C1q 的消耗，是疾病活动的生物标志物。相反，在感染性和炎症性疾病中存在 C1q 水平升高，并且可能作为诊断生物标志物。C1q 水平升高的机制尚不完全清楚，但据认为可调节适应性免疫反应，因为 C1q 已知会影响抗原呈递细胞的成熟状态，并且 C1q 直接影响 T 细胞，导致高 C1q 条件下 T 细胞活性降低。在这篇综述中，我们提供了有关 C1q 在健康和疾病中循环水平的当前文献的全面概述，并讨论了 C1q 如何通过调节适应性免疫来既能预防感染又能维持耐受。
