Chinese Academy of Sciences (CAS) & Shandong Province Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Center for Ocean Mega-Science, Chinese Academy of Sciences, Qingdao, China.
Laboratory for Marine Biology and Biotechnology, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao, China.
Front Immunol. 2022 Feb 25;13:813173. doi: 10.3389/fimmu.2022.813173. eCollection 2022.
In the complement system, C3 is a central component in complement activation, immune defense and immune regulation. In all pathways of complement activation, the pivotal step is conversion of the component C3 to C3b and C3a, which is responsible to eliminate the pathogen and opsonization. In this study, we examined the immunological properties of C3 and its activated fragment C3a from Japanese flounder () (PoC3 and PoC3a), a teleost species with important economic value. PoC3 is composed of 1655 amino acid residues, contains the six domains and highly conserved GCGEQ sequence of the C3 family. We found that expression occurred in nine different tissues and was upregulated by bacterial challenge. In serum, PoC3 was able to bind to a broad-spectrum of bacteria, and purified native PoC3 could directly kill specific pathogen. When PoC3 expression in Japanese flounder was knocked down by siRNA, serum complement activity was significantly decreased, and bacterial replication in fish tissues was significantly increased. Recombinant PoC3a (rPoC3a) exhibited apparent binding capacities to bacteria and Japanese flounder peripheral blood leukocytes (PBL) and induce chemotaxis of PBL. Japanese flounder administered rPoC3a exhibited enhanced resistance against bacterial infection. Taken together, these results indicate that PoC3 is likely a key factor of complement activation, and PoC3 and PoC3a are required for optimal defense against bacterial infection in teleost.
在补体系统中，C3 是补体激活、免疫防御和免疫调节的核心成分。在补体激活的所有途径中，关键步骤是将 C3 转化为 C3b 和 C3a，这负责消除病原体和调理作用。在这项研究中，我们研究了来自日本牙鲆（PoC3 和 PoC3a）的 C3 及其激活片段 C3a 的免疫学特性，日本牙鲆是一种具有重要经济价值的硬骨鱼类。PoC3 由 1655 个氨基酸残基组成，包含六个结构域和 C3 家族高度保守的 GCGEQ 序列。我们发现，PoC3 在 9 种不同组织中表达，并受到细菌挑战的上调。在血清中，PoC3 能够与广谱细菌结合，并且纯化的天然 PoC3 可以直接杀死特定的病原体。当通过 siRNA 敲低日本牙鲆中的 PoC3 表达时，血清补体活性显著降低，并且鱼类组织中的细菌复制显著增加。重组 PoC3a（rPoC3a）表现出明显的与细菌和日本牙鲆外周血白细胞（PBL）的结合能力，并诱导 PBL 的趋化性。给予 rPoC3a 的日本牙鲆表现出增强的对细菌感染的抵抗力。总之，这些结果表明 PoC3 可能是补体激活的关键因素，PoC3 和 PoC3a 是硬骨鱼类最佳防御细菌感染所必需的。
