Fibrinogen-related proteins (FREPs) are widely found in both vertebrates as well as invertebrates, and they play a crucial role in host immunity. In this study, we isolated a novel ficolin gene (Mnfico3) from the oriental river prawn Macrobrachium nipponense. The complete cDNA sequence of Mnfico3 was 1133 bp long, containing an open reading frame of 765 bp coding for Mnfico3, a protein consisting of 254 amino acids. The Mnfico3 protein contained a putative N-terminal signal peptide and a fibrinogen-related protein domain present at the C-terminal. Phylogenetic analysis indicated that Mnfico3 had a closer evolutionary relationship with vertebrate ficolins than with its invertebrate homologues. Tissue distribution analysis indicated that Mnfico3 was predominantly expressed in muscle, in which its transcription was increased following bacterial challenge by Aeromonas veronii. Function analysis using recombinant protein revealed that rMnFico3 had broad-spectrum binding capacity to a variety of microorganisms and pathogen-associated molecular pattern (PAMP) ligands. Furthermore, rMnFico3 exhibited Ca²⁺-dependent agglutinating activity against microbes in vitro, and ability to attach to the hemocyte surface which promoted phagocytosis and subsequent clearance of invasive bacteria in vivo. Silencing rMnFico3 in prawn through RNAi did not alter the expression of antimicrobial peptide genes (ALF and Crustin). These results manifested that MnFico3 functioned as a potential pattern recognition receptor (PPR) to mediate cellular immune response by recognizing PAMPs, agglutinating invasive microbes, and promoting phagocytosis of hemocytes.

纤维蛋白原相关蛋白（FREP）广泛存在于脊椎动物和无脊椎动物中，它们在宿主免疫中发挥着至关重要的作用。在这项研究中，我们从东方河虾日本沼虾中分离出一种新的 ficolin 基因 ( Mnfico 3)。 Mnfico 3的完整cDNA序列长1133 bp，包含编码Mnfico3的765 bp开放阅读框，Mnfico3是由254个氨基酸组成的蛋白质。 Mnfico3 蛋白含有假定的 N 端信号肽和存在于 C 端的纤维蛋白原相关蛋白结构域。系统发育分析表明，Mnfico3 与脊椎动物 ficolins 的进化关系比与无脊椎动物同源物的进化关系更密切。组织分布分析表明， Mnfico 3 主要在肌肉中表达，在受到维罗尼气单胞菌的细菌攻击后，其转录增加。使用重组蛋白的功能分析表明，rMnFico3对多种微生物和病原体相关分子模式（PAMP）配体具有广谱结合能力。此外，rMnFico3在体外表现出Ca ²⁺依赖性的抗微生物凝集活性，并且能够附着在血细胞表面，从而促进体内侵袭细菌的吞噬作用和随后的清除。通过 RNAi 沉默对虾中的 rMnFico3 并没有改变抗菌肽基因（ALF 和 Crustin）的表达。这些结果表明，MnFico3作为一种潜在的模式识别受体（PPR），通过识别PAMP、凝集入侵微生物、促进血细胞吞噬来介导细胞免疫反应。