Functional characterization of the mouse lectin ficolin-B

无花果蛋白酶是蛋白质的聚集蛋白家族的成员，其在人类和小鼠中能够识别微生物表面上的病原体相关分子模式（PAMP）。无花果蛋白酶通过在与其特异性PAMP结合后引发血清中的补体级联反应来触发先天免疫系统的活化。我们最近发表了关于小鼠ficolin-B合成的第一个观察结果，令人惊讶的是，该蛋白质位于巨噬细胞的细胞内。同时，其他人已经表明纤维胶凝蛋白-B不与丝氨酸蛋白酶结合，因此不能激活补体。这些发现的相关性和小鼠纤维胶凝蛋白B对细菌攻击的作用机制仍有待阐明。我们的初步数据表明，ficolin-B的表达是在激活过程中上调，但在成熟的巨噬细胞和骨髓来源的树突状细胞的下调，这表明在细胞激活的早期阶段，在病原体的遭遇，ficolin-B的关键作用。此外，结合试验表明，一些菌株的葡萄球菌。金黄色葡萄球菌和肺炎链球菌是纤维胶凝蛋白-B的靶标。在这个项目中，我们建议研究ficolin-B在免疫细胞中表达的调节，其分子靶结构的鉴定，以及其在细胞活化中的作用。通过这种方式，我们试图表征纤维胶凝蛋白-B介导的先天免疫应答，并测试我们的假设，即纤维胶凝蛋白-B在免疫应答中起作用。

Ficolins are members of the collectin family of proteins which in humans and mice are able to recognize pathogen associated molecular patterns (PAMPs) on microbial surfaces. Ficolins trigger the activation of the innate immune system by initiating the complement cascade in serum upon binding to their specific PAMPs. We recently published the first observation on mouse ficolin-B synthesis and showed that, surprisingly, the protein is localized intracellularly in macrophages. In parallel, others have shown that ficolin-B does not associate to serine proteases and, therefore, is unable to activate complement. The relevance of these findings and the mechanism of action of mouse ficolin-B upon bacterial challenge remain to be elucidated. Our preliminary data indicate that ficolin-B expression is up-regulated during activation but down-regulated during maturation of macrophages and bone marrow-derived dendritic cells suggesting a critical role of ficolin-B during early stages of cell activation upon pathogen encounter. In addition, binding assays reveal that some strains of Staph. aureus and Streptococcus pneumoniae are targets of ficolin-B. In this project we propose to study the regulation of ficolin-B expression in immune cells, the identification of its molecular target structure, and its role in cell activation. In this way, we attempt to characterize the ficolin-B-mediated innate immune response and test our hypothesis that ficolin-B plays a role in the immune response.