Functional characterization of the mouse lectin ficolin-B

Ficolins是人类和小鼠中能够识别微生物表面病原体相关分子模式（PAMPs）的集合蛋白家族的成员。Ficolins通过与特异性PAMPs结合，在血清中启动补体级联反应，从而触发先天免疫系统的激活。我们最近发表了对小鼠ficolin-B合成的首次观察结果，并令人惊讶地表明，该蛋白位于巨噬细胞的细胞内。与此同时，其他研究表明，ficolin-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ficolin-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，在巨噬细胞和骨髓来源的树突状细胞的激活过程中，ficolin-B的表达上调，而在成熟过程中则下调，这表明在遇到病原体时，ficolin-B在细胞激活的早期阶段发挥了关键作用。此外，结合实验显示，一些葡萄球菌菌株。金黄色葡萄球菌和肺炎链球菌是ficolin-B的靶标。本课题拟对免疫细胞中ficolin-B的表达调控、分子靶结构的鉴定及其在细胞活化中的作用进行研究。通过这种方式，我们试图表征ficolin-B介导的先天免疫反应，并验证我们的假设，即ficolin-B在免疫反应中发挥作用。

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.