高甘露糖糖基化修饰对罗非鱼四聚体IgM结构及功能的调控作用

IgM plays an important role in the resistance to pathogen infection and immune response. In the studies of human IgM, it has been demonstrated that the high mannose modification of IgM heavy chain affects the formation of different polymeric IgM, and also regulates the binding of IgM to MBL. Recently, the study of grass carp IgM heavy chain confirmed that there is heterogeneity of N-glycosylation modification at the Asn 565 site of different IgM polymers, but the effect of this modification heterogeneity on the function of grass carp IgM has not been reported. Therefore, whether the teleost IgM heavy chain exist high mannose modification like that in mammalian? Whether the different content of high mannose regulate the teleost IgM structure? In addition, affects the function of IgM tetramers? They still need to be studied in depth. The present study combines the advanced techniques in immunology and glycomics research to analyze the high mannose modification levels of different affinity IgM heavy chain in tilapia serum. The purpose is to, 1) accurately identify the high mannose content of the teleost fish IgM heavy chain, 2) clarify the regulation of high mannose modification on the structure and function of teleost IgM isomer, and 3) to explore the N-glycosylation modification of the IgM Fc region regulate the function of the Fab region. It is expected to fully reveal the regulation of N-glycosylation modification on the structure and function of teleost IgM, and provide sufficient theoretical support for the study of Ig molecules in classical immunology.

IgM在机体抵抗病原菌感染和免疫应答中发挥重要作用。在人IgM的研究中已经证实，高甘露糖修饰影响着不同聚体IgM的形成，同时调节IgM与MBL的结合。近期，草鱼IgM的研究中证实，不同聚体IgM重链的第Asn 565位点存在N-糖基化修饰的不均一性，但其不均一性对草鱼IgM功能的影响仍未见报道。因此，硬骨鱼IgM重链是否存在类似哺乳动物的高甘露糖修饰？高甘露糖含量差异是否调节IgM聚体结构差异？进而影响IgM四聚体的功能？仍有待深入研究。本研究结合免疫学与糖组学研究中的先进技术，分析罗非鱼血清中不同亲和力IgM重链的高甘露糖修饰水平，目的在于：1）精确鉴定硬骨鱼IgM重链的高甘露糖含量，2）阐明高甘露糖对硬骨鱼IgM结构与功能的调节作用，3）探究IgM抗体Fc区的修饰程度对Fab区的功能的影响。期望充分揭示N-糖基化修饰对硬骨鱼IgM结构与功能差异的调节作用。

免疫球蛋白IgM是硬骨鱼类血清中含量最高的免疫球蛋白，在机体抵御病原菌感染的免疫防御中发挥重要作用。本研究以罗非鱼为主要研究对象，以TNP-KLH抗原免疫罗非鱼，对血清中的IgM抗体效价、亲和力及IgM重链位点特异性的N-糖基化修饰水平进行分析。结果阐明：1）罗非鱼血清中TNP特异性IgM抗体效价与抗体亲和力在免疫后显著上调；2）IgM的抗体亲和力越高，重链末端Asn-509位点的高甘露糖含量越高，IgM四聚体的刚性越强；3）高亲和力IgM与MR的结合能力更强，能显著促进巨噬细胞对病原菌的吞噬。本研究是首次在硬骨鱼类中阐明IgM重链位点特异性的高甘露糖含量在调节IgM的结构和功能上具有重要作用，为理解N-糖基化修饰对免疫球蛋白结构及功能的调控提供了新的理论知识。相关研究成果发表在Talanta, Dev. Comp. Immunol.与J. Immunol.等期刊上。