Studies on the functions of serine proteases and a novel-protein with low molecular size which are involved in the lectin complete pathway

存在于血清中的甘露糖结合凝集素（MBL）通过凝集素途径激活补体系统。人MBL与称为MASP的两种类型的Clr/Cls样丝氨酸蛋白酶相关，并且在MBL-MASP与碳水化合物结合后，MASP切割C4、C2和C3。MBL还与SMAP复合，SMAP是MASP-2的剪接变体。本研究的目的是阐明凝集素途径的激活机制，与经典途径的比较。主要研究成果如下：1）从人血清中分离MASP-1和MASP-2，并成功分离MASP-1和sMAP。MASP-1活化C3和C2，而MASP-2活化C4和C2。作为Clr和Cls的血清抑制剂的Cl抑制剂也抑制MASP-1和MASP-2。2)MBL形成具有不同分子大小的低聚物。其中，MBL三聚体制剂含有MASP-1和SMAP，而具有更高分子尺寸的MBL寡聚体含有MASP-2和新鉴定的MASP-3。3)在人血清中，发现MBL和Clq分别与MASP、sMAP和Clr.Cls复合。人血清中不存在MBL-Clr、Cls复合物和Clq-MASP、SMAP复合物。4)与MBL一样，纤维胶凝蛋白/P35（其是一种人血清凝集素）与MASP- 1、MASP-2和SMAP相关。该复合物激活补体系统，这意味着纤维胶凝蛋白/P35-MASP以及MBL-MASP的补体激活可以被认为是凝集素途径。

Mannose-binding lectin (MBL) present in serum activates the complement system via the lectin pathway. Human MBL is associated with two types of Clr/Cls-like serine protease termed MASP and upon binding of MBL-MASP to carbohydrates, MASP cleaves C4, C2 and C3. MBL is also complexed with SMAP, a splicing variant of MASP-2. This study was aimed at elucidation of the activation mechanism of the lectin pathway in comparison with that of the classical pathway. Major achievements are as follows.1) MASP-1 and MASP-2 were isolated from human serum and successfully separated MASP-1 was copurified with sMAP. MASP-1 activated C3 and C2, while MASP-2 activated C4 and C2. Cl inhibitor which is a serum inhibitor of Clr and Cls also inhibited both MASP-1 and MASP-2. 2) MBL forms oligomers with different molecular sizes. Among them, MBL trimer preparations contained MASP-1 and SMAP, while MBL oligomers with higher molecular sizes contained MASP-2 and newly identified MASP-3. 3) In human serum, MBL and Clq were found to be complexed with MASP, sMAP and Clr.Cls, respectively. Neither MBL-Clr, Cls complex nor Clq-MASP, SMAP complex was present in human serum. 4) Like MBL, ficolin/P35 which is a human serum lectin was associated with MASP- 1, MASP-2 and SMAP. The complex activated the complement system, implying that complement activation by ficolin/P35-MASP as well as MBL-MASP can be considered to be termed as the lectin pathway.