Studies on the complement activation by human serum lectin.

人血清甘露聚糖结合蛋白（MBP）是甘露糖和N-乙酰葡糖胺的特异性凝集素，在人补体的帮助下可裂解甘露聚糖包被的SRBC。半抗原糖的存在有效地抑制了血清MBP的激活，并且完全依赖于C4的存在，表明激活是由MBP的糖结合活性启动的，并通过经典途径进行。用<125>C_1q标记的C_1r ~（2-）s ~（2-）与MBP-甘露聚糖-SRBC复合物结合，并能支持MBP致敏的SRBC裂解，表明MBP一旦固定在细胞表面，就能像C_1q一样启动经典途径的激活。在CA^&lt;2+&gt;存在的情况下，用纯化的人血清MBP致敏，然后与豚鼠补体孵育，显示集落形成明显减少 ...更多信息 与未用凝集素致敏的人相比，其杀菌作用与凝集素和补体的浓度有关。该反应的C4依赖性表明MBP的补体依赖性杀菌作用是通过经典途径表达的。MBP可使细菌聚集。Scatchard曲线分析<125>表明，MBP与细菌结合的解离常数（Kd）为6 × 10 ~（-1）~（-9）~（-1）~（-1）~（-9）~（-1）D ~（-1）M，最大结合容量为30，000个MBP/个细胞。这种结合被甘露糖和N-乙酰葡萄糖胺所抑制，表明MBP识别构成细菌细胞壁粗糙核心的甘露庚糖和N-乙酰葡萄糖胺，因此，MBP-配体（细菌）复合物可能通过经典途径激活补体，直接与C1 r ^^-_2s^^-_2结合，而不涉及C1 q，最终杀死细菌。这些发现表明血清凝集素在宿主防御中的生理意义，与大肠杆菌粗糙菌株在哺乳动物中的无毒性一致。少

Human serum mannan-binding protein (MBP), which is a lectin specific for mannose and N-acetylglucosamine, was shown to lyse mannan-coated SRBC with the help of human complement. The activation by erum MBP was inhibited effectively by the presence of haptenic sugars and dependent absolutely upon the presence of C4, indicating that the actaivation is initiated by the sugar binding activity of MBP and proceeds through the classical pathway. ^<125>I-labeled C1r^^-_2s^^-_2 was shown to bind to MBP-mannan-SRBC complex regardless of the presence of C1q-depleted human complement had an ability to support to lyse SRBC sensitized with MBP, suggesting that MBP, once fixed on cell surfaces, functions as C1q does to initiate the activation of the classical pathway.The bacteria, rugh strains of Escherichia coli, K-12 and B, which had been sensitized with purified human serum MBP in the presence of CA^<2+>, followed by incubation with guinea pig complement, showed a marked decrease of colony forming … More ability compared with those not sensitized with the lectin. The bactericidal effect depended on the concentrations of the lectin and complement. The C4-dependency of the reaction indicated that the complement-dependent bactericidal action by MBP is expressed through the classical pathway. The bacteria were aggregated by MBP. Scatchard polt analysis of ^<125>I-labeled BMP binding to the bacteria showed that the dissociation constant (K_d) and the maximum binding capacity was 6x10<@1-9<@D1M and 30,000 molecules of MBP per a cell, respectively. The binding was inhibited by mannose, N-acetylglucosamine, suggesting that MBP recognized mannoheptose and N-acetylgucosamine constituting the rough core oligosaccharides of the bacterial cell wall.Thus, MBP-ligand (the bacteria) complex activates complement via the classical pathway possibly through the binding directly to C1r^^-_2s^^-_2 without the involvement of C1q and eventually the bacteria are killed. These findings demonstrate the physiological significance of the serum lectin in host defense, being consistent with the avirulence of E.coli rough strains in mammals. Less