The Complement System (CS) plays an important role in the immune response against leptospirosis and can be activated by the Alternative and Lectin Pathways (Innate Immunity) and by the Classical Pathway (Acquired Immunity). Here we analyzed a broad range of nonpathogenic and pathogenic Leptospira strains considering their interaction with each CS pathway. We determined bacterial survival rate and CS protein deposition in the presence of purified proteins, specific component depleted sera and NHS treated with the chelating agents EDTA (inhibits all three activation pathways) or EGTA (inhibits the Classical and Lectin Pathways). We suggest that the Lectin and the Alternative Pathways have an important role to eliminate saprophytic leptospires since i) approximately 50% survival of both saprophytic strains was observed in the presence of MBL-deficient serum; ii) approximately 50% survival of Leptospira biflexa Patoc I was observed in the presence of NHS – EGTA and iii) C1q-depleted serum caused significant bacterial lysis. In all serovars investigated the deposition of C5–C9 proteins on saprophytic Leptospira strains was more pronounced when compared to pathogenic species confirming previous studies in the literature. No difference on C3 deposition was observed between nonpathogenic and pathogenic strains. In conclusion, Leptospira strains interact to different degrees with CS proteins, especially those necessary to form MAC, indicating that some strains and specific ligands could favor the binding of certain CS proteins.

补体系统（CS）在对钩端螺旋体病的免疫反应中起重要作用，可以通过替代途径和凝集素途径（先天免疫）和经典途径（后天免疫）激活。在这里，我们考虑到它们与每个CS途径的相互作用，分析了广泛的非致病性和致病性钩端螺旋体菌株。我们确定了在存在纯化蛋白，特定成分耗尽的血清和用螯合剂EDTA（抑制所有三个激活途径）或EGTA（抑制经典途径和凝集素途径）处理过的NHS的存在下的细菌存活率和CS蛋白沉积。我们建议，凝集素和替代途径从那以后，以消除腐生钩端螺旋体了重要作用I）在MBL缺陷型血清存在下，两种腐生菌株的存活率约为50％；ii）在NHS-EGTA存在下，观察到双挠钩端螺旋体Patoc I约有50％的存活率，并且iii）耗尽C1q的血清引起明显的细菌裂解。在所有研究的血清中，与致病菌相比，腐生钩端螺旋体菌株上C5–C9蛋白的沉积更为明显，这证实了文献中的先前研究。在非致病性和致病性菌株之间未观察到C3沉积的差异。总之，钩端螺旋体 菌株与CS蛋白（特别是形成MAC的那些蛋白）以不同程度的相互作用，表明某些菌株和特定配体可能会促进某些CS蛋白的结合。