Binding of human complement C1 sterase inhibitor to Leptospira spp.

Leptospirosis is an important zoonosis of global importance caused by bacteria Leptospira spp. Pathogenic Leptospira is resistant to Complement System killing while non-pathogenic Leptospira is rapidly killed by exposure to normal human serum (NHS). Pathogenic Leptospira interact with Complement Regulators such as Factor H, C4b binding protein and Vitronectin avoiding Complement activation and killing by Alternative and Classical Pathways. One important regulator is C1-inhibitor (C1INH) that interacts with C1s or MASPs controlling the cleavage of C4 and C2 molecules, thereby inhibiting the activation of the Classical and Lectin Pathways. In this study, we demonstrate that attenuated, saprophytic and pathogenic Leptospira interact with C1INH that maintain its regulatory capacity of interaction with C1s preventing the activation of Complement system. Although the interaction with C1INH is not crucial for pathogenic Leptospira survival, it seems to be important for the survival of attenuated and saprophytic Leptospira in normal human serum.