Strategies used byLeptospiraspirochetes to evade the host complement system

Leptospires are highly invasive spirochetes equipped with efficient strategies for dissemination in the host. TheLeptospiragenus currently comprises 64 species divided into two major clades: the saprophytes composed of nonpathogenic, free-living organisms, and the pathogens encompassing all the species that cause mild or severe infections in humans and animals. While saprophytes are highly susceptible to the lytic action of the complement system, pathogenic (virulent) strains have evolved virulence strategies that allow efficient colonization of a variety of hosts and target organs, including mechanisms to circumvent hosts' innate and acquired immune responses. PathogenicLeptospiraavoid complement-mediated killing by recruiting host complement regulatory proteins and by targeting complement proteins using own and host-expressed proteases. This review outlines the role of complement in eradicating saprophyticLeptospiraand the stratagems adopted by pathogenicLeptospirato maneuver the host complement system for their benefit. (AU)