Does the complement system work for or against the host during parasite infections

Abstract

Studies regarding the role of the complement system in parasitic infections have demonstrated that the complement system often fails to achieve the intended task of destroying the parasite. The reason for this failure is the development of efficient mechanisms for the parasites to evade attack or the subversion of the complement system (i.e., using components of the complement system to facilitate the infection progress). In this review, we intend to demonstrate the complexity of the interaction between parasites and the complement system in schistosomiasis mansoni, leishmaniases and malaria. The complement system is activated through the classical, alternative or lectin pathways, but in many circumstances, it facilitates infection, as occurs in leishmaniases, or exerts almost no protective effects against the parasite, as observed in schistosomiasis mansoni, due to the evasion mechanisms and biological characteristics of the parasite. In malaria, the complement system participates in erythrocyte invasion and, depending on the degree of activation, in different pathogenic mechanisms related to the uncomplicated or severe manifestations of malaria. This review is not comprehensive; however, we emphasize the systems and components necessary for an understanding of complement system-parasite interactions