Role of reactive oxygen species in infection by the intracellular Leishmania parasites

Abstract

While encountering pathogens, generation of reactive oxygen species (ROS) is one of the earliest antimicrobial defence mechanisms put forward by phagocytic cells. The elevated level of ROS is expected to dampen the persistence of the microbes within the host cell. As a direct approach, ROS damages pathogen’s DNA through distortion of bases. In an indirect way, it activates pro- inflammatory cytokines, thus creating an environment not suitable for the microorganisms. ROS has also been found to cause apoptosis of the host cell, thereby ensuring complete elimination of the pathogen. However, intra-macrophage protozoan parasite, Leishmania sp., efficiently subverts this antimicrobial defence mecha- nism of macrophages for their successful survival and propagation of the fatal disease, Leishmaniasis. They either activate negative regulatory molecules of macrophages to impair the activation of pro-oxidant enzymes or upregulate anti- oxidant molecules to neutralise the oxidative burst. This chapter mainly high- lights the important role played by ROS in defence against intracellular infection and how Leishmania overcomes this antimicrobial defence arsenal and success- fully survives within macrophages.