Immune evasion strategies in protozoan-host interactions

Book excerpt: The protozoa are the most ancient members of the animal kingdom and they have evolved the intracellular parasitism to ensure their survival strategies. Protozoan parasites that infect humans are extremely diverse among eukaryotes. They are responsible for many human diseases such as amebiasis, Chagas disease, malaria, toxoplasmosis, leishmaniasis and African sleeping sickness. The ability of protozoans to cause disease depends on the nature and number of infecting organisms, the route of infection, the virulence factors associated with the microorganism, and the strength of host defenses. This host-parasite interaction is also subject to constant change as the infection proceeds and can lead to a range of outcomes, from elimination of the pathogen to death of the host, depending on the states of latency and the extent of colonization that the protozoan achieves in the course of infection. Several species of parasitic protozoa harbor specialized virulence factors whose products can overcome the host´s immunity and promote their survival. These factors act at several different checkpoints of the host immune responses, from the first components of the innate immune response to the induction and maintenance of adaptive memory responses. Many protozoan species have evolved mechanisms that modulate and inhibit host sensors, microRNA circuits and signaling pathways that permit the host to detect infection. These factors can act, inter alia, by inhibiting the complement cascade, subverting phagocyte activation and impairing leukocyte migratory responses, so undermining the immune system thus facilitating the pathogen evasion and its continued persistence in the host. In this research topic we welcome the contribution of original research article as well as reviews on the field.