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Chapter 17 : Adaptive Immune Effector Mechanisms against Intracellular Protozoa and Gut-Dwelling Nematodes
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This chapter covers the acquired immune responses to two types of parasites. The first is the immune response associated with intracellular protozoa, and the principal examples will be Leishmania, Toxoplasma, and Trypanosoma cruzi. The chapter then discusses the immune responses associated with control of helminth infections, particularly focusing on gut-dwelling nematodes. The current model for macrophage activation is that IFN-γ primes cells, and additional signals, such as tumor necrosis factor (TNF), trigger activation of the cell. The relative importance of IL-4 and IL-13 in resistance is also influenced by host genetic background and highlighted by studies in the Trichuris muris system. Here, IL-4KO mice on a C57BL/6 background are uniformly susceptible and develop chronic infections whereas WT mice expel their worm burden. This chapter reviews the effector mechanisms associated with resistance to a select group of parasites, particularly focusing on parasites that illustrate the diversity of effector mechanisms contributing to protective immunity. The immune responses required for eliminating intracellular protozoa are quite different from those required to control gut-dwelling nematodes and can be divided into type 1 and type 2 responses. However, while type 1 or type 2 responses may dominate following infection with intracellular protozoa or gut-dwelling nematodes, respectively, the effector mechanisms required for resistance to any one particular parasite are often tailored to the biological characteristics of that parasite, which in some cases remain to be defined.