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==Overview==
==Overview==
Although the innate immune system provides an effective first line of defence, '''[[T cells|T cells]]''' are fundamental in the development of immunity, demonstrated using T-cell deprived mice that fail to resolve otherwise non-lethal infections of, for example, ''T. cruzi''.
*Both CD4<sup>+</sup> and CD8<sup>+</sup> cells are required for protection, e.g CD4<sup>+</sup> cells protect against the blood stage of a Plasmodium infection (erythrocytes do not express MHC class I), while CD8<sup>+</sup> cells are required to mediate immunity against the liver stage (hepatocytes do not express MHC class II).
*T<sub>H</sub>1 cells are required to fight intracellular protozoa - the release of IFNγ activates macrophages to kill the protozoa residing within them
*Helminth infections require both T<sub>H</sub>1 and T<sub>H</sub>2 responses, e.g. during ''S. mansoni'' the secretion of IFNγ by T<sub>H</sub>1 cells activates mechanisms that destroy larvae in the lungs, although the T<sub>H</sub>2 subset, secreting IL-5, predominate. IL-5 is responsible for the eosinophilia associated with parasite infections.
*T<sub>H</sub>2 cells are required for the destruction of intestinal worms, where they induce mucosal mast cells and interact with [[Eosinophils|eosinophils]]
While cell-mediated immunity is important in tissue infections, such as Leishmania, specific antibodies are important in controlling parasites that live in the bloodstream, e.g. malaria. Mechanisms of antibody-mediated immunity include:
*Directly damaging protozoa
*Activating [[Complement|complement]], and the subsequent Membrane Attack Complex
*Blocking attachment to host cells
*Enhancing macrophage phagocytosis
*Involvement in antibody-dependent cell-mediated cytotoxicity
==Humoral==
==Humoral==