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Cells of the innate immune system

Natural killer (NK) and other innate cells

Both cytotoxic and IFN-y producing NK cells are quickly induced upon T. cruzi infection.25 NK cell depletion reveals their crucial role in the control of acute infection.26 The protective role of NK cells likely preferentially relies on IFN-y production than on cytotoxicity. Indeed, NK cells expressing granulysin, a cytotoxic protein expressed by humans (absent in mouse) and able to kill intracellular amasti- gotes,27 do not significantly contribute to the control of infection.28 However, cytotoxic NK cells can directly kill trypomastigotes in vitro.29 IFN-y production by NK cells requires the indirect action of parasites on accessory cells producing IL-1230,31. The protective effect of IFN-y released by NK cells mainly relies on activation of macrophages and other cells to limit T. cruzi replication during the early acute phase of the infection.25

Innate lymphoid cells32 other than NK cells have to date not been investigated in T. cruzi infection, at odds of “innate-like” lymphocytes such as B1-B cells, invariant natural killer T (iNKT) cells and Y&-T cell subsets.33 Plasma B cells, recently identified has important rapid producers of cytokines,34 are discussed later in this chapter.

T. cruzi associated with IL-12 triggers rapid production of IFN-y by iNKT cells. Depending on the cytokine environment, they might exert beneficial or harmful effects,3,35 as Y&-T lymphocytes, probably in relation to subsets presenting different properties in different tissues.36,37 Liver y& T could contribute to the particularly efficient control of parasite multiplication in this organ.38

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