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Activation of innate immune cells by Trypanosoma cruzi-derived molecules such as GPI anchors and DNA induces proinflammatory cytokine production and host defense mechanisms. In this study, we demonstrate that DNA from T. cruzi stimulates cytokine production by APCs in a TLR9-dependent manner and synergizes with parasite-derived GPI anchor, a TLR2 agonist, in the induction of cytokines by macrophages. Compared with wild-type animals, T. cruzi-infected Tlr9−/− mice displayed elevated parasitemia and decreased survival. Strikingly, infected Tlr2−/− Tlr9−/− mice developed a parasitemia equivalent to animals lacking MyD88, an essential signaling molecule for most TLR, but did not show the acute mortality displayed by MyD88−/− animals. The enhanced susceptibility of Tlr9−/− and Tlr2−/− Tlr9−/− mice was associated with decreased in vivo IL-12/IFN-γ responses. Our results reveal that TLR2 and …