We previously demonstrated that IL-10 is critical in the control of acute inflammation during development of Trichinella spiralis in the muscle. In this study, we use gene-targeted knockout mice, adoptive transfer of specific T cell populations, and in vivo Ab treatments to determine the mechanisms by which inflammation is controlled and effector T cell responses are moderated during muscle infection. We report that CD4(+)CD25(-) effector T cells, rather than CD4(+)CD25(+) regulatory T cells, suppress inflammation by an IL-10-dependent mechanism that limits IFN-gamma production and local inducible NO synthase induction. Conversely, we show that depletion of regulatory T cells during infection results in exaggerated Th2 responses. Finally, we provide evidence that, in the absence of IL-10, TGF-beta participates in control of local inflammation in infected muscle and promotes parasite survival.