CD4+ T cells are trigger and target of the glucocorticoid response that prevents lethal immunopathology in toxoplasma infection

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Abstract
Synthetic glucocorticoids (GCs) are commonly used in the treatment of inflammatory diseases, but the role of endogenous GCs in the regulation of host-protective immune responses is poorly understood. Here we show that GCs are induced during acute Toxoplasma gondii infection and directly control the T cell response to the parasite. When infected with toxoplasma, mice that selectively lack GC receptor (GR) expression in T cells (GRlck-Cre) rapidly succumb to infection despite displaying parasite burdens indistinguishable from control animals and unaltered levels of the innate cytokines IL-12 and IL-27. Mortality in the GRlck-Cre mice was associated with immunopathology and hyperactive Th1 cell function as revealed by enhanced IFN-γ and TNF production in vivo. Unexpectedly, these CD4+ T lymphocytes also overexpressed IL-10. Importantly, CD4+ T cell depletion in wild-type or GRlck-Cre mice led to ablation of the GC response to infection. Moreover, in toxoplasma-infected RAG−/− animals, adoptive transfer of CD4+ T lymphocytes was required for GC induction. These findings establish a novel IL-10–independent immunomodulatory circuit in which CD4+ T cells trigger a GC response that in turn dampens their own effector function. In the case of T. gondii infection, this self-regulatory pathway is critical for preventing collateral tissue damage and promoting host survival.

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