Endogenous Glucocorticoids Protect Against Cytokine-Mediated Lethality During Viral Infection

Abstract

Certain cytokines activate the hypothalamic-pituitary-adrenal axis for glucocorticoid release, and these hormones can protect against cytokine-mediated pathologies. However, endogenous activation of such a pathway has not been established during infections. A prominent glucocorticoid response peaks 36 h following murine CMV (MCMV) infection, coincident with circulating levels of the cytokines IL-12, IFN-gamma, TNF, and IL-6, and dependent on IL-6 for maximal release. These studies examined functions of the hormone induction. Mice rendered glucocorticoid deficient by adrenalectomy were more susceptible than intact mice to MCMV-induced lethality, and the increased sensitivity was reversed by hormone replacement. Lack of endogenous glucocorticoids resulted in increases in IL-12, IFN-gamma, TNF, and IL-6 production, as well as in mRNA expression for a wider range of cytokines, also including IL-1 alpha and IL-1 beta. Viral burdens did not increase, and actually decreased, in the livers of glucocorticoid-deficient mice. TNF, but not IFN-gamma, was required for increased lethality in the absence of endogenous hormone. These results conclusively demonstrate the importance of induced endogenous glucocorticoids in protection against life-threatening effects resulting from infection-elicited cytokine responses. Taken together with the dependence on induced IL-6, they document existence of an immune system-hypothalamic-pituitary-adrenal axis pathway for regulating endogenous responses to viral infections.