IL-1-induced inflammation promotes development of leishmaniasis in susceptible BALB/c mice

The role of host-derived IL-1 on the course of Leishmania major infection in susceptible BALB/c mice was assessed. Manifestations of the disease were more severe in mice deficient in the physiological inhibitor of IL-1, the IL-1 receptor antagonist (IL-1Ra) in comparison with control mice. In mice lacking one of the IL-1 genes (IL-1alpha or IL-1beta), there was delayed development of the disease and more attenuated systemic inflammatory responses. IL-1alpha-deficient mice were slightly more resistant to L. major infection compared with IL-1beta-knockout mice. During disease progression in IL-1Ra KO and control mice, myeloid-derived suppressor cells invaded the spleen, concomitant to suppression of T cell-mediated immunity and expression of systemic high levels of pro-inflammatory cytokines. In IL-1-deficient mice, T(h)1 responses were still apparent, even at late stages of the disease. Thus, dose-dependent effects of IL-1 were shown to influence the pathogenesis of murine leishamaniasis in susceptible BALB/c mice. Physiological and supra-physiological levels of IL-1 in the microenvironment promoted an exacerbated form of disease, whereas sub-physiological doses of IL-1 induced a less progressive disease. Thus, manipulation of IL-1 levels in the host, using the IL-1Ra or specific antibodies, has the potential to alleviate symptoms of visceral manifestations of leishmaniasis.