IFN-β Impairs Superoxide-Dependent Parasite Killing in Human Macrophages: Evidence for a Deleterious Role of SOD1 in Cutaneous Leishmaniasis

Abstract

Type I IFNs (IFN-α/β) have only recently gained considerable attention as immunomodulators in nonviral infectious diseases. IFN-β has been shown to protect, in a NO-dependent manner, against murine Old World leishmaniasis caused by Leishmania major, but data in New World leishmaniasis are lacking. We found that IFN-β dose-dependently increases parasite burden in Leishmania amazonensis- as well as Leishmania braziliensis-infected human macrophages, independent of endogenous or exogenous NO. However, IFN-β significantly reduced superoxide release in Leishmania-infected as well as uninfected human macrophages. This decrease in superoxide production was paralleled by a significant IFN-β-mediated increase in superoxide dismutase 1 (SOD1) protein levels. Additionally, IFN-β inhibition of leishmanicidal activity was mimicked by SOD1 and antagonized by either pharmacological or small interfering RNA-mediated inhibition of SOD1. Finally, pronounced SOD1 expression in situ was demonstrated in biopsies from New World cutaneous leishmaniasis patients. These findings reveal a hitherto unknown IFN-β/SOD1 axis in Leishmania infection and suggest that inhibition of SOD-associated pathways could serve as strategy in the treatment of L. amazonensis as well as L. braziliensis infection, major human pathogens.