Slc11a1-mediated resistance to Salmonella enterica serovar Typhimurium and Leishmania donovani infections does not require functional inducible nitric oxide synthase or phagocyte oxidase activity

Solute carrier family 11a member 1 (Slc11a1; formerly natural resistance-associated macrophage protein 1) encodes a late endosomal/ lysosomal protein/divalent cation transporter, which regulates iron homeostasis in macrophages. During macrophage activation, Slc11a1 exerts pleiotropic effects on gene regulation and function, including generation of nitric oxide (NO) via inducible NO synthase (iNOS; encoded by Nos2A) and of reactive oxygen intermediates (ROI) via the phagocyte oxidase complex. As NO and ROI have potent antimicrobial activity in macrophages, it was assumed that their activities would contribute to Slc11a1-regulated innate resistance to Salmonella enterica serovar Typhimurium and Leishmania donovani. By intercrossing mice with gene disruptions at Nos2A and Cybb (encoding gp91phox, the heavy chain subunit of cytochrome b-245 and an essential component of phagocyte NADPH oxidase) onto equivalent Slc11a1 wild-type and mutant genetic backgrounds, we demonstrate that neither iNOS nor gp91phox activity is required for Slc11a1-mediated innate resistance to either infection. Functional gp91phox and iNOS are required to control S. enterica serovar Typhimurium in non-Slc11a1-regulated phases of infection. For L. donovani, an organ-specific requirement for iNOS to clear parasites from the spleen was observed at 50 days post-infection, but neither iNOS nor gp91phox influenced late-phase infection in the liver. This contrasted with Leishmania major infection, which caused rapid lesion growth and death in iNOS knockout mice and some exacerbation of disease with gp91phox deficiency. This highlights the adaptive differences in tissue and cellular tropisms between L. donovani and L. major and the different genes and mechanisms that regulate visceral versus cutaneous forms of the disease.