Hypoxia in Leishmania major Skin Lesions Impairs the NO-Dependent Leishmanicidal Activity of Macrophages

Abstract

Cure of infections with Leishmania major is critically dependent on the ability of macrophages to induce the type 2 nitic oxide (NO) synthase (NOS2) that produces high levels of NO in the presence of ample oxygen. Therefore, we analyzed the oxygen levels found in leishmanial skin lesions and their effect on the NOS2-dependent leishmanicidal activity of macrophages (MΦ). When L. major skin lesions of self-healing C57BL/6 mice reached their maximum size, the infected tissue displayed low oxygen levels (pO2∼21 Torr). MΦ activated under these oxygen tensions failed to produce sufficient amounts of NO to clear L. major. Nos2-deficient and hypoxic wild-type macrophages displayed a similar phenotype. Killing was restored when MΦ were reoxygenated or exposed to a NO donor. The resolution of the lesion in C57BL/6 mice was paralleled by an increase of lesional pO2. When mice were kept under normobaric hypoxia, this caused a persistent suppression of the lesional pO2 and a concurrent increase of the parasite load. In Nos2-deficient mice, there was no effect of atmospheric hypoxia. Low oxygen levels found at leishmanial skin lesions impaired the NOS2-dependent leishmanicidal activity of MΦ. Hence, tissue oxygenation represents an underestimated local milieu factor that participates in the persistence of Leishmania.

Cutaneous Na+ Storage Strengthens the Antimicrobial Barrier Function of the Skin and Boosts Macrophage-Driven Host Defense

“…3D). Elimination of L. major depends on classical MΦ activation and subsequent NO production (Diefenbach et al, 1998; Liew et al, 1990; Mahnke et al, 2014). Accordingly, the killing of L. major was abrogated in LPS-treated Nos2 −/− MΦ co-stimulated with either HS, or INF-γ (Figures 3E & S2F).…”

“…The number of parasites in the tissue was determined by limiting dilution analysis (Mahnke et al, 2014). Skin Nfat5 mRNA levels and skin infiltration of CD68 + MΦ was assessed as described earlier (Machnik et al, 2009).…”

Hypoxic regulation of neutrophil function and consequences for Staphylococcus aureus infection

“…This relative lack of molecular oxygen can be further amplified in pathological conditions, such as organ inflammation or ischaemia, and within solid tumours, due to damaged vasculature, compartmentalisation of infection, and high metabolic activity and oxygen requirements of pathogens and host cells. Hypoxia has been demonstrated in numerous pathological environments through in vitro and in vivo sampling: by microelectrode pO 2 measurement of wounds and venous ulcers [24]; by blood gas analysis of abscesses, a characteristic feature of staphylococcal infection [25]; by staining for hypoxia inducible factor (HIF), which increases exponentially below 6% oxygen, in chronic obstructive pulmonary disease [26]; by pimonidazole staining in pulmonary infection [27]; and by luminescence-based in vivo optical imaging in skin infection [28]. Interestingly, in a murine model of acute colitis, neutrophils actively contributed to the hypoxic microenvironment by depletion of molecular oxygen through NADPH oxidase activity and, hence, induced stabilisation of epithelial HIF [29].…”

Induction, Propagation, and Activity of Host Nitric Oxide: Lessons from Leishmania Infection

“…In vitro, although hypoxia increases expression of iNOS through hypoxia-inducible factor 1/ (HIF-1/) and NF-kB activation, it tends to limit production of NO in most cell types [49]. In vivo, low oxygen availability impairs production of NO by iNOS and promotes persistence of Leishmania parasites in the skin [50]. In addition, elevated Na + concentrations in the infected skin were found to increase iNOS expression and thus limit L. major infection [51].…”

“…x 7 the control of Leishmania infection in vivo [70] ( Figure 2C). The discrepancy between potent killing of Leishmania parasite by activated macrophages in vitro and sublethal restriction of parasite metabolism in vivo may originate from lower concentrations of NO-derived products in vivo, possibly as a consequence of hypoxia in the infected tissue [50].…”