IFN-γ mediated signaling improves fungal clearance in experimental pulmonary mucormycosis.

Abstract

We established three immunocompetent murine models of pulmonary mucormycosis to determine the involvement of the adaptive immune response in host resistance in pulmonary mucormycosis, a rapidly fatal disease caused mainly by Rhizopus spp. Immunocompetent BALB/c, C57BL/6, and Swiss mice were inoculated with R. oryzae via the intratracheal route. The inoculation resulted in an angioinvasive infection that spread to the brain, spleen, kidney, and liver. After 7 and 30 days of R. oryzae infection, C57BL/6 and BALB/c mice showed the lowest fungal load and highest production of IFN-γ and IL-2 by splenocytes, respectively. Swiss mice showed a higher fungal load 30 days p.i. and was associated with a weak development of the Th-1 profile. To confirm our findings, R. oryzae-infected IFN-γ-/- mice were evaluated after 60 days, where the mice still showed viable fungi in the lungs. This study showed, for the first time, that pulmonary mucormycosis in three widely used mouse strains resulted in an acute fungal dissemination without immunosuppression whose outcome varies according to the genetic background of the mice . We also identified the partial role of IFN-γ in the efficient elimination of R. oryzae during pulmonary infection.

Is the production of reactive oxygen and nitrogen species by macrophages associated with better infectious control in the experimental disseminated and pulmonary mucormycosis?

“…In the present study, BALB/c and Swiss mice strains showed more and less resistance, respectively, against in vivo R. oryzae infection, as previously reported (30,31). The course of infection was characterized by similar fungal load on day 7 for both mouse strain, followed by a decreased fungal load on day 30, that was more expressive in BALB/c mice (Fig 2A).…”

“…Generally, high levels of ROS production by macrophages are linked to intracellular events, including the activation of transcription factors such as NFκB (71), and induction of mitogenesis (72). In addition, in vitro , and in vivo studies already showed that R. oryzae could trigger a Th-17 response mediated by high amounts of IL-23 by dendritic cells (73), and also the association of high levels of IL-17 and IFN-γ with better R. oryzae elimination by immunocompetent BALB/c and C57BL/6 mice (30,31). Considering the studies above and the evidence found here, we hypothesized that adaptive immune responses developed by BALB/c mice were essential to enhance the fungicidal activity of peritoneal macrophages and efficiently kill R. oryzae .…”

“…Quantitative colony culture is a wide method for organ fungal burden determination in per gram tissue in which whole tissue is grinding into suspension before inoculating onto culture plates. However this methods causes non-viability in Mucorales (21), and to avoid damage to fragile hyphal and consequent false-negative results in our quantitative analysis (34), the fragment method was employed in our set of experiments, as previously reported (30,31,35). For this, ten fragments (2 × 2 mm) of the brain, liver, lung, spleen, and kidneys were cultured on Sabouraud agar plates at 25ºC for a maximum of seven days.…”

“…Nevertheless, the effect of immunosuppressive drugs restricts the evaluation of the immunological mechanisms involved in fungal resistance. Recently, our group has focused on studies exploring Rhyzopus -host interplay using immunocompetent models, inducing both disseminated and pulmonary mucormycosis (30,31). Using BALB/c and Swiss mice, we determined a resistant and less resistant model of mucormycosis, respectively.…”

“…Using BALB/c and Swiss mice, we determined a resistant and less resistant model of mucormycosis, respectively. While BALB/c mice has been shown better capacity in decreasing fungal load until 30 days of intravenous and intratracheal infection, Swiss mice has been shown be less responsive to R. oryzae infectious and consequently more prolonged viable fungal presence in internal organs (30,31). We and others (32,33) have highlighting the importance of evaluating immune response in immunocompetent mice to understand the mechanisms involved in the resistance to Mucorales agents, as well as, the mucormycosis pathogenesis in immunocompetent individuals (21,22).…”