Exposure to the mold, Aspergillus, is ubiquitous and generally has no adverse consequences in immunocompetent persons. However, invasive and allergic aspergillosis can develop in immunocompromised and atopic individuals, respectively. Previously, we demonstrated that mouse lung eosinophils produce IL-17 in response to stimulation by live conidia and antigens of A. fumigatus. Here, we utilized murine models of allergic and acute pulmonary aspergillosis to determine the association of IL-23, IL-23R and RORgammat with eosinophil IL-17 expression. Following A. fumigatus stimulation, a population of lung eosinophils expressed RORgammat, the master transcription factor for IL-17 regulation. Eosinophil RORgammat expression was demonstrated by flow cytometry, confocal microscopy, western blotting and an mCherry reporter mouse. Both nuclear and cytoplasmic localization of RORgammat in eosinophils were observed, although the former predominated. A population of lung eosinophils also expressed IL-23R. While expression of IL-23R was positively correlated with expression of RORgammat, expression of RORgammat and IL-17 was similar when comparing lung eosinophils from A. fumigatus-challenged wild-type and IL-23p19-/- mice. Thus, in allergic and acute models of pulmonary aspergillosis, lung eosinophils express IL-17, RORgammat and IL-23R. However, IL-23 is dispensable for production of IL-17 and RORgammat.

Ras signaling in response to environmental cues is critical for cellular morphogenesis in eukaryotes. This signaling is tightly regulated and its activation involves multiple players. Sometimes Ras signaling may be hyperactivated. In C. albicans, a human pathogenic fungus, we demonstrate that dynamics of hyperactivated Ras1 (Ras1G13V or Ras1 in Hsp90 deficient strains) can be reliably differentiated from that of normal Ras1 at (near) single molecule level using fluorescence correlation spectroscopy (FCS). Ras1 hyperactivation results in significantly slower dynamics due to actin polymerization. Activating actin polymerization by jasplakinolide can produce hyperactivated Ras1 dynamics. In a sterol-deficient hyperfilamentous GPI mutant of C. albicans too, Ras1 hyperactivation results from Hsp90 downregulation and causes actin polymerization. Hyperactivated Ras1 co-localizes with G-actin at the plasma membrane rather than with F-actin. Depolymerizing actin with cytochalasin D results in faster Ras1 dynamics in these and other strains that show Ras1 hyperactivation. Further, ergosterol does not influence Ras1 dynamics.

Aspergillus fumigatus causes invasive pulmonary disease in immunocompromised hosts and allergic asthma in atopic individuals. We studied the contribution of lung eosinophils to these fungal diseases. By in vivo intracellular cytokine staining and confocal microscopy, we observed that eosinophils act as local sources of IL-23 and IL-17. Remarkably, mice lacking eosinophils had a >95% reduction in the percentage of lung IL-23p19+ cells as well as markedly reduced IL-23 heterodimer in lung lavage fluid. Eosinophils killed A. fumigatus conidia in vivo. Eosinopenic mice had higher mortality rates, decreased recruitment of inflammatory monocytes, and decreased expansion of lung macrophages after challenge with conidia. All of these functions underscore a potential protective role for eosinophils in acute aspergillosis. Given the postulated role for IL-17 in asthma pathogenesis, we assessed whether eosinophils could act as sources of IL-23 and IL-17 in models where mice were sensitized to either A. fumigatus antigens or ovalbumin (OVA). We found IL-23p19+ IL-17AF+ eosinophils in both allergic models. Moreover, close to 95% of IL-23p19+ cells and >90% of IL-17AF+ cells were identified as eosinophils. These data establish a new paradigm in acute and allergic aspergillosis whereby eosinophils act not only as effector cells but also as immunomodulatory cells driving the IL-23/IL-17 axis and contributing to inflammatory cell recruitment.