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.

Aspergillus fumigatus is an opportunistic fungal pathogen that causes lethal invasive pulmonary disease in immunocompromised hosts and allergic asthma in sensitized individuals. This dissertation explores how eosinophils may protect hosts from acute infection while driving asthma pathogenesis by co-producing IL-23 and IL-17 in both contexts. In an acute model of pulmonary aspergillosis, eosinophils were observed to associate with and kill A. fumigatus spores in vivo. In addition, eosinopenia was correlated with higher mortality rates, decreased recruitment of inflammatory monocytes to the lungs, and decreased expansion of lung macrophages. As IL-17 signaling must occur on a local level to elicit its stereotypical response, such as the up-regulation of antimicrobial peptides and specific chemokines from stromal cells, eosinophils were discovered to be a significant source of pulmonary IL-17 as well as one of its upstream inducers, IL-23. In the context of asthma, this discovery opens a new paradigm whereby eosinophils might be driving asthma pathogenesis.