The ubiquitous fungus Aspergillus fumigatus can lead to severe pulmonary disease in immunocompromised patients, such as fungal pneumonia or allergic bronchopulmonary aspergillosis (ABPA) in cystic fibrosis patients. The anti-microbial regenerating islet-derived 3 (Reg3) family of lectins have been shown to play a role in intestinal immunity; however, their role during fungal infections in the lung has not been characterized. Here, we investigated the impact of Reg3gamma (Reg3g) on pulmonary A. fumigatus infection.
Expression of the Reg3 family was analyzed by PCR and ELISA from lung tissues of B6 mice infected with A. fumigatus. To determine if Reg3 proteins adhere to A. fumigatus, recombinant mouse Reg3g-human IgG1 (Reg3g-Fc) and Reg3beta-Fc fusion proteins were expressed in 293T cells, purified with protein G and used to stain A. fumigatus organisms by flow cytometry. To assess the immune response to A. fumigatus, B6 and Reg3g-/- mice were infected by oropharyngeal aspiration, and the expression of IL-17, IL-22 and IL-23 were analyzed by PCR, ELISA and flow cytometry. IL-17 production by small intestinal lamina propria lymphocytes was analyzed by flow cytometry.
Pulmonary infection with A. fumigatus increased the expression of Reg3b, Reg3d and Reg3g in lung tissue. Recombinant Reg3 proteins were capable of binding to A. fumigatus organisms, indicating a potential role in host defense. Reg3g-/- mice were not defective in fungal clearance, and produced increased IL-17 following infection. Further, naí¯ve Reg3g-/- mice were found to have increased numbers of CD4 T cells producing IL-17 (Th17 cells) in small intestinal lamina propria, suggesting a role for commensal bacteria in the gut. In support, antibiotic treatment of Reg3g-/- mice suppressed their pulmonary ovalbumin-specific Th17 response.
This data suggests that Reg3g may be involved in anti-fungal immunity by binding to inhaled A. fumigatus organisms and perhaps decreasing its virulence. More importantly, however, Reg3g suppresses pulmonary Th17 responses by altering the gut microbiome. This data has implications for allergic bronchopulmonary aspergillosis, and suggests that Reg3g-sensitive commensal bacteria contribute to pulmonary Th17-driven inflammation.
Full conference title:
- AAA 5th (2012)