A Murine Inhalation Model to Characterize Pulmonary Exposure to Dry Aspergillus fumigatus Conidia

Abstract

Most murine models of fungal exposure are based on the delivery of uncharacterized extracts or liquid conidia suspensions using aspiration or intranasal approaches. Studies that model exposure to dry fungal aerosols using whole body inhalation have only recently been described. In this study, we aimed to characterize pulmonary immune responses following repeated inhalation of conidia utilizing an acoustical generator to deliver dry fungal aerosols to mice housed in a nose only exposure chamber. Immunocompetent female BALB/cJ mice were exposed to conidia derived from Aspergillus fumigatus wild-type (WT) or a melanin-deficient (Δalb1) strain. Conidia were aerosolized and delivered to mice at an estimated deposition dose of 1×105 twice a week for 4 weeks (8 total). Histopathological and immunological endpoints were assessed 4, 24, 48, and 72 hours after the final exposure. Histopathological analysis showed that conidia derived from both strains induced lung inflammation, especially at 24 and 48 hour time points. Immunological endpoints evaluated in bronchoalveolar lavage fluid (BALF) and the mediastinal lymph nodes showed that exposure to WT conidia led to elevated numbers of macrophages, granulocytes, and lymphocytes. Importantly, CD8+ IL17+ (Tc17) cells were significantly higher in BALF and positively correlated with germination of A. fumigatus WT spores. Germination was associated with specific IgG to intracellular proteins while Δalb1 spores elicited antibodies to cell wall hydrophobin. These data suggest that inhalation exposures may provide a more representative analysis of immune responses following exposures to environmentally and occupationally prevalent fungal contaminants.

Influence of Aspergillus fumigatus conidia viability on murine pulmonary microRNA and mRNA expression following subchronic inhalation exposure

“…After examining miRNAs that had demonstrated the most significant changes following subchronic A. fumigatus exposure, IPA identified miR‐29a‐3p which targets two critical genes in the inflammatory response, Clec7a and TGF‐ β. Clec7A is important relative to conidia germination and align with previous studies that have reported A. fumigatus germination to elicit an inflammatory response due to the recognition of β‐glucan on the hyphal cell wall . Previous studies from our laboratory showed germination of A. fumigatus conidia in the lungs of mice exposed to viable A. fumigatus conidia . These results are further supported by increased Clec7A expression in the viable vs. HIC group at both time points.…”

Subchronic exposures to fungal bioaerosols promotes allergic pulmonary inflammation in naïve mice

“…Short term A. fumigatus spore inhalation exposures (4 weeks) were found to induce an acute inflammation highlighted by a notable CD8 + IL‐17A + (Tc17) response that correlated with in vivo spore germination . In the present study, subchronic exposures (13 weeks) in naïve animals skewed the immune response towards an allergic phenotype resulting in significant expansion of diverse subpopulations of CD4 + T cells and Tc17 cells no longer detectable.…”

Developments in the field of allergy in 2016 through the eyes of Clinical and Experimental Allergy

“…Notably, the repeated exposures of A. fumigatus spores resulted in a dose‐dependent and multifocal peribronchial and perivascular inflammation characterized by mononuclear phagocytes, granulocytes, and lymphocytes and concomitant epithelial mucus hypersecretion, goblet cell metaplasia, subepithelial fibrosis, and enhanced airway hyperresponsiveness (AHR). Interestingly, in contrast to the short course exposure, the pulmonary infiltrate was predominately consisted of CD4 + IL‐13 + T cells and an antifungal CD4 + IFN‐ß + IL‐17A + IL‐13 + T cell response, revealing a dynamic shift in the dysregulated immune response following subchronic exposure of inhaled fungi. Understanding the signals involved in the oscillation of these CD4 + T cell populations between antifungal/allergic Th1, Th2, Th17 phenotypes will provide a better understanding of the underlying pathways that contribute to the fungal association with allergic disease.…”

“…To address these methodologic limitations, Buskirk et al developed an acoustical generator system (AGS) for delivering dry aerosolized fungal spores to mice housed in a multi‐animal exposure chamber. Aerosolized spores are delivered into a nose‐only inhalation chamber, where mice inhale the spores.…”

“…Aerosolized spores are delivered into a nose‐only inhalation chamber, where mice inhale the spores. Employing this system, the authors previously demonstrated that short‐term inhalational exposures of mice (4 weeks) to Aspergillus fumigatus ( A. fumigatus ) induced a significant pulmonary cellular infiltrate dominated by CD8 + IL‐17A + (Tc17) T cells, which correlated with spore germination . In a follow‐up study, Nayak et al now report that a 13‐week subchronic exposure of BALB/cJ mice with A. fumigatus spores induced a different immunopathologic phenotype .…”