RATIONALE: Indoor Stachybotrys chartarum exposure is a perceived public health threat in the United States. To date, the pulmonary immune responses to S. chartarum following inhalation exposure are incompletely characterized.
METHODS: Female B6C3F1/N mice (n=3-7) repeatedly inhaled one of two strains of S. chartarum (estimated pulmonary dose of 1x104 conidia) or air twice a week for 4 and 13 weeks. Lungs and bronchoalveolar lavage fluid (BALF) were collected 24 and 48 hours following exposure and processed for histology, mRNA, proteomic, and flow cytometry analyses.
RESULTS: At 4 weeks post exposure, a mixed T cell response was observed (increased IL-13 and IFNγ) that shifted towards a CD4+ IL-13+ Th2 phenotype after 13 weeks. BALF was composed primarily of eosinophils, neutrophils, and macrophages. Histology revealed a neutrophilic infiltrate after exposure to a strain producing fungal fragments and high mycotoxin, whereas infiltrates resulting from a strain producing fewer fragments and less mycotoxin were primarily of macrophages and lymphocytes. By 13 weeks, both strains induced significant pulmonary arterial remodeling, apparently independent from mycotoxin production, supported by increased csf2, il4, il13, and ifnγ expression. Gene and protein expression for Retnla and Chil3, proteins involved in pulmonary inflammation and remodeling, were also increased.
CONCLUSIONS: A mixed pulmonary T cell response at 4 weeks that shifts towards a Th2 dominant response after 13 weeks was observed following exposure to two strains of S. chartarum. Identification of pulmonary arterial remodeling at 13 weeks was supported by cellular, molecular, and proteomic analyses. The degree of fungal fragmentation appeared to drive pulmonary immune responses.