No abstract

Aspergillus fumigatus is a pathogen causing diverse respiratory disorders. Several studies have suggested that fungal proteases may play a role in the pathogenicity of fungi. Since the airways are the most common route for entry of A. fumigatus, this study focused on the ability of fungal proteases to induce the release of proinflammatory cytokines and to cause cell detachment in human pulmonary epithelial cell lines. It was shown that fungal serine protease activity induced the production of interleukin (IL)-8 and IL-6 and monocyte chemotactic protein-1 and caused cell detachment in a dose-dependent fashion. Chymostatin, antipain, phenylmethylsulfonyl fluoride, and heat treatment completely inhibited fungal protease activity, cytokine production and cell detachment; antileukoprotease partially inhibited these activities. By causing cell detachment, fungal proteases may decrease the physical barrier function of the epithelium; however, by eliciting a cytokine response, the epithelium may signal the mucosal inflammatory response against A. fumigatus.

Proteases secreted by Aspergillus fumigatus induce the production of cytokines by epithelial cells, including interleukin (IL)-6 and IL-8. In the present study, we focused on the mechanism(s) by which A. fumigatus-derived proteases elicit cytokine production in epithelial cells. In the epithelial cell line A549, IL-6 and IL-8 mRNA levels were enhanced by proteases as a result of transcriptional induction of the respective genes. Transcriptional induction of both genes coincided with enhanced DNA binding of nuclear factor (NF)-kappaB and NF-IL6, whereas activator protein-1 was unlikely to be involved. The enhanced transcriptional activity could be inhibited by the addition of chymostatin, showing serine protease dependency. Posttranscriptional mechanisms affecting the stability of IL-6 and IL-8 mRNAs were not involved in protease-induced IL-6 and IL-8 production. These data show that after exposure to A. fumigatus-derived proteases, IL-6 and IL-8 gene expressions are up-regulated as a result of transcriptional mechanisms.

No abstract

Fungus-induced obstructive airway disease in atopic individuals can be differentiated into two categories: first, uncomplicated asthmatic reactions due to high but transient exposure to fungal spores (fungal asthma), resulting in a TH2-type response with immunoglobulin E-mediated reactions and eosinophilic inflammation; and second, a more complex asthmatic reaction due to colonization of the mucus-epithelial surface by virulent protease-producing fungi. The latter condition stimulates as exaggerated immunological response including all subclasses of antibodies directed against the microorganism and an intense eosinophilic infiltrate of the airways. The authors propose that the exaggerated inflammatory response in allergic bronchopulmonary fungosis damages epithelial cells and underlying tissue cells, resulting in inefficient elimination of the microorganisms and damage to matrix proteins of the lung tissue by proteases released by both the fungi and degranulating eosinophils. The positive effects of corticosteroids in the treatment of allergic bronchopulmonary aspergillosis probably results from the dampening of the inflammatory response and an increase of the efficiency of killing the fungi. Sensitization to fungi is high in childhood and declines rapidly with age, suggesting that younger children may be less proficient in clearing fungi from the airways. We propose that insufficient treatment of fungal asthma may result in damage to the bronchial mucosa and formation of bronchiectasis.