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Chapter 19 : Interactions of Aspergillus with the Mucosa
Category: Clinical Microbiology; Fungi and Fungal Pathogenesis
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A normally functioning mucosa is critical to the prevention of microbial colonization and infection. Normal sinus mucosa exhibits scattered submucosal tubuloacinar cells, but no true glandular layer. A number of in vitro models have been used to study the interaction between Aspergillus and the nasal mucosa. Perhaps the most straightforward approach is to propagate ciliated epithelial cells obtained from nasal epithelial swabs or nasal biopsies in tissue culture plates; these preparations can be used to study the production of cytokines or other morphological changes following exposure to Aspergillus spp. A more sophisticated model consists of growing nasal epithelial cells to confluence on collagen-containing membranes before enabling an air-liquid interface to form; this model can be used to assess the integrity of the epithelium following direct exposure to Aspergillus spp. or culture filtrates. Acute invasive Aspergillus sinusitis was initially described in patients with profound and prolonged neutropenia. Perhaps the most obvious connection with mucosal dysfunction and Aspergillus-related disease is seen in cystic fibrosis. The respiratory epithelium has multiple mechanisms of defense against Aspergillus that function in the absence of leukocytes. Surfactant protein D also inhibits the binding of A. fumigatus conidia to pulmonary epithelial cells in vitro. However, it is highly probable that conidia do adhere to and invade pulmonary epithelial cells during the initiation of invasive pulmonary aspergillosis.
Scanning electron micrograph showing the interaction of an A. fumigatus conidium with a type II pneumocyte (A549 cell). Magnification, × 11,000. Bar, 3 μm.
Scanning electron micrograph of an A. fumigatus hypha emerging from an endothelial cell and penetrating into the vascular lumen. Magnification, × 18,000. Bar, 2 μm.