Background: The role of airway epithelium in the development of invasive aspergillosis in immunocompromised hosts has rarely been studied although patients at risk for this infection have frequent epithelial damage. We have therefore developed an in vitro model of airway epithelium. Human nasal epithelial cells (HNEC) were recovered from nasal polyps and cultured in an air-liquid interface allowing cell differentiation after 14 days ( 1 ). The aim of the study was: (i) to in vitro determine whether A. fumigatus and Penicillium chrysogenum, a non pathogenic fungus, conidia enter airway HNEC, (ii) to determine the percent internalization of conidia, (iii) to determine whether conidia germinate inside of HNEC, (iv) and to define the mechanism of A. fumigatus conidia internalization. Methods: We have employed immunofluorescence, electron (EM), confocal and conventional microscopy to characterize phagocytosis of conidia and vacuolar environments of the internalized A. fumigatus conidia. Results: HNEC internalized 40% of the bound conidia of A. fumigatus. Similar results were obtained for P. chrysogenum. Most of the internalized conidia remained viable inside HNEC although germination was severely delayed for at least 12 hrs. EM showed the presence of conidia enclosed within vacuoles of intact HNEC. The vacuoles containing conidia were positive for the lysosomal membrane protein LAMP-1 confirming that internalized conidia traffic into a late endosomal-lysosomal compartment. In conclusion, we have demonstrated for the first time that A. fumigatus conidia are phagocyted by HNEC in an in vitro model of air-liquid interface. This phagocytosis is not specific to A. fumigatus. This finding indicates that, in some circumstances, A.fumigatus might invade pulmonary tissue directly from the respiratory tract without reaching the alveoli. Reference: 1 F. Botterel et al, Aspergillus fumigatus causes in vitro electrophysiological and morphological modifications in human nasal epithelial cells, Histology and Histopathology 2002, 17, 1095-1101.
Full conference title:
The 15 th Congress of the International Society for Human and Animal Mycology
- ISHAM 15th (2003)