Binding and germination of Aspergillus fumigatus conidia on cultured A549 pneumocytes.

Invasive pulmonary aspergillosis is acquired through inhalation of conidia. Little is known about early interactions between Aspergillus fumigatus conidia and alveolar epithelial cells, so an in vitro model was developed to study binding between conidia and A549 cells, a line of type II pneumocytes. Conidia rapidly became attached to confluent monolayers of A549 cells in serum-free medium, reaching a plateau within 40 min. Scanning electron microscopy (EM) showed a random pattern of early adherence; viable conidia subsequently became clustered on pneumocyte surfaces. Following germination of pneumocyte-adherent conidia for 12 h, direct penetration of epithelial cells by hyphae could be demonstrated by scanning and transmission EM. These data suggest that an early event following inhalation of A. fumigatus conidia may be binding of conidia to pneumocytes, followed by hyphal penetration of the epithelial cell layer.