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.

IntroductionReceptor-mediated agonists, such as FMLP, induce an early, phospholipase D (PLD)-mediated accumulation of phosphatidic acid (PA) which may play a role in the activation of NADPH oxidase in human PMN. We have determined the effect of changes in PA production on 02 consumption in intact PMN and the level of NADPH oxidase activity measured in a cell-free assay. (13, 14) and others (15-18) have demonstrated that FMLP also activates a phospholipase D (PLD) that hydrolyzes choline-containing phosphoglycerides (PC) such that PA is the first metabolite formed. In this pathway, DG is generated by PA phosphohydrolase (PAP)-catalyzed dephosphorylation of PA (19). The differences in the temporal sequence of formation ofPA and DG via these pathways and the fact that interconversions between these metabolites modulates their accumulation during stimulation, complicate efforts aimed at understanding the individual involvement of PA or DG in the activation of PMN NADPH oxidase.A role for DG (6)(7)(8)(20)(21)(22)

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