Enhanced binding of Aspergillus fumigatus spores to A549 epithelial cells and extracellular matrix proteins by a component from the spore surface and inhibition by rat lung lavage fluid

摘要

BACKGROUND—Aspergillusfumigatus is a pathogenic fungus which causes a range ofdiseases, particularly in the human lung. The pathological mechanism isunknown but may involve a complex mixture of biomolecules which candiffuse from the spore surface. This material is known asA fumigatus diffusate (AfD) and haspreviously been shown to have a range of immunosuppressive functions.It is hypothesised that AfD may influence the binding of spores toextracellular matrix (ECM) proteins and lung epithelial cells, therebyaffecting the ability of the fungus to cause infection.
METHODS—The binding ofspores to ECM proteins and to epithelial cells was carried out using adirect binding assay in microtitre plates and spores were counted byphase contrast microscopy. Rat bronchoalveolar lavage (BAL) fluid wasenriched for surfactant protein D (SP-D) using maltose agarose affinitychromatography. The effects of AfD and the SP-D enriched BAL fluid wereassessed by pre-incubation with ECM proteins or epithelial cells in thedirect binding assay.
RESULTS—AfD enhancedthe binding of spores to laminin by 137% and to A549 epithelial cellsby 250%. SP-D enriched BAL fluid inhibited spore binding to ECMproteins and epithelial cells. Pre-incubation of ECM proteins andepithelial cells with SP-D enriched BAL fluid prevented the enhancementof spore binding by AfD, and pre-incubation of ECM proteins andepithelial cells with AfD prevented the inhibition of spore binding bySP-D enriched BAL fluid. This pretreatment did not prevent theenhancement of spore binding, giving an increase of 95% for collagenI, 80% for fibronectin, 75% for laminin, and 150% for A549 cells.
CONCLUSIONS—Thehypothesis that AfD would affect spore binding to ECM proteins andepithelial cells was confirmed. Rat BAL fluid, with SP-D as thepossible bioactive agent, prevented this enhancement. The in vivosignificance is unclear but the enhanced binding of spores may increasethe chance of fungal infection in the lung which could be prevented bythe protective effects of lung surfactant components (possibly SP-D).The results suggest that there may be competition between AfD and a BALfluid component (possibly SP-D) for the same or similar binding siteson ECM proteins and epithelial cells. Whether this competition occursin vivo requires further investigation.