Aspergillus fumigatus germ tube growth and not conidia ingestion induces expression of inflammatory mediator genes in the human lung epithelial cell line A549

Abstract

Inhalation of conidia is the main cause of invasive pulmonary aspergillosis (IPA) and the respiratory epithelium is the first line of defence. To explore the triggering factor for the inflammatory response to Aspergillus fumigatus, the species mainly responsible for IPA, this study analysed the differential expression of three inflammatory genes in A549 cells after challenge with live and killed conidia. The influence of steroids, one of the main risk factors for developing IPA, was also investigated. Quantification of mRNAs of the inflammatory mediator genes encoding interleukin (IL)-8, tumour necrosis factor (TNF)-a and granulocyte-monocyte colony-stimulating factor (GM-CSF) was carried out using real-time PCR. Ingestion rates were studied for the conidia of A. fumigatus and Penicillium chrysogenum using a fluorescence brightener. Similar results were obtained for both species, with ingestion rates ranging from 35 to 40 %. Exposure of A549 cells to live A. fumigatus conidia only induced a four-to fivefold increase in the mRNA levels of the three genes, starting 8 h after the initial contact. Both inactivation of live A. fumigatus conidia and treatment by dexamethasone (10 "7 M) prevented the overexpression of TNF-a, IL-8 and GM-CSF. Fungal growth, rather than conidia ingestion, appears to be the main stimulus for the production of inflammatory mediators by epithelial cells, and this production is inhibited by steroid therapy. These results underline the role that the epithelium plays in the innate response against IPA. INTRODUCTIONInvasive pulmonary aspergillosis (IPA) is an opportunistic infection whose incidence is increasing at the same rate as the number of severely immunocompromised patients (Lin et al., 2001). Neutropenia and high-dose steroid treatments are the main risk factors for IPA, and these underline the importance of an appropriate inflammatory response if fungal invasion is to be avoided. Most authors stress the important roles that alveolar macrophages and neutrophils play in controlling infection (Romani, 2004;Walsh et al., 2005). The release of innate immune-related molecules from professional phagocytic cells in the course of Aspergillus fumigatus infection has been widely studied (Meier et al., 2003;Pylkkanen et al., 2004;Cortez et al., 2006). However, the respiratory epithelium is the first tissue that inhaled conidia encounter, and it probably participates in the efficient coordinated response against IPA. In animal models of IPA, most inhaled conidia are trapped in the upper respiratory tract, and the respiratory epithelium coordinates with alveolar macrophages (Stephens-Romero et al., 2005).A few studies have investigated the production of inflammatory mediators by studying the human lung epithelial cell line A549 after stimulation with moulds or mould extracts (Borger et al., 1999; Kauffman et al., 2000; Huttunen et al., 2003;Zhang et al., 2005; Tai et al., 2006). These studies have focused on fungi as the source of allergens, and on species other than A. fumigatus, which are Abbrevi...

Cystic Fibrosis Transmembrane Conductance Regulator Regulates Epithelial Cell Response to Aspergillus and Resultant Pulmonary Inflammation

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Impact of cigarette smoke exposure on host-bacterial pathogen interactions

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