Influenza causes substantial morbidity and mortality, and highly pathogenic and drug-resistant strains are likely to emerge in the future. Protease-activated receptor 1 (PAR1) is a thrombin-activated receptor that contributes to inflammatory responses at mucosal surfaces. The role of PAR1 in pathogenesis of virus infections is unknown. Here, we demonstrate that PAR1 contributed to the deleterious inflammatory response after influenza virus infection in mice. Activating PAR1 by administering the agonist TFLLR-NH 2 decreased survival and increased lung inflammation after influenza infection. Importantly, both administration of a PAR1 antagonist and PAR1 deficiency protected mice from infection with influenza A viruses (IAVs). Treatment with the PAR1 agonist did not alter survival of mice deficient in plasminogen (PLG), which suggests that PLG permits and/or interacts with a PAR1 function in this model. PAR1 antagonists are in human trials for other indications. Our findings suggest that PAR1 antagonism might be explored as a treatment for influenza, including that caused by highly pathogenic H5N1 and oseltamivir-resistant H1N1 viruses.

Background: Invasive aspergillosis, which is mainly caused by the fungus Aspergillus fumigatus, is an increasing problem in immunocompromised patients. Infection occurs by inhalation of airborne conidia, which are first encountered by airway epithelial cells. Internalization of these conidia into the epithelial cells could serve as a portal of entry for this pathogenic fungus.

Protease-activated receptor-2 (PAR2), a receptor highly expressed in the respiratory tract, can influence inflammation at mucosal surfaces. Although the effects of PAR2 in the innate immune response to bacterial infection have been documented, knowledge of its role in the context of viral infection is lacking. We thus investigated the role of PAR2 in influenza pathogenesis in vitro and in vivo. In vitro, stimulation of PAR2 on epithelial cells inhibited influenza virus type A (IAV) replication through the production of IFN-γ. In vivo, stimulation of PAR2 using specific agonists protected mice from IAV-induced acute lung injury and death. This effect correlated with an increased clearance of IAV in the lungs associated with increased IFN- γ production and a decreased presence of neutrophils and RANTES release in bronchoalveolar fluids. More importantly, the protective effect of the PAR2 agonist was totally abrogated in IFN- γ-deficient mice. Finally, compared with wild-type mice, PAR2-deficient mice were more susceptible to IAV infection and displayed more severe lung inflammation. In these mice higher neutrophil counts and increased RANTES concentration but decreased IFN- γ levels were observed in the bronchoalveolar lavages. Collectively, these results showed that PAR2 plays a protective role during IAV infection through IFN-γ production and decreased excessive recruitment of inflammatory cells to lung alveoli.

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...