LSC Abstract – Toll-like receptor 4 (TLR4) in idiopathic pulmonary fibrosis (IPF)

Introduction: IPF is a devastating lung disease with a median survival of 3 years. The etiology is unknown. IPF deteriorates upon viral or bacterial lung infection although pulmonary infection (pneumonia) in healthy lungs rarely induces fibrosis. Bacterial lipopolysaccharide (LPS) activates TLR4 initiating pro-inflammatory pathways. Since TLR4 has been linked to hepatic fibrosis and scleroderma, we investigate the role of TLR4 in IPF. Methods: Lung sections of IPF patients were analysed for TLR4 expression (IHC, IF, qPCR). Primary human lung fibroblasts (HLF LONZA®), isolated normal lung fibroblasts (NLFB), as well as fibroblasts from IPF lungs (IPF-FB) were exposed to LPS and TGF-β and evaluated by qPCR, flow cytometry for pro-fibrotic mediator expression. Results: TLR4 is expressed in fibroblast foci of IPF lungs as well as in HLF, NLFB, IPF-FB. LPS had no direct pro-fibrotic effect on HLF in vitro . As a model for pneumonia in normal lung, NLFB were exposed simultaneously to LPS and TGF-β, which reduced pro-fibrotic connective tissue growth factor (CTGF) significantly compared to TGF-β alone (p To model pneumonia in IPF lung, HLF were differentiated into myofibroblasts by TGF-β. In myofibroblasts CTGF expression was not reduced after LPS. Our in vitro model was confirmed in preliminary experiments using IPF-FB. Conclusion: TLR4 is present in fibroblast foci of IPF lungs. LPS stimulation had no direct pro-fibrotic effect on HLF in vitro , but can influence the pro-fibrotic effect of TGF-β dependent on time of exposure. These findings might explain why pneumonia in healthy individuals does not lead to fibrosis opposed to IPF, where infection often induces disease progression.