TLR5 participates in the TLR4 receptor complex and biases towards MyD88-dependent signaling in environmental lung injury

Abstract

23Lung disease causes significant morbidity and mortality, and is exacerbated by environmental 24 injury, e.g. through lipopolysaccharide (LPS) or ozone (O3). Toll-like receptors (TLRs) orchestrate 25 immune responses to injury by recognizing pathogen-or danger-associated molecular patterns. 26 TLR4, the prototypic receptor for LPS, also mediates inflammation after O3, triggered by 27 endogenous hyaluronan. Regulation of TLR4 signaling is incompletely understood. TLR5, the 28 flagellin receptor, is expressed in alveolar macrophages, and regulates immune responses to 29 environmental injury. Using in vivo animal models of TLR4-mediated inflammations (LPS, O3, 30 hyaluronan), we show that TLR5 impacts the in vivo response to LPS, hyaluronan and O3. We 31 demonstrate that immune cells of human carriers of a dominant negative TLR5 allele have 32 decreased inflammatory response to O3 exposure ex vivo and LPS exposure in vitro. Using 33 primary murine macrophages, we find that TLR5 physically associates with TLR4 and biases 34 TLR4 signaling towards the MyD88 pathway. Our results suggest an updated paradigm for 35 TLR4/TLR5 signaling. 36Word count: 155 37 TLR, that modulates TLR4 signaling in response to its own ligands. TLR4-TLR5 interaction has 62 been reported once (19), wherein TLR4 was shown to promote nitric oxide production after 63 flagellin exposure. We therefore hypothesized that the reciprocal interaction may also be true, i.e. 64 TLR5 participates in TLR4 signaling after environmental lung injury. TLR5, the prototypic receptor 65 for bacterial flagellin, is expressed in alveolar macrophages (20), is induced after injury (21) and 66