Abstract Endotoxin-driven acute lung injury (ALI) engages TLR4 signaling across multiple lung compartments, however, the functional roles of epithelial cells remain understudied. To address the knowledge gaps, we generated mice with epithelial cell-specific TLR4 ablation in alveolar type II (AT2) cells or airway secretory Club cells to evaluate their responses upon exposure to bacterial endotoxin, lipopolysaccharide (LPS). Wild-type (WT), TLR4 knockout (TLR4-KO), and epithelial cell-specific knockout (SPC-TLR4-KO and CCSP-TLR4-KO) mice were intranasally administered with LPS (0.25mg/kg) for 24 hours, and their responses were evaluated by Bronchoalveolar Lavage cytology, semi-quantitative histopathology, and inflammatory transcriptional level. Baseline phenotypes under PBS-treatment conditions were indistinguishable across genotypes. TLR4 ablation in AT2 cells (SPC-TLR4-KO) markedly attenuated LPS-induced ALI to a level similar to the complete TLR4-KO. Total BAL cells and the recruiting neutrophils were significantly reduced, injury scores were lower, and the increased proinflammatory cytokine expression, including IL-1/IL-6/TNF, declined, while macrophages adopted an M2-skewed state. In contrast, TLR4 ablation in Club cells produced only minimal protection, with a narrower phenotype: IL-1β and TNF were slightly decreased compared to WT mice, whereas IL-6 remained elevated; the total number of immune cells and neutrophil recruitment were not significantly altered, and tissue injury improved only modestly. Our results suggested that AT2-derived TLR4 signaling is the dominant driver of the neutrophil-centric acute phase pulmonary inflammation and the associated parenchymal injury, whereas Club-cell TLR4 primarily modulates inflammatory response without governing early neutrophil recruitment. These findings name the AT2-TLR4 inflammatory/chemokine axis as a tractable, cell-type-targeted entry point to blunt early endotoxin-induced lung injuries. This abstract is funded by: NIAID NIH R01-AI133351; R01-AI176537
Song et al. (Fri,) studied this question.