TLR4–MyD88–NF-κB Signaling in the Airway Epithelium Promotes Acinetobacter baumannii Clearance

BACKGROUND: Acinetobacter baumannii is a high-priority Gram-negative respiratory pathogen associated with high morbidity and mortality. While many components of the innate immune response to A. baumannii have been studied, the specific role of the airway epithelium in coordinating the innate immune response to A. baumannii is largely undefined. In this study we demonstrate that NF-κB signaling within airway epithelial cells is essential for effective pulmonary clearance of A. baumannii. METHODS: To understand the role of epithelial signaling, we utilized several mouse models of infection. RESULTS: Using both pharmacological and conditional knockouts of the NF-κB subunit RelA (p65) in airway epithelial cells of mice, we observed substantial defects in bacterial clearance from the airways and lungs. This impaired clearance was associated with significant reductions in early neutrophil recruitment to the airway, which was linked to decreased expression of key neutrophil chemokines (G-CSF, GM-CSF, and CCL20) at both the transcript and protein levels. RNA sequencing of sorted airway epithelial cells revealed that NF-κB activity was required for transcription of inflammatory and chemotactic genes. Administration of exogenous neutrophil chemokines was able to restore early neutrophil recruitment in epithelial RelA-deficient mice, but only partially rescued bacterial clearance, suggesting additional mechanisms beyond granulocyte chemokine induction. We also show that airway epithelial expression of TLR4 and its adaptor protein MyD88 are also required for effective bacterial clearance from the airway, identifying a TLR4-MyD88-NF-κB axis. CONCLUSIONS: These findings highlight the airway epithelium as a critical site of innate immune sensing and coordinating the pulmonary host defense against A. baumannii.