Macrophages reshape cytokine responses and bacterial spatial organization in an airway epithelial cell culture model

Abstract

The increasing prevalence of antibiotic-resistant bacterial infections highlights the need for physiologically relevant in vitro models that recapitulate host-pathogen interactions. Pseudomonas aeruginosa is a clinically important opportunistic pathogen associated with hospital-acquired infections and chronic airway diseases, including cystic fibrosis, where dysregulated inflammatory responses contribute to disease progression. While air-liquid interface (ALI) models have advanced the study of airway epithelium, most of these modes lack immune components, limiting their ability to capture immune-epithelial interactions. Here, we expanded a previously established dual-cell ALI model incorporating human monocyte-derived macrophages to investigate how immune context, bacterial dose, and time influence early infection dynamics. Standard BCi-NS1.1 epithelial monocultures and macrophage co-cultures were infected with P. aeruginosa (PAO1) at low (100 colony-forming units (CFU) and high (1000 CFU) inoculum and analyzed over 10, 16, and 24 h post-infection (hpi). Macrophage presence did not significantly alter total bacterial burden but markedly influenced cytokine responses and bacterial spatial organization. Pro-inflammatory cytokines (interleukin (IL)-1, IL-1{beta}, Tumor Necrosis Factor (TNF)-) were enhanced in dual-cell culture models, while IL-6 exhibited a threshold-dependent response detectable only at higher bacterial loads. Confocal imaging revealed that macrophages altered bacterial distribution, promoting a more dispersed pattern compared to the clustered organization observed in epithelial monocultures. These effects were most pronounced at lower bacterial inocula. Together, our findings demonstrate that macrophages reshape early infection dynamics by modulating inflammatory signaling and bacterial spatial organization without affecting overall bacterial burden. This study highlights the importance of incorporating immune cells into in vitro airway models.