Divergent Adhesion–Proliferation Profiles in 16HBE Cells May Contribute to Differential Risk Assessment of <i>P. aeruginosa</i> Bioaerosol Exposure: Primary NHBE Comparison

Bioaerosols are important components of atmospheric aerosols. Substantial evidence demonstrates a significant positive association between bioaerosol exposure and adverse respiratory outcomes, yet accurate health risk assessment remains constrained due to inadequate in vitro exposure models. Thus, an exposure system at the air–liquid interface was established to simulate exposure of environmentally relevant Pseudomonas aeruginosa(P. aeruginosa bioaerosol to respiratory epithelial cells. The primary normal human bronchial epithelial (NHBE) cells and immortalized 16HBE cell line were used as comparative exposure models. NHBE cells exhibited significantly higher sensitivity to 105 CFU/m3 P. aeruginosa bioaerosol, with cell viability decreasing by 58.3% ± 1.4% in NHBE cells versus 43.8% ± 14.9% in 16HBE cells (p < 0.05). Distinct immune recognition mechanisms were further observed, and 16HBE cells recognized P. aeruginosa through toll-like receptors, RIG-I-like receptors (RLRs), NOD-like receptors (NLRs), and cytosolic DNA-sensing (cGAS-STING), whereas NHBE cells primarily relied on NLRs, triggering a distinct downstream immune effector. Further, immortalization of cells resulted in baseline alterations. 16HBE cells demonstrated impaired barrier integrity and reduced proliferative capacity but compensatory hyperactivation of pattern recognition receptors, whereas NHBE cells mounted a comprehensive immune response concurrent with greater cytotoxicity. Reduced cytotoxicity of the P. aeruginosa bioaerosol in 16HBE cells underestimated bioaerosol risk significantly. This study elucidated functional disparities between immortalized cells and primary cells and revealed the limitation of cell lines in health risk assessment.