Chronic smoke exposure reduces epithelial IL-33 expression and barrier integrity in cell culture

<bold>Background:</bold> Ex-vivo human airway studies have shown reduced epithelial IL-33 expression in current vs ex-smokers. However, epithelial cell culture studies have shown cigarette smoke (CS) increases IL-33 expression. These studies use short term exposure (≤72 hours) and the effect of long-term CS exposure on IL-33 expression is unclear. <bold>Methods:</bold> Calu-3 cells cultured at air liquid interface were exposed to cigarette smoke extract (CSE) (0, 0.001, 0.003, 0.01, 0.03 optical density (OD) at 320nm (n=3)) for 28 days. We measured IL-33 gene expression by real-time PCR along with markers of epithelial barrier integrity (trans-epithelial electrical resistance (TEER) and tight junction gene expression). <bold>Results:</bold> CSE exposure caused a concentration dependent reduction of IL-33 expression with maximal effects at 0.03 OD (p=0.0004, Figure 1). CSE also reduced TEER and tight junction gene expression (claudin-3, occludin and zona occludens-1 (ZO-1)) at 0.03 CSE only (p<0.01). There was no effect on cell viability (p>0.05). <fig><object-id>erj;64/suppl_68/PA890/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig> Figure 1: IL-33 gene expression following 28 days of CSE <bold>Conclusion:</bold> Chronic CSE exposure reduced IL-33 expression and epithelial integrity in cell culture without causing cell death. These changes may reflect the direct effects of long-term cigarette smoke exposure on the airway epithelium.