Cigarette Smoke Induces the Pro-inflammatory Response of Lung Macrophages via Activation of the IL-33/ST2-Dependent Pathway

Cigarette smoke broadly affects the immune system, but the mechanisms by which it disrupts lung innate immunity and impairs macrophage-mediated homeostasis in healthy individuals remain unclear. This study investigates airway inflammation induced by chronic cigarette smoke extract (CSE) exposure by profiling pulmonary macrophages. CSE was generated by bubbling smoke from ten Marlboro cigarettes into 10 ml PBS to obtain 100% CSE, and C57BL/6 mice received 10% CSE intranasally 3 times per week for 4 wk. Chronic CSE exposure induced neutrophilic airway inflammation and augmented pulmonary Th17 and Th1 responses. Among macrophage subsets, CSE exposure promoted the expansion of CD11c⁺CD11b^- alveolar macrophages (AMs) and upregulated IL-17A across macrophage subsets in lung tissue. In the lung, epithelial-derived IL-33 was significantly increased and was associated with enhanced IL-33/ST2 axis activity in IL-17A⁺ macrophages. In AMs, sequential CSE and IL-33 stimulation significantly increased ST2 expression and an IL-33/ST2-mediated pro-inflammatory response marked by elevated IL-6. Moreover, CSE exposure reprogrammed AMs with enhanced MAPK and NF-κB signaling. Notably, IL-33-stimulated macrophages after CSE exposure skewed naive CD4⁺ T cells toward Th17 differentiation. These findings suggest that CSE-activated, IL-33/ST2-driven pro-inflammatory macrophages drive neutrophilic inflammation and Th17 skewing, linking innate and adaptive immune responses in airway inflammation.