TLR9 and chronic obstructive pulmonary disease: This study aimed to elucidate the immunoregulatory mechanism of NETs in COPD, employing human neutrophils, airway epithelial cells (AECs), dendritic cells (DCs), and a long-term CS-induced COPD mouse model, alongside cyclic guanosine monophosphate-adenosine monophosphate synthase and toll-like receptor 9 knockout mice (cGAS-−/−, TLR9−/−); Additionally, bronchoalveolar lavage fluid (BALF) of COPD patients was examined.