TLR4 upregulation underpins airway neutrophilia in smokers with chronic obstructive pulmonary disease and acute respiratory failure

Activation of Toll-like receptors (TLR) seems to be involved in the pathogenesis of chronic obstructive pulmonary disease (COPD). Upon TLR activation the release of defensins, including human beta defensin 2 (HBD-2), may occur. In this study, we explored the innate responses in patients with respiratory failure, with and without COPD, requiring intubation and mechanical ventilation. Mini–bronchoalveolar lavage (mini-BAL) samples were collected from nonsmoker subjects without COPD (n = 10), smokers without COPD (n = 6), and smokers with COPD (n = 15). TLR4, TLR2, and HBD-2 expression was evaluated by immunocytochemistry; interleukin (IL)–8, IP-10, and HBD-2 concentrations were evaluated by enzyme-linked immunosorbent assay; chemotactic activity toward neutrophils and lymphocytes; and cell apoptosis was evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling [TUNEL] and by flow cytometry with anti-TLR4 and with HBD-2 depleted and not depleted mini-BAL). COPD mini-BAL showed increased neutrophil numbers, reduced neutrophil apoptosis, increased TLR4 and HBD-2 expression, increased neutrophil chemotactic activity, reduced IP-10 concentrations, and reduced lymphocyte chemotactic activity compared with those in nonsmoker subjects without COPD. In the smokers without COPD the mini-BAL showed reduced TLR4 and HBD-2 expression, higher IP-10 concentrations, and higher chemotactic activity than in patients with COPD. The blocking of TLR4 activation and HBD-2 depletion increased neutrophil apoptosis. No differences were observed for TLR2 expression and IL-8 concentrations. This study strengthens the contribution of TLR4 to promoting airway neutrophilia in COPD.