Cigarette smoking in asthma patients causes insensitivity to inhaled glucocorticoids (GCs). We tested the hypothesis that smoking causes GC insensitivity in alveolar macrophages (AMs) obtained from patients with asthma.
Nineteen asthmatic nonsmokers (ANSs) and 13 asthmatic smokers (ASMs) underwent BAL. AMs were cultured with or without dexamethasone, 0.1 to 1,000 nmol/L, for 2 h before lipopolysaccharide (LPS) [1 μg/mL] stimulation. After 6 h, supernatants were harvested for enzyme-linked immunosorbent assay, and messenger RNA was collected for real-time (RT)-polymerase chain reaction (PCR).
ASMs had higher numbers of AMs per milliliter of BAL fluid than ANSs (1.98 vs 0.75 × 106 cells/mL, respectively; p = 0.007). Cigarette smoking significantly attenuated the LPS response for all three cytokines tested among ANSs vs ASMs (tumor necrosis factor [TNF]-α, 31.6 vs 10.6 ng/mL, respectively (p = 0.01); interleukin [IL]-6, 25.8 vs 10.8 ng/mL, respectively (p = 0.002); IL-8, 62.5 vs 36.1 ng/mL, respectively (p = 0.001)). There was no difference in dexamethasone dose-response curves between ANSs and ASMs (p > 0.05 for all comparisons). The inhibitory concentration of 50% (IC50) for IL-6 was 120.6 vs 83.3, respectively, and for TNF-α it was 4.9 vs 8.6, respectively; an IC50 was not achieved for IL-8. RT-PCR also showed no difference in the suppression of cytokine messenger RNA levels between groups, with IL-8 being the most GC-insensitive cytokine.
Cigarette smoking in patients with asthma increases the number of airway AMs and attenuates their response to LPS, which may have implications in host immune function. Cigarette smoking does not alter the GC sensitivity of AMs in patients with asthma. There was differential cytokine sensitivity, with IL-8 being the least GC-sensitive cytokine. GC-insensitive IL-8 production from AMs may be a mechanism by which neutrophils are attracted into the airways.