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Long-term tobacco smokers with chronic obstructive pulmonary disease (COPD) or chronic bronchitis display an excessive accumulation of neutrophils in the airways; an inflammation that responds poorly to established therapy. Thus, there is a need to identify new molecular targets for the development of effective therapy. Here, we hypothesized that the neutrophil-mobilizing cytokine interleukin (IL)-26 (IL-26) is involved in airway inflammation amongst long-term tobacco smokers with or without COPD, chronic bronchitis or colonization by pathogenic bacteria. By analyzing bronchoalveolar lavage (BAL), bronchail wash (BW) and induced sputum (IS) samples, we found increased extracellular IL-26 protein in the airways of long-term smokers in vivo without further increase amongst those with clinically stable COPD. In human alveolar macrophages (AM) in vitro, the exposure to water-soluble tobacco smoke components (WTC) enhanced IL-26 gene and protein. In this cell model, the same exposure increased gene expression of the IL-26 receptor complex (IL10R2 and IL20R1) and nuclear factor κ B (NF-κB); a proven regulator of IL-26 production. In the same cell model, recombinant human IL-26 in vitro caused a concentration-dependent increase in the gene expression of NF-κB and several pro-inflammatory cytokines. In the long-term smokers, we also observed that extracellular IL-26 protein in BAL samples correlates with measures of lung function, tobacco load, and several markers of neutrophil accumulation. Extracellular IL-26 was further increased in long-term smokers with exacerbations of COPD (IS samples), with chronic bronchitis (BAL samples ) or with colonization by pathogenic bacteria (IS and BW samples). Thus, IL-26 in the airways emerges as a promising target for improving the understanding of the pathogenic mechanisms behind several pulmonary morbidities in long-term tobacco smokers.

T lymphocytes are believed to play an important role in the pathogenesis of chronic obstructive pulmonary disease (COPD). How T cells are recruited to the lungs and contribute to the inflammatory process is largely unknown. COPD is a heterogeneous disease, and discriminating disease phenotypes based on distinct molecular and cellular pathways may provide new approaches for individualized diagnosis and therapies. Bronchoalveolar lavage (BAL) and blood samples were obtained from 40 never-smokers, 40 smokers with normal lung function, and 38 COPD patients. T-cell chemokine receptor expression was analyzed with flow cytometry, and soluble BAL cytokines and chemokines were measured using a cytokine multiplex assay. Correlations with gender and clinical characteristics including lung imaging were investigated using multivariate modeling. Th1/Tc1- and Th2/Tc2-associated soluble analytes and T-cell chemokine receptors were analyzed as cumulative Th1/Tc1 and Th2/Tc2 immune responses. A higher expression of chemokine receptor CCR5 on CD8⁺ T cells in BAL and higher percentage of CXCR3⁺CD8⁺ T cells in blood was found in female smokers with COPD compared to those without COPD. CCR5 expression on CD4⁺ and CD8⁺ T cells was lower in BAL from male smokers with COPD compared to those without COPD. Among female smokers with COPD, Th1/Tc1 immune response was linked to BAL macrophage numbers and goblet cell density, and Th2/Tc2 response was associated with the measures of emphysema on high-resolution computed tomography. The highly gender-dependent T-cell profile in COPD indicates different links between cellular events and clinical manifestations in females compared to males. Our findings may reveal mechanisms of importance for the difference in clinical course in female COPD patients compared to males.