CD4 and chronic obstructive pulmonary disease: Th17 cells have been implicated as important inflammatory mediators in COPD with increased IL-17-expressing CD4 T cells and concentrations of related cytokines detected in the bronchial submucosa, airway epithelium, lung tissue, BALF and peripheral blood of COPD patients, compared to smokers without COPD and their healthy counterparts [33–37].