Induced sputum and bronchial mucosal expression of interleukin‐13 is not increased in chronic obstructive pulmonary disease

Background:  The Th2 cytokine interleukin‐13 (IL‐13) has been implicated in the pathogenesis of chronic obstructive pulmonary disease (COPD). We sought to examine IL‐13 expression in COPD subjects in induced sputum and bronchus specimens. We hypothesized that inflammatory cells expressing IL‐13 localize to the airway smooth muscle bundle and bronchial glands.Methods:  Interleukin‐13 was measured in sputum samples from subjects with COPD (n = 34) across a range of severity (Global initiative for chronic Obstructive Lung Disease 2–4) and controls (n = 14) using ELISA. IL‐13+ cells and inflammatory cells were enumerated within surgically resected proximal airway using immunohistochemical techniques from subjects with COPD (n = 10), smoking (n = 10) and nonsmoking controls (n = 8).Results:  Sputum IL‐13 was measurable in only 6/34 subjects with COPD and was not found in the smoking or nonsmoking control subjects. In subjects with COPD and controls there was a paucity of IL‐13+ cells. The distribution of inflammatory cells within different airway compartments was similar in COPD and controls except for an increase in CD3+ lymphocytes within bronchial glands in COPD (P = 0.04).Conclusions:  Our findings do not support a role for IL‐13 in COPD. However, the tissue localization of inflammatory cells to airway compartments, particularly the increase of T cells in glands in COPD may be important in disease.