Polymeric immunoglobulin receptor down-regulation in chronic obstructive pulmonary disease: Persistence in the cultured epithelium and role of transforming growth factor-β

Rationale: The generation of protective secretory IgA relies on the epithelial polymeric immunoglobulin receptor (pIgR). pIgR expression is reduced in chronic obstructive pulmonary disease (COPD), but correlation to disease severity and underlying mechanisms remains unknown. Objectives: To address the hypothesis that pIgR down-regulation in COPD concerns severe disease in relation to aberrant programming of the bronchial epithelium. Methods: Surgical lung tissue and primary bronchial epithelium (cultured in air-liquid interface, ALI) obtained from a large series of patients (n = 116) were studied for pIgR expression and regulation. Measurements and Main Results: pIgR immunostaining in the bronchial epithelium is decreased in severe COPD. In contrast, pIgR transcription was up-regulated in smokers with or without COPD. In ALI (vs. submerged) cultures, pIgR expression was strongly induced, whereas pIgR expression and IgA-transcytosis capacity were decreased in cultures from subjects with severe COPD as compared with control subjects. In addition, COPD cultures released more transforming growth factor-β₁ (TGF-β₁ ), reflecting increased epithelial TGF-β₁ immunostaining in COPD lung tissue. Finally, besides inducing epithelial dedifferentiation, exogenous TGF- β₁ dose-dependently inhibited pIgR production, whereas pIgR increased on blockade of TGF-β₁ activity during ALI differentiation. Conclusions: pIgR down-regulation in COPD correlates with disease severity, and the bronchial epithelium reconstituted in vitro from these patients retains its aberrant imprinting for pIgR expression. This study also links pIgR down-regulation to TGF-β- driven reprogramming of the bronchial epithelium, which results in impaired lung IgA immunity in patients with COPD.