Reduced epithelial expression of secretory component in small airways correlates with airflow obstruction in chronic obstructive pulmonary disease

The epithelial polymeric immunoglobulin receptor/transmembrane secretory co mponent (plgR/SC) transports into secretions polymeric immunoglobulin A (pl gA), which is considered the first line of defense of the respiratory tract . The present study, done with quantitative immunohistochemistry, evaluated epithelial expression of secretory component (SC) and Clara cell protein ( CC16) and neutrophil infiltration into the airways of eight patients with s evere chronic obstructive pulmonary disease (COPD) who were undergoing lung transplantation, as compared with these processes in six nonsmoking patien ts with pulmonary hypertension who were used as controls and in lung specim ens from five smokers without chronic bronchitis. Staining for SC was signi ficantly decreased in the COPD patients as compared with the controls, both in large (mean optical density [MOD]: 23.4 [range: 21.1 to 27.8] Versus 42 .2 [range: 28.2 to 49.3], p = 0.003) and in small airways (MOD: 30.8 [range : 20.3 to 39.4] versus 41.5 [range: 39.2 to 46.2], p = 0.003). SC expressio n in small airways correlated strongly with functional parameters such as F EV, (Kendall's tau (K) = 0.76, p = 0.008), FVC (K = 0.64, p = 0.03), and mi dexpiratory flow at 50% of VC (MEF50) (K = 0.74, p = 0.01). The reduced exp ression of SC in large airways correlated with neutrophil infiltration in s ubmucosal glands (K = -0.47, p = 0.03). Expression of CC16 in the bronchial epithelium of COPD patients was also significantly decreased as compared w ith that of controls, especially in small airways (MOD: 28.3 [range: 26.8 t o 32.4] versus 45.8 [range: 40.7 to 56.0], p = 0.002), but no correlation w as observed with lung function tests. In conclusion, this study shows that reduced expression of SC in airway epithelium is associated with airflow ob struction and neutrophil infiltration in severe COPD.