Abstract
The aim of this study was to study the expression of various claudins in sarcoidosis, usual interstitial pneumonia (UIP), and normal human lung. The expression and cell-specific localization of claudin-1, -2, -3, -4, -5, and -7 was analyzed by IHC. Bronchiolar epithelial cells showed mostly strong expression for claudin-1, -2, -3, -4, and -7 and mainly weak expression for claudin-5 in UIP, sarcoidosis, and normal lung. Three claudins, claudin-3, -4, and -7, were expressed in normal alveolar epithelium, mainly in type II pneumocytes. Claudin-5 was expressed strongly in endothelium of normal lung, and its staining was extremely intense in endothelium of UIP. Moderate or strong expression for claudin-1, -2, -3, -4, and -7 was observed in metaplastic alveolar- and bronchiolar-type epithelium in UIP and also in metaplastic alveolar-type epithelium in sarcoidosis. Expression of claudin-5 was mainly weak in metaplastic alveolar- and bronchiolar-type epithelium in UIP. We conclude that claudin-1, -2, -3, -4, -5, and -7 are expressed in UIP and sarcoidosis, and furthermore, the most prominent enhancement of staining is localized in metaplastic alveolar- and bronchiolar-type epithelium in UIP compared with the healthy lung.