Barrier function of human pleura mesothelium is constituted by tight junctions

Pleural mesothelium is responsible for liquid formation which lubricates pleural surfaces, which is necessary for the process of breathing. Information on human pleural barrier function and molecular composition however, is scarce. Moreover, effects of pleural inflammation have not been analyzed on molecular level. Methods Barrier function of healthy human visceral and parietal pleura specimens was analyzed in the Ussing chamber. Expression of tight junction (TJ) proteins was studied by Western blot and confocal laser scanning microscopy. In a comparative approach, inflamed human pleura specimens were analyzed. Results Transmesothelial resistance was 14.4 ± 1.9 Ω· m2 in visceral and 17.9 ± 3.0 Ω· m2 in parietal pleura. Western blots revealed occludin, claudin-1, -3, and -5, in both, visceral and parietal pleura. Claudin-7 was detected in visceral pleura only. Confocal microscopy showed a colocalization of occludin with claudins. In inflamed pleura, a decrease of sealing claudins together with an induction of claudin-2, a paracellular cation and water channel, was detected. Conclusion Barrier function in human pleura is in accordance with expression of claudins known to be key determinants of epithelial barrier properties. In inflamed tissue, a perturbation of claudin expression may directly account for decreased barrier function.