Claudins have not been studied in other disease states of the mesothelium although it could be expected that they play a role in derangements of pleural fluid homeostasis and in pleuritis. Exposure of mesothelial cell monolayers to hydrogen peroxide lowers their transepithelial resistance with a simultaneous decrease in occludin and ZO-1 expression [111] . Thus oxidative stress, involved in many diseases, such as inflammation, may be one factor causing loosening of mesothelial barriers. In line with this, a recent article showed that the levels claudins 1, 3, 5 and 7 decreased and claudin 2 increased in mesothelial cells due to pleural inflammation [112] .