CLDN1 and crescentic glomerulonephritis: Kirk et al. performed an immunohistochemical analysis of claudin expression in human renal cortex and found that claudin-1 was expressed in the parietal epithelium of Bowman's capsule, distal convoluted tubule, and collecting duct [7].Smeets et al. demonstrated, using the genetic cell lineage tracing method, that, in a murine model of crescentic glomerulonephritis (induced by injection of anti-mouse nephrotoxic serum), the majority of the cell population in crescentic lesions is derived from PECS and that these lesions are positive for claudin-1 [3].