Podoplanin-positive cells are a hallmark of encapsulating peritoneal sclerosis

Background. Encapsulating peritoneal sclerosis (EPS) and simple peritoneal sclerosis are important complications of long-term peritoneal dialysis (PD). Podoplanin is expressed by mesothelial cells and lymphatic vessels, which are involved in inflammatory reactions in the peritoneal cavity. Methods. We studied 69 peritoneal biopsies from patients on PD (n = 16), patients with EPS (n = 18) and control biopsies taken at the time of hernia repair (n = 15) or appendectomy (n = 20). Immunohistochemistry was performed to localize podoplanin. Additionally, markers of endothelial cells, mesothelial cells, myofibroblasts (smooth muscle actin), proliferating cells, and double labelling for smooth muscle actin/podoplanin were used on selected biopsies. Results. Podoplanin was present on the endothelium of lymphatic vessels in the submesothelial fibrous tissue and on mesothelial cells. In patients on PD and in biopsies with appendicitis, the mesothelial cells demonstrated a cuboidal appearance and circumferential podoplanin staining, with gaps between the cells. The number of lymphatic vessels was variable, but prominent at sites of fibrosis. In patients with EPS, a diffuse infiltration of podoplanin-positive cells with a fibroblastic appearance was present in 15 out of 18 biopsies. This pattern was focally present in 3 out of 16 on PD and none in the 35 controls. The podoplanin-positive cells did not express the endothelial marker or the mesothelial marker (calretinin). Conclusions. EPS is characterized by a population of podoplanin and smooth muscle actin double-positive cells. Podoplanin might be a suitable morphological marker supporting the diagnosis and might be involved in the pathogenesis of EPS.