Increased Lymphatic Vessels in Patients with Encapsulating Peritoneal Sclerosis

♦ Background The angiogenic response is partly involved in the progression of encapsulating peritoneal sclerosis (EPS). However, the details of the angiogenic response, especially for lymphatic vessels in patients with EPS, remain unclear. In addition, because of technical limitations, morphology studies reported to date have examined only the parietal peritoneum. The morphologies of parietal and visceral lymphatic vessels in patients with EPS both need to be analyzed.♦ Methods We examined peritoneal samples from 18 patients with EPS who underwent enterolysis of the visceral peritoneum and compared them with samples from 17 autopsy cases (controls). To examine the angiogenic response, we performed immunohistochemistry for the endothelial markers CD34 (blood vessels) and podoplanin (lymphatic vessels) and for the cell proliferation marker Ki-67. Immunogold electron microscopy analysis for podoplanin was also performed. In 7 of 18 cases, we compared differences in the angiogenic response of the parietal and visceral peritoneal membranes.♦ Results Angiogenic responses were more frequent in the compact zone than in regenerated layers. The number of capillaries positive for anti-CD34 and anti-podoplanin monoclonal antibodies per unit area of visceral peritoneal tissue was, respectively, 41.1 ± 29.3/mm 2 in EPS patients and 2.7 ± 4.4/mm 2 in controls ( p ≤ 0.01) and 48.1 ± 43.9/mm 2 in EPS patients and 4.1 ± 5.4/mm 2 in controls ( p ≤ 0.01). The percentage of capillaries positive for anti–Ki-67, CD34, and podoplanin was 4.6% in EPS patients ( p ≤ 0.01) and 0.8% in controls ( p = 0.09). The immunogold electron microscopy analysis revealed that podoplanin was localized to endothelial cells with anchoring filaments, a specific feature of lymphatic vessels. Furthermore, compared with parietal peritoneal membrane, visceral peritoneal membrane had a more prominent podoplanin-positive capillary profile, but not a prominent CD34-positive capillary profile. In addition, fibroblast-like cells double-positive for podoplanin and smooth muscle actin were markedly increased in the degenerated layer, as previously reported.♦ Conclusions Our study demonstrated that lymphatic vessels are increased in the visceral peritoneum of patients with EPS.