Increased endothelial thrombomodulin (TM) expression in pregnancies complicated by IUGR

Thrombomodulin (TM) is a cell surface receptor playing an important role in endothelial cell anticoagulant activity. TM is also known as a factor of angiogenesis; low TM activity correlates with impaired angiogenesis. Since vascular lesions with disorders of the placental coagulation and inadequate angiogenesis can be associated with IUGR, we hypothesized that thrombomodulin expression in the villous vasculature and syncytiotrophoblast of placentae complicated by IUGR might differ from those of normal pregnancies. Representative tissue samples of normal, IUGR as well as 1st and 2nd trimester (n = 12) placentae were collected. Immunohistochemistry (APAAP) of paraffin tissue sections was performed using monoclonal antibodies specific for TM and PECAM. The percentage of immunopositive vessels and the intensity of immunoreactivity was assessed. Vascular endothelium and syncytiotrophoblast stained positive for TM. Immunoreactivity for TM in villous vasculature rose significantly with gestational age. Villous vessels of IUGR placentae, showed a higher expression of TM, compared to placentae of appropriately grown fetus (p < 0.05). The number of terminal villi and the number of blood vessels per intermediate villi was significantly reduced in IUGR placentae (p < 0.05). These differences reflect inadequate vascularisation and impaired angiogenesis in IUGR.