Expression of CD105 (endoglin) in arteriolar endothelial cells of human endometrium throughout the menstrual cycle

The cellular mechanisms underlying normal and pathological endometrial bleeding are not well understood, although abnormalities in the structure of endometrial blood vessels may lead to menstrual disorders. Endothelial cells in different organs are heterogeneous and differ in structure, function, antigen composition, metabolic properties and responses to growth factors. Immunostaining was performed with anti-CD105, CD31, CD34 and von Willebrand factor (vWF), and lectin binding with Ulex europaeus agglutinin 1 (UEA 1), Bandeieraea simplicifolia agglutinin 1 (BS 1), Dolichos biflorus agglutinin (DBA) and Peanut agglutinin (PNA) to characterize endothelial cells in human endometrium throughout the menstrual cycle. Serial sections fixed with formalin were stained with primary antibodies and lectins after antigen retrieval. Positive staining for CD31, CD105 and vWF was confined to the vascular endothelium. Endothelial expression of CD31 was observed in all types of vessel, including single cells, and strong staining was found during the early proliferative and mid-secretory phases. Anti-vWF stained arterioles and veins, but there was little positive staining of capillaries. In contrast, staining for CD105 was confined to the arterioles. Although anti-CD34 strongly stained endothelial cells of small vessels and capillaries, staining was also observed on some non-endothelial stromal cells. Strong positive staining for UEA 1 was observed in endothelial cells of all types of vessel throughout the menstrual cycle. Binding of PNA, DBA and BS 1 was confined to the apical region of glandular epithelial cells. This study demonstrates that the differential binding of anti-CD31, CD34, CD105, vWF and UEA 1 distinguishes between endometrial populations of endothelial cells.