are endothelial cells keratin positive
(A) CD31 expression in lymph nodes showing positive marginal (subcapsular) sinuses, high endothelial venules (HEV), and capillaries. In contrast, marginal sinuses are negative for CD34 (B) and vWF (C). (D) Most of the cells present in lymph nodes including EC from capillaries and HEV are stained for Fli-1.D31, a member of the immunoglobulin superfamily, is a 130-kDa transmembrane glycoprotein also designated as PECAM-1 (platelet endothelial cell adhesion molecule 1). It is present on the surface of platelets, monocytes, macrophages, and neutrophils and is a constituent of the endothelial intercellular junction.