Cells with positively expressed CD31 and CD34 are stained pale brown in the LEDVT group where CD31 and CD34 show positive expressions. As for VECs in the normal group, some areas are stained lightly or even not stained. (A) Immunocytochemical staining of CD31 and CD34 in endothelial cells in vitro; (B) AOD of CD31 and CD34 in endothelial cells; (C) proportion of CD31 and CD34 positive cells in peripheral blood; (D) statistical analysis of proportion of CD31 and CD34 positive cells in peripheral blood. Abbreviation: AOD, average optional density.