Abstract
Human endothelial cells (ECs) synthesize, store, and secrete von Willebrand factor multimeric strings and coagulation factor (F) VIII. It is not currently known if ECs produce other coagulation factors for active participation in coagulation. We found that 3 different types of human ECs in primary culture produce clotting factors necessary for FX activation via the intrinsic (FVIII-FIX) and extrinsic (tissue factor [TF]-FVII) coagulation pathways, as well as prothrombin. Human dermal fibroblasts were used as comparator cells. TF, FVII, FIX, FX, and prothrombin were detected in ECs, and TF, FVII, FIX, and FX were detected in fibroblasts. In addition, FVII, FIX, FX, and prothrombin were detected by fluorescent microscopy in EC cytoplasm (associated with endoplasmic reticulum and Golgi proteins). FX activation occurred on human umbilical vein EC surfaces without the addition of external coagulation proteins, proteolytic enzymes, or phospholipids. Tumour necrosis factor, which suppresses the generation of activated protein C and increases TF, augmented FX activation. Fibroblasts also produced TF, but (in contrast to ECs) were incapable of activating FX without the exogenous addition of FX and had a marked increase in FX activation following the addition of both FX and FVII. We conclude that human ECs produce their own coagulation factors that can activate cell surface FX without the addition of exogenous proteins or phospholipids.