Evidence for direct transfer of tissue factor from monocytes to platelets in whole blood

Varying specificity of anti-tissue factor (anti-TF) antibodies gives rise to erroneous conclusions on TF positivity of platelets. Although monocytes are a well established source of TF in whole blood, there is no consensus whether platelets express or acquire TF from external sources. To test whether platelets can acquire TF expressed in monocytes, we studied a transfer of TF-yellow fluorescent protein (TF-YFP) from monocytes nucleofected with TF-YFP to platelets in a whole blood model. Platelets isolated from whole blood were found positive for TF when immunostained with anti-TF antibody from one supplier, whereas no platelet TF antigen was found in whole blood immunostained with anti-TF antibody from another supplier. Both antibodies recognized TF in monocytes. Platelets isolated from whole blood reconstituted with monocytes expressing TF-YFP fusion protein were found positive for TF-YFP only after stimulation with lipopolysaccharide (LPS). Taken together, TF protein could be transferred from monocytes upon stimulation with LPS. Blood Coagul Fibrinolysis 23:345-350 (C) 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins.