CXCL4/PF4 is a secreted chemokine that is expressed by megakaryocytes and restrains the coagulation cascade. It is released by activated platelets and regulates Thrombin/Thrombomodulin complexes, activated Protein C (APC), Coagulation Factor Xa, and Fibrin. The anticoagulant heparin neutralizes CXCL4 procoagulant effects. Complexes of heparin and CXCL4 trigger antibody formation that causes the pathological syndrome HITT
