CXCL4, or Platelet factor 4 (PF4), is a small cytokine belonging to the CXC chemokine family. This chemokine is released from the alpha granules of activated platelets in the form of a homotetramer which has high affinity for heparin and is involved in platelet aggregation. CXCL4 is chemotactic for neutrophils and monocytes and also functions as an inhibitor of hematopoiesis, angiogenesis and T-cell function. CXCL4/PF4 is up-regulated in human liver fibrosis and that it plays a nonredundant, functional role in experimental liver fibrosis by mediating stellate cell proliferation, migration, and intrahepatic immune cell recruitment.