Recombinant Human Platelet Factor-4/CXCL4. Platelet Factor-4 (PF-4) is a small cytokine belonging to the CXC chemokine family that is also known as chemokine (C-X-C motif) ligand 4 (CXCL4). The gene for human CXCL4 is located on human chromosome 4. This chemokine is released from alpha-granules of activated platelets during platelet aggregation and neutralizes the anticoagulant effect of heparin. It interacts with a splice variant of the chemokine receptor CXCR3 besides be chemotactic for neutrophils, fibroblasts and monocytes. Recombinant human CXCL4 contains 70 amino acids binds with high affinity to heparin. Specifically, Human and mouse CXCL4 share about a 60 % identity.