PF4
Description
The PF4 (platelet factor 4) is a protein-coding gene located on chromosome 4.
Platelet factor 4 (PF4) is a small cytokine belonging to the CXC chemokine family, also known as chemokine (C-X-C motif) ligand 4 (CXCL4). This chemokine is released from alpha-granules of activated platelets during platelet aggregation and promotes blood coagulation by moderating the effects of heparin-like molecules. Due to these roles, it is predicted to play a role in wound repair and inflammation. It is usually found in a complex with proteoglycan.
== Genomics == The gene for human PF4 is located on human chromosome 4.
== Function == Platelet factor-4 is a 70-amino acid protein that is released from the alpha-granules of activated platelets and binds with high affinity to heparin. Its major physiologic role appears to be neutralization of heparin-like molecules on the endothelial surface of blood vessels, thereby inhibiting local antithrombin activity and promoting coagulation. As a strong chemoattractant for neutrophils and fibroblasts, PF4 probably has a role in inflammation and wound repair. PF4 is chemotactic for neutrophils, fibroblasts and monocytes, and interacts with a splice variant of the chemokine receptor CXCR3, known as CXCR3-B.
== Clinical significance == The heparin:PF4 complex is the antigen in heparin-induced thrombocytopenia (HIT), an idiosyncratic autoimmune reaction to the administration of the anticoagulant heparin. PF4 autoantibodies have also been found in patients with thrombosis and features resembling HIT but no prior administration of heparin.
PF4 is released during platelet aggregation. It binds more strongly to heparin than to the chondroitin-4-sulfate chains of its carrier molecule, neutralizing heparin's anticoagulant effect. PF4 is chemotactic for neutrophils and monocytes. It inhibits endothelial cell proliferation, with the short form being a more potent inhibitor than the longer form.
PF4 is also known as CXCL4, PF-4, SCYB4.
