Platelet factor-4

Platelet factor-4 (PF4) is a small cytokine belonging to the CXC chemokine family that is also known as chemokine (C-X-C motif) ligand 4 (CXCL4). This chemokine is released from 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 anticoagulant effects.

Structure

PF4 is composed of four identical subunits, each with a molecular weight of approximately 7.8 kDa. The protein is stored in alpha-granules of platelets and is chemotactic for neutrophils and monocytes. It 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.

Function

PF4 plays a role in wound repair and inflammation. It promotes clot formation by modulating the activity of thrombin, an enzyme that converts soluble fibrinogen into insoluble strands of fibrin, as well as supporting the propagation of a clot after it has formed. PF4 also has non-hemostatic roles, including promoting angiogenesis, the growth of new blood vessels, and regulating immune response and inflammation.

Clinical significance

PF4 is the antigen in heparin-induced thrombocytopenia (HIT), a rare but serious complication of heparin therapy. In HIT, the body forms antibodies against a complex of heparin and PF4, leading to platelet activation and thrombosis. PF4 can also be used as a biomarker in myocardial infarction and other conditions.

See also

• Chemokine
• Cytokine
• Heparin-induced thrombocytopenia
• Platelet