Platelet factor 4

Platelet factor 4 (PF4) is a small Cytokine 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 anticoagulant activity and promoting coagulation. As a strong chemoattractant for neutrophils and fibroblasts, PF4 probably has a role in inflammation and wound healing.

Structure

PF4 is a member of the CXC chemokine family of molecules and is also known as CXCL4. It is a tetramer composed of four identical subunits, each with a molecular weight of approximately 7.8 kDa.

Function

PF4 is released from the alpha-granules of activated platelets during platelet aggregation, and promotes blood coagulation by neutralizing the anticoagulant effect of heparin-like molecules on the endothelial surface of blood vessels. It also has potent chemoattractant activity for neutrophils and fibroblasts, suggesting a role in inflammation and wound healing.

Clinical significance

PF4 is the target of the autoimmune response in heparin-induced thrombocytopenia (HIT), a serious complication of heparin therapy. In HIT, antibodies are formed against the complex of heparin and PF4, leading to platelet activation and thrombosis.

See also

• Chemokine
• CXC chemokine
• Heparin-induced thrombocytopenia