Platelet factor 4

Platelet factor 4 (PF4) is a small is_associated_with::cytokine belonging to the CXC is_associated_with::chemokine family that is also known as chemokine (C-X-C motif) ligand 4 (CXCL4). This chemokine is released from alpha-granules of activated is_associated_with::platelets during platelet aggregation, and promotes blood is_associated_with::coagulation by moderating the effects of is_associated_with::heparin-like molecules. Due to these roles, it is predicted to play a role in is_associated_with::wound repair and is_associated_with::inflammation. It is usually found in a complex with is_associated_with::proteoglycan.

Genomics
The is_associated_with::gene for human PF4 is located on human is_associated_with::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 III 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 is_associated_with::neutrophils, is_associated_with::fibroblasts and is_associated_with::monocytes, and interacts with a splice variant of the chemokine receptor CXCR3, known as CXCR3B.

Clinical significance
The heparin:PF4 complex is the antigen in is_associated_with::heparin-induced thrombocytopenia, an idiosyncratic autoimmune reaction to the administration of the anticoagulant is_associated_with::heparin. PF4 autoantibodies have also been found in patients with thrombosis and features resembling HIT but no prior administration of heparin.

The human platelet factor 4 kills malaria parasites within is_associated_with::erythrocytes by selectively lysing the parasite's digestive vacuole.