Platelet factor 4

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

Antibodies

There are a set of prothrombotic conditions caused by monoclonal antibodies against Platelet factor 4 (anti-PF4) that presents with recurrent thrombosis and persistent thrombocytopenia. At least one author has called these Monoclonal gammopathy of thrombotic 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.

Antibodies against PF4 have been implicated in cases of thrombosis and thrombocytopenia subsequent to vaccination with the Oxford–AstraZeneca or the Janssen COVID-19 vaccine. This phenomenon has been termed vaccine-induced immune thrombotic thrombocytopenia (VITT).

Expression changes

Changes in the expression of PF4 have been associated with symptoms of long COVID.

It is increased in patients with systemic sclerosis that also have interstitial lung disease.

Malaria

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

References

References

1. (July 1990). "Structural and functional comparison of the genes for human platelet factor 4 and PF4alt". Blood.
2. (1999). "Physical mapping of the CXC chemokine locus on human chromosome 4". Cytogenetics and Cell Genetics.
3. "Entrez Gene: PF4 platelet factor 4 (chemokine (C-X-C motif) ligand 4)".
4. (June 2003). "An alternatively spliced variant of CXCR3 mediates the inhibition of endothelial cell growth induced by IP-10, Mig, and I-TAC, and acts as functional receptor for platelet factor 4". The Journal of Experimental Medicine.
5. (1 March 2025). "Investigation of Patient With Monoclonal Gammopathy of Thrombotic Significance Unmasks New Type of Platelet-Activating Anti-Platelet Factor 4 Antibody". The Hematologist.
6. (19 June 2025). "Spectrum of anti-PF4 disorders widens - CAP TODAY". www.captodayonline.com.
7. (March 2007). "Drug-induced immune-mediated thrombocytopenia--from purpura to thrombosis". The New England Journal of Medicine.
8. (July 2008). "A spontaneous prothrombotic disorder resembling heparin-induced thrombocytopenia". The American Journal of Medicine.
9. (April 2021). "Thrombosis and Thrombocytopenia after ChAdOx1 nCoV-19 Vaccination". The New England Journal of Medicine.
10. (April 2021). "Thrombotic Thrombocytopenia after ChAdOx1 nCov-19 Vaccination". The New England Journal of Medicine.
11. (June 2021). "Vaccine-Induced Immune Thrombotic Thrombocytopenia (VITT): What We Know and Don't Know". Blood.
12. (January 2022). "Long-term perturbation of the peripheral immune system months after SARS-CoV-2 infection". BMC Medicine.
13. (December 2016). "Changes in plasma CXCL4 levels are associated with improvements in lung function in patients receiving immunosuppressive therapy for systemic sclerosis-related interstitial lung disease". Arthritis Research & Therapy.
14. (December 2012). "Platelet factor 4 activity against P. falciparum and its translation to nonpeptidic mimics as antimalarials". Cell Host & Microbe.