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 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.[5] It is usually found in a complex with proteoglycan.
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.[5][7]
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.[9][10] 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.[11] PF4 autoantibodies have also been found in patients with thrombosis and features resembling HIT but no prior administration of heparin.[12]
↑Lasagni L, Francalanci M, Annunziato F, Lazzeri E, Giannini S, Cosmi L, etal. (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. 197 (11): 1537–1549. doi:10.1084/jem.20021897. PMC2193908. PMID12782716.
↑Kanack AJ, Shah S, Padmanabhan A (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. 22 (2). doi:10.1182/hem.V22.2.2025213.
↑"Spectrum of anti-PF4 disorders widens - CAP TODAY". www.captodayonline.com. 19 June 2025. Retrieved 22 June 2025.
↑Warkentin TE (March 2007). "Drug-induced immune-mediated thrombocytopenia--from purpura to thrombosis". The New England Journal of Medicine. 356 (9): 891–893. doi:10.1056/NEJMp068309. PMID17329695.
↑Warkentin TE, Makris M, Jay RM, Kelton JG (July 2008). "A spontaneous prothrombotic disorder resembling heparin-induced thrombocytopenia". The American Journal of Medicine. 121 (7): 632–636. doi:10.1016/j.amjmed.2008.03.012. PMID18589060.
↑Schultz NH, Sørvoll IH, Michelsen AE, Munthe LA, Lund-Johansen F, Ahlen MT, etal. (April 2021). "Thrombosis and Thrombocytopenia after ChAdOx1 nCoV-19 Vaccination". The New England Journal of Medicine. 384 (22): 2124–2130. doi:10.1056/NEJMoa2104882. ISSN0028-4793. PMC8112568. PMID33835768.
Kolset SO, Mann DM, Uhlin-Hansen L, Winberg JO, Ruoslahti E (April 1996). "Serglycin-binding proteins in activated macrophages and platelets". Journal of Leukocyte Biology. 59 (4): 545–54. doi:10.1002/jlb.59.4.545. PMID8613703. S2CID23125881.