Platelet factor 4
Encyclopedia
Platelet factor 4 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 platelet
s 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
. It is usually found in a complex with proteoglycan
.
PF4 is chemotactic for neutrophils, fibroblast
s and monocyte
s, and interacts with a splice variant of the chemokine receptor CXCR3, known as CXCR3B. The gene
for human PF4 is located on human chromosome 4.
The heparin:PF4 complex is the antigen in heparin-induced thrombocytopenia
, 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.
Cytokine
Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...
belonging to the CXC chemokine
Chemokine
Chemokines are a family of small cytokines, or proteins secreted by cells. Their name is derived from their ability to induce directed chemotaxis in nearby responsive cells; they are chemotactic cytokines...
family that is also known as chemokine (C-X-C motif) ligand 4 (CXCL4) . This chemokine is released from alpha-granules
Platelet alpha-granule
In platelets, the term "alpha granules" is used to describe granules containing several growth factors.-Contents:Contents include insulin-like growth factor 1, platelet-derived growth factor, TGFβ, platelet factor 4 and other clotting proteins In platelets, the term "alpha granules" is used to...
of activated platelet
Platelet
Platelets, or thrombocytes , are small,irregularly shaped clear cell fragments , 2–3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes. The average lifespan of a platelet is normally just 5 to 9 days...
s during platelet aggregation, and promotes blood coagulation
Coagulation
Coagulation is a complex process by which blood forms clots. It is an important part of hemostasis, the cessation of blood loss from a damaged vessel, wherein a damaged blood vessel wall is covered by a platelet and fibrin-containing clot to stop bleeding and begin repair of the damaged vessel...
by moderating the effects of heparin
Heparin
Heparin , also known as unfractionated heparin, a highly sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule...
-like molecules. Due to these roles, it is predicted to play a role in wound repair and inflammation
Inflammation
Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the organism to remove the injurious stimuli and to initiate the healing process...
. It is usually found in a complex with proteoglycan
Proteoglycan
Proteoglycans are proteins that are heavily glycosylated. The basic proteoglycan unit consists of a "core protein" with one or more covalently attached glycosaminoglycan chain. The point of attachment is a Ser residue to which the glycosaminoglycan is joined through a tetrasaccharide bridge...
.
PF4 is chemotactic for neutrophils, fibroblast
Fibroblast
A fibroblast is a type of cell that synthesizes the extracellular matrix and collagen, the structural framework for animal tissues, and plays a critical role in wound healing...
s and monocyte
Monocyte
Monocytes are a type of white blood cell and are part of the innate immune system of vertebrates including all mammals , birds, reptiles, and fish. Monocytes play multiple roles in immune function...
s, and interacts with a splice variant of the chemokine receptor CXCR3, known as CXCR3B. The gene
Gene
A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...
for human PF4 is located on human chromosome 4.
The heparin:PF4 complex is the antigen in heparin-induced thrombocytopenia
Heparin-induced thrombocytopenia
Heparin-induced thrombocytopenia is the development of thrombocytopenia , due to the administration of various forms of heparin, an anticoagulant...
, an idiosyncratic autoimmune reaction to the administration of the anticoagulant heparin
Heparin
Heparin , also known as unfractionated heparin, a highly sulfated glycosaminoglycan, is widely used as an injectable anticoagulant, and has the highest negative charge density of any known biological molecule...
. PF4 autoantibodies
Autoantibody
An autoantibody is an antibody manufactured by the immune system that is directed against one or more of the individual's own proteins. It is derived from the Greek "auto" which means "self", "anti" which means "against" and "body"...
have also been found in patients with thrombosis and features resembling HIT but no prior administration of heparin.