Factor VIII is an essential element for a correct clotting process. However, its function is closely related to another clotting factor, von Willebrand factor (vWF).

This factor is normally produced by endothelial cells, i.e. the cells that line the inner wall of the blood vessels, and by megakaryocytes, or platelet precursors. Once it has been produced, von Willebrand factor can be either be stored inside the endothelial cells or immediately released into the plasma, where it recognises and binds with factor VIII to create the factor VIII-von Willebrand factor complex.

Once it has bound to factor VIII, von Willebrand factor plays a protective and supportive role with a number of functions. The most important are:

  • the stabilisation of factor VIII and protection against the action of activated protein C, a protein that tends to attack and break down the factor VIII circulating in the plasma;
  • transportation of factor VIII to points in which a lesion has occurred and the clotting process must be activated;
  • protection of factor VIII from attack by

This last function would appear to be particularly important, as the development of inhibitors is still one of the main challenges to be faced in the treatment of haemophilia.

Von Willebrand factor has recently attracted special interest in the field of scientific research and would appear to be a promising element that could play a significant role in both the prevention and the treatment of inhibitors.




  • Peyvandi F. et al, (2011). Role of von Willebrand factor in the haemostasis. Blood Transfusion, 9(2), s3–s8.
  • Peyvandi F. et al, (2016). A Randomized Trial of Factor VIII and Neutralizing Antibodies in Hemophilia A. The New England Journal of Medicine, 374(21), 2054-64.
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Learn more about the meaning of the words you read on this page and learn about the entire glossary on hemophilia.

Phase of haemostasis during which the clot forms.

It is a complex process constituted by a number of biochemical reactions that follow one another according to a specific sequence and that involve a number of proteins, including clotting factors, thrombin and fibrinogen.

A group of proteins with enzymatic functions involved in the clotting process.

All clotting factors are assigned a Roman numeral, although each one also has a proper name.

Some are produced by the liver, whereas others are synthesised by the endothelial cells that make up the inner lining of the blood vessels.

A protein belonging to the clotting factor category, a group of enzymes involved in the blood-clotting process.

It is encoded by a gene on the long arm of the X chromosome.

Factor VIII is also known as anti-haemophilic factor (AHF).