Factor VIII (FVIII) is an essential blood-clotting protein, also known as anti-hemophilic factor (AHF). In humans, factor VIII is encoded by the F8 gene. Defects in this gene result in hemophilia A, a recessive X-linked coagulation disorder. Factor VIII is produced in liver sinusoidal cells and endothelial cells outside the liver throughout the body. This protein circulates in the bloodstream in an inactive form, bound to another molecule called von Willebrand factor, until an injury that damages blood vessels occurs. In response to injury, coagulation factor VIII is activated and separates from von Willebrand factor. The active protein (sometimes written as coagulation factor VIIIa) interacts with another coagulation factor called factor IX. This interaction sets off a chain of additional chemical reactions that form a blood clot.Factor VIII participates in blood coagulation; it is a cofactor for factor IXa, which, in the presence of Ca2+ and phospholipids, forms a complex that converts factor X to the activated form Xa. The factor VIII gene produces two alternatively spliced transcripts. Transcript variant 1 encodes a large glycoprotein, isoform a, which circulates in plasma and associates with von Willebrand factor in a noncovalent complex. This protein undergoes multiple cleavage events. Transcript variant 2 encodes a putative small protein, isoform b, which consists primarily of the phospholipid binding domain of factor VIIIc. This binding domain is essential for coagulant activity.People with high levels of factor VIII are at increased risk for deep vein thrombosis and pulmonary embolism.
Under FDA pressure, unheated product was pulled from US markets, but was sold to Asian, Latin American, and some European countries. The product was tainted with HIV, a concern that had been discussed by Bayer and the U.S. Food and Drug Administration (FDA).In the early 1990s, pharmaceutical companies began to produce recombinant synthesized factor products, which now prevent nearly all forms of disease transmission during replacement therapy. History
Factor VIII  was first discovered in 1937, but it was not until 1979 that its purification by Edward Tuddenham, Frances Rotblat and coworkers led to the molecular identification of the protein. See also
Ralph Kekwick
Frances Rotblat
Edward Shanbrom
Edward Tuddenham
Ryan White

References
Further reading
External links
GeneReviews/NCBI/NIH/UW entry on Hemophilia A
The Coagulation Factor VIII Protein
Factor+VIII at the US National Library of Medicine Medical Subject Headings (MeSH)
Overview of all the structural information available in the PDB for UniProt: P00451 (Human Factor VIII) at the PDBe-KB.