Weibel-Palade body
In
physiology,
Weibel-Palade bodies are
organelles in the
endothelium, the cells lining all
blood vessels. They are
named after the two
scientists who first described them in
1964. They play a dual role in blood coagulation
haemostasis and
inflammation.
There are two major constituents of Weibel-Palade bodies. One is
von Willebrand factor (vWF), a multimeric
protein involved in
blood coagulation. The second is
P-selectin, which binds to passing immune cells (
leukocytes). This allows the fast moving leukocytes in the blood to bind to the cells lining the blood vessels and slow down in a series of steps called the
leukocyte adhesion cascade. Subsequently, leukocytes transmigrate across the
endothelium and enter the surrounding tissue where they can migrate to the site of
infection.
The importance of Weibel-Palade bodies are highlighted by some human disease mutations. Mutations within vWF are the usual cause of the most common inherited bleeding disorder,
von Willebrand disease. VWD has an estimated prevalence in some human populations of up to 1%, and is most often characterised by prolonged and variable
mucocutaneous bleeding. Type III von Willebrand Disease is a severe bleeding disorder, not unlike severe
haemophilia type A or B. VWF acts in primary
haemostasis to recruit
platelets at a site of injury, and is also important in secondary
hemostasis, acting as a chaperone for
coagulation factor VIII (FVIII).
Multimeric vWF is assembled in the
Golgi apparatus from vWF dimers. The Golgi then buds off vesicles, covered in a
lipid bilayer, which consist almost exclusively of vWF. The only parallel organelle in physiology is the
alpha granule of
platelets, which also contains vWF. Weibel-Palade bodies are the main source of vWF, though, and α-granules probably play a minor role.
Weibel-Palade bodies were initially described by the
Swiss anatomist Ewald R. Weibel and the
Romanian physiologist George Emil Palade in
1964. Prof. Palade was to win the
Nobel Prize in Physiology for Medicine in
1974 for his work on the function of organelles in
cells. Their observation was published in: Weibel ER, Palade GE.
New cytoplasmic components in arterial endothelia. Journal of Cell Biology 1964;23:101-112 (
fulltext).
*
Endothelium*
Von Willebrand factor*
Platelet*
