Weibel-Palade bodies are small storage granules located in endothelial cells comprising the intima of the heart and blood vessels. They are found in arteries, capillaries, veins, and the endocardium, but notably not in the lymphatic vessels. These bodies function to store two principal molecules, P-selectin and Von Willebrand factor. These two agents play a role in inflammation and hemostasis. Von Willebrand factor is essential for blood coagulation. It functions to bind coagulation factor VIII in the presence of vessel injury. vWF then cross-links basement membrane collagen of the vessel to gp1b seen on platelets. This process of platelet adhesion is one of the first steps of clot formation and maturation. P-selectin plays a major role in the ability to increase the permeability of endothelial cells, permitting the components of the cell-mediated immune system (leukocytes) to roll, marginate, and enter the extracellular focus of inflammation. P-selectin also plays a role in platelet aggregation, as it is activated and transported into the cell membrane by thrombin.
There are many other protein molecules stored in Weibel-Palade bodies which include interleukin 8, endothelin 1, eotaxin-3, osteoprotegerin, angiopoietin-2, and alpha-1,3-fucosyltransferase VI. These are mediators of inflammation, immune response, angiogenesis, and vessel caliber/response to stressors.
Weibel-Palade bodies manufacture all these proteins molecules and assemble them in the Golgi complex. Immature Weibel-Palade bodies are often located near the cell nucleus where they acquire most membrane proteins. As they mature the Weibel-Palade bodies, disperse along microtubules. With time, Weibel-Palade bodies may also diffuse with their bodies to form large congregations.