Weibel-Palade body

On the neutrophil, the major selectin expressed is L-selectin. This molecule is constitutively expressed on mature neutrophils but may be expressed at low levels (50% of adult) in neonates. Stimulation of endothelial cells with thrombin, histamine, IL-1 and some other agents induces neutrophils (and other leukocytes) to leave the circulation and adhere to the endothelium. They do this by rolling onto the surface of the endothelium, to which they attach via P-selectin translocated from storage sites in Weibel-Palade bodies to the surface of the endothelium upon activation. The expression of P-selectin is short-lived and is replaced on the endothelial surface by E-selectin (whose expression is also regulated by some cytokines), which continues the endothelial-leukocyte interaction. 

Hannah Ml, Williams R, Kaur J, Hewlett LJ, Cutler DF. Biogenesis of Weibel-Palade bodies. Semin. Cell Dev. Biol. 2002 13 313-324. 

Thirdly, there are the selectins, a family of Ca Mependent carbohydrate-binding proteins which function to control leukocyte interactions with vascular endothelium (Tedder et al, 1995). There are three closely related members of the selectin family, namely L (leukocyte)-, P (platelet)-, and E (endothelial)-selectin. P-selectin is expressed in the Weibel-Palade bodies of endothelial cells and in the a-granules of platelets. It is rapidly mobilized to the sur ce of endothelial cells and platelets in response to a variety of inflammatory agents such as fiuombin, histamine, complement factors, fiee radicals and cytokines (Tedder et al, 1995). P-selectin mediates the adhesion of neutrophils and monocytes to activated platelets and endothelial cells. Platelets can be bound to the endothelium indirectly by adhering to leukocytes bound to the endothelium. 

Barkalow, F. J., Goodman, M. J., and Mayadas, T. N., Cultured murine cerebral micro vascular endothelial cells contain von Willebrand factor-positive Weibel-Palade bodies and support rapid cytokine-induced neutrophil adhesion, Microcirculation, 3, 19, 1996. 

Stimulation of cultured endothelial cells with thrombin, histamine, or H202 results in a rapid (within minutes) translocation of P-selectin (CD62P) to the cell surface from secretory granules known as Weibel-Palade bodies. In contrast, induction of endothelial E-selectin (CD62E) expression is dependent upon de novo synthesis following stimulation with cytokines such as IL-1 a and TNF-a.57 58 P- and E-selectin are only transiently expressed on the cell surface, during which time they bind to the sialylated Lewis X antigens of neutrophils and monocytes.59-61 Both selectins are implicated in leucocyte extravasation associated with the acute inflammatory response.62-63... 

Valentijn KM et al (2011) Functional architecture of Weibel-Palade bodies. Blood 117(19) 5033-5043... 

FIGURE 12.16 In this case, the neoplastic epithelioid hemangioendothelioma cells contained cytoplasmic Weibel-Palade bodies. X 20,000. 

FIGURE 12.58 Ultrastructurally, this pseudomesotheliomatous epithelioid hemangioendothelioma contained Weibel-Palade bodies in many of the neoplastic cells. X 42,000. 

For example, glomerular microvascular endothelial cells in culture should maintain the characteristic fenestration, the presence of Weibel-Palade bodies (both observed by transmission electron microscopy), the basal expression of von Willebrand factor and CD 31 (plate-let-endothelial cell adhesion molecule-1) and the binding of lectin Ulex Europaeus (for human cells) [18,19]. 

The lymphatic endothelium has a number of similarities with vascular endothelium. It forms a continuous lining and has typical cytoskeletal fibers such as microtubules, intermediate fibers, and actin in both fiber bundle form and mafric form. There are numerous caveolae, Weibel-Palade bodies, but lymphatic endothelium has fewer interendothehal adhesion complexes and a discontinuous basement membrane. The residues of the basement membrane are attached to interstitial collagen via anchoring filaments [Leak and Burke, 1968] that provide relatively hrm attachment of the endothelium to interstitial structures. 

A small fraction of the precursor vWf is not processed but is secreted constitutively from the cells along with the processed vWf. It appears that this constitutively secreted vWf is functionally different from vWf that is secreted from the Weibel-Palade bodies after endothelial cell stimulation. The vWf originating from the Weibel-Palade bodies is aggregated into larger multimers and binds more avidly to platelets and extracellular matrix components (269). 

Sprouting capillaries (Wakui 1988) are characterised by small, slitlike lumina and thick-walled endothehal cells that contain numerous cytoplasmic organelles. In densely fibrotic lesions, regenerating endothelial cells contained numerous free ribosomes, cistern of the rough endoplasmic reticulum, numerous microfilaments, and Weibel-Palade bodies (Kawanami et al. 1995). The microfilaments often showed dense insertion sites along the abluminal plasmalemma. 

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