granule

Gray platelet syndrome (GPS) is an alpha granule deficiency typically characterized by large platelets, mild to moderate thrombocytopenia, and bleeding caused by homozygous or compound heterozygous mutations in the NBEAL2.

(29) This partially active FV is then stored in platelet alpha granules, where it appears that this partial activation also renders platelet FV resistant to circulating inhibitors.

Interestingly, although the release of alpha granules was similar in all investigated groups, the levels of growth factors differed between them.

P-Selectin is an adhesion molecule found in the Weibel- Palade bodies of endothelial cells and the alpha granules of platelets.4 Although P-Selectin is present on the extracellular surfaces of both activated platelets and activated endothelium, most of the sPS detected in the blood is derived from platelets.4 Activated platelets express P-Selectin on their membranes, and from there, it dissociates and is disseminated by the blood.4

Since factor V, vWF and fibrinogen are also included in alpha granules, some aggregation defect is also observed in specific deficiencies of these.

For example, PLT alpha granules, whose contents are released into the vascular space following PLT activation, are rich in many important mediators of hemostatic and nonhemostatic processes, such as procoagulants factor V and von Willebrand factor, mitogens like PLT-derived growth factor, other cytokines such as RANTES (chemokine ligand 5; regulated on activation, normal T cell expressed and secreted), immunoglobulins, and antimicrobial proteins.