In platelets, the term "alpha granules" is used to describe granules containing several growth factors.
Contents include insulin-like growth factor 1, platelet-derived growth factor, TGFβ, platelet factor 4 (which is a heparin-binding chemokine) and other clotting proteins (such as thrombospondin, fibronectin, factor V, and von Willebrand factor).
The alpha granules express the adhesion molecule P-selectin and CD63. These are transferred to the membrane after synthesis.
The other type of granules within platelets are called dense granules.
A deficiency of alpha granules is known as gray platelet syndrome.