Platelet alpha-granule

In platelets, the term "alpha granules" is used to describe granules containing several growth factors.

Contents
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, 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.

Clinical significance
A deficiency of alpha granules is known as grey platelet syndrome.