Background：CD9 is a 24 kD type III transmembrane protein also known as tetraspanin, MRP-1 and DRAP-24. It is a member of the tetraspan family （spanning the membrane four times） found on platelets, B cell progenitors, activated lymphocytes, granulocytes, endothelial cells and epithelial cells. CD9 induces adhesion, platelet aggregation, and B cell development. CD9 has been shown to associate with CD63, CD81, CD82, and CD36 and to bind to b1 integrins.
