ACP5,TRAP5b,SPENCDI,ACP5(acid phosphatase 5,tartrate resistant) is also named as TRAP,TrATPase and belongs to the metallophosphoesterase superfamily. It is an iron-containing glycoprotein with a molecular mass of approximately 34 kD. ACP5 is a histochemical marker of the osteoclast. It is also characteristic of monohistiocytes,particularly alveolar macrophages,and is associated with diverse pathological conditions,including hairy cell leukemia and AIDS encephalopathy.