Transforming growth factor-beta (TGF-β) plays a critical role in bone remodeling. TGF-β
stimulates matrix protein synthesis, has dramatic effects on the bone cells responsible for
bone formation and resorption, and is abundant in bone and bone-conditioned media.
Multiple sources of TGF-β have been described. It was initially purified from platelets. Two
distinct forms of TGF-β have been purified from bone. The second form, TGF-/βII, was initially
purified from bone but was then identified in platelets and also as the major TGF-β in the …

Although initially purified from platelets,'two distinct forms of TGFP have been purified from
bone. In fact, the second form, TGFP-I1 was identified initially in bone.'.'These two bone-
derived factors were called cartilage inducing factor A (CIF-A) and cartilage inducing factor B
(CIF-B) based on their capacity to induce the formation of extracellular matrix proteins which
are characteristic of cartilage. It was soon determined that CIF-A was equivalent to the first
form purified from platelets which is called TGFP-I. CIF-B is the same as TGFP-11, which …