Transforming Growth Factor (TGF) betas mediate many cell to cell interactions that occur during embryonic development. Three TGF betas have been identified in mammals. TGF beta 1, TGF beta 2 and TGF beta 3 are each synthesized as precursor proteins that are very similar in that each is cleaved to yield a 112 amino acid polypeptide that remains associated with the latent portion of the molecule. 

The TGF beta polypeptides are multifunctional; capable of influencing cell proliferation, differentiation, and other functions in a wide range of cell types. Transformed, as well as nonneoplastic tissues, release transforming growth factors; and essentially all mammalian cells possess a specific TGF receptor. The multi modal nature of TGF beta is seen in its ability to stimulate or inhibit cellular proliferation. In general, cells of mesenchymal origin appear to be stimulated by TGF beta whereas cells of epithelial or neuroectodermal origin are inhibited by the peptide. TGF beta 1, TGF beta 2, and TGF beta 1.2 appear to be equivalent in biological activity, although there does appear to be differences in binding to certain types of receptors. TGF beta 2 is produced by many cell types and has been found in the highest concentration in porcine platelets and mammalian bone. Latent TGF beta 2 is the prominent isoform found in body fluids such as amniotic fluid, breast milk, and the aqueous and vitreous humor of the eye.