The three mammalian isoforms of TGF-β, TGF-β1, β2, and β3, signal through the same receptor and elicit similar biological responses.  They are multifunctional cytokines that regulate cell proliferation, growth, differentiation and motility, as well as synthesis and deposition of the extracellular matrix.  They are involved in various physiological processes, including embryogenesis, tissue remodeling and wound healing.  They are secreted predominantly as latent complexes, which are stored at the cell surface and in the extracellular matrix.  The release of the biologically active TGF-β isoform from a latent complex involves proteolytic processing of the complex and/or induction of conformational changes by proteins such as thrombospondin-1.  TGF-β1 is the most abundant isoform secreted by almost every cell type.  It was originally identified for its ability to induce phenotypic transformation of fibroblasts, and recently it has been implicated in the formation of skin tumors.  Recombinant Human TGF-β1 is a 25.0 kDa protein composed of two identical 112 amino acid polypeptide chains linked by a single disulfide bond.