Transforming growth factor beta (TGF-beta) is an immunosuppressive cytokine. The transforming growth factor ? (TGF-?) family of cytokines is a group of closely related polypeptides of which TGF-beta 1 is the prototype. TGF-beta is one of the most immunosuppressive substances found in the human body. It is produced by a wide variety of cells and tissues and plays an important role in cell differentiation, growth, matrix formation, and the regulation of immune and inflammatory responses.