The cytokine transforming growth factor-β (TGF-β) plays an important role in the maintenance of T cell homeostasis, immune tolerance to self-antigens, and T cell differentiation during immune responses. | Turkish Journal of Biology Turk J Biol (2017) 41: 1-11 © TÜBİTAK doi: Review Article TGF-β: Its role in the differentiation and function of T regulatory and effector cells 1,2 1,2, Sujuan YANG , Songguo ZHENG * Center for Clinical Immunology, Third Affiliated Hospital at Sun Yat-sen University, Guangzhou, PR China 2 Division of Rheumatology, Department of Medicine, Hershey College of Medicine at Penn State University, Hershey, USA 1 Received: Accepted/Published Online: Final Version: Abstract: The cytokine transforming growth factor-β (TGF-β) plays an important role in the maintenance of T cell homeostasis, immune tolerance to self-antigens, and T cell differentiation during immune responses. TGF-β has pleiotropic effects on adaptive immune responses, especially on the differentiation of T helper and T regulatory cell populations, which depends on the T cell differentiation status and the stimulation conditions. This review provides an update about the roles of TGF-β in T cell responses, especially in the regulation of Treg development and biological features under steady state and inflammation. We also discuss the additional roles that TGF-β plays in the development and function of other T helper cells, such as Th1, Th2, Th9, Th17, and Th22 cells during inflammation. Key words: Transforming growth factor-β, T helper cells, T regulatory cells 1. Introduction Transforming growth factor-β (TGF-β) is a highly evolutionarily conserved cytokine consisting of three known mammalian family members (TGF-β1, -β2, and -β3) that regulate multiple physiological processes. TGF-β1 is produced by many types of immune cells and nonimmune cells. T cells, T regulatory (Treg) cells, macrophages, effector T cells, and thymic mesenchymal cells and tumor cells are the main sources of TGF-β1 production. As TGF-β1 mainly regulates immune responses and the current review focuses on the .