TGFB1 and colitis: Despite the controversy surrounding whether the expression of TGF-β is essential for Treg suppressive function, more recent evidence from transfer models of TGF-β1-deficient Treg shows that TGF-β1 produced by Treg is important in the prevention of colitis by suppressing the differentiation of Th1 cells 23 that are the mediators of the development of colitis 24.