TGFB1 and colitis: Although some studies have suggested that TGF-β1-deficient Treg cells are still capable of suppressing T-cell-mediated colitis (Fahlén et al., 2005; Kullberg et al., 2005), this suppression is completely abolished by an anti-TGF-β-blocking antibody (Fahlén et al., 2005), again highlighting the crucial role of TGF-β in Treg-cell-mediated suppression in vivo.