Controversy still exists as to whether TGF-β production by Treg cells is essential for their suppressive function, with different groups showing that Treg cells unable to produce TGF-β either are capable (Fahlén et al., 2005; Kullberg et al., 2005) or incapable (Li et al., 2007; Nakamura et al., 2004) of suppressing T cells in transfer colitis models. Here, TGFB1 is linked to colitis.