Imbalance between T regulatory (Treg) and T effector (Teff) cells is likely to contribute to the induction and perpetuation of liver damage in autoimmune hepatitis (AIH) and autoimmune sclerosing cholangitis (AISC) either through inability of Tregs to restrain proliferation and effector cytokine production by responders or through conversion of Tregs into T helper type 1 (Th1) or type 17 (Th17) effector lymphocytes. We investigated the effect of Treg skewing on the phenotypic and functional properties of CD4⁺CD127⁺CD25^high cells, an activated subset of Teff, in 32 patients with AIH and 20 with AISC and in 36 healthy subjects. In AIH/AISC we noted a substantial increase in peripheral blood–derived CD4⁺CD127⁺ CD25^high cells that display a Th1/Th17 phenotypic profile, as reflected by heightened interferon gamma and interleukin 17 (IL‐17) production as well as by high levels of T‐bet and related orphan receptor 3 expression, which is strongly correlated with disease activity. CD4⁺CD127⁺CD25^high cells are unresponsive to low‐dose IL‐2 and in patients have marked proliferative ability, further enhanced by stimulation with IL‐7. CD4⁺CD127⁺CD25^high cells obtained from CD4⁺ cells exposed to Treg polarizing conditions display enhanced IL‐10 production; up‐regulate CD49b and LAG‐3, markers of T regulatory 1 cells; and effectively suppress responder cell proliferation in both healthy subjects and AIH/AISC patients through a mechanism which is dependent on interferon gamma and IL‐17. The suppressive function of CD4⁺CD127⁺CD25^high cells is maintained upon proinflammatory challenge in healthy subjects but not in AIH/AISC. Conclusion: Treg skewing confers activated Teff phenotypic and functional properties of T regulatory 1 cells in health and in AIH/AISC, though suppressive function is lost in patients upon proinflammatory challenge; protracted modulation of the inflammatory environment is required to attenuate the effector potential while boosting immunoregulatory properties in Teff. (Hepatology 2017;66:1570–1584).

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