Introduction In autoimmune hepatitis (AIH) CD4^posCD25^high regulatory T-cells (T-regs), a subset central to immune-tolerance, are numerically defective and impaired in their ability to control effector cell function. At variance with CD4 effectors, T-regs, classically known as CD25^high and FOXP3^pos, express low levels of the activation marker CD127. The aim of the current study was to provide a phenotypic and functional profile of CD4^posCD25^highCD127^lowT-regs (CD127^lowT-regs) in AIH and to explore to what extent absence or low levels of CD127 impact on T-reg ability to suppress.

Methods 20 ANA/SMA+ AIH patients and 12 healthy subjects (HS) were studied. T-reg phenotype was determined by flow cytometry using antibodies to CD4, CD25, CD127, CTLA-4 and Galectin-9, a molecule linked to T-reg ability to suppress. T-reg transcription factor and cytokine profile were assessed by intracellular staining. CD127^lowT-reg ability to suppress was evaluated in a proliferation assay following co-culture with CD25^neg target cells.

Results In AIH CD4^posCD25^high cells contained fewer CD127^low cells than in HS. Compared to conventional CD4^posCD25^high (cT-regs), CD127^lowT-regs from both AIH and HS had a) higher numbers of FOXP3^pos, CTLA-4^pos, Galectin-9^pos and IL-10^pos cells; b) lower numbers of T-bet^pos, RORC^pos, IFNg^pos and IL-17^pos cells; and c) similar numbers of TGF-b^pos cells. In AIH, CD127^lowT-regs contained fewer FOXP3^pos, CTLA-4^pos, Galectin-9^pos, IL-10^pos and TGF-b^pos cells and higher frequencies of T-bet^pos, RORC^pos, IFNg^pos and IL-17^pos cells than in HS. CD127^lowT-regs inhibited CD25^neg cell proliferation more effectively than cT-regs, though less markedly in AIH than in HS. In AIH, treatment with anti-IFNg and anti-IL-17 neutralising antibodies ameliorated the suppressive ability of cT-regs, while leaving unchanged that of CD127^lowT-regs; exposure to anti-IL-10 neutralising antibodies reduced cT-reg suppression in HS, but not in AIH.

Conclusion CD127^low T-regs bear the phenotypic and functional signature of “true T-regs”. Low numbers and reduced suppressive function of CD127^lowT-regs in AIH may contribute to breakdown of immune-tolerance by permitting effector cells to perpetrate hepatocyte damage.

Competing interests None declared.