The impaired immune regulation of autoimmune hepatitis is linked to a defective galectin-9/tim-3 pathway

Abstract

In autoimmune hepatitis (AIH), liver-damaging CD4 T cell responses are associated with defective CD4 posCD25 pos regulatory T cells (T-regs). Galectin-9 (Gal9), a β-galactosidase-binding protein expressed by T-regs, is key to their function, inhibiting T helper 1 immune responses by binding T cell immunoglobulin and mucin domain 3 (Tim-3) on CD4 effector cells. We investigated whether impaired immunoregulation in AIH results from reduced expression of Gal9 in T-regs and/or Tim-3 on CD4 effector cells. Circulating Gal9 posCD4 posCD25 pos and Tim-3 posCD4 posCD25 neg T cell phenotype was assessed by flow cytometry in 75 AIH patients. To evaluate whether Tim-3 expression renders CD4 posCD25 neg T cells amenable to T-reg control, purified CD4 posCD25 negTim-3 pos (Tim-3 pos) and CD4 posCD25 negTim-3 neg (Tim-3 neg) cells were cocultured with T-regs. To determine whether Gal9 expression is essential to function, T-regs were treated with small interfering RNA (siRNA) to repress Gal-9 translation; T-reg suppressor function was assessed by proliferation. In AIH, Tim-3 pos cells within CD4 posCD25 neg cells and their T-bet pos and RORC pos subsets were fewer and contained higher numbers of interferon-γ (IFNγ) pos and interleukin (IL)-17 pos cells than healthy subjects (HS). In AIH and HS, Tim-3 pos cells proliferated less vigorously and were more susceptible to T-reg control than Tim-3 neg cells. In AIH, Gal9 posT-regs were fewer and contained less FOXP3 pos, IL-10 pos, and transforming growth factor β pos and more IFNγ pos and IL-17 pos cells than HS. siRNA treatment of Gal-9 pos T-regs drastically reduced T-reg ability to suppress CD4 posCD25 neg and Tim-3 pos cell proliferation in AIH and HS. Tim-3 pos cell percentage correlated inversely with aminotransferase and CD25 negT-bet pos cell values. Conclusion: Reduced levels of Tim-3 on CD4 posCD25 neg effector cells and of Gal9 in T-regs contribute to impaired immunoregulation in AIH by rendering effector cells less prone to T-reg control and T-regs less capable of suppressing. © 2012 American Association for the Study of Liver Diseases.