title: 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(pos) CD25(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(pos) CD4(pos) CD25(pos) and Tim-3(pos) CD4(pos) CD25(neg) T cell phenotype was assessed by flow cytometry in 75 AIH patients. To evaluate whether Tim-3 expression renders CD4(pos) CD25(neg) T cells amenable to T-reg control, purified CD4(pos) CD25(neg) Tim-3(pos) (Tim-3(pos)) and CD4(pos) CD25(neg) Tim-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(pos) CD25(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(pos) T-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(pos) CD25(neg) and Tim-3(pos) cell proliferation in AIH and HS. Tim-3(pos) cell percentage correlated inversely with aminotransferase and CD25(neg) T-bet(pos) cell values.
  
  
  CONCLUSIONS
  Reduced levels of Tim-3 on CD4(pos) CD25(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.
authors.affiliation: Institute of Liver Studies, King's College London School of Medicine at King's College Hospital, Denmark Hill, London, United Kingdom.
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Liberal
authors.forename: Charlotte R
authors.initials: CR
authors.lastname: Grant
authors.forename: Beth S
authors.initials: BS
authors.lastname: Holder
authors.forename: Yun
authors.initials: Y
authors.lastname: Ma
authors.forename: Giorgina
authors.initials: G
authors.lastname: Mieli-Vergani
authors.forename: Diego
authors.initials: D
authors.lastname: Vergani
authors.forename: Maria Serena
authors.initials: MS
authors.lastname: Longhi
mesh_terms: D000293:Adolescent; D002648:Child; D005260:Female; D037161:Galectins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D000072597:Hepatitis A Virus Cellular Receptor 2; D019693:Hepatitis, Autoimmune / Q000276:immunology* / Q000378:metabolism*; D006801:Humans; D053645:Interleukin-2 Receptor alpha Subunit / Q000378:metabolism; D008099:Liver / Q000276:immunology / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000276:immunology / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics; D012008:Recurrence; D015398:Signal Transduction / Q000276:immunology*; D050378:T-Lymphocytes, Regulatory / Q000276:immunology / Q000378:metabolism; D055815:Young Adult
chemical_list: D037161:Galectins; C448908:HAVCR2 protein, human; D000072597:Hepatitis A Virus Cellular Receptor 2; D053645:Interleukin-2 Receptor alpha Subunit; C105032:LGALS9 protein, human; D008565:Membrane Proteins; D034741:RNA, Small Interfering