title: Murine hepatic stellate cells veto CD8 T cell activation by a CD54-dependent mechanism.
abstract: The liver has a role in T cell tolerance induction, which is mainly achieved through the functions of tolerogenic hepatic antigen-presenting cells (APCs) and regulatory T cells. Hepatic stellate cells (HSCs) are known to have various immune functions, which range from immunogenic antigen presentation to the induction of T cell apoptosis. Here we report a novel role for stellate cells in vetoing the priming of naive CD8 T cells. Murine and human HSCs and stromal cells (but not hepatocytes) prevented the activation of naive T cells by dendritic cells, artificial APCs, and phorbol 12-myristate 13-acetate/ionomycin by a cell contact-dependent mechanism. The veto function for inhibiting T cell activation was directly correlated with the activation state of HSCs and was most pronounced in HSCs from fibrotic livers. Mechanistically, high expression levels of CD54 simultaneously restricted the expression of interleukin-2 (IL-2) receptor and IL-2 in T cells, and this was responsible for the inhibitory effect because exogenous IL-2 overcame the HSC veto function.
  
  
  CONCLUSIONS
  Our results demonstrate a novel function of HSCs in the local skewing of immune responses in the liver through the prevention of local stimulation of naive T cells. These results not only indicate a beneficial role in hepatic fibrosis, for which increased CD54 expression on HSCs could attenuate further T cell activation, but also identify IL-2 as a key cytokine in mediating local T cell immunity to overcome hepatic tolerance.
authors.affiliation: Institutes of Molecular Medicine and Experimental Immunology, University of Bonn, Bonn, Germany.
authors.forename: Frank A
authors.initials: FA
authors.lastname: Schildberg
authors.forename: Alexandra
authors.initials: A
authors.lastname: Wojtalla
authors.forename: Sören V
authors.initials: SV
authors.lastname: Siegmund
authors.forename: Elmar
authors.initials: E
authors.lastname: Endl
authors.forename: Linda
authors.initials: L
authors.lastname: Diehl
authors.forename: Zeinab
authors.initials: Z
authors.lastname: Abdullah
authors.forename: Christian
authors.initials: C
authors.lastname: Kurts
authors.forename: Percy A
authors.initials: PA
authors.lastname: Knolle
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000473:pathology / Q000502:physiology; D017209:Apoptosis / Q000502:physiology; D018414:CD8-Positive T-Lymphocytes / Q000187:drug effects / Q000473:pathology* / Q000502:physiology; D002450:Cell Communication / Q000502:physiology*; D002460:Cell Line; D002478:Cells, Cultured; D003713:Dendritic Cells / Q000473:pathology / Q000502:physiology; D004195:Disease Models, Animal; D055166:Hepatic Stellate Cells / Q000187:drug effects / Q000473:pathology* / Q000502:physiology; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000502:physiology*; D007376:Interleukin-2 / Q000494:pharmacology; D008103:Liver Cirrhosis / Q000473:pathology / Q000503:physiopathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D023421:Models, Animal; D050378:T-Lymphocytes, Regulatory / Q000473:pathology / Q000502:physiology
chemical_list: D007376:Interleukin-2; D018799:Intercellular Adhesion Molecule-1