Regulatory CD4+CD25+ T cells (Tregs) are defective numerically and functionally in autoimmune hepatitis (AIH). We have investigated and compared the mechanism of action of Tregs in healthy subjects and in AIH patients using Transwell experiments, where Tregs are cultured either in direct contact with or separated from their targets by a semipermeable membrane. We also studied Treg FOXP3 expression and effect on apoptosis. Direct contact is necessary for Tregs to suppress proliferation and IFN-γ production by CD4+CD25− and CD8+ T cells in patients and controls. Moreover, in both, direct contact of Tregs with their targets leads to increased secretion of regulatory cytokines IL-4, IL-10, and TGF-β, suggesting a mechanism of linked immunosuppression. Tregs/CD4+CD25− T cell cocultures lead to similar changes in IFN-γ and IL-10 secretion in patients and controls, whereas increased TGF-β secretion is significantly lower in patients. In contrast, in patients, Tregs/CD8+ T cell cocultures lead to a higher increase of IL-4 secretion. In AIH, Treg FOXP3 expression is lower than in normal subjects. Both in patients and controls, FOXP3 expression is present also in CD4+CD25− T cells, although at a low level and not associated to suppressive function. Both in patients and controls, addition of Tregs does not influence target cell apoptosis, but in AIH, spontaneous apoptosis of CD4+CD25− T cells is reduced. In conclusion, Tregs act through a direct contact with their targets by modifying the cytokine profile and not inducing apoptosis. Deficient CD4+CD25− T cell spontaneous apoptosis may contribute to the development of autoimmunity.

Acetaminophen‐induced acute liver failure (AALF) is associated with innate immunity activation, which contributes to the severity of hepatic injury and clinical outcome. A marked increase in hepatic macrophages (h‐mϕ) is observed in experimental models of AALF, but controversy exists regarding their role, implicating h‐mϕ in both aggravation and resolution of liver injury. The role of h‐mϕ in human AALF is virtually unexplored. We sought to investigate the role of chemokine (C‐C motif) ligand 2 (CCL2) in the recruitment of circulating monocytes to the inflamed liver and to determine how the h‐mϕ infiltrate and liver microenvironment may contribute to tissue repair versus inflammation in AALF. We evaluated circulating monocytes, their chemokine (C‐C motif) receptor 2 (CCR2) expression, and serum CCL2 levels in patients with AALF. Cell subsets and numbers of circulation‐derived (MAC387+) or resident proliferating (CD68/Ki67+) h‐mϕ in hepatic immune infiltrates were determined by immunohistochemistry. Inflammatory cytokine levels were determined in whole and laser microdissected liver tissue by proteome array. In AALF, circulating monocytes were depleted, with the lowest levels observed in patients with adverse outcomes. CCL2 levels were high in AALF serum and hepatic tissue, and circulating monocyte subsets expressed CCR2, suggesting CCL2‐dependent hepatic monocyte recruitment. Significant numbers of both MAC387+ and CD68+ h‐mϕ were found in AALF compared with control liver tissue with a high proportion expressing the proliferation marker Ki67. Levels of CCL2, CCL3, interleukin (IL)‐6, IL‐10, and transforming growth factor‐β1 were significantly elevated in AALF liver tissue relative to chronic liver disease controls. Conclusion: In AALF, the h‐mϕ population is expanded in areas of necrosis, both through proliferation of resident cells and CCL2‐dependent recruitment of circulating monocytes. The presence of h‐mϕ within an anti‐inflammatory/regenerative microenvironment indicates that they are implicated in resolution of inflammation/tissue repair processes during AALF. (HEPATOLOGY 2012)

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