Depletion of Foxp3+ Regulatory T Cells Promotes Profibrogenic Milieu of Cholestasis-Induced Liver Injury

Background: Accumulating evidence suggests that Foxp3+ regulatory T (Treg) cells act as inhibitory mediators of inflammation; however, the in vivo mechanism underlying this protection remains elusive in liver diseases. Aims: To clarify the in vivo role of Foxp3+ Treg cells in liver fibrosis, we used the DEREG mouse, which expresses the diphtheria toxin receptor under control of the Foxp3 promoter, allowing for specific deletion of Foxp3+ Treg cells. Methods: Bile duct ligation-induced liver injury and fibrosis were assessed by histopathology, fibrogenic gene expression, and measurement of cytokine and chemokine levels. Results: Depletion of Foxp3+ Treg cells enhanced Th17 cell response as demonstrated by the increase of IL-17+ cells and related gene expressions including Il17f, Il17ra, and Rorgt in the fibrotic livers of DEREG mice. Of note, infiltration of CD8+ T cells and Cd8 gene expression was significantly increased in the livers of DEREG mice. Consistent with increased IL-17+ and CD8+ T cell responses, DEREG mice generated higher levels of inflammatory cytokines (TNF-α, IL-6, and IL-12p70) and chemokines (MCP-1, MIP-1α, and RANTES). These results were concordant with severity of liver fibrosis and hepatic enzyme levels (ALT and ALP). Conclusions: The present findings demonstrate that Foxp3+ Treg cells inhibit the profibrogenic inflammatory milieu through suppression of pro-fibrogenic CD8+ and IL-17+ T cells.