Th2-polarization of CD4+ T-cells is locally induced and drives liver fibrogenesis

Liver fibrosis arises in the course chronic inflammation following mechanisms that are well-conserved across different etiologies. CD4+ T-cells are key players in the orchestration of immune response. In numerous organs Th2-polarized GATA3+ CD4+ T-cells have been demonstrated to drive fibrosis through the release of profibrogenic cytokines such as IL-13. In the liver Th2-cells can perpetuate matrix deposition in archetypical Th2-diseases, however, it is unclear whether the Th2-fibrosis paradigm can be applied to antigen-independent entities, as well. We aimed at investigating whether Th2 pathways are generally activated in chronic liver inflammation.

Whole human liver tissue was obtained from explants during transplantation and tumor resection. Quantitative PCR was performed to study expression of Th2-associated genes. Hepatic CD4+ T-cells were isolated and analyzed accordingly. Using cell lines of different liver resident cells in vitro interaction with CD4+ T-cells under different stimuli was investigated in order to unravel putative mechanisms of local Th2-induction. Furthermore, origin and release of Th2-stimulating cytokines including IL-33 was assessed in vitro and in situ. Various animal models were used to confirm the observations in vivo.

Th2-genes were critically regulated in liver fibrosis and cirrhosis largely independent of underlying liver disease. In line, primary hepatic CD4+ T-cells displayed a Th2-like phenotype, paralleled by elevated serum levels of IL-4, IL-13, IL-25, IL-33 and TSLP. Hepatic Il33 and its receptor St2 showed stage-dependent upregulation. Immunofluorescence revealed intimate cross-talk between GATA3+ T-cells and hepatic macrophages and stellate cells. Interestingly, FISH analysis could identify macrophages and biliary progenitor cells as a source of IL-33. Congruently, mouse models with pronounced ductal reaction exhibited highest IL-33 expression. Besides IL-33, we observed reciprocal cell-cell interaction involving hepatocytes under inflammatory conditions leading to a Th2-shift in T-cells and consecutive activation/proliferation of hepatic stellate cells, partially dependent on IL-13. Moreover, primary CD11b+ liver macrophages can also secrete Th2-cytokines upon stimulation.

Our data indicate that Th2-polarized CD4+ T-cells are implicated in liver fibrosis. Local inflammatory environment due to soluble factors and cell-cell contact favors a Th2-phenotype mainly through IL33.