Chronic liver injury promotes hepatic inflammation, representing a prerequisite for organ fibrosis. We hypothesized a contribution of chemokine receptor CCR6 and its ligand, CCL20, which may regulate migration of T-helper (Th)17, regulatory, and gamma-delta (γδ) T cells. CCR6 and CCL20 expression was intrahepatically up-regulated in patients with chronic liver diseases (n = 50), compared to control liver (n = 5). Immunohistochemistry revealed the periportal accumulation of CCR6+ mononuclear cells and CCL20 induction by hepatic parenchymal cells in liver disease patients. Similarly, in murine livers, CCR6 was expressed by macrophages, CD4 and γδ T-cells, and up-regulated in fibrosis, whereas primary hepatocytes induced CCL20 upon experimental injury. In two murine models of chronic liver injury (CCl4 and methionine-choline-deficient diet), Ccr6−/− mice developed more severe fibrosis with strongly enhanced hepatic immune cell infiltration, compared to wild-type (WT) mice. Although CCR6 did not affect hepatic Th-cell subtype composition, CCR6 was explicitly required by the subset of interleukin (IL)-17- and IL-22-expressing γδ T cells for accumulation in injured liver. The adoptive transfer of WT γδ, but not CD4 T cells, into Ccr6−/− mice reduced hepatic inflammation and fibrosis in chronic injury to WT level. The anti-inflammatory function of hepatic γδ T cells was independent of IL-17, as evidenced by transfer of Il-17−/− cells. Instead, hepatic γδ T cells colocalized with hepatic stellate cells (HSCs) in vivo and promoted apoptosis of primary murine HSCs in a cell-cell contact-dependent manner, involving Fas-ligand (CD95L). Consistent with γδ T-cell-induced HSC apoptosis, activated myofibroblasts were more frequent in fibrotic livers of Ccr6−/− than in WT mice. Conclusion: γδ T cells are recruited to the liver by CCR6 upon chronic injury and protect the liver from excessive inflammation and fibrosis by inhibiting HSCs.

Hepatic apoptosis is involved in the progression of alcoholic liver disease (ALD). Caspase-8, the apical initiator in death receptor-mediated apoptosis, has been implicated in acute liver injury and in non-alcoholic steatohepatitis. However, the relevance of Caspase-8 in the pathogenesis of ALD remains unclear. In the present study, we investigated the impact of Caspase-8 in human and murine alcohol-induced apoptosis and in ALD. We investigated human samples from ALD patients, primary mouse hepatocytes, and hepatocyte-specific Caspase-8 knockout (Casp8Δhepa) mice in acute and chronic models of ethanol (EtOH) administration. Caspase-8 activation was detected in liver biopsies from ALD patients, as well as in livers of wild-type (WT) mice after chronic ethanol feeding for 8 weeks using the Lieber-DeCarli model. Lack of Caspase-8 expression in Casp8Δhepa animals failed to prevent alcohol-induced liver damage and apoptosis. Instead, inhibition of Caspase-8 shifted the ethanol-induced death signals towards pronounced activation of the intrinsic, mitochondria-dependent apoptosis pathway in Casp8Δhepa livers involving enhanced release of cytochrome c, stronger Caspase-9 activation and specific morphological changes of mitochondria. In vitro and in vivo intervention using a pan-caspase inhibitor markedly attenuated alcohol-induced hepatocyte damage in a Caspase-8-independent manner. Surprisingly, EtOH-fed Casp8Δhepa mice displayed significantly attenuated steatosis and reduced hepatic triglyceride and free fatty acids content. Caspase-8 is dispensable for alcohol-induced apoptosis, but plays an unexpected role for alcohol-dependent fat metabolism. We provide evidence that simultaneous inhibition of extrinsic and intrinsic apoptosis signaling using pan-caspase inhibitors in vivo might be an optimal approach to treat alcohol-induced liver injury.

The development of immunosuppression during polymicrobial sepsis is associated with the failure of dendritic cells (DC) to promote the polarization of T helper (Th) cells toward a protective Th1 type. The aim of the study was to test potential immunomodulatory approaches to restore the capacity of splenic DC to secrete interleukin (IL) 12 that represents the key cytokine in Th1 cell polarization. Murine polymicrobial sepsis was induced by cecal ligation and puncture (CLP). Splenic DC were isolated at different time points after CLP or sham operation, and stimulated with bacterial components in the presence or absence of neutralizing anti-IL-10 antibodies, murine interferon (IFN) γ, and/or granulocyte macrophage colony-stimulating factor (GM-CSF). DC from septic mice showed an impaired capacity to release the pro-inflammatory and Th1-promoting cytokines tumor necrosis factor α, IFN-γ, and IL-12 in response to bacterial stimuli, but secreted IL-10. Endogenous IL-10 was not responsible for the impaired IL-12 secretion. Up to 6 h after CLP, the combined treatment of DC from septic mice with IFN-γ and GM-CSF increased the secretion of IL-12. Later, DC from septic mice responded to IFN-γ and GM-CSF with increased expression of the co-stimulatory molecule CD86, while IL-12 secretion was no more enhanced. In contrast, splenic macrophages from septic mice during late sepsis responded to GM-CSF with increased cytokine release. Thus, therapy of sepsis with IFN-γ/GM-CSF might be sufficient to restore the activity of macrophages, but fails to restore DC function adequate for the development of a protective Th1-like immune response.

No abstract