Hepatology : official journal of the American Association for the Study of Liver Diseases
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Patients with alcohol-related liver disease (ALD) have antibodies directed to alcohol dehydrogenase (ADH), anti-ADH titers being associated with disease severity and active alcohol consumption. ADH-specific T-cell responses have not been characterized. We aimed to define anti-ADH cellular immune responses and their association with active alcohol consumption and disease severity. Using cultures of peripheral blood mononuclear cells (PBMCs) from 25 patients with alcohol-related cirrhosis (ARC; 12 were actively drinking or abstinent for <6 months, and 13 were abstinent for >6 months) and hepatic mononuclear cells (HMCs) from 14 patients with ARC who were undergoing transplantation, we investigated T-cell reactivity to 25 overlapping peptides representing the full human ADH protein (beta 1 subunit). ADH-specific peripheral T-cell responses were assessed by the quantification of T-cell proliferation and cytokine production and were correlated with the clinical course. In active alcohol consumers, proliferative T-cell responses targeted ADH31-95 and other discontinuous sequences in the ADH peptide, whereas only one sequence was targeted in abstinents. ADH peptides induced the production of interferon-γ (IFN-γ), interleukin-4 (IL-4), and IL-17. IL-4 production was lower in active drinkers versus abstinents, and IL-17 production was higher. Peptides inducing IFN-γ production outnumbered those inducing T-cell proliferation. The intensity of the predominantly T helper 1 (Th 1) responses directly correlated with disease severity. Similar to PBMCs in abstinents, ADH peptides induced weak T-cell proliferation and a similar level of IL-4 production in HMCs but less vigorous Th 1 and T helper 17 responses. ⋯ This suggests that Th 1 responses to ADH in ARC are induced by alcohol consumption. A Th 1/T helper 2 imbalance characterizes T-cell responses in active drinkers with ARC, whereas IL-4 production prevails in abstinents. This identifies new targets for immunoregulatory therapies in ALD patients for halting detrimental effector T-cell responses, which may encourage liver fibrogenesis and progression to end-stage liver disease.
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Ischemia-reperfusion (I/R) injury is a process whereby an initial hypoxic insult and subsequent return of blood flow leads to the propagation of innate immune responses and organ injury. The necessity of the pattern recognition receptor, Toll-like receptor (TLR)4, for this innate immune response has been previously shown. However, TLR4 is present on various cell types of the liver, both immune and nonimmune cells. Therefore, we sought to determine the role of TLR4 in individual cell populations, specifically, parenchymal hepatocytes (HCs), myeloid cells, including Kupffer cells, and dendritic cells (DCs) subsequent to hepatic I/R. When HC-specific (Alb-TLR4(-/-) ) and myeloid-cell-specific (Lyz-TLR4(-/-) ) TLR4 knockout (KO) mice were subjected to warm hepatic ischemia, there was significant protection in these mice, compared to wild type (WT). However, the protection afforded in these two strains was significantly less than global TLR4 KO (TLR4(-/-) ) mice. DC-specific TLR4(-/-) (CD11c-TLR4(-/-) ) mice had significantly increased hepatocellular damage, compared to WT mice. Circulating levels of high-mobility group box 1 (HMGB1) were significantly reduced in Alb-TLR4(-/-) mice, compared to WT, Lyz-TLR4(-/-) , CD11c-TLR4(-/-) mice and equivalent to global TLR4(-/-) mice, suggesting that TLR4-mediated HMGB1 release from HCs may be a source of HMGB1 after I/R. HCs exposed to hypoxia responded by rapidly phosphorylating the mitogen-activated protein kinases, c-Jun-N-terminal kinase (JNK) and p38, in a TLR4-dependent manner; inhibition of JNK decreased release of HMGB1 after both hypoxia in vitro and I/R in vivo. ⋯ These results provide insight into the individual cellular response of TLR4. The parenchymal HC is an active participant in sterile inflammatory response after I/R through TLR4-mediated activation of proinflammatory signaling and release of danger signals, such as HMGB1.
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Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), an adaptor protein for inflammasome receptors, is essential for inducing caspase-1 activation and the consequent secretion of interleukin-1β (IL-1β), which is associated with local inflammation during liver ischemia/reperfusion injury (IRI). However, little is known about the mechanisms by which the ASC/caspase-1/IL-1β axis exerts its function in hepatic IRI. This study was designed to explore the functional roles and molecular mechanisms of ASC/caspase-1/IL-1β signaling in the regulation of inflammatory responses in vitro and in vivo. With a partial lobar liver warm ischemia (90 minutes) model, ASC-deficient and wild-type mice (C57BL/6) were sacrificed at 6 hours of reperfusion. Separate animal cohorts were treated with an anti-IL-1β antibody or control immunoglobulin G (10 mg/kg/day intraperitoneally). We found that ASC deficiency inhibited caspase-1/IL-1β signaling and led to protection against liver ischemia/reperfusion (IR) damage, local enhancement of antiapoptotic functions, and down-regulation of high mobility group box 1 (HMGB1)-mediated, toll-like receptor 4 (TLR4)-driven inflammation. Interestingly, the treatment of ASC-deficient mice with recombinant HMGB1 re-created liver IRI. Moreover, neutralization of IL-1β ameliorated the hepatocellular damage by inhibiting nuclear factor kappa B (NF-κB)/cyclooxygenase 2 signaling in IR-stressed livers. In parallel in vitro studies, the knockout of ASC in lipopolysaccharide-stimulated bone marrow-derived macrophages depressed HMGB1 activity via the p38 mitogen-activated protein kinase pathway and led to the inhibition of TLR4/NF-κB and ultimately the depression of proinflammatory cytokine programs. ⋯ ASC-mediated caspase-1/IL-1β signaling promotes HMGB1 to produce a TLR4-dependent inflammatory phenotype and leads to hepatocellular injury. Hence, ASC/caspase-1/IL-1β signaling mediates the inflammatory response by triggering HMGB1 induction in hepatic IRI. Our findings provide a rationale for a novel therapeutic strategy for managing liver injury due to IR.