Th2-associated alternative Kupffer cell activation promotes liver fibrosis without inducing local inflammation

Cirrhosis is the final outcome of liver fibrosis. Kupffer cell-mediated hepatic inflammation is considered to aggravate liver injury and fibrosis. Alternatively-activated macrophages are able to control chronic inflammatory events and trigger wound healing processes. Nevertheless, the role of alternative Kupffer cell activation in liver harm is largely unclear. Thus, we evaluated the participation of alternatively-activated Kupffer cells during liver inflammation and fibrosis in the murine model of carbon tetrachloride-induced hepatic damage. To stimulate alternative activation in Kupffer cells, 20 Taenia crassiceps (Tc) larvae were inoculated into BALBc/AnN female mice. Six weeks post-inoculation, carbon tetrachloride or olive oil were orally administered to Tc-inoculated and non-inoculated mice twice per week during other six weeks. The initial exposure of animals to T. crassiceps resulted in high serum concentrations of IL-4 accompanied by a significant increase in the hepatic mRNA levels of Ym-1, with no alteration in iNOS expression. In response to carbon tetrachloride, recruitment of inflammatory cell populations into the hepatic parenchyma was 5-fold higher in non-inoculated animals than Tc-inoculated mice. In contrast, carbon tetrachloride-induced liver fibrosis was significantly less in non-inoculated animals than in the Tc-inoculated group. The latter showed elevated IL-4 serum levels and low IFN-γ concentrations during the whole experiment, associated with hepatic expression of IL-4, TGF-β, desmin and α-sma, as well as increased mRNA levels of Arg-1, Ym-1, FIZZ-1 and MMR in Kupffer cells. These results suggest that alternative Kupffer cell activation is favored in a Th2 microenvironment, whereby such liver resident macrophages could exhibit a dichotomic role during chronic hepatic damage, being involved in attenuation of the inflammatory response but at the same time exacerbation of liver fibrosis.     

Liver inflammation and cytokine production, but not acute phase protein synthesis, accompany the adult liver progenitor (oval) cell response to chronic liver injury

Oval cells are facultative liver progenitor cells, which are invoked during chronic liver injury in order to replenish damaged hepatocytes and bile duct cells. Previous studies have observed inflammation and cytokine production in the liver during chronic injury. Further, it has been proposed that inflammatory growth factors may mediate the proliferation of oval cells during disease progression. We have undertaken a detailed examination of inflammation and cytokine production during a time course of liver injury and repair, invoked by feeding mice a choline-deficient, ethionine-supplemented (CDE) diet. We show that immediately following initial liver injury, B220-expressing leucocytes transiently infiltrate the liver. This inflammatory response occurred immediately before oval cell numbers began to expand in the liver, suggesting that the two events may be linked. Two waves of liver cytokine production were observed during the CDE time course. The first occurred shortly following commencement of the diet, suggesting that it may represent a hepatic acute phase response. However, examination of acute phase marker expression in CDE-fed mice did not support this hypothesis. The second wave of cytokine expression correlated with the expansion of oval cell numbers in the liver, suggesting that these factors may mediate oval cell proliferation. No inflammatory signalling was detected following withdrawal of the injury stimulus. In summary, our results document a close correlation between inflammation, cytokine production and the expansion of oval cells in the liver during experimental chronic injury.     

Pharmacological Inhibition of the Chemokine CXCL16 Diminishes Liver Macrophage Infiltration and Steatohepatitis in Chronic Hepatic Injury

Non-alcoholic fatty liver disease (NAFLD) is a major cause of morbidity and mortality in developed countries, resulting in steatohepatitis (NASH), fibrosis and eventually cirrhosis. Modulating inflammatory mediators such as chemokines may represent a novel therapeutic strategy for NAFLD. We recently demonstrated that the chemokine receptor CXCR6 promotes hepatic NKT cell accumulation, thereby controlling inflammation in experimental NAFLD. In this study, we first investigated human biopsies (n = 20), confirming that accumulation of inflammatory cells such as macrophages is a hallmark of progressive NAFLD. Moreover, CXCR6 gene expression correlated with the inflammatory activity (ALT levels) in human NAFLD. We then tested the hypothesis that pharmacological inhibition of CXCL16 might hold therapeutic potential in NAFLD, using mouse models of acute carbon tetrachloride (CCl₄)- and chronic methionine-choline-deficient (MCD) diet-induced hepatic injury. Neutralizing CXCL16 by i.p. injection of anti-CXCL16 antibody inhibited the early intrahepatic NKT cell accumulation upon acute toxic injury in vivo. Weekly therapeutic anti-CXCL16 administrations during the last 3 weeks of 6 weeks MCD diet significantly decreased the infiltration of inflammatory macrophages into the liver and intrahepatic levels of inflammatory cytokines like TNF or MCP-1. Importantly, anti-CXCL16 treatment significantly reduced fatty liver degeneration upon MCD diet, as assessed by hepatic triglyceride levels, histological steatosis scoring and quantification of lipid droplets. Moreover, injured hepatocytes up-regulated CXCL16 expression, indicating that scavenging functions of CXCL16 might be additionally involved in the pathogenesis of NAFLD. Targeting CXCL16 might therefore represent a promising novel therapeutic approach for liver inflammation and steatohepatitis.     

Fibroblast stimulation in schistosomiasis. V. Egg granuloma macrophages spontaneously secrete a fibroblast-stimulating factor

Isolated intact egg granulomas from the liver of Schistosoma mansoni-infected mice have been previously shown to elaborate factors in vitro that can stimulate fibroblasts for biological functions that are of potential importance in the pathogenesis of hepatic fibrosis in schistosomiasis. We report here that cell cultures obtained from monodispersed granuloma cell suspensions, and specifically enriched for macrophages (95% to 100%) spontaneously elaborated fibroblast proliferation-stimulating activity in vitro. These cells possessed functional and phenotyptic characteristics of activated macrophages. In contrast, control peritoneal macrophages from uninfected mice lacked such phenotypic characteristics, and did not spontaneously elaborate fibrogenic activity in vitro. The granuloma macrophage activity was present, pre-formed within the isolated cells, and was continuously elaborated during 72 hr of incubation. By gel infiltration chromatography (Sephacryl S-200 sf), fibroblast-stimulating activity was identified in two pooled fractions, one with estimated molecular radius (Mr) of 46 kd to 57 kd and the other with Mr of 10 kd to 16 kd. Preparative isoelectric focusing in granular gel of crude macrophage culture supernatants identified peak activity in fractions with pI approximately 5. Two different serine esterase inhibitors had no effect on the ability of crude granuloma macrophage supernatants to stimulate fibroblast proliferation. Whereas crude and chromatographed fractions of granuloma macrophage supernatant were active for fibroblasts, they had minimal or no interleukin 1 (IL 1) activity when tested in a thymocyte proliferation assay. In contrast, resident peritoneal macrophages from the same infected mice spontaneously secreted substantial IL 1 and fibroblast-stimulating activity in vitro. We conclude that egg granuloma macrophages are activated in vivo to secrete fibrogenic molecules functionally distinct from IL 1, which might contribute to the pathogenesis of hepatic fibrosis in schistosomiasis.     

Roles of heterogenous hepatic macrophages in the progression of liver diseases

Hepatic macrophages are key immune cells associated with the broad ranges of liver diseases including steatosis, inflammation and fibrosis. Hepatic macrophages interact with other immune cells and orchestrate hepatic immune circumstances. Recently, the heterogenous populations of hepatic macrophages have been discovered termed residential Kupffer cells and monocyte-derived macrophages, and identified their distinct population dynamics during the progression of various liver diseases. Liver injury lead to Kupffer cells activation with induction of inflammatory cytokines and chemokines, which triggers recruitment of inflammatory monocyte-derived macrophages. To understand liver pathology, the functions of different subtypes of liver macrophages should be regarded with different perspectives. In this review, we summarize recent advances in the roles of hepatic macrophages under liver damages and suggest hepatic macrophages as promising therapeutic targets for treating liver diseases.     

Essential fatty acid deficiency inhibits the in vivo generation of leukotriene B4 and suppresses levels of resident and elicited leukocytes in acute inflammation

Essential fatty acid (EFA) deficiency exerts an anti-inflammatory effect in several models of inflammation. In an effort to understand underlying mechanisms, the effect of EFA deficiency on the generation of eicosanoids and the elicitation of leukocytes in a model of acute inflammation was examined. Acute inflammation was induced by the i.p. injection of zymosan in mice. The injection of zymosan in normal mice was followed by a short burst of eicosanoid synthesis lasting 2 hr. Leukotriene (LT)B4, LTC4, LTD4, and LTE4, thromboxane B2, and 6-keto-prostaglandin F1 alpha were detected using high pressure liquid chromatography and specific radioimmunoassays. This initial phase of eicosanoid production was followed by a more prolonged infiltration of leukocytes (predominantly polymorphonuclear neutrophils (PMN)) lasting 48 hr with little eicosanoid synthesis. When challenged with zymosan, EFA-deficient mice exhibited a marked decrease in the production of eicosanoids during the early phase. No LTB could be detected at all. The number of resident peritoneal macrophages in EFA-deficient mice was also substantially decreased, and the influx of PMN during the inflammatory response was markedly diminished. In order to establish that the generation of eicosanoids during the early phase of this model of acute inflammation played a causal role in the later infiltration of PMN, the effect of the mixed lipoxygenase/cyclooxygenase inhibitor, BW755C, on LTB formation and PMN influx in this model of inflammation was assessed in control animals. BW755C completely blocked LTB synthesis and inhibited the subsequent influx of PMN. In conclusion, EFA deficiency inhibits eicosanoid generation, depresses levels of resident macrophages, and markedly diminishes the influx of PMN in the acute inflammatory response. The decrease in PMN influx appears to result from the inhibition of the antecedent generation of LTB.     

Ultrastructure and number of Kupffer cells in the mouse liver during acute CCl4 poisoning

The ultrastructure and the number of Kupffer cells in different zones of hepatic lobules of mice were studied following CCl4 injection. Migration of the Kupffer cells to necrotic zones of the hepatic lobule after CCl4 administration was detected. These data allow a tentative suggestion that the Kupffer cells are conditionally resident macrophages.     

Alternative M2 activation of Kupffer cells by PPARdelta ameliorates obesity-induced insulin resistance

Macrophage infiltration and activation in metabolic tissues underlie obesity-induced insulin resistance and type 2 diabetes. While inflammatory activation of resident hepatic macrophages potentiates insulin resistance, the functions of alternatively activated Kupffer cells in metabolic disease remain unknown. Here we show that in response to the Th2 cytokine interleukin-4 (IL-4), peroxisome proliferator-activated receptor delta (PPARdelta) directs expression of the alternative phenotype in Kupffer cells and adipose tissue macrophages of lean mice. However, adoptive transfer of PPARdelta(-/-) (Ppard(-/-)) bone marrow into wild-type mice diminishes alternative activation of hepatic macrophages, causing hepatic dysfunction and systemic insulin resistance. Suppression of hepatic oxidative metabolism is recapitulated by treatment of primary hepatocytes with conditioned medium from PPARdelta(-/-) macrophages, indicating direct involvement of Kupffer cells in liver lipid metabolism. Taken together, these data suggest an unexpected beneficial role for alternatively activated Kupffer cells in metabolic syndrome and type 2 diabetes.     

Infection induces a positive acute phase apolipoprotein E response from a negative acute phase gene: role of hepatic LDL receptors

Apolipoprotein E (apoE) plays important roles in lipid homeostasis, anti-inflammation, and host defense. Since tissue apoE mRNA levels have been reported to decrease during inflammatory responses, we were surprised to find that plasma apoE levels were significantly elevated during septic infections in both humans and mice. This apparent paradox was also observed during lipopolysaccharide-induced acute inflammation in mice: plasma levels of apoE increased up to 4-fold despite sharply decreased apoE gene expression in the liver, macrophages, and extrahepatic tissues. We hypothesized that apoE levels were augmented by decreased plasma clearance. Our analysis revealed that apoE associated principally with HDL in mice and that apoE was cleared from the circulation principally via LDL receptors. The acute inflammatory response decreased LDL receptor expression in the liver and significantly reduced the rate of apoE clearance. In contrast, the same inflammatory stimuli increased LDL receptor expression in macrophages. Our results define a novel acute phase mechanism that increases circulating apoE levels as apoE production decreases. Diminished hepatic LDL receptor expression may thus cooperate with elevated LDL receptor expression in macrophages to facilitate the forward transport of apoE and its associated lipids to these key defense cells.     

Genetic control of the innate resistance of mice to Salmonella typhimurium: Ity gene is expressed in vivo by 24 hours after infection

The early response of inbred mice to infection with S. typhimurium is controlled by the mouse Chromosome 1 locus, Ity. To better understand the expression of this gene, the initial interactions between the reticuloendothelial system (RES) and i.v. injected salmonellae were compared in resistant (Ityr) and susceptible (Itys) mice. In both mouse strains 99% of the bacteria was cleared from the blood within 2 hr, and uptake of S. typhimurium by splenic and hepatic macrophages was similar regardless of Ity genotype. In vivo phagocytosis of bacteria was followed by a 30 to 60% decline in viable bacteria, which was attributed to the bactericidal activity of RES macrophages. Experiments with radiolabeled S. typhimurium strains TML and TML/TS27 (a temperature-sensitive mutant) confirmed that the efficiency of this early phase killing was not under Ity control. Despite the equivalent uptake and initial bactericidal activity by resident macrophages, bacterial numbers in the RES organs of Itys mice were significantly greater than in Ityr mice by approximately 24 hr after infection. These data suggest that Ity regulates the level of surviving intracellular bacteria that accumulate within resident macrophages of the liver and spleen.     

The expression and localization of plasma platelet-activating factor acetylhydrolase in endotoxemic rats

The production of platelet-activating factor (PAF) and PAF-like phospholipids that also bind the PAF receptor are implicated in numerous pathological situations including bacterial endotoxemia and injury-induced oxidative damage. PAF and PAF-like phospholipids are hydrolyzed and inactivated by the enzyme PAF acetylhydrolase. In the intact rat, infusion of lipopolysaccharide (LPS) into a mesenteric vein served as an acute, liver-focused model of endotoxemia. We determined that the liver responds to LPS exposure with the production of plasma-type PAF acetylhydrolase mRNA and protein expression specifically in the resident macrophages of the liver. Liver macrophages, defined immunohistochemically using antibodies against ED1, present in livers from saline-treated animals contained no detectable PAF acetylhydrolase. Twenty-four hours following in vivo LPS administration, immunohistochemistry detected a slight increase in the number of ED1 staining cells and the ED1-positive cells now contained an abundance of PAF acetylhydrolase. The systemic administration of LPS resulted in increased expression of PAF acetylhydrolase in several tissues. Of the tissues examined, the greatest increase in PAF acetylhydrolase expression was observed in lung followed by increases in spleen, liver, kidney, and thymus. Additionally, the expression of PAF acetylhydrolase mRNA increased in circulating leukocytes and in peritoneal macrophages in response to systemic exposure to LPS. We examined the regulation of PAF acetylhydrolase expression and demonstrated the administration of the PAF receptor antagonists, BN 50739 and WEB 2170, inhibited by 50% the increase in PAF acetylhydrolase expression in response to LPS. The up-regulation of the plasma-type PAF acetylhydrolase expression constitutes an important mechanism for elevating the local and systemic ability to inactivate PAF and oxidized phospholipids in order to minimize PAF-mediated pathophysiology consequent from exposure to endotoxin. The abundance of PAF acetylhydrolase production in the liver lobule likely limits endotoxin-mediated tissue damage due to PAF synthesis.     

Lysophosphatidylinositols in inflammation and macrophage activation: Altered levels and anti-inflammatory effects

Lysophosphatidylinositols (LPI) are bioactive lipids that are implicated in several pathophysiological processes such as cell proliferation, migration and tumorigenesis and were shown to play a role in obesity and metabolic disorders. Often, these effects of LPI were due to activation of the G protein-coupled receptor GPR55. However, the role of LPI and GPR55 in inflammation and macrophage activation remains unclear. Therefore, we thought to study the effect of macrophage activation and inflammation on LPI levels and metabolism. To do so, we used J774 and BV2 cells in culture activated with lipopolysaccharides (LPS, 100?ng/mL) as well as primary mouse alveolar and peritoneal macrophages. We also quantified LPI levels in the cerebellum, lung, liver, spleen and colon of mice with a systemic inflammation induced by LPS (300?μg/kg) and in the colon of mice with acute colitis induced by dextran sulfate sodium (DSS) or trinitrobenzene sulfonic acid (TNBS) and chronic DSS-induced colitis.Our data show that LPS-induced macrophage activation leads to altered LPI levels in both the cells and culture medium. We also show that cytosolic phospholipase A2α (cPLA2α) and α/β?hydrolase domain 6 (ABHD6) are among the enzymes implicated in LPI metabolism in J774 macrophages. Indeed, ABHD6 and cPLA2α inhibition increased 20:4-LPI levels in LPS-activated macrophages. Furthermore, incubation of LPS-activated cells with LPI decreased J774 activation in a GPR55-dependent manner. In vivo, LPI levels were altered by inflammation in the liver, spleen and colon. These alterations are tissue dependent and could highlight a potential role for LPI in inflammatory processes.     

Time course of pulmonary pathology, cytokine influx and their correlation on augmentation of antigen challenge by influenza A virus infection

A murine model of influenza A virus exacerbation of allergen induced airway inflammation, pulmonary histopathological changes, bronchoalveolar lavage fluid (BALF) analysis, cytokine influx and the time course of these events have been studied. The present study was undertaken to determine the relative contributions of Thl/Th2 cytokines to the histopathological changes in the lungs observed at 9, 12, 24 and 48 hr following antigen challenge in mice previously immunized with influenza A virus. BALF analysis of acute phase group revealed statistically significant increase in neutrophils at 9 hr, macrophages at 12 hr, lymphocytes and eosinophils at 24 hr, as compared to OVA-sensitized control mice. These changes were associated with an alteration in the levels of IL-4, IL-5 and IFN-gamma. A peak of IL-4 at 24 hr significantly enhanced bronchiolar and perivascular histopathology, whereas increased IL-5 level peaking at 24 hr was correlated with the enhanced infiltration of eosinophils in both BALF and lung tissue. There was simultaneous depletion of IL-10 an anti-inflammatory cytokine leading to persistence of pulmonary inflammation in case of acute phase group. Histopathology at 24 and 48 hr showed severe denudation of bronchiolar lining epithelium surrounded by dense chronic inflammatory infiltrate. Chronic interstitial infiltrate with focal loss of architecture, marked oedema, extravasation of RBCs from congested blood vessels and laying down of reticulin fibres was observed in acute phase. Thus, infection with influenza A virus on pre-existing asthmatic immunopathology elicits a cascade of Th2 cytokines with influx of inflammatory cells in BALF, mucosal and interstitial inflammation leading to asthma exacerbations.     

Impaired macrophage autophagy increases the immune response in obese mice by promoting proinflammatory macrophage polarization

Recent evidence that excessive lipid accumulation can decrease cellular levels of autophagy and that autophagy regulates immune responsiveness suggested that impaired macrophage autophagy may promote the increased innate immune activation that underlies obesity. Primary bone marrow-derived macrophages (BMDM) and peritoneal macrophages from high-fat diet (HFD)-fed mice had decreased levels of autophagic flux indicating a generalized impairment of macrophage autophagy in obese mice. To assess the effects of decreased macrophage autophagy on inflammation, mice with a Lyz2-Cre-mediated knockout of Atg5 in macrophages were fed a HFD and treated with low-dose lipopolysaccharide (LPS). Knockout mice developed systemic and hepatic inflammation with HFD feeding and LPS. This effect was liver specific as knockout mice did not have increased adipose tissue inflammation. The mechanism by which the loss of autophagy promoted inflammation was through the regulation of macrophage polarization. BMDM and Kupffer cells from knockout mice exhibited abnormalities in polarization with both increased proinflammatory M1 and decreased anti-inflammatory M2 polarization as determined by measures of genes and proteins. The heightened hepatic inflammatory response in HFD-fed, LPS-treated knockout mice led to liver injury without affecting steatosis. These findings demonstrate that autophagy has a critical regulatory function in macrophage polarization that downregulates inflammation. Defects in macrophage autophagy may underlie inflammatory disease states such as the decrease in macrophage autophagy with obesity that leads to hepatic inflammation and the progression to liver injury.     

Hepatic catabolism of serum amyloid A during an acute phase response and chronic inflammation

Degradation of serum amyloid A (SAA) was studied in isolated perfused livers of mice treated with either a single injection of casein to induce an acute phase response or with 14 daily casein injections to maintain chronic inflammation. Littermates administered sterile saline served as controls. Radioiodinated SAA and apolipoprotein A-I, reconstituted with high-density lipoproteins in vivo, were studied in parallel. Degradation was monitored by appearance of acid-soluble radioactivity in the perfusate. Induction of an acute phase response reduced hepatic catabolism of SAA by 14% (from 8.6 +/- 1.2% to 7.4 +/- 1.1%/g liver in 3 hr, P less than 0.05, n = 16). The acute phase response had no effect on apolipoprotein A-I degradation or bile production. Livers from animals receiving 14 daily injections of casein were 31% less active than control livers at degrading SAA (8.1 +/- 1.6%/g/3 hr for treated group vs. 11.7 +/- 2.3%/g/3 hr for control group, P less than 0.025). Apolipoprotein A-I degradation was decreased but differences were not statistically significant and bile production was the same in both treatment groups. However, livers from treated animals were larger (mean weight 1.8 g) than those from controls (1.5 g) (P less than 0.05), although amyloid fibrils were not detected by Congo red stain. The size of the degradation products was analyzed by column chromatography. Elution profiles of perfusates from livers of chronically inflamed animals contained a peak corresponding to the molecular weight of amyloid A which was not present in perfusates from control liver. We conclude that hepatic catabolism of SAA is decreased both early and late in an inflammatory response and intermediate degradation products corresponding in size to amyloid A are released into the circulation following prolonged inflammation.     

Inhibition of Hedgehog Delays Liver Regeneration through Disrupting the Cell Cycle

Liver regeneration is a complicated biological process orchestrated by various liver resident cells. Hepatic cell proliferation and reconstruction of the hepatic architecture involve multiple signaling pathways. It has been reported that the Hh signal is involved in liver regeneration. However, the signal transduction pathways and cell types involved are ill studied. This study aimed to investigate hedgehog signal response cell types and the specific molecular mechanism involved in the process of liver regeneration. Partial hepatectomy (PH) of 70% was performed on ICR (Institute of Cancer Research) mice to study the process of liver regeneration. We found that the hedgehog signal was activated significantly after PH, including hedgehog ligands, receptors and intracellular signaling molecules. Ligand signals were mainly expressed in bile duct cells and non-parenchymal hepatic cells, while receptors were expressed in hepatocytes and some non-parenchymal cells. Inhibition of the hedgehog signal treated with vismodegib reduced the liver regeneration rate after partial hepatectomy, including inhibition of hepatic cell proliferation by decreasing Cyclin D expression and disturbing the cell cycle through the accumulation of Cyclin B. The current study reveals the important role of the hedgehog signal and its participation in the regulation of hepatic cell proliferation and the cell cycle during liver regeneration. It provides new insight into the recovery of the liver after liver resection.     

Immunodetection of cyclooxygenase-2 (COX-2) is restricted to tissue macrophages in normal rat liver and to recruited mononuclear phagocytes in liver injury and cholangiocarcinoma

It has been suggested that cyclooxygenase-2 (COX-2)-mediated prostaglandin synthesis is associated with liver inflammation and carcinogenesis. The aim of this study is to identify the cellular source of COX-2 expression in different stages, from acute liver injury through liver fibrosis to cholangiocarcinoma (CC). We induced in rats acute and “chronic” liver injury (thioacetamide (TAA) or carbon tetrachloride (CCl₄)) and CC development (TAA) and assessed COX-2 gene expression in normal and damaged liver tissue by RT-PCR of total RNA. The cellular localization of COX-2 protein in liver tissue was analyzed by immunohistochemistry as well as in isolated rat liver cells by Western blotting. The findings were compared with those obtained in human cirrhotic liver tissue. The specificity of the antibodies was tested by 2-DE Western blot and mass spectrometric identification of the positive protein spots. RT-PCR analysis of total RNA revealed an increase of hepatic COX-2 gene expression in acutely as well as “chronically” damaged liver. COX-2-protein was detected in those ED1⁺/ED2⁺ cells located in the non-damaged tissue (resident tissue macrophages). In addition COX-2 positivity in inflammatory mononuclear phagocytes (ED1⁺/ED2⁻), which were also present within the tumoral tissue was detected. COX-2 protein was clearly detectable in isolated Kupffer cells as well as (at lower level) in isolated “inflammatory” macrophages. Similar results were obtained in human cirrhotic liver. COX-2 protein is constitutively detectable in liver tissue macrophages. Inflammatory mononuclear phagocytes contribute to the increase of COX-2 gene expression in acute and chronic liver damage induced by different toxins and in the CC microenvironment.     

Ly6Chi Monocyte Recruitment Is Responsible for Th2 Associated Host-Protective Macrophage Accumulation in Liver Inflammation due to Schistosomiasis

Accumulation of M2 macrophages in the liver, within the context of a strong Th2 response, is a hallmark of infection with the parasitic helminth, Schistosoma mansoni, but the origin of these cells is unclear. To explore this, we examined the relatedness of macrophages to monocytes in this setting. Our data show that both monocyte-derived and resident macrophages are engaged in the response to infection. Infection caused CCR2-dependent increases in numbers of Ly6C^hi monocytes in blood and liver and of CX₃CR1⁺ macrophages in diseased liver. Ly6C^hi monocytes recovered from liver had the potential to differentiate into macrophages when cultured with M-CSF. Using pulse chase BrdU labeling, we found that most hepatic macrophages in infected mice arose from monocytes. Consistent with this, deletion of monocytes led to the loss of a subpopulation of hepatic CD11c^hi macrophages that was present in infected but not naïve mice. This was accompanied by a reduction in the size of egg-associated granulomas and significantly exacerbated disease. In addition to the involvement of monocytes and monocyte-derived macrophages in hepatic inflammation due to infection, we observed increased incorporation of BrdU and expression of Ki67 and MHC II in resident macrophages, indicating that these cells are participating in the response. Expression of both M2 and M1 marker genes was increased in liver from infected vs. naive mice. The M2 fingerprint in the liver was not accounted for by a single cell type, but rather reflected expression of M2 genes by various cells including macrophages, neutrophils, eosinophils and monocytes. Our data point to monocyte recruitment as the dominant process for increasing macrophage cell numbers in the liver during schistosomiasis.     

IL-1β Production through the NLRP3 Inflammasome by Hepatic Macrophages Links Hepatitis C Virus Infection with Liver Inflammation and Disease

Chronic hepatitis C virus (HCV) infection is a leading cause of liver disease. Liver inflammation underlies infection-induced fibrosis, cirrhosis and liver cancer but the processes that promote hepatic inflammation by HCV are not defined. We provide a systems biology analysis with multiple lines of evidence to indicate that interleukin-1β (IL-1β) production by intrahepatic macrophages confers liver inflammation through HCV-induced inflammasome signaling. Chronic hepatitis C patients exhibited elevated levels of serum IL-1β compared to healthy controls. Immunohistochemical analysis of healthy control and chronic hepatitis C liver sections revealed that Kupffer cells, resident hepatic macrophages, are the primary cellular source of hepatic IL-1β during HCV infection. Accordingly, we found that both blood monocyte-derived primary human macrophages, and Kupffer cells recovered from normal donor liver, produce IL-1β after HCV exposure. Using the THP-1 macrophage cell-culture model, we found that HCV drives a rapid but transient caspase-1 activation to stimulate IL-1β secretion. HCV can enter macrophages through non-CD81 mediated phagocytic uptake that is independent of productive infection. Viral RNA triggers MyD88-mediated TLR7 signaling to induce IL-1β mRNA expression. HCV uptake concomitantly induces a potassium efflux that activates the NLRP3 inflammasome for IL-1β processing and secretion. RNA sequencing analysis comparing THP1 cells and chronic hepatitis C patient liver demonstrates that viral engagement of the NLRP3 inflammasome stimulates IL-1β production to drive proinflammatory cytokine, chemokine, and immune-regulatory gene expression networks linked with HCV disease severity. These studies identify intrahepatic IL-1β production as a central feature of liver inflammation during HCV infection. Thus, strategies to suppress NLRP3 or IL-1β activity could offer therapeutic actions to reduce hepatic inflammation and mitigate disease.