Role of neutrophils in the pathogenesis of acute inflammatory liver injury

Polymorphonuclear leukocytes (neutrophils) are essential in the defense against invading microorganisms, tissue trauma or any inciting inflammatory signals. Hepatic infiltration of neutrophils is an acute response to recent or ongoing liver injury, hepatic stress or unknown systemic inflammatory signals. Once neutrophils reach the liver, they can cause mild-to-severe tissue damage and consequent liver failure. For neutrophils to appear in the liver, neutrophils have to undergo systemic activation (priming) by inflammatory mediators such as cytokines, chemokines, complement factors, immune complexes, opsonized particles and other biologically active molecules, e.g., platelet activating factor. Neutrophils accumulated in the hepatic microvasculature (sinusoids and postsinusoidal venules) can extravasate (transmigrate) into the hepatic parenchyma if they receive a signal from distressed cells. Transmigration can be mediated by a chemokine gradient established towards the hepatic parenchyma and generally involves orchestration by adhesion molecules on neutrophils (beta(2) integrins) and on endothelial cells (intracellular adhesion molecules, ICAM-1). After transmigration, neutrophils adhere to distressed hepatocytes through their beta(2) integrins and ICAM-1 expressed on hepatocytes. Neutrophil contact with hepatocytes mediate oxidative killing of hepatocytes by initiation of respiratory burst and neutrophil degranulation leading to hepatocellular oncotic necrosis. Neutrophil-mediated liver injury has been demonstrated in a variety of diseases and chemical/drug toxicities. Relevant examples are discussed in this review.     

Pathophysiological roles of interleukin-18 in inflammatory liver diseases

Summary: Innate immune response to microbes sometimes determines the nature of the following specific immune response. Kupffer cells, a potent constituent of innate immunity, play a key role in developing the type 1 immune response by interleukin (IL)-12 production. Furthermore, Kupffer cells have the potential to induce liver injury by production of IL-18. Propionibacterium acnes -primed lipopolysaccharide (LPS)-challenged liver injury is the prototype of IL-18-induced tissue injury, in which IL-18 acts on natural killer cells to increase Fas ligand (FasL) that causes liver injury by induction of Fas-dependent hepatocyte apoptosis. LPS induces IL-18 secretion from Kupffer cells in a caspase-1-dependent manner. Indeed, caspase-1-deficient mice are resistant to P. acnes and LPS-induced liver injury. However, administration of soluble FasL induces acute liver injury in P. acnes -primed caspase-1-deficient mice but does not do so in IL-18-deficient mice, indicating that IL-18 release in a caspase-1-independent fashion is essential for this liver injury. Therefore, a positive feedback loop between FasL and IL-18 plays an important role in the pathogenesis of endotoxin-induced liver injury.     

Protective role of interleukin-18 against Fas-mediated liver injury

Interleukin (IL)-18 plays an important role in the pathogenesis of several liver diseases as well as Fas-mediated apoptosis. However, the effects of IL-18 on Fas-mediated liver injury have not been well elucidated. Therefore, we examined the effects of IL-18 on Fas-mediated apoptosis in in vitro and in vivo experiments. We found that recombinant IL-18 protected mouse hepatocellular carcinoma cell lines, BNL5, from Fas-mediated apoptosis in a dose-dependent manner with up-regulation of both nuclear factor (NF) kappaB and X-linked inhibitors of apoptosis (XIAP). IL-18 transgenic (Tg) mice were also protected from Fas-mediated liver injury and this was further confirmed by histological study and TUNEL staining. In IL-18 Tg mice, up-regulation of XIAP and down-regulation of caspase 3 were observed after injection of anti-Fas, which was consistent with the in vitro findings. These results suggest that IL-18 suppresses Fas-mediated apoptosis of hepatocytes by up-regulation of NFkappaB and XIAP, following inhibition of caspase-3 activity. This observation raises the possibility that IL-18 could be a therapeutic strategy for Fas-mediated liver injury as a negative regulator of XIAP.     

Role of interleukin-18 in human natural killer cell is associated with interleukin-2

Human natural killer (NK) cells constitute an important cellular component of innate immunity, capable of killing infected and transformed cells. The proliferation and activation of NK cells are regulated by various cytokines. Interleukin-18 (IL-18) promotes NK cell activation; however, whether the effects of IL-18 on NK cell are associated with other cytokines is still unknown. In this study, we observed that IL-18 induced NK cell apoptosis and inhibited NK cell expansion in the presence of low concentrations of interleukin-2 (IL-2), while high concentrations of IL-2 overcame these effects of IL-18, and high concentrations of IL-2 promoted the stimulatory activity of IL-18 on NK cells. At a low concentration of IL-2, IL-18 induced NK cell apoptosis in part through activation of the FasL/Fas- and TNFα/TNFR-mediated death receptor signaling by enhancing FasL expression and inhibiting c-FLIP_long expression. However, high concentrations of IL-2 strongly blocked IL-18-induced NK cell apoptosis through alleviating IL-18-induced FasL expression and activation of Fas-mediated death signaling and increasing anti-apoptosis molecule (Bcl-X_L). These results reveal that the effects of IL-18 on human NK cell are associated with IL-2 concentration and suggest the importance of IL-2 level in cytokine immunotherapy.     

Role of interleukin-18 in human natural killer cell is associated with interleukin-2

Human natural killer (NK) cells constitute an important cellular component of innate immunity, capable of killing infected and transformed cells. The proliferation and activation of NK cells are regulated by various cytokines. Interleukin-18 (IL-18) promotes NK cell activation; however, whether the effects of IL-18 on NK cell are associated with other cytokines is still unknown. In this study, we observed that IL-18 induced NK cell apoptosis and inhibited NK cell expansion in the presence of low concentrations of interleukin-2 (IL-2), while high concentrations of IL-2 overcame these effects of IL-18, and high concentrations of IL-2 promoted the stimulatory activity of IL-18 on NK cells. At a low concentration of IL-2, IL-18 induced NK cell apoptosis in part through activation of the FasL/Fas- and TNFα/TNFR-mediated death receptor signaling by enhancing FasL expression and inhibiting c-FLIP(long) expression. However, high concentrations of IL-2 strongly blocked IL-18-induced NK cell apoptosis through alleviating IL-18-induced FasL expression and activation of Fas-mediated death signaling and increasing anti-apoptosis molecule (Bcl-X(L)). These results reveal that the effects of IL-18 on human NK cell are associated with IL-2 concentration and suggest the importance of IL-2 level in cytokine immunotherapy.     

Regulatory effects of interleukin-11 during acute lung inflammatory injury.

The role of interleukin-11 (IL-11) was evaluated in the IgG immune complex model of acute lung injury in rats. IL-11 mRNA and protein were both up-regulated during the course of this inflammatory response. Exogenously administered IL-11 substantially reduced, in a dose-dependent manner, the intrapulmonary accumulation of neutrophils and the lung vascular leak of albumin. These in vivo anti-inflammatory effects of IL-11 were associated with reduced NF-kappaB activation in lung, reduced levels of tumor necrosis factor alpha (TNF-alpha) in bronchoalveolar lavage (BAL) fluids, and diminished up-regulation of lung vascular ICAM-1. It is interesting that IL-11 did not affect BAL fluid content of the CXC chemokines, macrophage inflammatory protein-2 (MIP-2) and cytokine-inducible neutrophil chemoattractant (CINC); the presence of IL-11 did not affect these chemokines. However, BAL content of C5a was reduced by IL-11. These data indicate that IL-11 is a regulatory cytokine in the lung and that, like other members of this family, its anti-inflammatory properties appear to be linked to its suppression of NF-kappaB activation, diminished production of TNF-alpha, and reduced up-regulation of lung vascular ICAM-1.     

Role of cell adhesion molecules in leukocyte recruitment in the liver and gut

This article reviews the evidence that adhesion molecules are critical in leukocyte recirculation and pathogenesis of diseases affecting the closely related tissues of the liver and gut, which offer novel opportunities for treatment.     

Expression of interleukin-18 in the lung after endotoxemia or hemorrhage-induced acute lung injury

Hemorrhage and endotoxemia are important risk factors for the development of acute lung injury. Interleukin (IL)-18 is a recently described cytokine released in its mature, active form after pro-IL-18 is cleaved by the IL-1 converting enzyme (ICE). IL-18 has multiple immunomodulating properties, including induction of interferon-gamma (IFN-gamma), IL-1beta, tumor necrosis factor-alpha, and intercellular adhesion molecule-1. To examine the possible involvement of IL-18 in acute lung injury, we examined its expression, as well as that of IFN-gamma, IL-12, and ICE, using murine hemorrhage or endotoxemia models. The amounts of IL-18 messenger RNA (mRNA) increased in the lung after hemorrhage or endotoxemia. However, only endotoxemia was associated with elevations in lung and plasma concentrations of IL-18 protein. ICE expression was increased in the lungs after endotoxemia but not after hemorrhage. Although IFN-gamma expression increased in the lungs after hemorrhage or endotoxemia, elevations in lung IL-12 mRNA levels were found only after endotoxemia. These results indicate that hemorrhage and endotoxemia induce different patterns of immunomodulatory cytokine expression in the lungs. In particular, differences in the expression of ICE after hemorrhage or endotoxemia may affect generation of the active forms of downstream cytokines, including IL-18. IFN-gamma expression in the lungs after hemorrhage appears to occur through a pathway independent of IL-12 and IL-18. IL-18 may play a role in modulating the development of acute lung injury after endotoxemia but not after hemorrhage.     

Leukocyte recruitment and the acute inflammatory response

Leukocyte recruitment is a hallmark feature of the inflammatory response. This review summarizes the generally accepted paradigm of leukocyte recruitment based on studies using intravital microscopy to visualize the microcirculation. The role of selectins and alpha4-integrin in rolling as well as integrin-mediated adhesion is discussed. However, it is becoming increasingly clear that the recruitment cascade within organs differs and therefore the review also attempts to highlight what is and is not known regarding leukocyte recruitment into the brain microvasculature. In the second part of this review, we provide some discussion of mechanisms by which the inflammatory response may be terminated. Particular emphasis on nuclear factor Nf kappaB and how IL10, IL13 and secreted leukocyte protease inhibitor (SLPI) may impact upon the Nf kappaB-dependent inflammatory response is presented.     

Role of airway recruitment and derecruitment in lung injury

The mechanical forces generated during the ventilation of patients with acute lung injury causes significant lung damage and inflammation. Low-volume ventilation protocols are commonly used to prevent stretch-related injury that occurs at high lung volumes. However, the cyclic closure and reopening of pulmonary airways at low lung volumes, i.e., derecruitment and recruitment, also causes significant lung damage and inflammation. In this review, we provide an overview of how biomedical engineering techniques are being used to elucidate the complex physiological and biomechanical mechanisms responsible for cellular injury during recruitment/derecruitment. We focus on the development of multiscale, multiphysics computational models of cell deformation and injury during airway reopening. These models, and the corresponding in vitro experiments, have been used to both elucidate the basic mechanisms responsible for recruitment/derecruitment injury and to develop alternative therapies that make the epithelium more resistant to injury. For example, models and experiments indicate that fluidization of the cytoskeleton is cytoprotective and that changes in cytoskeletal structure and cell mechanics can be used to mitigate the mechanotransduction of oscillatory pressure into inflammatory signaling. The continued application of biomedical engineering techniques to the problem of recruitment/derecruitment injury may therefore lead to novel and more effective therapies.     

Macrophage and perisinusoidal cell kinetics in acute liver injury.

Perisinusoidal cells (PSCs) are currently regarded as the major source of extracellular matrix proteins during hepatic fibrogenesis in response to liver injury. However, the cellular mechanisms underlying their response to injury are not fully understood. One hypothesis is that the PSCs are stimulated by peptide growth factors produced by hepatic macrophages (Kupffer cells) in response to parenchymal cell damage. In this study we have investigated the kinetics of the PSC and macrophage populations in acute carbon tetrachloride-induced hepatic injury in rats. PSCs were identified immunohistochemically by detection of cytoplasmic desmin; monocytes and macrophages were detected using the monoclonal antibodies ED1 and ED2; cells in S phase were identified by immunohistochemical detection of nuclear-incorporated bromodeoxyuridine. The results showed an expansion of the desmin-positive PSC population, predominantly within the damaged perivenular zones, which reached a peak on days 3 and 4 following administration of carbon tetrachloride; this was contributed to by local PSC proliferation. The PSC response was preceded by an expansion of the macrophage population resulting from both local macrophage proliferation and influx of blood monocytes. These results are in keeping with the hypothesis that the PSC response to acute liver injury is mediated, at least in part, by hepatic macrophages.     

Role of macrophage inflammatory peptide-2 in cerulein-induced acute pancreatitis and pancreatitis-associated lung injury

Acute pancreatitis is an inflammatory process of variable severity, and leukocytes are thought to play a key role in the development of pancreatitis and pancreatitis-associated lung injury. The effects of mediators released by these inflammatory cells may induce tissue damage. The aim of our study was to evaluate the role of the chemokine, macrophage inflammatory protein-2 (MIP-2), in the pathogenesis of cerulein-induced pancreatitis and pancreatitis-associated lung injury. The severity of pancreatitis was measured by serum amylase, pancreatic edema, acinar cell necrosis, and myeloperoxidase activity. Lung injury was quantitated by evaluating lung microvascular permeability and lung myeloperoxidase activity. To determine the role of MIP-2 in the pathophysiology of the disease, anti-MIP-2 antibody was administered either 1 hour before or 2 hours after the start of cerulein administration. MIP-2 concentrations increased in serum, pancreas, and lung tissues in mice treated with cerulein. Anti-MIP-2 antibody administrated either before or after cerulein partially protected against pancreas and lung injury. These results show that MIP-2 plays a key role in the pathophysiology of acute pancreatitis and that MIP-2 blockade may improve the outcome of the disease.     

维甲酸降低放射性肺损伤大鼠肺组织中IL-18 mRNA及蛋白的水平

观察IL 18在放射性肺损伤大鼠肺组织的变化及维甲酸对其影响。健康雌性SD大鼠 6 0只随机分为 3组 :正常对照组 (C组 )、单纯照射组 (R组 )、维甲酸治疗组 (W组 ) ,每组 2 0只。后 2组动物行直线加速器全胸部照射 ,单次剂量 15Gy ,距离 1m ,照射面积 4.5cm× 4.5cm ,剂量率 2Gy/min ,W组维甲酸灌服剂量 2 0mg/kg ,C、R组以等量生理盐水灌服直至活杀。用免疫组化染色、原位杂交、图像分析的方法观察IL 18在放射性过程肺中的变化特点。IL 18免疫组化在照射后 30、6 0d明显增强 (P <0.0 1) ,W组 5、30、6 0d明显减弱 (P <0.0 1)。IL 18mRNA在照射后15d明显增强 (P <0 .0 5 ) ,W组 5、15、6 0d明显减弱 (P <0.0 1)。IL 18参与放射性肺损伤的发生、发展。而维甲酸无论从转录水平还是蛋白质水平都能有效抑制IL 18,为治疗放射性肺损伤提供了实验依据     

Role of interleukin-18 (IL-18) in mycobacterial infection in IL-18-gene-disrupted mice

Immunity to mycobacterial infection is closely linked to the emergence of T cells that secrete cytokines, gamma interferon (IFN-gamma), interleukin-12 (IL-12), and tumor necrosis factor alpha (TNF-alpha), resulting in macrophage activation and recruitment of circulating monocytes to initiate chronic granuloma formation. The cytokine that mediates macrophage activation is IFN-gamma, and, like IL-12, IL-18 was shown to activate Th1 cells and induce IFN-gamma production by these cells. In order to investigate the role of IL-18 in mycobacterial infection, IL-18-deficient mice were infected with Mycobacterium tuberculosis and Mycobacterium bovis BCG Pasteur, and their capacities to control bacterial growth, granuloma formation, cytokine secretion, and NO production were examined. These mice developed marked granulomatous, but not necrotic, lesions in their lungs and spleens. Compared with the levels in wild-type mice, the splenic IFN-gamma levels were low but the IL-12 levels were normal in IL-18-deficient mice. The reduced IFN-gamma production was not secondary to reduced induction of IL-12 production. The levels of NO production by peritoneal macrophages of IL-18-deficient and wild-type mice did not differ significantly. Granulomatous lesion development by IL-18-deficient mice was inhibited significantly by treatment with exogenous recombinant IL-18. Therefore, IL-18 is important for the generation of protective immunity to mycobacteria, and its main function is the induction of IFN-gamma expression.     

Association between plasma interleukin-18 levels and liver injury in chronic hepatitis C virus infection and non-alcoholic fatty liver disease

There is significant upregulation of interleukin-18 (IL-18) expression in viral infectious diseases and in some chronic hepatic diseases, especially (i) hepatitis C virus (HCV) infection, (ii) HCV infection with persistently normal ALT levels (PNAL), and (iii) non-alcoholic fatty liver disease (NAFLD). The aim of this study was a better understanding of the implications of plasma IL-18 levels in the above-mentioned liver diseases. Thirty-four patients with HCV infection, 13 with NAFLD, and 10 controls were enrolled. The HCV-RNA and HCV-genotypes and the serum or plasma levels of IL-18, aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma-glutamyltranspeptidase (gamma-GT), alkaline phosphatase, total cholesterol, triglycerides, alpha(1)-fetoprotein, and ferritin were evaluated. Patients with HCV showed higher levels of IL-18 than the NAFLD patients (p <0.01) and the controls (p <0.005). Patients with NAFLD showed higher values of body mass index and liver disease parameters, compared to HCV-infected subjects or controls. These data confirm previous reports of enhanced expression of IL-18 in patients with HCV and NAFLD, compared to healthy subjects, and suggest that IL-18 is important as a marker of liver diseases.     

Plasma levels of interleukin-18 and interleukin-18 binding protein are elevated in patients with chronic liver disease

Interleukin 18 (IL-18) is a recently described proinflammatory cytokine. In mouse models it has been shown to play a key role in the development of liver injury. IL-18 binding protein (IL-18BP) is a naturally occurring antagonist of IL-18. In this study we investigated whether IL-18/IL-18BP levels are altered in patients with chronic liver disease (CLD). We measured IL-18 and IL-18BP plasma levels in 153 patients with CLD and 41 healthy controls by a specific ELISA. Plasma levels of IL-18 were significantly higher in CLD patients than in healthy controls. Cirrhotics had higher levels than noncirrhotics. IL-18 levels increased with disease progression. IL-18BP plasma levels paralled the increase of IL-18 with disease progression, except in stage Child C cirrhosis. IL-18 and IL-18BP levels were elevated independent of the etiology of CLD. IL-18 and IL-18BP correlated with laboratory parameters of inflammation and liver injury. Plasma levels of IL-18 and its antagonist, IL-18BP, are elevated in CLD and correlate with severity of disease. IL-18BP may not be sufficient to counteract the overwhelming proinflammatory response in end stage liver disease.     

Role of interleukin-6 in bleomycin-induced lung inflammatory changes in mice

Interleukin-6 (IL-6) is known to be involved in the pathogenesis of various inflammatory diseases, but its role in bleomycin (BLM)-induced lung injury and subsequent fibrotic changes remains to be determined. We evaluated the role of IL-6 in the lung inflammatory changes induced by BLM using wild-type (WT) and IL-6-deficient (IL-6(-/-)) mice. The mice were treated intratracheally with 1 mg/kg BLM and killed 2, 7, or 21 days later. Lung Inflammation in the acute phase (Days 2 and 7) was assessed by differential cell counts in bronchoalveolar lavage (BAL) fluid and cytokine levels in the lung. Lung fibrotic changes were evaluated on Day 21 by histopathology and collagen assay. On Day 2, BLM administration induced significant increases in the numbers of total cells, macrophages, and neutrophils in BAL fluid, which were attenuated in IL-6(-/-) mice (P < 0.05). Lung pathology also showed inflammatory cell accumulation, which was attenuated in the IL-6(-/-) mice compared with WT mice. In WT mice, elevated levels of TGF-beta(1) and CCL3 were observed 2 and 7 days after BLM challenge, respectively. On Day 7, BLM-induced inflammatory cell accumulation did not differ between the genotypes. Lung pathology 21 days after BLM challenge revealed significant fibrotic changes with increased collagen content, which was attenuated in IL-6(-/-) mice. Although the TGF-beta(1) level in the lung did not differ between the genotypes on Day 21, CCL3 was significantly lower in IL-6(-/-) mice. These results indicate that IL-6 may play an important role in the pathogenesis of BLM-induced lung injury and subsequent fibrotic changes.