Human hepatocytes express an array of proinflammatory cytokines after agonist stimulation or bacterial invasion

Elucidating Mechanisms of Tolerance to Salmonella Typhimurium across Long-Term Infections Using the Collaborative Cross

Understanding the molecular mechanisms underlying resistance and tolerance to pathogen infection may present the opportunity to develop novel interventions. Resistance is the absence of clinical disease with a low pathogen burden, while tolerance is minimal clinical disease with a high pathogen burden. Salmonella is a worldwide health concern. We studied 18 strains of collaborative cross mice that survive acute Salmonella Typhimurium (STm) infections. We infected these strains orally and monitored them for 3 weeks. Five strains cleared STm (resistant), six strains maintained a bacterial load and survived (tolerant), while seven strains survived >7 days but succumbed to infection within the study period and were called “delayed susceptible.” Tolerant strains were colonized in the Peyer’s patches, mesenteric lymph node, spleen, and liver, while resistant strains had significantly reduced bacterial colonization. Tolerant strains had lower preinfection core body temperatures and had disrupted circadian patterns of body temperature postinfection sooner than other strains. Tolerant strains had higher circulating total white blood cells than resistant strains, driven by increased numbers of neutrophils. Tolerant strains had more severe tissue damage and higher circulating levels of monocyte chemoattractant protein 1 (MCP-1) and interferon gamma (IFN-γ), but lower levels of epithelial neutrophil-activating protein 78 (ENA-78) than resistant strains. Quantitative trait locus (QTL) analysis revealed one significant association and six suggestive associations. Gene expression analysis identified 22 genes that are differentially regulated in tolerant versus resistant animals that overlapped these QTLs. Fibrinogen genes (Fga, Fgb, and Fgg) were found across the QTL, RNA, and top canonical pathways, making them the best candidate genes for differentiating tolerance and resistance.

The Effects of Matriptase Inhibition on the Inflammatory and Redox Homeostasis of Chicken Hepatic Cell Culture Models

The function of the transmembrane serine protease matriptase is well described in mammals, but it has not been elucidated in avian species yet. Hence, the aim of the present study was to assess the effects of the 3-amidinophenylalanine (3-AphA)-type matriptase inhibitors MI432 and MI460 on the inflammatory and oxidative state of chicken primary hepatocyte mono-cultures and hepatocyte-nonparenchymal cell co-cultures, the latter serving as a proper model of hepatic inflammation in birds. Cell cultures were exposed to MI432 and MI460 for 4 and 24 h at 10, 25, and 50 µM concentrations, and thereafter the cellular metabolic activity, extracellular interleukin (IL-)6, IL-8, H₂O₂ and malondialdehyde concentrations were monitored. Both inhibitors caused a transient moderate reduction in the metabolic activity following 4 h exposure, which was restored after 24 h, reflecting the fast hepatic adaptation potential to matriptase inhibitor administration. Furthermore, MI432 triggered an intense elevation in the cellular proinflammatory IL-6 and IL-8 production after both incubation times in all concentrations, which was not coupled to enhanced oxidative stress and lipid peroxidation based on unchanged H₂O₂ production, malondialdehyde levels and glutathione peroxidase activity. These data suggest that physiological matriptase activities might have a key function in retaining the metabolic and inflammatory homeostasis of the liver in chicken, without being a major modulator of the hepatocellular redox state.

Escherichia coli Affects Expression of Circadian Clock Genes in Human Hepatoma Cells

Recent research has indicated that dysbiosis of the gut microbiota can lead to an altered circadian clock of the mammalian host. Herein we developed an original system that allows real-time circadian studies of human HepG2 hepatoma cells co-cultured with bacteria. The HepG2 cells with stably integrated firefly luciferase reporter under the control of PERIOD2 promoter were co-cultured with E. coli strains isolated from human fecal samples from healthy individuals. The two E. coli strains differ in the phylogenetic group and the number of ExPEC virulence-associated genes: BJ17 has only two, and BJ23 has 15 of 23 tested. In the first 24 h, the E. coli BJ17 affected the HepG2 circadian clock more than BJ23. Cosinor analysis shows a statistically significant change in the amplitude of PER1 and 2 and the phase advance of PER3. A high percentage of necrotic and apoptotic cells occurred at 72 h, while a correlation between the number of ExPEC genes and the influence on the HepG2 core clock gene expression was observed. Our study reveals that the E. coli genetic background is important for the effect on the mammalian circadian clock genes, indicating possible future use of probiotic E. coli strains to influence the host circadian clock.

Extracellular vesicle release and uptake by the liver under normo- and hyperlipidemia

Liver plays a central role in elimination of circulating extracellular vesicles (EVs), and it also significantly contributes to EV release. However, the involvement of the different liver cell populations remains unknown. Here, we investigated EV uptake and release both in normolipemia and hyperlipidemia. C57BL/6 mice were kept on high fat diet for 20-30 weeks before circulating EV profiles were determined. In addition, control mice were intravenously injected with ^99mTc-HYNIC-Duramycin labeled EVs, and an hour later, biodistribution was analyzed by SPECT/CT. In vitro, isolated liver cell types were tested for EV release and uptake with/without prior fatty acid treatment. We detected an elevated circulating EV number after the high fat diet. To clarify the differential involvement of liver cell types, we carried out in vitro experiments. We found an increased release of EVs by primary hepatocytes at concentrations of fatty acids comparable to what is characteristic for hyperlipidemia. When investigating EV biodistribution with ^99mTc-labeled EVs, we detected EV accumulation primarily in the liver upon intravenous injection of mice with medium (326.3 ± 19.8 nm) and small EVs (130.5 ± 5.8 nm). In vitro, we found that medium and small EVs were preferentially taken up by Kupffer cells, and liver sinusoidal endothelial cells, respectively. Finally, we demonstrated that in hyperlipidemia, there was a decreased EV uptake both by Kupffer cells and liver sinusoidal endothelial cells. Our data suggest that hyperlipidema increases the release and reduces the uptake of EVs by liver cells. We also provide evidence for a size-dependent differential EV uptake by the different cell types of the liver. The EV radiolabeling protocol using ^99mTc-Duramycin may provide a fast and simple labeling approach for SPECT/CT imaging of EVs biodistribution.

Immortalized stem cell-derived hepatocyte-like cells: An alternative model for studying dengue pathogenesis and therapy

Suitable cell models are essential to advance our understanding of the pathogenesis of liver diseases and the development of therapeutic strategies. Primary human hepatocytes (PHHs), the most ideal hepatic model, are commercially available, but they are expensive and vary from lot-to-lot which confounds their utility. We have recently developed an immortalized hepatocyte-like cell line (imHC) from human mesenchymal stem cells, and tested it for use as a substitute model for hepatotropic infectious diseases. With a special interest in liver pathogenesis of viral infection, herein we determined the suitability of imHC as a host cell target for dengue virus (DENV) and as a model for anti-viral drug testing. We characterized the kinetics of DENV production, cellular responses to DENV infection (apoptosis, cytokine production and lipid droplet metabolism), and examined anti-viral drug effects in imHC cells with comparisons to the commonly used hepatoma cell lines (HepG2 and Huh-7) and PHHs. Our results showed that imHC cells had higher efficiencies in DENV replication and NS1 secretion as compared to HepG2 and Huh-7 cells. The kinetics of DENV infection in imHC cells showed a slower rate of apoptosis than the hepatoma cell lines and a certain similarity of cytokine profiles to PHHs. In imHC, DENV-induced alterations in levels of lipid droplets and triacylglycerols, a major component of lipid droplets, were more apparent than in hepatoma cell lines, suggesting active lipid metabolism in imHC. Significantly, responses to drugs with DENV inhibitory effects were greater in imHC cells than in HepG2 and Huh-7 cells. In conclusion, our findings suggest superior suitability of imHC as a new hepatocyte model for studying mechanisms underlying viral pathogenesis, liver diseases and drug effects.

A model system resembling normal human liver cells is needed for advancement of hepatotropic infectious disease research. Here we show that immortalized cells (imHC) derived from human stem cells have a higher efficiency of DENV replication and a lower rate of cell death in response to DENV infection than the cancer cell-derived model systems currently used. The imHC also have active fat metabolism and respond well to anti-viral drug treatment, making them an attractive model for the initial stage of drug discovery and testing.

In utero inflammatory challenge induces an early activation of the hepatic innate immune response in late gestation fetal sheep

Chorioamnionitis is associated with inflammatory end-organ damage in the fetus. Tissues in direct contact with amniotic fluid drive a pro-inflammatory response and contribute to this injury. However, due to a lack of direct contact with the amniotic fluid, the liver contribution to this response has not been fully characterized. Given its role as an immunologic organ, we hypothesized that the fetal liver would demonstrate an early innate immune response to an in utero inflammatory challenge. Fetal sheep (131 ± 1 d gestation) demonstrated metabolic acidosis and high cortisol and norepinephrine values within 5 h of exposure to intra-amniotic LPS. Likewise, expression of pro-inflammatory cytokines increased significantly at 1 and 5 h of exposure. This was associated with NF-κB activation, by inhibitory protein IκBα degradation, and nuclear translocation of NF-κB subunits (p65/p50). Corroborating these findings, LPS exposure significantly increased pro-inflammatory innate immune gene expression in fetal sheep hepatic macrophages in vitro. Thus, an in utero inflammatory challenge induces an early hepatic innate immune response with systemic metabolic and stress responses. Within the fetal liver, hepatic macrophages respond robustly to LPS exposure. Our results demonstrate that the fetal hepatic innate immune response must be considered when developing therapeutic approaches to attenuate end-organ injury associated with in utero inflammation.

The Receptor for Advanced Glycation Endproducts (RAGE) Contributes to Severe Inflammatory Liver Injury in Mice

Background: The receptor for advanced glycation end products (RAGE) is a multiligand receptor involved in a number of processes and disorders. While it is known that RAGE-signaling can contribute to toxic liver damage and fibrosis, its role in acute inflammatory liver injury and septic multiorgan failure is yet undefined. We examined RAGE in lipopolysaccharide (LPS) induced acute liver injury of D-galN sensitized mice as a classical model for tumor necrosis factor alpha (TNF-α) dependent inflammatory organ damage.

Methods: Mice (Rage–/– and C57BL/6) were intraperitoneally injected with D-galN (300 mg/kg) and LPS (10 μg/kg). Animals were monitored clinically, and cytokines, damage associated molecular pattern molecules (DAMPs) as well as liver enzymes were determined in serum. Liver histology, hepatic cytokines as well as RAGE mRNA expression were analyzed. Cellular activation and functionality were evaluated by flow cytometry both in bone marrow- and liver-derived cells.

Results: Genetic deficiency of RAGE significantly reduced the mortality of mice exposed to LPS/D-galN. Hepatocyte damage markers were reduced in Rage–/– mice, and liver histopathology was less severe. Rage–/– mice produced less pro-inflammatory cytokines and DAMPs in serum and liver. While immune cell functions appeared normal, TNF-α production by hepatocytes was reduced in Rage–/– mice.

Conclusions: We found that RAGE deletion attenuated the expression of pro-inflammatory cytokines and DAMPs in hepatocytes without affecting cellular immune functions in the LPS/D-galN model of murine liver injury. Our data highlight the importance of tissue-specific RAGE-signaling also in acute inflammatory liver stress contributing to sepsis and multiorgan failure.

Human unconventional T cells in Plasmodium falciparum infection

Malaria is an old scourge of humankind and has a large negative impact on the economic development of affected communities. Recent success in malaria control and reduction of mortality seems to have stalled emphasizing that our current intervention tools need to be complemented by malaria vaccines. Different populations of unconventional T cells such as mucosal-associated invariant T (MAIT) cells, invariant natural killer T (iNKT) cells and γδ T cells are gaining attention in the field of malaria immunology. Significant advances in our basic understanding of unconventional T cell biology in rodent malaria models have been made, however, their roles in humans during malaria are less clear. Unconventional T cells are abundant in skin, gut and liver tissues, and long-lasting expansions and functional alterations were observed upon malaria infection in malaria naïve and malaria pre-exposed volunteers. Here, we review the current understanding of involvement of unconventional T cells in anti-Plasmodium falciparum immunity and highlight potential future research avenues.

Key features and homing properties of NK cells in the liver are shaped by activated iNKT cells

The contribution of natural killer (NK) cells to the clearance of hepatic viral infections is well recognized. The recently discovered heterogeneity of NK cell populations renders them interesting targets for immune interventions. Invariant natural killer T (iNKT) cells represent a key interaction partner for hepatic NK cells. The present study addressed whether characteristics of NK cells in the liver can be shaped by targeting iNKT cells. For this, the CD1d-binding pegylated glycolipid αGalCerMPEG was assessed for its ability to modulate the features of NK cells permanently or transiently residing in the liver. In vivo administration resulted in enhanced functionality of educated and highly differentiated CD27⁺ Mac-1⁺ NK cells accompanied by an increased proliferation. Improved liver homing was supported by serum-derived and cellular factors. Reduced viral loads in a mCMV infection model confirmed the beneficial effect of NK cells located in the liver upon stimulation with αGalCerMPEG. Thus, targeting iNKT cell-mediated NK cell activation in the liver represents a promising approach for the establishment of liver-directed immune interventions.

MCU-knockdown attenuates high glucose-induced inflammation through regulating MAPKs/NF-κB pathways and ROS production in HepG2 cells

Mitochondrial Ca2+ is a key regulator of organelle physiology and the excessive increase in mitochondrial calcium is associated with the oxidative stress. In the present study, we investigated the molecular mechanisms linking mitochondrial calcium to inflammatory and coagulative responses in hepatocytes exposed to high glucose (HG) (33mM glucose). Treatment of HepG2 cells with HG for 24 h induced insulin resistance, as demonstrated by an impairment of insulin-stimulated Akt phosphorylation. HepG2 treatment with HG led to an increase in mitochondrial Ca2+ uptake, while cytosolic calcium remained unchanged. Inhibition of MCU by lentiviral-mediated shRNA prevented mitochondrial calcium uptake and downregulated the inflammatory (TNF-α, IL-6) and coagulative (PAI-1 and FGA) mRNA expression in HepG2 cells exposed to HG. The protection from HG-induced inflammation by MCU inhibition was accompanied by a decrease in the generation of reactive oxygen species (ROS). Importantly, MCU inhibition in HepG2 cells abrogated the phosphorylation of p38, JNK and IKKα/IKKβ in HG treated cells. Taken together, these data suggest that MCU inhibition may represent a promising therapy for prevention of deleterious effects of obesity and metabolic diseases.

Clearance of Apoptotic Cells by Tissue Epithelia: A Putative Role for Hepatocytes in Liver Efferocytosis

Toxic substances and microbial or food-derived antigens continuously challenge the liver, which is tasked with their safe neutralization. This vital organ is also important for the removal of apoptotic immune cells during inflammation and has been previously described as a “graveyard” for dying lymphocytes. The clearance of apoptotic and necrotic cells is known as efferocytosis and is a critical liver function to maintain tissue homeostasis. Much of the research into this form of immunological control has focused on Kupffer cells, the liver-resident macrophages. However, hepatocytes (and other liver resident cells) are competent efferocytes and comprise 80% of the liver mass. Little is known regarding the mechanisms of apoptotic and necrotic cell capture by epithelia, which lack key receptors that mediate phagocytosis in macrophages. Herein, we discuss recent developments that increased our understanding of efferocytosis in tissues, with a special focus on the liver parenchyma. We discuss the impact of efferocytosis in health and in inflammation, highlighting the role of phagocytic epithelia.

The Synergistic Role of Light-Feeding Phase Relations on Entraining Robust Circadian Rhythms in the Periphery

The feeding and fasting cycles are strong behavioral signals that entrain biological rhythms of the periphery. The feeding rhythms synchronize the activities of the metabolic organs, such as liver, synergistically with the light/dark cycle primarily entraining the suprachiasmatic nucleus. The likely phase misalignment between the feeding rhythms and the light/dark cycles appears to induce circadian disruptions leading to multiple physiological abnormalities motivating the need to investigate the mechanisms behind joint light-feeding circadian entrainment of peripheral tissues. To address this question, we propose a semimechanistic mathematical model describing the circadian dynamics of peripheral clock genes in human hepatocyte under the control of metabolic and light rhythmic signals. The model takes the synergistically acting light/dark cycles and feeding rhythms as inputs and incorporates the activity of sirtuin 1, a cellular energy sensor and a metabolic enzyme activated by nicotinamide adenine dinucleotide. The clock gene dynamics was simulated under various light-feeding phase relations and intensities, to explore the feeding entrainment mechanism as well as the convolution of light and feeding signals in the periphery. Our model predicts that the peripheral clock genes in hepatocyte can be completely entrained to the feeding rhythms, independent of the light/dark cycle. Furthermore, it predicts that light-feeding phase relationship is a critical factor in robust circadian oscillations.

Nonstructural 5A Protein of Hepatitis C Virus Interferes with Toll-Like Receptor Signaling and Suppresses the Interferon Response in Mouse Liver

The hepatitis C virus nonstructural protein NS5A is involved in resistance to the host immune response, as well as the viral lifecycle such as replication and maturation. Here, we established transgenic mice expressing NS5A protein in the liver and examined innate immune responses against lipopolysaccharide (LPS) in vivo. Intrahepatic gene expression levels of cytokines such as interleukin-6, tumor necrosis factor-α, and interferon-γ were significantly suppressed after LPS injection in the transgenic mouse liver. Induction of the C-C motif chemokine ligand 2, 4, and 5 was also suppressed. Phosphorylation of the signal transducer and activator of transcription 3, which is activated by cytokines, was also reduced, and expression levels of interferon-stimulated genes, 2’-5’ oligoadenylate synthase, interferon-inducible double-stranded RNA-activated protein kinase, and myxovirus resistance 1 were similarly suppressed. Since LPS binds to toll-like receptor 4 and stimulates the downstream pathway leading to induction of these genes, we examined the extracellular signal-regulated kinase and IκB-α. The phosphorylation levels of these molecules were reduced in transgenic mouse liver, indicating that the pathway upstream of the molecules was disrupted by NS5A. Further analyses revealed that the interaction between interleukin-1 receptor-associated kinase-1 and tumor necrosis factor receptor associated factor-6 was dispersed in transgenic mice, suggesting that NS5A may interfere with this interaction via myeloid differentiation primary response gene 88, which was shown to interact with NS5A. Since the gut microbiota, a source of LPS, is known to be associated with pathological conditions in liver diseases, our results suggest the involvement of NS5A in the pathogenesis of HCV infected-liver via the suppression of innate immunity.

Prolonged Endoplasmic Reticulum-Stressed Hepatocytes Drive an Alternative Macrophage Polarization

Relatively little is known about the effects of hepatocytes on hepatic macrophages, particularly under the situation of endoplasmic reticulum (ER) stress. We examined the effects of hepatocytes conditioned media (CM) from HepG2 treated with ER stress inducers, tunicamycin or thapsigargin, on the secretion of cytokines, expression of ER stress markers, and polarization of phorbol myristate acetate-activated THP-1 cells (pTHP-1). We found that CM decreased the production of the proinflammatory cytokines including tumor necrosis factor α, interleukin 6 (IL-6), and IL-1β as well as other cytokines and chemokines from pTHP-1 cells. These effects are mediated by the inhibition of TLR4 expression and nuclear factor κB signaling pathway. In addition, hepatocytes CM increased the expression of binding immunoglobulin protein and the transcription factor C/EBP homologous protein (CHOP) in pTHP-1 cells. Preconditioning with ER stress inhibitor, small molecular chaperone 4-phenylbutyrate before addition of ER stressors, attenuated the ER stress in macrophages, the property of hepatocytes CM to alter tumor necrosis factor α production and nuclear factor κB expression by macrophages. Remarkably, treatment of macrophage with these CM leads to an alternative activation of macrophages mediated by peroxisome proliferator-activated receptor γ signaling pathway, which might be resulted from the secretion of IL-10 and IL-4 as well as releasing apoptotic bodies from hepatocytes under ER stress. Our results highlight a mechanism of ER stress transmission from hepatocytes to macrophage that drives an alternative activation of macrophages, which depends on the exposure of hepatocytes to severe and prolonged ER stress.

Myeloperoxidase-Hepatocyte-Stellate Cell Cross Talk Promotes Hepatocyte Injury and Fibrosis in Experimental Nonalcoholic Steatohepatitis

AIMS

Myeloperoxidase (MPO), a highly oxidative enzyme secreted by leukocytes has been implicated in human and experimental nonalcoholic steatohepatitis (NASH), but the underlying mechanisms remain unknown. In this study, we investigated how MPO contributes to progression from steatosis to NASH.

RESULTS

In C57Bl/6J mice fed a diet deficient in methionine and choline to induce NASH, neutrophils and to a lesser extent inflammatory monocytes are markedly increased compared with sham mice and secrete abundant amounts of MPO. Through generation of HOCl, MPO directly causes hepatocyte death in vivo. In vitro experiments demonstrate mitochondrial permeability transition pore induction via activation of SAPK/JNK and PARP. MPO also contributes to activation of hepatic stellate cells (HSCs), the most important source of collagen in the liver. In vitro MPO-activated HSCs have an activation signature (MAPK and PI3K-AKT phosphorylation) and upregulate COL1A1, α-SMA, and CXCL1. MPO-derived oxidative stress also activates transforming growth factor β (TGF-β) in vitro, and TGF-β signaling inhibition with SB-431542 decreased steatosis and fibrosis in vivo. Conversely, congenital absence of MPO results in reduced hepatocyte injury, decreased levels of TGF-β, fewer activated HSCs, and less severe fibrosis in vivo.

INNOVATION AND CONCLUSION

Cumulatively, these findings demonstrate important cross talk between inflammatory myeloid cells, hepatocytes, and HSCs via MPO and establish MPO as part of a proapoptotic and profibrotic pathway of progression in NASH, as well as a potential therapeutic target to ameliorate this disease.

Mesenchymal stem cell-derived exosomes promote hepatic regeneration in drug-induced liver injury models

Introduction

Mesenchymal stem cell-conditioned medium (MSC-CM) has been shown to have protective effects against various cellular-injury models. This mechanism of protection, however, has yet to be elucidated. Recently, exosomes were identified as the active component in MSC-CM. The aim of this study is to investigate the effect of MSC-derived exosomes in an established carbon tetrachloride (CCl₄)-induced liver injury mouse model. This potential effect is then validated by using in vitro xenobiotic-induced liver-injury assays: (1) acetaminophen (APAP)- and (2) hydrogen peroxide (H₂O₂)-induced liver injury.

Methods

The exosomes were introduced concurrent with CCl₄ into a mouse model through different routes of administration. Biochemical analysis was performed based on the blood and liver tissues. Subsequently the exosomes were treated in APAP and H₂O₂-toxicants with in vitro models. Cell viability was measured, and biomarkers indicative of regenerative and oxidative biochemical responses were determined to probe the mechanism of any hepatoprotective activity observed.

Results

In contrast to mice treated with phosphate-buffered saline, CCl₄ injury in mice was attenuated by concurrent-treatment exosomes, and characterized by an increase in hepatocyte proliferation, as demonstrated with proliferating cell nuclear antigen (PCNA) elevation. Significantly higher cell viability was demonstrated in the exosomes-treated group compared with the non-exosome-treated group in both injury models. The higher survival rate was associated with upregulation of the priming-phase genes during liver regeneration, which subsequently led to higher expression of proliferation proteins (PCNA and cyclin D1) in the exosomes-treated group. Exosomes also inhibited the APAP- and H₂O₂-induced hepatocytes apoptosis through upregulation of Bcl-_xL protein expression. However, exosomes do not mitigate hepatocyte injury via modulation of oxidative stress.

Conclusions

In summary, these results suggest that MSC-derived exosomes can elicit hepatoprotective effects against toxicants-induced injury, mainly through activation of proliferative and regenerative responses.

Molecular mechanisms of hepatic apoptosis

Apoptosis is a prominent feature of liver diseases. Causative factors such as alcohol, viruses, toxic bile acids, fatty acids, drugs, and immune response, can induce apoptotic cell death via membrane receptors and intracellular stress. Apoptotic signaling network, including membrane death receptor-mediated cascade, reactive oxygen species (ROS) generation, endoplasmic reticulum (ER) stress, lysosomal permeabilization, and mitochondrial dysfunction, is intermixed each other, but one mechanism may dominate at a particular stage. Mechanisms of hepatic apoptosis are complicated by multiple signaling pathways. The progression of liver disease is affected by the balance between apoptotic and antiapoptotic capabilities. Therapeutic options of liver injury are impacted by the clear understanding toward mechanisms of hepatic apoptosis.

Molecular mechanisms of hepatic apoptosis. Cell Death Dis. 2014;5:e996. [PMID: 24434519 PMCID: PMC4040708 DOI: 10.1038/cddis.2013.499]

Apoptosis is a prominent feature of liver diseases. Causative factors such as alcohol, viruses, toxic bile acids, fatty acids, drugs, and immune response, can induce apoptotic cell death via membrane receptors and intracellular stress. Apoptotic signaling network, including membrane death receptor-mediated cascade, reactive oxygen species (ROS) generation, endoplasmic reticulum (ER) stress, lysosomal permeabilization, and mitochondrial dysfunction, is intermixed each other, but one mechanism may dominate at a particular stage. Mechanisms of hepatic apoptosis are complicated by multiple signaling pathways. The progression of liver disease is affected by the balance between apoptotic and antiapoptotic capabilities. Therapeutic options of liver injury are impacted by the clear understanding toward mechanisms of hepatic apoptosis.

Chemokines in chronic liver allograft dysfunction pathogenesis and potential therapeutic targets

Despite advances in immunosuppressive drugs, long-term success of liver transplantation is still limited by the development of chronic liver allograft dysfunction. Although the exact pathogenesis of chronic liver allograft dysfunction remains to be established, there is strong evidence that chemokines are involved in organ damage induced by inflammatory and immune responses after liver surgery. Chemokines are a group of low-molecular-weight molecules whose function includes angiogenesis, haematopoiesis, mitogenesis, organ fibrogenesis, tumour growth and metastasis, and participating in the development of the immune system and in inflammatory and immune responses. The purpose of this review is to collect all the research that has been done so far concerning chemokines and the pathogenesis of chronic liver allograft dysfunction and helpfully, to pave the way for designing therapeutic strategies and pharmaceutical agents to ameliorate chronic allograft dysfunction after liver transplantation.

Macrophage secretory products induce an inflammatory phenotype in hepatocytes

AIM: To investigate the influence of macrophages on hepatocyte phenotype and function.

METHODS: Macrophages were differentiated from THP-1 monocytes via phorbol myristate acetate stimulation and the effects of monocyte or macrophage-conditioned medium on HepG2 mRNA and protein expression determined. The in vivo relevance of these findings was confirmed using liver biopsies from 147 patients with hepatitis C virus (HCV) infection.

RESULTS: Conditioned media from macrophages, but not monocytes, induced a transient morphological change in hepatocytes associated with upregulation of vimentin (7.8 ± 2.5-fold, P = 0.045) and transforming growth factor (TGF)-β1 (2.6 ± 0.2-fold, P < 0.001) and downregulation of epithelial cadherin (1.7 ± 0.02-fold, P = 0.017) mRNA expression. Microarray analysis revealed significant upregulation of lipocalin-2 (17-fold, P < 0.001) and pathways associated with inflammation, and substantial downregulation of pathways related to hepatocyte function. In patients with chronic HCV, real-time polymerase chain reaction and immunohistochemistry confirmed an increase in lipocalin-2 mRNA (F0 1.0 ± 0.3, F1 2.2 ± 0.2, F2 3.0 ± 9.3, F3/4 4.0 ± 0.8, P = 0.003) and protein expression (F1 1.0 ± 0.5, F2 1.3 ± 0.4, F3/4 3.6 ± 0.4, P = 0.014) with increasing liver injury. High performance liquid chromatography-tandem mass spectrometry analysis identified elevated levels of matrix metalloproteinase (MMP)-9 in macrophage-conditioned medium, and a chemical inhibitor of MMP-9 attenuated the change in morphology and mRNA expression of TGF-β1 (2.9 ± 0.2 vs 1.04 ± 0.1, P < 0.001) in macrophage-conditioned media treated HepG2 cells. In patients with chronic HCV infection, hepatic mRNA expression of CD163 (F0 1.0 ± 0.2, F1/2 2.8 ± 0.3, F3/4 5.3 ± 1.0, P = 0.001) and MMP-9 (F0 1.0 ± 0.4, F1/2 2.8 ± 0.3, F3/4 4.1 ± 0.8, P = 0.011) was significantly associated with increasing stage of fibrosis.

CONCLUSION: Secreted macrophage products alter the phenotype and function of hepatocytes, with increased expression of inflammatory mediators, suggesting that hepatocytes actively participate in liver injury.

Defense Mechanisms of Hepatocytes Against Burkholderia pseudomallei

The Gram-negative facultative intracellular rod Burkholderia pseudomallei causes melioidosis, an infectious disease with a wide range of clinical presentations. Among the observed visceral abscesses, the liver is commonly affected. However, neither this organotropism of B. pseudomallei nor local hepatic defense mechanisms have been thoroughly investigated so far. Own previous studies using electron microscopy of the murine liver after systemic infection of mice indicated that hepatocytes might be capable of killing B. pseudomallei. Therefore, the aim of this study was to further elucidate the interaction of B. pseudomallei with these cells and to analyze the role of hepatocytes in anti-B. pseudomallei host defense. In vitro studies using the human hepatocyte cell line HepG2 revealed that B. pseudomallei can invade these cells. Subsequently, B. pseudomallei is able to escape from the vacuole, to replicate within the cytosol of HepG2 cells involving its type 3 and type 6 secretion systems, and to induce actin tail formation. Furthermore, stimulation of HepG2 cells showed that IFNγ can restrict growth of B. pseudomallei in the early and late phase of infection whereas the combination of IFNγ, IL-1β, and TNFα is required for the maximal antibacterial activity. This anti-B. pseudomallei defense of HepG2 cells did not seem to be mediated by inducible nitric oxide synthase-derived nitric oxide or NADPH oxidase-derived superoxide. In summary, this is the first study describing B. pseudomallei intracellular life cycle characteristics in hepatocytes and showing that IFNγ-mediated, but nitric oxide- and reactive oxygen species-independent, effector mechanisms are important in anti-B. pseudomallei host defense of hepatocytes.

Perturbations in ataxia telangiectasia mutant signaling pathways after drug-induced acute liver failure and their reversal during rescue of animals by cell therapy

Superior insights into molecular mechanisms of liver failure, which are not fully understood, will help strategies for inducing liver regeneration. We examined hepatotoxic mechanisms in mice homozygous for the severe combined immune deficiency mutation in the protein kinase, DNA-activated, catalytic polypeptide. Mice were treated with rifampicin, phenytoin, and monocrotaline. The ensuing acute liver failure was characterized by serological, histological, and mRNA studies. Subsequently, we studied whether transplantation of hepatocytes could rescue animals with liver failure. We found extensive liver damage in these animals, with mortality over several days. The expression of multiple hepatic genes was rapidly altered, including those representing pathways in oxidative/metabolic stress, inflammation, DNA damage-repair, and ataxia telangiectasia mutant (Atm) signaling pathways. This led to liver cell growth arrest involving cyclin-dependent kinase inhibitor 1A. Transplantation of hepatocytes with microcarriers in the peritoneal cavity efficiently rescued animals with liver failure. Molecular abnormalities rapidly reversed, including in hepatic Atm and downstream signaling pathways; and residual hepatocytes overcame cyclin-dependent kinase inhibitor 1A-induced cell growth arrest. Reseeding of the liver with transplanted hepatocytes was not required for rescue because native hepatocytes overcame cell growth-arrest to regenerate the liver. This likely resulted from paracrine signaling from hepatocytes in the peritoneal cavity. We concluded that Atm signaling played critical roles in the pathological features of liver failure. These studies should help redirect examination of pathophysiologic and therapeutic mechanisms in liver failure.

HCV+ hepatocytes induce human regulatory CD4+ T cells through the production of TGF-beta

Background

Hepatitis C Virus (HCV) is remarkably efficient at establishing persistent infection and is associated with the development of chronic liver disease. Impaired T cell responses facilitate and maintain persistent HCV infection. Importantly, CD4⁺ regulatory T cells (Tregs) act by dampening antiviral T cell responses in HCV infection. The mechanism for induction and/or expansion of Tregs in HCV is unknown.

Methodology/Principal Findings

HCV-expressing hepatocytes were used to determine if hepatocytes are able to induce Tregs. The infected liver environment was modeled by establishing the co-culture of the human hepatoma cell line, Huh7.5, containing the full-length genome of HCV genotype 1a (Huh7.5-FL) with activated CD4⁺ T cells. The production of IFN-γ was diminished following co-culture with Huh7.5-FL as compared to controls. Notably, CD4⁺ T cells in contact with Huh7.5-FL expressed an increased level of the Treg markers, CD25, Foxp3, CTLA-4 and LAP, and were able to suppress the proliferation of effector T cells. Importantly, HCV⁺ hepatocytes upregulated the production of TGF-β and blockade of TGF-β abrogated Treg phenotype and function.

Conclusions/Significance

These results demonstrate that HCV infected hepatocytes are capable of directly inducing Tregs development and may contribute to impaired host T cell responses.

Hepatic steatosis causes induction of the chemokine RANTES in the absence of significant hepatic inflammation

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum ranging from simple steatosis to cirrhosis. Hepatocellular lipid accumulation is a hallmark of both nonalcoholic steatosis and steatohepatitis (NASH). The latter develops upon pro-inflammatory cell infiltration and is widely considered as the first relevant pathophysiological step in NAFLD-progression. The chemokine CCL5/RANTES plays an important role in the progression of hepatic inflammation and fibrosis. We here aimed to investigate its expression in NAFLD. Incubation of primary human hepatocytes with palmitic acid induced a dose-dependent lipid accumulation, and corresponding dose-dependent RANTES induction in vitro. Furthermore, we observed significantly elevated hepatic RANTES expression in a dietary model of NAFLD, in which mice were fed a high-fat diet for 12 weeks. This diet induced significant hepatic steatosis but only minimal inflammation. In contrast to the liver, RANTES expression was not induced in visceral adipose tissue of the group fed with high-fat diet. Finally, RANTES serum levels were elevated in patients with ultrasound-diagnosed NAFLD. In conclusion, our data indicate hepatocytes as cellular source of elevated hepatic as well as circulating RANTES levels in response to hepatic steatosis. Noteworthy, upregulation of RANTES in response to lipid accumulation occurs in the absence of relevant inflammation, which further indicates that hepatic steatosis per se has pathophysiological relevance and should not be considered as benign.

Networks inferred from biochemical data reveal profound differences in toll-like receptor and inflammatory signaling between normal and transformed hepatocytes

Systematic study of cell signaling networks increasingly involves high throughput proteomics, transcriptional profiling, and automated literature mining with the aim of assembling large scale interaction networks. In contrast, functional analysis of cell signaling usually focuses on a much smaller sets of proteins and eschews computation but focuses directly on cellular responses to environment and perturbation. We sought to combine these two traditions by collecting cell response measures on a reasonably large scale and then attempting to infer differences in network topology between two cell types. Human hepatocytes and hepatocellular carcinoma cell lines were exposed to inducers of inflammation, innate immunity, and proliferation in the presence and absence of small molecule drugs, and multiplex biochemical measurement was then performed on intra- and extracellular signaling molecules. We uncovered major differences between primary and transformed hepatocytes with respect to the engagement of toll-like receptor and NF-κB-dependent secretion of chemokines and cytokines that prime and attract immune cells. Overall, our results serve as a proof of principle for an approach to network analysis that is systematic, comparative, and biochemically focused. More specifically, our data support the hypothesis that hepatocellular carcinoma cells down-regulate normal inflammatory and immune responses to avoid immune editing.

Genome-wide comparison between IL-17 and combined TNF-alpha/IL-17 induced genes in primary murine hepatocytes

Background

Cytokines such as TNF-alpha and IL-1beta are known for their contribution to inflammatory processes in liver. In contrast, the cytokine IL-17 has not yet been assigned a role in liver diseases. IL-17 can cooperate with TNF-alpha to induce a synergistic response on several target genes in different cell lines, but no data exist for primary hepatocytes. To enhance our knowledge on the impact of IL-17 alone and combined with TNF-alpha in primary murine hepatocytes a comprehensive microarray study was designed. IL-1beta was included as this cytokine is suggested to act in a similar manner as the combination of TNF-alpha and IL-17, especially with respect to its role in mRNA stabilization.

Results

The present microarray analysis demonstrates that primary murine hepatocytes responded to IL-17 stimulation by upregulation of chemokines and genes, which are functionally responsible to increase and sustain inflammation. Cxcl2, Nfkbiz and Zc3h12a were strongly induced, whereas the majority of the genes were only very moderately up-regulated. Promoter analysis revealed involvement of NF-kappaB in the activation of many genes. Combined stimulation of TNF-alpha/IL-17 resulted in enhanced induction of gene expression, but significantly synergistic effects could be applied only to a few genes, such as Nfkbiz, Cxcl2, Zc3h12 and Steap4. Comparison of the gene expression profile obtained after stimulation of TNF-alpha/IL-17 versus IL-1beta proposed an "IL-1beta-like effect" of the latter cytokine combination. Moreover, evidence was provided that modulation of mRNA stability may be a major mechanism by which IL-17 regulates gene expression in primary hepatocytes. This assumption was exemplarily proven for Nfkbiz mRNA for the first time in hepatocytes. Our studies also suggest that RNA stability can partially be correlated to the existence of AU rich elements, but further mechanisms like the RNase activity of the up-regulated Zc3h12a have to be considered.

Conclusions

Our microarray analysis gives new insights in IL-17 induced gene expression in primary hepatocytes highlighting the crosstalk with the NF-kappaB signaling pathway. Gene expression profile suggests IL-17 alone and in concert with TNF-alpha a role in sustaining liver inflammatory processes. IL-17 might exceed this function by RNA stabilization.

Cytotoxic T cell immunity against the non-immunogenic, murine, hepatocellular carcinoma Hepa1-6 is directed towards the novel alternative form of macrophage colony stimulating factor

Mouse Hepa1-6 hepatocellular carcinoma (HCC) cells were transduced with the membrane form of macrophage colony stimulating factor (mM-CSF). When mM-CSF transduced Hepa1-6 cells were injected subcutaneously into mice, these cells did not form tumors. The spleens of these immunized mice contained cytotoxic CD8+ T lymphocytes (CTL) that killed the unmodified Hepa1-6 cells. We show that the alternative form of macrophage colony stimulating factor (altM-CSF) induced CTL-mediated immunity against Hepa1-6 cells. AltM-CSF is restricted to the H-2D(b) allele. CTLs killed RMA-S cells loaded with exogenous altM-CSF peptide. Vaccination of mice with dendritic cells pulsed with the altM-CSF peptide stimulated anti-Hepa1-6 CTLs. Hyper-immunization of mice with mM-CSF Hepa1-6 cells showed inflammation of the liver and kidneys. Although altM-CSF was expressed within liver and kidney cells, its intensity was lower than Hepa1-6 cells. AltM-CSF was detected within the human HepG2 cell line. These studies suggest that altM-CSF may be a tumor antigen for HCC.

Rat hepatocyte invasion by Listeria monocytogenes and analysis of TNF-alpha role in apoptosis

Listeria monocytogenes, etiological agent of severe human foodborne infection, uses sophisticated mechanisms of entry into host cytoplasm and manipulation of the cellular cytoskeleton, resulting in cell death. The host cells and bacteria interaction may result in cytokine production as Tumor Necrosis Factor (TNF) alpha. Hepatocytes have potential to produce pro-inflammatory cytokines as TNF-alpha when invaded by bacteria. In the present work we showed the behavior of hepatocytes invaded by L. monocytogenes by microscopic analysis, determination of TNF-alpha production by bioassay and analysis of the apoptosis through TUNEL technique. The presence of bacterium, in ratios that ranged from 5 to 50,000 bacteria per cell, induced the rupture of cellular monolayers. We observed the presence of internalized bacteria in the first hour of incubation by electronic microscopy. The levels of TNF-alpha increased from first hour of incubation to sixth hour, ranging from 0 to 3749 pg/mL. After seven and eight hours of incubation non-significant TNF-alpha levels decrease occurred, indicating possible saturation of cellular receptors. Thus, the quantity of TNF-alpha produced by hepatocytes was dependent of the incubation time, as well as of the proportion between bacteria and cells. The apoptosis rate increased in direct form with the incubation time (1 h to 8 + 24 h), ranging from 0 to 43%, as well as with the bacteria : cells ratio. These results show the ability of hepatocyte invasion by non-hemolytic L. monocytogenes, and the main consequences of this phenomenon were the release of TNF-alpha by hepatocytes and the induction of apoptosis. We speculate that hepatocytes use apoptosis induced by TNF-alpha for release bacteria to extracellular medium. This phenomenon may facilitate the bacteria destruction by the immune system.

Hepatic interleuklin 15 (IL-15) expression: implications for local NK/NKT cell homeostasis and development

Interleukin 15 (IL-15) is critical for the development of human and murine natural killer (NK) cells and hepatic-derived NK T cells (NKT) in mice, and for the homeostatic maintenance of NK/NKT and CD8(+) memory T cells. The lymphocyte repertoire of an adult human liver includes significant populations of NK and NKT-like cells, which may arise locally from hepatic haematopoietic stem cells (HSCs). We investigated hepatic IL-15 levels and the expression of IL-2/IL-15-receptor beta-chain (IL-2/IL-15Rbeta; CD122) on mature hepatic lymphocytes and HSCs. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect secreted/intracellular IL-15 transcripts. IL-15 protein was localized using immunohistochemistry; levels were measured by enzyme-linked immunosorbent assay IL-2/IL-15Rbeta expression by flow-cytometry. Normal hepatic IL-15 protein was detected at 0.43 ng/100 mg total protein (n = 11, range 0.10 ng-0.9 ng). There was a significant increase in HCV-infected tissue (1.78 ng, P < 0.005, n = 11, range 0.18-2.43 ng). The staining pattern suggests that infiltrating monocytes and tissue resident Kupffer cells are the main producers. IL-15 protein was detected in supernatants from cultured liver biopsy specimens in the absence of stimulation (mean 175.8 pg/100 mg wet tissue, n = 3), which increased significantly upon stimulation (P < 0.05, mean 231.21 pg). On average, 61% of hepatic HSCs expressed IL-2/IL-15Rbeta suggesting a local lymphopoietic role. Eighty per cent of NK and 45.8% of CD56(+) T cells expressed IL-2/IL-15Rbeta, suggesting involvement in local CD56(+) cell activation and expansion. Constitutive expression of IL-15 protein and IL-2/IL-15Rbeta on hepatic lymphocytes suggests a key role in the generation and maintenance of the unique hepatic lymphoid repertoire. The significant increase observed in HCV-infected liver suggests a role for IL-15 in host antiviral responses in the liver.

Limited role for CXC chemokines in the pathogenesis of alpha-naphthylisothiocyanate-induced liver injury

Alpha-naphthylisothiocyanate (ANIT) is a hepatotoxin that causes severe neutrophilic inflammation around portal tracts and bile ducts. The chemotactic signals that provoke this inflammatory response are unknown. In this study, we addressed the possibility that ANIT upregulates CXC chemokines in the liver and that these compounds mediate hepatic inflammation and tissue injury after ANIT treatment. Mice treated with a single dose of ANIT (50 mg/kg) exhibited rapid hepatic induction of the CXC chemokine macrophage inflammatory protein-2 (MIP-2). MIP-2 derived primarily from hepatocytes, with no apparent contribution by biliary cells. In ANIT-treated mice, the induction of MIP-2 coincided with an influx of neutrophils to portal zones; this hepatic neutrophil recruitment was suppressed by 50% in mice that lack the receptor for MIP-2 (CXCR2(-/-)). Interestingly, despite their markedly reduced degree of hepatic inflammation, CXCR2(-/-) mice displayed just as much hepatocellular injury and cholestasis after ANIT treatment as wild-type mice. Moreover, after long-term exposure, ANIT CXCR2(-/-) mice developed liver fibrosis that was indistinguishable from that in wild-type mice. In summary, our data show that CXC chemokines are responsible for some of the hepatic inflammation that occurs in response to ANIT but that these compounds are not essential to the pathogenesis of either acute or chronic ANIT hepatotoxicity.

Human hepatic stellate cells express CCR5 and RANTES to induce proliferation and migration

Activated hepatic stellate cells (HSCs) are the main producers of extracellular matrix in the fibrotic liver and are involved in the regulation of hepatic inflammation. The aim of this study was to characterize the role of regulated on activation, normal T-cell expressed, and presumably secreted (RANTES) in activated HSCs. RANTES mRNA and protein secretion were strongly induced after stimulating HSCs with TNF-alpha, IL-1beta, or CD40L. RANTES production was NF-kappaB dependent, because inhibitor-kappaB (IkappaB) superrepressor and dominant-negative IkappaB kinase-2 almost completely blocked RANTES expression. NF-kappaB activation was sufficient to drive RANTES expression as demonstrated by the strong induction of RANTES in HSCs expressing NF-kappaB-inducing kinase. The JNK/activator protein-1 pathway also contributed to RANTES expression as demonstrated by the blocking effects of the JNK inhibitor SP600125. HSCs responded to stimulation with recombinant human (rh)RANTES with an increase in intracellular calcium concentration and a rapid increase in free radical formation. Furthermore, rhRANTES induced ERK phosphorylation, ERK-dependent [3H]thymidine incorporation, and HSC proliferation. Additionally, rhRANTES induced focal adhesion kinase phosphorylation and a substantial increase in HSC migration. HSCs functionally expressed chemokine receptor-5 (CCR5), as shown by flow-cytometric analysis and RT-PCR, and the inhibitory effects of a blocking CCR5 antibody on rhRANTES-induced ERK activation, proliferation, and migration. Diphenylene iodonium and N-acetylcysteine inhibited rhRANTES-induced ERK activation and HSC proliferation, indicating that NADPH oxidase-dependent production of reactive oxygen species was required. In conclusion, RANTES and CCR5 represent potential mediators of 1) HSC migration and proliferation and 2) a cross-talk between HSCs and leukocytes during fibrogenesis.

HGF-, EGF-, and dexamethasone-induced gene expression patterns during formation of tissue in hepatic organoid cultures

Corticosteroids, hepatocyte growth factor (HGF), and epidermal growth factor (EGF) play important roles in hepatic biology. We have previously shown that these molecules are required for formation of tissue with specific histology in complex organoid cultures. Dexamethasone suppresses growth and induces hepatocyte maturation; HGF and EGF are needed for formation of the nonepithelial elements. All three are needed for formation of the biliary epithelium. The gene expression patterns by which corticosteroids, HGF, and EGF mediate their effects in hepatic tissue formation are distinct. These patterns affect many gene families and are described in detail. In terms of main findings, dexamethasone induces expression of both HNF4 and C/EBPalpha, essential transcription factors for hepatocyte differentiation. It suppresses hepatocyte growth by suppressing many molecules associated with growth in liver and other tissues, including IL-6, CXC-chemokine receptor, amphiregulin, COX-2, HIF, etc. HGF and EGF induce all members of the TGF-beta family. They also induced multiple CNS-related genes, probably associated with stellate cells. Dexamethasone, as well as HGF and EGF, induces expression of HNF6-beta, associated with biliary epithelium formation. Combined addition of all three molecules is associated with mature histology in which hepatocyte and biliary lineages are separate and HNF4 is expressed only in hepatocyte nuclei. In conclusion, the results provide new and surprising information on the gene expression alterations by which corticosteroids, HGF, and EGF exert their effects on formation of hepatic tissue. The results underscore the usefulness of the organoid cultures for generating information on histogenesis, which cannot be obtained by other culture or whole animal models.

Exaggerated hepatic injury due to acetaminophen challenge in mice lacking C-C chemokine receptor 2

Monocyte chemoattractant protein-1 is one of the major C-C chemokines that has been implicated in liver injury. The C-C chemokine receptor, CCR2, has been identified as the primary receptor that mediates monocyte chemoattractant protein-1 (MCP-1) responses in the mouse. Accordingly, the present study addressed the role of CCR2 in mice acutely challenged with acetaminophen (APAP). Mice genetically deficient in CCR2 (CCR2(-/-)) and their wild-type counterparts (CCR2(+/+)) were fasted for 10 hours before receiving an intraperitoneal injection of APAP (300 mg/kg). Liver and serum samples were removed from both groups of mice before and at 24 and 48 hours post APAP. Significantly elevated levels of MCP-1 were detected in liver samples from CCR2(+/+) and CCR2(-/-) mice at 24 hours post-APAP. Although CCR2(+/+) mice exhibited no liver injury at any time after receiving APAP, CCR2(-/-) mice exhibited marked evidence of necrotic and TUNEL-positive cells in the liver, particularly at 24 hours post-APAP. Enzyme-linked immunosorbent assay analysis of liver homogenates from both groups of mice at the 24 hours time point revealed that liver tissue from CCR2(-/-) mice contained significantly greater amounts of immunoreactive IFN-gamma and TNF-alpha. The in vivo immunoneutralization of IFN-gamma or TNF-alpha significantly attenuated APAP-induced liver injury in CCR2(-/-) mice and increased hepatic IL-13 levels. Taken together, these findings demonstrate that CCR2 expression in the liver provides a hepatoprotective effect through its regulation of cytokine generation during APAP challenge.

The Human Liver Contains Multiple Populations of NK Cells, T Cells, and CD3+CD56+ Natural T Cells with Distinct Cytotoxic Activities and Th1, Th2, and Th0 Cytokine Secretion Patterns

The human liver contains significant numbers of T cells, NK cells, and lymphocytes that coexpress T and NK cell receptors. To evaluate their functional activities, we have compared the cytotoxic activities and cytokines produced by normal adult hepatic CD3+CD56− (T) cells, CD3−CD56+ (NK) cells, and CD3+CD56+ (natural T (NT)) cells. In cytotoxicity assays using immunomagnetic bead-purified NK cell, T cell, and NT cell subpopulations as effectors, fresh hepatic NK cells lysed K562 targets, while NT cells could be induced to do so by culturing with IL-2. Both NT and T cells were capable of redirected cytolysis of P815 cells using Abs to CD3. Flow cytometric analysis of cytokine production by fresh hepatic lymphocyte subsets activated by CD3 cross-linking or PMA and ionomycin stimulation indicated that NT cells and T cells could produce IFN-γ, TNF-α, IL-2, and/or IL-4, but little or no IL-5, while NK cells produced IFN-γ and/or TNF-α only. The majority of NT cells produced inflammatory (Th1) cytokines only; however, ∼6% of all hepatic T cells, which included 5% of Vα24 TCR-bearing NT cells and 2% of γδTCR+ cells, simultaneously produced IFN-γ and IL-4. The existence of such large numbers of cytotoxic lymphocytes with multiple effector functions suggests that the liver is an important site of innate immune responses, early regulation of adaptive immunity, and possibly peripheral deletion of autologous cells.

On the Role of Feedback in Promoting Conflicting Goals of the Adaptive Immune System

We explored here the implications of two premises. 1) In their response over days or weeks to pathogen invasion, cells of the immune system combine several overlapping and perhaps contradictory goals. 2) The immune system has ways to monitor progress toward these goals via receptors that bind chemicals whose concentrations are related to such progress. We illustrate with simple mathematical models how such monitoring can lead to feedbacks that improve the efficiency of a given effector type in accomplishing its specialized task, and also how feedbacks can shift the balance among a variety of effectors toward a preponderance of the more effective. Specific suggestions are given for feedback molecules.

Adhesion of lymphocytes to hepatic endothelium

Chronic inflammation occurs when factors that regulate the process of leucocyte recruitment are disrupted, and it is dependent on recruitment, activation, and retention of lymphocytes within tissue microenvironments. The molecular mechanisms that mediate lymphocyte adhesion to vascular endothelial cells have been described by several groups, but the signals involved in the recruitment of lymphocytes via the hepatic circulation have yet to be elucidated fully. This article considers the liver as a model of organ specific lymphocyte recruitment. In this context, the roles of leucocyte and endothelial adhesion molecules and chemokines in lymphocyte recruitment are discussed. The article also reviews the mechanisms that regulate lymphocyte recirculation to the liver under both physiological and pathological conditions and draws parallels with other organs such as the gut and skin.

Macrophage Inflammatory Protein-2 Is Required for Neutrophil Passage Across the Epithelial Barrier of the Infected Urinary Tract

IL-8 is a major human neutrophil chemoattractant at mucosal infection sites. This study examined the C-X-C chemokine response to mucosal infection, and, specifically, the role of macrophage inflammatory protein (MIP)-2, one of the mouse IL-8 equivalents, for neutrophil-epithelial interactions. Following intravesical Escherichia coli infection, several C-X-C chemokines were secreted into the urine, but only MIP-2 concentrations correlated to neutrophil numbers. Tissue quantitation demonstrated that kidney MIP-2 production was triggered by infection, and immunohistochemistry identified the kidney epithelium as a main source of MIP-2. Treatment with anti-MIP-2 Ab reduced the urine neutrophil numbers, but the mice had normal tissue neutrophil levels. By immunohistochemistry, the neutrophils were found in aggregates under the pelvic epithelium, but in control mice the neutrophils crossed the urothelium into the urine. The results demonstrate that different chemokines direct neutrophil migration from the bloodstream to the lamina propria and across the epithelium and that MIP-2 serves the latter function. These findings suggest that neutrophils cross epithelial cell barriers in a highly regulated manner in response to chemokines elaborated at this site. This is yet another mechanism that defines the mucosal compartment and differentiates the local from the systemic host response.