Toll-like receptor 2 contributes to liver injury by Salmonella infection through Fas ligand expression on NKT cells in mice

RNA Methylation and Transcriptome Analysis Reveal Key Regulatory Pathways Related to Cadmium-Induced Liver Damage

Cadmium (Cd) is a prevalent environmental and industrial contaminant that causes significant damage to liver function. However, the role of m6A methylation─a critical epigenetic modification─in Cd-induced liver injury remains poorly understood. This study aimed to investigate the effects of m6A methylation in Cd-induced liver damage. A mouse model of Cd-induced liver injury was established, and exposure to CdCl2 (20 mg/kg) for 90 days resulted in reduced m6A methylation levels. Using methylated RNA immunoprecipitation sequencing (MeRIP-seq) and RNA sequencing (RNA-Seq), we characterized the m6A methylation profiles in both control and Cd-exposed groups. A total of 8355 unique m6A peaks and 1,101 unique m6A-modified genes were identified. Among these, 673 genes exhibited differential m6A methylated modifications, including 463 hyper-methylated and 210 hypo-methylated genes. Conjoint analysis of MeRIP-seq and RNA-Seq data unveiled genes that showed both differential methylation and expression. These genes were significantly enriched in the AGE-RAGE and PI3K-Akt signaling pathway. Through bioinformatics screening, five key genes (Il-1β, Ccl2, Tlr2, Itgax, and Ccr2) were identified, and expression validation indicated that Itgax and Ccr2 may play pivotal roles in Cd-induced liver injury. Notably, elevated expression of methyltransferase-like 14 (METTL14) was observed in both in vivo and in vitro models. Inhibition of Mettl14 can regulate Cd-induced liver inflammation through m6A-dependent regulation of Ccr2 expression. Collectively, our findings highlight the crucial role of Mettl14 and Ccr2 in Cd-induced liver injury, providing novel insights into the epigenetic mechanisms underlying liver diseases and potential biomarkers for diagnosis and therapy.

Immune checkpoint molecule Tim-3 promotes NKT cell apoptosis and predicts poorer prognosis in Sepsis

BACKGROUND

Sepsis is a leading cause of death among critically ill patients, which is defined as life-threatening organ dysfunction caused by a deregulated host immune response to infection. Immune checkpoint molecule Tim-3 plays important and complex roles in regulating immune responses and in inducing immune tolerance. Although immune checkpoint blockade would be expected as a promising therapeutic strategy for sepsis, but the underlying mechanism remain unknown, especially under clinical conditions.

METHODS

Tim-3 expression and apoptosis in NKT cells were compared in septic patients (27 patients with sepsis and 28 patients with septic shock). Phenotypic and functional characterization of Tim-3+ NKT cells were analysed, and then the relationship between Tim-3 + NKT cells and clinical prognosis were investigated in septic patients. α-lactose (Tim-3/Galectin-9 signalling inhibitor) and Tim-3 mutant mice (targeting mutation of the Tim-3 cytoplasmic domain) were utilized to evaluate the protective effect of Tim-3 signalling blockade following septic challenge.

RESULTS

There is a close correlation between Tim-3 expression and the functional status of NKT cells in septic patients, Upregulated Tim-3 expression promoted NKT cell activation and apoptosis during the early stage of sepsis, and it was associated with worse disease severity and poorer prognosis in septic patients. Blockade of the Tim-3/Galectin-9 signal axis using α-lactose inhibited in vitro apoptosis of NKT cells isolated from septic patients. Impaired activity of Tim-3 protected mice following septic challenge.

CONCLUSIONS

Overall, these findings demonstrated that immune checkpoint molecule Tim-3 in NKT cells plays a critical role in the immunopathogenesis of septic patients. Blockade of immune checkpoint molecule Tim-3 may be a promising immunomodulatory strategy in future clinical practice for the management of sepsis.

Interactions between Dietary Micronutrients, Composition of the Microbiome and Efficacy of Immunotherapy in Cancer Patients

The effectiveness of immunotherapy in cancer patients depends on the activity of the host's immune system. The intestinal microbiome is a proven immune system modulator, which plays an important role in the development of many cancers and may affect the effectiveness of anti-cancer therapy. The richness of certain bacteria in the gut microbiome (e.g., Bifidobacterium spp., Akkermanisa muciniphila and Enterococcus hire) improves anti-tumor specific immunity and the response to anti-PD-1 or anti-PD-L1 immunotherapy by activating antigen-presenting cells and cytotoxic T cells within the tumor. Moreover, micronutrients affect directly the activities of the immune system or regulate their function by influencing the composition of the microbiome. Therefore, micronutrients can significantly influence the effectiveness of immunotherapy and the development of immunorelated adverse events. In this review, we describe the relationship between the supply of microelements and the abundance of various bacteria in the intestinal microbiome and the effectiveness of immunotherapy in cancer patients. We also point to the function of the immune system in the case of shifts in the composition of the microbiome and disturbances in the supply of microelements. This may in the future become a therapeutic target supporting the effects of immunotherapy in cancer patients.

Comparative RNA-Seq analysis reveals insights in Salmonella disease resistance of chicken; and database development as resource for gene expression in poultry

Salmonella, one of the major infectious diseases in poultry, causes considerable economic losses in terms of mortality and morbidity, especially in countries that lack effective vaccination programs. Besides being resistant to diseases, indigenous chicken breeds are also a potential source of animal protein in developing countries. For understanding the disease resistance, an indigenous chicken line Kashmir faverolla, and commercial broiler were selected. RNA-seq was performed after challenging the chicken with Salmonella Typhimurium. Comparative differential expression results showed that following infection, a total of 3153 genes and 1787 genes were differentially expressed in the liver and spleen, respectively. The genes that were differentially expressed included interleukins, cytokines, NOS2, Avβ-defensins, toll-like receptors, and other immune-related gene families. Most of the genes and signaling pathways involved in the innate and adaptive immune responses against bacterial infection were significantly enriched in the Kashmir faverolla. Pathway analysis revealed that most of the enriched pathways were MAPK signaling pathway, NOD-like receptor signaling pathway, TLR signaling pathway, PPAR signaling pathway, endocytosis, etc. Surprisingly some immune-related genes like TLRs were upregulated in the susceptible chicken breed. On postmortem examination, the resistant birds showed small lesions in the liver compared to large necrotic lesions in susceptible birds. The pathological manifestations and RNA sequencing results suggest a balancing link between resistance and infection tolerance in Kashmir faverolla. Here we also developed an online Poultry Infection Database (https://skuastk.org/pif/index.html), the first publicly available gene expression resource for disease resistance in chickens. The available database not only shows the data for gene expression in chicken tissues but also provides quick search, visualization and download capacity.

Interrelationship between Toll-like receptors and infection after orthotopic liver transplantation

Early microbial recognition by the innate immune system is accomplished by Toll-like receptors (TLRs), with resultant initiation of a pro-inflammatory response against infecting organisms. In spite of presence of an abundance of Toll-like receptors on the surface of the liver, gut bacteria does not elicit an inflammatory reaction in healthy individuals due to tolerance to these TLRs, suggesting that the inflammatory responses seen in the liver are the result of breakdown of this tolerance. While orthotopic liver transplantation is often life saving in many instances, death following this procedure is most commonly due to infection that occurs in up to 80% of transplant recipients, most commonly due to microbial causes in up to 70% of cases and viral infections in 20%, while fungal infections affect only 8% of cases. The probability of acquiring infection following hepatic transplantation is heightened due to affection of the innate immune defense mechanisms of the host following this procedure. Single nucleotide polymorphisms of TLRs have been associated with increased likelihood of either development of post-transplant infection or eradication of infecting organism. However, conflicting reports from other studies reveal that prevalence of this single nucleotide polymorphism is not increased in infected patients.

License to Kill: When iNKT Cells Are Granted the Use of Lethal Cytotoxicity

Invariant Natural Killer T (iNKT) cells are a non-conventional, innate-like, T cell population that recognize lipid antigens presented by the cluster of differentiation (CD)1d molecule. Although iNKT cells are mostly known for mediating several immune responses due to their massive and diverse cytokine release, these cells also work as effectors in various contexts thanks to their cytotoxic potential. In this Review, we focused on iNKT cell cytotoxicity; we provide an overview of iNKT cell subsets, their activation cues, the mechanisms of iNKT cell cytotoxicity, the specific roles and outcomes of this activity in various contexts, and how iNKT killing functions are currently activated in cancer immunotherapies. Finally, we discuss the future perspectives for the better understanding and potential uses of iNKT cell killing functions in tumor immunosurveillance.

NKT Cells in Neurological Diseases

Natural killer T (NKT) cells are a unique subset of T lymphocytes with the expression of T cell receptor (TCR) and NK cell lineage receptors. These cells can rapidly release large quantities of cytokines and function as a bridge between innate and adaptive immunity. To date, multiple reports have investigated the role of NKT cells under various pathological conditions, such as cancer, autoimmune disease, and infection. Knowledge about NKT cells in neurological diseases is increasing, albeit limited. Here, we review evidence for the involvement of NKT cells in neurological diseases, and discuss immunotherapeutic potential and future study goals. As the development and function of NKT cells become increasingly well understood, the next few years should yield many new insights into NKT cell function, and mechanistic regulation in neurological disorders.

Immunomodulation by gut microbiota: role of Toll-like receptor expressed by T cells

A close relationship exists between gut microbiota and immune responses. An imbalance of this relationship can determine local and systemic immune diseases. In fact the immune system plays an essential role in maintaining the homeostasis with the microbiota that normally resides in the gut, while, at the same time, the gut microbiota influences the immune system, modulating number and function of effector and regulatory T cells. To achieve this aim, mutual regulation between immune system and microbiota is achieved through several mechanisms, including the engagement of toll-like receptors (TLRs), pathogen-specific receptors expressed on numerous cell types. TLRs are able to recognize ligands from commensal or pathogen microbiota to maintain the tolerance or trigger the immune response. In this review, we summarize the latest evidences about the role of TLRs expressed in adaptive T cells, to understand how the immune system promotes intestinal homeostasis, fights invasion by pathogens, and is modulated by the intestinal microbiota.

Invariant natural killer T cells: boon or bane in immunity to intracellular bacterial infections?

Invariant natural killer T (iNKT) cells represent a specialized subset of innate lymphocytes that recognize lipid and glycolipid antigens presented to them by nonclassical MHC-I CD1d molecules and are able to rapidly secrete copious amounts of a variety of cytokines. iNKT cells possess the ability to modulate innate as well as adaptive immune responses against various pathogens. Intracellular bacteria are one of the most clinically significant human pathogens that effectively evade the immune system and cause a myriad of diseases of public health concern globally. Emerging evidence suggests that iNKT cells can confer immunity to intracellular bacteria but also inflict pathology in certain cases. We summarize the current knowledge on the contribution of iNKT cells in the host defense against intracellular bacterial infections, with a focus on the underlying mechanisms by which these cells induce protective or pathogenic reactions including the pathways of direct action (acting on infected cells) and indirect action (modulating dendritic, NK and T cells). The rational exploitation of iNKT cells for prophylactic and therapeutic purposes awaits a profound understanding of their functional biology.

Toll-like receptor regulation of effector T lymphocyte function

The landmark discovery of pattern-recognition receptors, including Toll-like receptors (TLRs), furthered our understanding on how the host rapidly responds to invading pathogens. For over a decade now, extensive research has demonstrated the crucial role of multiple TLRs in the detection of a broad range of molecules expressed by microbial pathogens as well as host-derived danger signals. TLR activation is the hallmark of the innate immune response. Recent evidence, however, demonstrates that cells of the adaptive immune response use these innate signaling pathways as well. This review discusses recent findings regarding TLR functionality in T lymphocytes with a specific emphasis on the promotion of T helper cell-dependent inflammation through direct TLR signaling.

Central role of liver in anticancer and radioprotective activities of Toll-like receptor 5 agonist

Vertebrate Toll-like receptor 5 (TLR5) recognizes bacterial flagellin proteins and activates innate immune responses to motile bacteria. In addition, activation of TLR5 signaling can inhibit growth of TLR5-expressing tumors and protect normal tissues from radiation and ischemia-reperfusion injuries. To understand the mechanisms behind these phenomena at the organismal level, we assessed nuclear factor kappa B (NF-κB) activation (indicative of TLR5 signaling) in tissues and cells of mice treated with CBLB502, a pharmacologically optimized flagellin derivative. This identified the liver and gastrointestinal tract as primary CBLB502 target organs. In particular, liver hepatocytes were the main cell type directly and specifically responding to systemic administration of CBLB502 but not to that of the TLR4 agonist LPS. To assess CBLB502 impact on other pathways, we created multireporter mice with hepatocytes transduced in vivo with reporters for 46 inducible transcription factor families and found that along with NF-κB, CBLB502 strongly activated STAT3-, phenobarbital-responsive enhancer module (PREM), and activator protein 1 (AP-1-) -driven pathways. Livers of CBLB502-treated mice displayed induction of numerous immunomodulatory factors and massive recruitment of various types of immune cells. This led to inhibition of growth of liver metastases of multiple tumors regardless of their TLR5 status. The changed liver microenvironment was not, however, hepatotoxic, because CBLB502 induced resistance to Fas-mediated apoptosis in normal liver cells. Temporary occlusion of liver blood circulation prevented CBLB502 from protecting hematopoietic progenitors in lethally irradiated mice, indicating involvement of a factor secreted by responding liver cells. These results define the liver as the key mediator of TLR5-dependent effects in vivo and suggest clinical applications for TLR5 agonists as hepatoprotective and antimetastatic agents.

Imaging natural killer T cells in action

Natural killer T (NKT) cells were first recognized more than two decades ago as a distinct lymphocyte lineage that regulates a broad range of immune responses. The activation of NKT cells paradoxically can lead to either suppression or stimulation of immune responses, but despite this uncertainty, many investigators are hopeful that immune therapies can be developed based on NKT cell modulation. To date, the biology of NKT cells is not well characterized and details of their development have only just started to emerge. It remains unclear how NKT cells migrate from the thymus to the peripheral organs and tissues, and in turn play such diverse roles from one type of immune response to another. Despite this, recent advances in intravital microscopy represent a powerful tool for revealing new insights into NKT cellular dynamics, their patrolling and immunoregulatory functions, which could not have been gained by non-microscopy means. Indeed, imaging has revolutionized the way we visualize with exceptional resolution the cells of the immune system. Instead of seeking a comprehensive review of NKT cell biology, this review attempts to highlight some of the recent studies that use in vivo imaging technologies to address NKT cell responses in a variety of animal models.

TLR4-mediated IL-12 production enhances IFN-γ and IL-1β production, which inhibits TGF-β production and promotes antibody-induced joint inflammation

Introduction

Toll-like receptor (TLR)4 promotes joint inflammation in mice. Despite that several studies report a functional link between TLR4 and interleukin-(IL-)1β in arthritis, TLR4-mediated regulation of the complicated cytokine network in arthritis is poorly understood. To address this, we investigated the mechanisms by which TLR4 regulates the cytokine network in antibody-induced arthritis.

Methods

To induce arthritis, we injected mice with K/BxN serum. TLR4-mediated pathogenesis in antibody-induced arthritis was explored by measuring joint inflammation, cytokine levels and histological alteration.

Results

Compared to wild type (WT) mice, TLR4^-/- mice showed attenuated arthritis and low interferon (IFN)-γ, IL-12p35 and IL-1β transcript levels in the joints, but high transforming growth factor (TGF)-β expression. Injection of lipopolysaccharide (LPS) enhanced arthritis and exaggerated joint cytokine alterations in WT, but not TLR4^-/- or IL-12p35^-/- mice. Moreover, STAT4 phosphorylation in joint cells and intracellular IL-12p35 expression in macrophages, mast cells and Gr-1⁺ cells were detected in WT mice with arthritis and enhanced by LPS injection. Therefore, IL-12p35 appears to act downstream of TLR4 in antibody-induced arthritis. TLR4-mediated IL-12 production enhanced IFN-γ and IL-1β production via T-bet and pro-IL-1β production. Recombinant IL-12, IFN-γ and IL-1β administration restored arthritis, but reduced joint TGF-β levels in TLR4^-/- mice. Moreover, a TGF-β blockade restored arthritis in TLR4^-/- mice. Adoptive transfer of TLR4-deficient macrophages and mast cells minimally altered joint inflammation and cytokine levels in macrophage- and mast cell-depleted WT mice, respectively, whereas transfer of WT macrophages or mast cells restored joint inflammation and cytokine expression. Gr-1⁺ cell-depleted splenocytes partially restored arthritis in TLR4^-/- mice.

Conclusion

TLR4-mediated IL-12 production by joint macrophages, mast cells and Gr-1⁺ cells enhances IFN-γ and IL-1β production, which suppresses TGF-β production, thereby promoting antibody-induced arthritis.

Direct engagement of TLR4 in invariant NKT cells regulates immune diseases by differential IL-4 and IFN-γ production in mice

During interaction with APCs, invariant (i) NKT cells are thought to be indirectly activated by TLR4-dependently activated APCs. However, whether TLR4 directly activates iNKT cells is unknown. Therefore, the expression and function of TLR4 in iNKT cells were investigated. Flow cytometric and confocal microscopic analysis revealed TLR4 expression on the surface and in the endosome of iNKT cells. Upon LPS stimulation, iNKT cells enhanced IFN-γ production, but reduced IL-4 production, in the presence of TCR signals, depending on TLR4, MyD88, TRIF, and the endosome. However, enhanced TLR4-mediated IFN-γ production by iNKT cells did not affect IL-12 production or CD1d expression by DCs. Adoptive transfer of WT, but not TLR4-deficient, iNKT cells promoted antibody-induced arthritis in CD1d(-/-) mice, suggesting that endogenous TLR4 ligands modulate iNKT cell function in arthritis. Furthermore, LPS-pretreated WT, but not TLR4-deficient, iNKT cells suppressed pulmonary fibrosis, but worsened hypersensitivity pneumonitis more than untreated WT iNKT cells, indicating that exogenous TLR4 ligands regulate iNKT cell functions in pulmonary diseases. Taken together, we propose a novel direct activation pathway of iNKT cells in the presence of TCR signals via endogenous or exogenous ligand-mediated engagement of TLR4 in iNKT cells, which regulates immune diseases by altering IFN-γ and IL-4 production.

MyD88 signaling promotes both mucosal homeostatic and fibrotic responses during Salmonella-induced colitis

Salmonella enterica serovar Typhimurium is a clinically important gram-negative, enteric bacterial pathogen that activates several Toll-like receptors (TLRs). While TLR signaling through the adaptor protein MyD88 has been shown to promote inflammation and host defense against the systemic spread of S. Typhimurium, curiously, its role in the host response against S. Typhimurium within the mammalian gastrointestinal (GI) tract is less clear. We therefore used the recently described Salmonella-induced enterocolitis and fibrosis model: wild-type (WT) and MyD88-deficient (MyD88(-/-)) mice pretreated with streptomycin and then orally infected with the ΔaroA vaccine strain of S. Typhimurium. Tissues were analyzed for bacterial colonization, inflammation, and epithelial damage, while fibrosis was assessed by collagen quantification and Masson's trichrome staining. WT and MyD88(-/-) mice carried similar intestinal pathogen burdens to postinfection day 21. Infection of WT mice led to acute mucosal and submucosal inflammation and edema, as well as significant intestinal epithelial damage and proliferation, leading to widespread goblet cell depletion. Impressive collagen deposition in the WT intestine was also evident in the submucosa at postinfection days 7 and 21, with fibrotic regions rich in fibroblasts and collagen. While infected MyD88(-/-) mice showed levels of submucosal inflammation and edema similar to WT mice, they were impaired in the development of mucosal inflammation, along with infection-induced epithelial damage, proliferation, and goblet cell depletion. MyD88(-/-) mouse tissues also had fewer submucosal fibroblasts and 60% less collagen. We noted that cyclooxygenase (Cox)-2 expression was MyD88-dependent, with numerous Cox-2-positive cells identified in fibrotic regions of WT mice at postinfection day 7, but not in MyD88(-/-) mice. Treatment of WT mice with the Cox-2 inhibitor rofecoxib (20 mg/kg) significantly reduced fibroblast numbers and collagen levels without altering colitis severity. In conclusion, MyD88 and Cox-2 signaling play roles in intestinal fibrosis during Salmonella-induced enterocolitis.

The invariant NKT cell subset in anti-viral defenses: a dark horse in anti-influenza immunity?

iNKT cells, a small subset of αβ TCR+ T cells, are capable of producing large amounts of cytokines upon activation through their TCR. Unlike conventional T cells that express highly diverse TCRs, iNKT cells express a glycolipid-reactive invariant TCR-α chain paired with a limited number of β chain(s). These cells recognize glycolipid antigens when presented on CD1d molecules found on APC or other cells. Although the immunoregulatory roles of iNKT cells in the context of autoimmune disease are fairly well characterized, several lines of evidence highlight the importance of this cell type in immune responses against microbial insults caused by bacterial, viral, and parasitic pathogens. Recent studies that have investigated the role of iNKT cells in immune responses against influenza virus have suggested an important role for these cells in innate defense mechanisms as well as antibody- and cell-mediated responses. This review highlights the important contributions of iNKT cells to immune responses against viral pathogens with particular emphasis on immunity to influenza infections.

Cytokine dependent and independent iNKT cell activation

Invariant NKT (iNKT) cells have been extensively studied throughout the last decade due to their ability to polarize and amplify the downstream immune response. Only recently however, have the various mechanisms underlying NKT cell activation begun to unfold. iNKT cells have the ability to respond as innate immune cells with minimal TCR involvement as well as through direct TCR recognition of glycolipid antigens. Additionally, the existence of several subsets of iNKT cells creates the potential for other unique pathways, which are not yet clearly defined. Here, we provide an overview of the known mechanisms of invariant NKT cell activation, focusing on cytokine driven pathways and the resulting cytokine responses.

Insights into the role of Toll-like receptors in modulation of T cell responses

The innate immune receptors, such as Toll-like receptors (TLRs), are intimately involved in the early sensing of invading microorganisms or their structural components. Engagement of TLRs with their ligands results in activation of several downstream intracellular pathways leading to activation of innate and adaptive immune system cells. It was initially thought that TLRs are primarily expressed by antigen-presenting cells (APCs), such as macrophages and dendritic cells, and that interactions between microbial ligands and TLRs in these cells will indirectly result in activation of cells of the adaptive immune system, especially T cells. However, it has now become evident that TLRs are also expressed by various T cell subsets, such as conventional αβT cells, regulatory T cells, and γδT cells as well as natural killer T cells. Importantly, it appears that at least in some of these T cell subsets, TLRs are functionally active, because stimulation of these cells with TLR agonists in the absence of APCs results in exertion of effector or regulatory functions of T cells. The present review attempts to summarize the recent findings related to TLR expression in different T cell subsets and the direct role of TLRs in the induction and regulation of T cell responses, including those responses that occur at mucosal surfaces. In addition, the potential use of TLR agonists for steering T cell responses as a prophylactic or therapeutic strategy in the context of infectious, allergic or autoimmune diseases is explored.

Toll-like receptors and adaptor molecules in liver disease: update

Toll-like receptors (TLRs) are pattern recognition receptors that recognize pathogen-associated molecular patterns and signal through adaptor molecules, myeloid differentiation factor 88 (MyD88), Toll/IL-1 receptor domain containing adaptor protein (TIRAP), Toll/IL-1 receptor domain containing adaptor inducing interferon-beta (TRIF), and TRIF-related adaptor molecule (TRAM) to activate transcription factors, nuclear factor (NF)-kappaB, activator protein 1 (AP-1), and interferon regulatory factors (IRFs) leading to the initiation of innate immunity. This system promptly initiates host defenses against invading microorganisms. Endogenous TLR ligands such as the products from dying cells may also engage with TLRs as damage-associated molecular patterns. Although Kupffer cells are considered the primary cells to respond to pathogen associated molecular patterns in the liver, recent studies provide evidence of TLR signaling in hepatic nonimmune cell populations, including hepatocytes, biliary epithelial cells, endothelial cells, and hepatic stellate cells. This review highlights advances in TLR signaling in the liver, the role of TLRs in the individual hepatic cell populations, and the implication of TLR signaling in acute and chronic liver diseases. We further discuss recent advances regarding cytosolic pattern recognition receptors, RNA helicases that represents a new concept in chronic hepatitis C virus infection.

Role of Kupffer cells in the induction of tolerance of orthotopic liver transplantation in rats

Because the role of Kupffer cells (KCs) in liver transplantation (LT) tolerance is not well understood, we investigated their role in liver allograft acceptance in rats. Male Sprague-Dawley rats were randomly assigned to either an LT group or a transplantation group pretreated with GdCl(3) (Gd group). The rats were postoperatively sacrificed at indicated times for histology and assessment of KC function, nuclear factor kappa B (NF-kappaB) activity, and cytokine production. KCs and T cells (TCs) were isolated from allografts to assess Fas/Fas ligand (FasL) expression. Cytotoxicity of KCs against TCs was monitored by coculturing of (3)H-thymidine TCs with KCs at various effector-to-target ratios. The results were as follows. First, grafts were spontaneously accepted in the LT group with evident apoptosis of TCs; however, inhibition of KCs by pretreatment with GdCl(3) decreased TC apoptosis and shortened the survival of allografts. Second, KCs in the LT group had increased levels of FasL messenger RNA and protein with respect to that in the Gd group. Third, by in vitro cocultivation assays, KCs induced TC apoptosis though elevated expression of FasL, and this process could be blocked by anti-FasL antibody. Fourth, there was a positive correlation between activation of NF-kappaB and FasL expression in KCs and interleukin-4 production in the LT group, and the activation of NF-kappaB was inhibited by pretreatment with GdCl(3). In conclusion, KC-induced depletion of TCs via the Fas/FasL pathway might play a critical role in LT tolerance. However, the tolerance is abrogated by suppression of FasL and IL-4 expression via inhibition of NF-kappaB activity by GdCl(3).

Hepatic NKT cells: friend or foe?

The innate immune system represents a critical first line of host response to infectious, injurious and inflammatory insults. NKT cells (natural killer T-cells) are an important, but relatively poorly understood, component of the innate immune response. Moreover, NKT cells are enriched within the liver, suggesting that within the hepatic compartment NKT cells probably fulfil important roles in the modulation of the immune response to infection or injury. NKT cells are characterized by their rapid activation and secretion of large amounts of numerous types of cytokines, including those within the Th1-type, Th2-type and Th17-type groups, which in turn can interact with a multitude of other cell types within the liver. In addition, NKT cells are capable of participating in a wide array of effector functions with regards to other cell types via NKT cell-surface-molecule expression [e.g. FASL (FAS ligand) and CD40L (CD40 ligand)] and the release of mediators (e.g. perforin and granzyme) contained in cellular granules, which in turn can activate or destroy other cells (i.e. immune or parenchymal cells) within the liver. Given the huge scope of potential actions that can be mediated by NKT cells, it has become increasingly apparent that NKT cells may fulfil both beneficial (e.g. clearance of virally infected cells) and harmful (e.g. induction of autoimmunity) roles in the setting of liver disease. This review will outline the possible roles which may be played by NKT cells in the setting of specific liver diseases or conditions, and will discuss the NKT cell in the context of its role as either a ‘friend’ or a ‘foe’ with respect to the outcome of these liver disorders.

Invariant NKT cells amplify the innate immune response to lipopolysaccharide

NKT cells are thought of as a bridge between innate and adaptive immunity. In this study, we demonstrate that mouse NKT cells are activated in response to Escherichia coli LPS, and produce IFN-gamma, but not IL-4, although activation through their TCR typically induces both IL-4 and IFN-gamma production. IFN-gamma production by NKT cells is dependent on LPS-induced IL-12 and IL-18 from APC. LPS induced IFN-gamma production by NKT cells does not require CD1d-mediated presentation of an endogenous Ag and exposure to a combination of IL-12 and IL-18 is sufficient to activate them. In mice that are deficient for NKT cells, innate immune cells are activated less efficiently in response to LPS, resulting in the reduced production of TNF and IFN-gamma. We propose that in addition to acting as a bridge to adaptive immunity, NKT cells act as an early amplification step in the innate immune response and that the rapid and complete initiation of this innate response depends on the early production of IFN-gamma by NKT cells.

Differential innate immune cell activation and proinflammatory response in Anaplasma phagocytophilum infection

Human granulocytic anaplasmosis (HGA) is caused by the obligate intracellular bacterium Anaplasma phagocytophilum. The critical role of gamma interferon (IFN-gamma) for induction of severe inflammatory histopathology, even in the absence of a significant bacterial load, was previously demonstrated in a murine model of HGA. We hypothesized that NK, NKT, and possibly CD8(+) cytotoxic T cells participate in the development of histopathologic lesions with A. phagocytophilum infection. Mice were mock infected or infected with low- or high-passage A. phagocytophilum and assayed for hepatic histopathology and splenocyte immunophenotype during the first 21 days after infection. Compared to high-passage A. phagocytophilum-infected mice, low-passage A. phagocytophilum-infected mice had more severe hepatic lesions and increased apoptosis. The hepatic histopathology severity in low-passage A. phagocytophilum-infected mice peaked on day 2 at the time of peak plasma IFN-gamma levels and gradually decreased through day 21. Low-passage A. phagocytophilum-infected mice also showed significantly increased levels of lymphocyte NK1.1/FasL expression on days 4 to 7 corresponding to early, severe hepatic inflammation, whereas the levels of NKT cells were substantially lower on day 4, suggesting that there was NKT cell involvement. This result supports the concept that NK1.1(+) cells, including NK and NKT cells, are major components in the early pathogenesis of A. phagocytophilum infection.

Enforced Expression of Bcl-2 Partially Restores Cell Numbers but Not Functions of TCRγδ Intestinal Intraepithelial T Lymphocytes in IL-15-Deficient Mice

IL-15 knockout (KO) mice have severely reduced numbers of TCRgammadelta intestinal intraepithelial T lymphocytes (i-IEL), suggesting requirements of IL-15 signaling in the development or maintenance of i-IEL. To determine an involvement of survival signals via Bcl-2 in IL-15-mediated homeostasis of TCRgammadelta i-IEL, we introduced a bcl-2 transgene into IL-15 KO mice. In situ apoptosis of TCRgammadelta i-IEL was decreased in Bcl-2 transgenic (Tg) x IL-15 KO mice compared with IL-15 KO mice. The enforced expression of Bcl-2 partially restored the numbers of TCRgammadelta i-IEL in IL-15 KO mice. However, effector functions of TCRgammadelta i-IEL, including cytokine production and cytotoxic activity, were not recovered in Bcl-2 Tg x IL-15 KO mice. Importantly, TCRgammadelta i-IEL in Bcl-2 Tg x IL-15 KO mice expressed a reduced level of eomesodermin, a transcription factor critical for effector functions of NK cells and CD8(+) T cells. Similar to the case of TCRgammadelta i-IEL, enforced expression of Bcl-2 restored the numbers but not the functions of NK cells in IL-15 KO mice. These results suggest that Bcl-2-mediated survival signal is involved in the IL-15-mediated homeostasis of TCRgammadelta i-IEL and NK cells, but other signals from IL-15 are critical for inducing transcription factors, such as eomesodermin for their effector functions.

Enhancement of NKT Cells and Increase in Regulatory T Cells Results in Improved Allograft Survival

BACKGROUND

Natural killer T (NKT) cells can serve as regulatory cells important in peripheral tolerance. In an experimental colitis model, it was shown that FK506 enhances the tolerizing effect of regulatory NKT cells induced by oral tolerance. We explored whether a subtherapeutic dose of FK506 could enhance the tolerizing effect of NKT cells induced by oral administration of donor spleen cells (SCs) in the pre-transplant period to prolong heart allograft survival.

METHODS

Heterotopic heart transplantation was performed from BALB/c to B6 mice. The B6 recipients were pre-treated with either BALB/c SCs (2 x 10(7)/mouse), or FK506 (1.0 mg/kg/d), or BALB/c SCs + FK506 by gavage every other day for a total of five feedings before transplantation.

RESULTS

Heart allograft survival was only significantly prolonged in the BALB/c SC + FK506 pre-fed mice. This was associated with a marked increase of NKT cells in both the liver and spleen of the recipients, and most importantly, 7 days after transplantation, an increase in CD25+CD4+ T cells expressing CTLA4 in the spleen.

CONCLUSIONS

In our model it appears that a subtherapeutic dose of FK506 enhanced the tolerizing effect of NKT cells induced by oral tolerance, prolonging allograft survival by generating CD25+CD4+ CTLA4 T cells. This appears to be an excellent in vivo model to generate regulatory T cells to allospecific transplant antigens.

Isomalto-oligosaccharides polarize Th1-like responses in intestinal and systemic immunity in mice

Isomalto-oligosaccharides (IMO) belong to a group of prebiotics that significantly increase the number of protective gut microflora. In the present study, we investigated the effects of IMO on intestinal and systemic immunity in mice. When mice were fed a diet supplemented with 20% IMO for 4 wk, the number of lactobacilli and the levels of IgA in feces were greater than those of mice fed the control diet (P < 0.05). Interferon-gamma (IFN-gamma) production by intestinal intraepithelial lymphocytes (i-IEL) in response to T-cell receptor (TCR) triggering was greater in mice fed IMO than in controls (P < 0.05), indicating T helper-1 (Th1) polarization of intestinal immunity by IMO. The proportion of natural killer (NK) T cells in the liver mononuclear cells (MNC), and the production of IFN-gamma by the liver MNC in response to TCR triggering were greater in mice fed IMO than in controls (P < 0.05), suggesting that the Th1/Th2 balance was shifted toward the Th1 lineage by IMO in systemic immunity. Furthermore, the proportion and activity of NK cells were greater in the spleens of the mice fed IMO than in the controls. Dietary IMO protected the mice from gamma-irradiation-induced lethality, accompanied by an inhibition of the translocation of Enterobacteriaceae. Notably, when mouse macrophage-like J774.1 cells were cultured with Lactobacillus gasseri in the presence of IMO, interleukin (IL)-12 production was greater than in the absence of IMO. These results suggest that IMO, in synergy with lactobacilli, upregulate the Th1 response and beneficially modulate host defense.

TLR-Dependent IL-4 Production by Invariant Vα14+Jα18+ NKT Cells to Initiate Contact Sensitivity In Vivo

LPS stimulated B-1 cell polyclonal in vivo IgM responses depend on IL-4 release by invariant Valpha14+Jalpha18+ NKT (iNKT) cells. The IgM Abs can recruit effector T cells to mediate contact sensitivity. LPS activates the B-1 cell response just 1 day later, and depends on CD1d, iNKT cells, IL-4, TLR4, and MyD88. LPS in vivo and in vitro stimulates rapid preferential production of IL-4 in hepatic iNKT cells within 2 h. TLR4 were demonstrated in iNKT cells by flow cytometry and functional studies. Thus, innate microbial stimulation via TLR can activate iNKT cell and B-1 cell collaboration. The result is polyclonal IgM Ab responses capable of recruiting Ag-specific T cells into tissues. This may be involved in the promotion of autoimmunity by infectious agents.

Both CD1d antigen presentation and interleukin-12 are required to activate natural killer T cells during Trypanosoma cruzi infection

Mechanisms of natural killer T (NKT)-cell activation remain unclear. Here, we report that during Trypanosoma cruzi infection, interleukin-12 (IL-12) deficiency or anti-CD1d antibody treatment prevents normal activation. The required IL-12 arises independently of MyD88. The data support a model of normal NKT-cell activation that requires IL-12 and TCR stimulation.

Hepatitis C core and nonstructural 3 proteins trigger toll-like receptor 2-mediated pathways and inflammatory activation

BACKGROUND AND AIMS

Recent evidence suggests that toll-like receptors (TLRs) recognize certain viruses. We reported that hepatitis C virus (HCV) core and nonstructural 3 (NS3) proteins activate inflammatory pathways in monocytes. The aim of this study was to investigate the role of TLRs in innate immune cell activation by core and NS3 proteins.

METHODS

Human monocytes, human embryonic kidney cells transfected with TLR2, and peritoneal macrophages from TLR2, MyD88 knockout, and wild-type mice were studied to determine intracellular signaling and proinflammatory cytokine induction by HCV proteins.

RESULTS

HCV core and NS3 proteins triggered inflammatory cell activation via the pattern recognition receptor TLR2 and failed to activate macrophages from TLR2 or MyD88-deficient mice. HCV core and NS3 induced interleukin (IL)-1 receptor-associated kinase (IRAK) activity, phosphorylation of p38, extracellular regulated (ERK), and c-jun N-terminal (JNK) kinases and induced AP-1 activation. Activation of nuclear factor-kappaB by core and NS3 was associated with increased IkappaBalpha phosphorylation. TLR2-mediated cell activation was dependent on the conformation of core and NS3 proteins and required sequences in the regions of aa 2-122 in core and aa 1450-1643 in NS3. Although cellular uptake of core and NS3 proteins was independent of TLR2 expression, cell activation required TLR2. HCV core protein and TLR2 showed intracellular colocalization. The hyper-elevated TNF-alpha induction by TLR2 ligands in monocytes of HCV-infected patients was not due to increased TLR2 expression.

CONCLUSIONS

HCV core and NS3 proteins trigger inflammatory pathways via TLR2 that may affect viral recognition and contribute to activation of the innate immune system.

Selective priming to Toll-like receptor 4 (TLR4), not TLR2, ligands by P. acnes involves up-regulation of MD-2 in mice

Lipopolysaccharide (LPS) triggers cytokine production through Toll-like receptor 4 (TLR4), which shares downstream signaling pathways with TLR2. We investigated the roles of TLR2 and TLR4 in Propionibacterium acnes (P. acnes)-primed, LPS-induced liver damage using selective TLR ligands. Stock LPS induced interleukin 8 in both TLR4- and TLR2-expressing human embryonic kidney (HEK) 293 cells. Purified LPS (TLR4 ligand) activated HEK/TLR4 cells, while peptidoglycan and lipoteichoic acid (TLR2 ligands) activated HEK/TLR2 cells, respectively. In mice, P. acnes priming resulted in increased liver messenger RNA (mRNA) and serum levels of tumor necrosis factor alpha, interleukin 12, and interferon gamma (IFN-gamma) by both stock LPS and purified LPS challenges compared with nonprimed controls. In contrast, P. acnes failed to sensitize to TLR2 ligands (peptidoglycan + lipoteichoic acid). In the liver, P. acnes-priming was associated with up-regulation of TLR4 and MD-2 proteins, and subsequent LPS challenge further increased MD-2 and CD14 mRNA levels. The lack of sensitization to TLR2 ligands by P. acnes correlated with no increase in hepatic TLR1 or TLR6 mRNA. In vitro, P. acnes pretreatment desensitized RAW macrophages to a secondary stimulation via both TLR2 and TLR4. However, IFN-gamma could selectively prevent desensitization to TLR4 but not to TLR2 ligands. Furthermore, P. acnes induced production of IFN-gamma in vivo as well as in isolated splenocytes. In vitro, P. acnes-primed Hepa 1-6 hepatocytes but not RAW macrophages produced increased MD-2 and CD14 mRNA levels after an LPS challenge. In conclusion, P. acnes priming to selective TLR4-mediated liver injury is associated with up-regulation of TLR4 and MD-2 and is likely to involve IFN-gamma and prevent TLR4 desensitization by P. acnes.

IL-6 prevents T cell-mediated hepatitis via inhibition of NKT cells in CD4+ T cell- and STAT3-dependent manners

The hepatoprotective effect of IL-6 on various forms of liver injury including T cell-mediated hepatitis has been well documented, and it is believed that induction of antiapoptotic proteins is an important mechanism. In this study, we provide evidence suggesting an additional mechanism involved in the protective role of IL-6 in T cell-mediated hepatitis. In NKT cell-depleted mice, Con A-induced liver injury is diminished; this can be restored by the adoptive transfer of liver mononuclear cells or NKT cells from wild-type mice, but not from IL-6-treated mice. In vitro IL-6 treatment inhibits the ability of mononuclear cells to restore Con A-induced liver injury in NKT-depleted mice, whereas the same treatment does not inhibit purified NKT cells from restoring the injury. The addition of CD3(+) T cells or CD4(+) T cells can restore the inhibitory effect of IL-6 on purified NKT cells, whereas the addition of CD3(+) T cells from CD4-deficient mice fails to restore this inhibitory effect. The expression of IL-6R was detected in 52.6% of hepatic CD3(+) T cells and 32.7% of hepatic CD4(+) T cells, but only in 3.9% of hepatic NK and 1.5% of hepatic NKT cells. Finally, treatment with IL-6 induces STAT3 activation in hepatic lymphocytes and hepatic T cells, and blocking such activation abolishes the inhibitory effect of IL-6 on hepatic lymphocytes to restore liver injury. Taken together, these findings suggest that in addition to its antiapoptotic abilities, as previously well documented, IL-6/STAT3 inhibits NKT cells via targeting CD4(+) T cells and consequently prevents T cell-mediated hepatitis.

Overexpression of Interleukin-15 increases susceptibility to lipopolysaccharide-induced liver injury in mice primed with Mycobacterium bovis bacillus Calmette-Guerin

Mice primed with Mycobacterium bovis bacillus Calmette-Guérin (BCG) are highly sensitive to lipopolysaccharide (LPS)-induced liver injury and lethality. We found that interleukin-15 (IL-15) transgenic (Tg) mice primed with BCG were more susceptible to LPS-induced liver injury than non-Tg mice. The numbers of CD44+ CD8+ T cells expressing intracellular gamma interferon (IFN-gamma) significantly increased in the livers of BCG-primed IL-15 Tg mice after LPS injection, and the depletion of CD8+ T cells from BCG-primed IL-15 Tg mice completely abolished the susceptibility to LPS-induced lethality. Liver T cells from BCG-primed IL-15 Tg mice produced IFN-gamma in vitro in response to LPS, which was inhibited by the addition of anti-IL-12 monoclonal antibody (MAb). In vivo treatment with anti-IL-12 MAb inhibited the appearance of CD44+ CD8+ T cells expressing intracellular IFN-gamma after LPS injection. These results suggest that the overexpression of IL-15 increases susceptibility to LPS-induced liver injury in BCG-primed mice via bystander activation of CD8+ T cells.

Kupffer cell-derived interleukin 10 is responsible for impaired bacterial clearance in bile duct-ligated mice

Extrahepatic cholestasis often evokes liver injury with hepatocyte apoptosis, aberrant cytokine production, and-most importantly-postoperative septic complications. To clarify the involvement of aberrant cytokine production and hepatocyte apoptosis in impaired resistance to bacterial infection in obstructive cholestasis, C57BL/6 mice or Fas-mutated lpr mice were inoculated intraperitoneally with 10(7) colony-forming units of Escherichia coli 5 days after bile duct ligation (BDL) or sham celiotomy. Cytokine levels in sera, liver, and immune cells were assessed via enzyme-linked immunosorbent assay or real-time reverse-transcriptase polymerase chain reaction. BDL mice showed delayed clearance of E. coli in peritoneal cavity, liver, and spleen. Significantly higher levels of serum interleukin (IL) 10 with lower levels of IL-12p40 were observed in BDL mice following E. coli infection. Interferon gamma production from liver lymphocytes in BDL mice was not increased after E. coli infection either at the transcriptional or protein level. Kupffer cells from BDL mice produced low levels of IL-12p40 and high levels of IL-10 in vitro in response to lipopolysaccharide derived from E. coli. In vivo administration of anti-IL-10 monoclonal antibody ameliorated the course of E. coli infection in BDL mice. Furthermore, BDL-lpr mice did not exhibit impairment in E. coli killing in association with little hepatic injury and a small amount of IL-10 production. In conclusion, increased IL-10 and reciprocally suppressed IL-12 production by Kupffer cells are responsible for deteriorated resistance to bacterial infection in BDL mice. Fas-mediated hepatocyte apoptosis in cholestasis may be involved in the predominant IL-10 production by Kupffer cells.

Activated natural killer T cells induce liver injury by Fas and tumor necrosis factor-alpha during alcohol consumption

BACKGROUND & AIMS

Chronic alcohol abuse induces liver injury and increases the severity of viral hepatitis, but the precise mechanisms responsible are not well understood. In particular, little is known about the role of natural killer T cells in alcohol-induced liver injury. Natural killer T cells are mediators of important regulator and effector functions making use of Fas and tumor necrosis factor (TNF)-alpha in apoptosis induction. This report analyzes the role of natural killer T cells, Fas, and TNF-alpha in a model of chronic alcohol consumption.

METHODS

Mice fed alcohol by intragastric tube were assayed for serum alanine aminotransferase values, liver histology, and liver mononuclear cells before and after activation of natural killer T cells by ligand alpha-galactosylceramide.

RESULTS

In alcohol-consuming animals, liver natural killer T cells increase, and further activation by alpha-galactosylceramide causes lethal liver injury. This is explained by alcohol-induced hepatocyte sensitization to cell-mediated lysis, which develops concomitant to increased cytolytic activity of natural killer T cells. Natural killer T cell-mediated apoptosis proceeds by the Fas pathway, and Fas is essential for alcohol-associated liver injury. TNF-alpha plays an additional role as a defect in TNF receptor-1 inhibits alcohol-associated liver injury. Alcohol-fed natural killer T cell-deficient Jalpha281(-/-) mice express a delay in alcohol-induced liver injury.

CONCLUSIONS

Alcohol consumption induces an increase of natural killer T cells in the liver and a high sensitivity of hepatocytes to cell-mediated lysis. Stimulation of natural killer T cells during alcohol consumption induces serious liver injury by a mechanism that involves concomitant signals by Fas and tumor necrosis factor receptor-1 on alcohol-stressed hepatocytes.

CD1-Dependent Regulation of Chronic Central Nervous System Inflammation in Experimental Autoimmune Encephalomyelitis

The existence of T cells restricted for the MHC I-like molecule CD1 is well established, but the function of these cells is still obscure; one implication is that CD1-dependent T cells regulate autoimmunity. In this study, we investigate their role in experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis, using CD1-deficient mice on a C57BL/6 background. We show that CD1-/- mice develop a clinically more severe and chronic EAE compared with CD1+/+ C57BL/6 mice, which was histopathologically confirmed with increased demyelination and CNS infiltration in CD1-/- mice. Autoantigen rechallenge in vitro revealed similar T cell proliferation in CD+/+ and CD1-/- mice but an amplified cytokine response in CD1-/- mice as measured by both the Th1 cytokine IFN-gamma and the Th2 cytokine IL-4. Investigation of cytokine production at the site of inflammation showed a CNS influx of TGF-beta1-producing cells early in the disease in CD1+/+ mice, which was absent in the CD1-/- mice. Passive transfer of EAE using an autoreactive T cell line induced equivalent disease in both groups, which suggested additional requirements for activation of the CD1-dependent regulatory pathway(s). When immunized with CFA before T cell transfer, the CD1-/- mice again developed an augmented EAE compared with CD1+/+ mice. We suggest that CD1 exerts its function during CFA-mediated activation, regulating development of EAE both through enhancing TGF-beta1 production and through limiting autoreactive T cell activation, but not necessarily via effects on the Th1/Th2 balance.

Regulation of Toll-like receptor-2 expression by the Gal-lectin of Entamoeba histolytica

The Gal/GalNAc lectin (Gal-lectin) of Entamoeba histolytica is a surface molecule involved in parasite adherence to host cells and is the most promising subunit vaccine candidate against amoebiasis. As macrophages are the major effector cells in host defense against amoebas, we studied the molecular mechanisms by which Gal-lectin activates macrophage. Microarray analysis showed that Gal-lectin up-regulated mRNAs of several cytokines and receptor genes involved in proinflammatory responses. The mechanism whereby the Gal-lectin regulates Toll-like receptor 2 (TLR-2) expression in macrophages was studied. Native Gal-lectin increased TLR-2 mRNA expression in a dose- and time-dependent fashion; peak response occurred with 1 microg/ml after 2 h stimulation. By immunoflourescence, enhanced surface expression of TLR-2 was observed after 12 h. With the use of nonoverlapping anti-Gal-lectin monoclonal antibodies that map to the carbohydrate recognition domain, amino acid 596-1082 was identified as the TLR-2 stimulating region. The Gal-lectin increased TLR-2 gene transcription, and the half-life of the mRNA transcripts was 1.4 h. Inhibition of nuclear factor (NF)-kappaB suppressed TLR-2 mRNA induction by the Gal-lectin. Moreover, cells pretreated with an inhibitor of p38 kinase (SB 208530) inhibited Gal-lectin induced TLR-2 mRNA expression by 40%. We conclude that the Gal-lectin activates NF-kappaB and MAP kinase-signaling pathways in macrophages culminating in the induction of several genes including TLR-2 and hypothesize that this could have a significant impact on macrophage activation and contribute to amoebic pathogenesis.