Activating immunity in the liver. I. Liver dendritic cells (but not hepatocytes) are potent activators of IFN-gamma release by liver NKT cells

Resident Immune Cells of the Liver in the Tumor Microenvironment

The liver is a central immunomodulator that ensures a homeostatic balance between protection and immunotolerance. A hallmark of hepatocellular carcinoma (HCC) is the deregulation of this tightly controlled immunological network. Immune response in the liver involves a complex interplay between resident innate, innate, and adaptive immune cells. The immune response in the liver is modulated by its continuous exposure to toxic molecules and microorganisms that requires a degree of immune tolerance to protect normal tissue from damage. In HCC pathogenesis, immune cells must balance a dual role that includes the elimination of malignant cells, as well as the repair of damaged liver tissue to maintain homeostasis. Immune response in the innate and adaptive immune systems extends to the cross-talk and interaction involving immune-regulating non-hematopoietic cells, myeloid immune cells, and lymphoid immune cells. In this review, we discuss the different immune responses of resident immune cells in the tumor microenvironment. Current FDA-approved targeted therapies, including immunotherapy options, have produced modest results to date for the treatment of advanced HCC. Although immunotherapy therapy to date has demonstrated its potential efficacy, immune cell pathways need to be better understood. In this review article, we summarize the roles of specific resident immune cell subsets and their cross-talk subversion in HCC pathogenesis, with a view to identifying potential new biomarkers and therapy options.

Hepatic Dendritic Cells in the Development and Progression of Metabolic Steatohepatitis

Metabolic Associated Fatty liver disease (MAFLD) is a global health problem and represents the most common cause of chronic liver disease in the world. MAFLD spectrum goes from simple steatosis to cirrhosis, in between metabolic steatohepatitis with progressive fibrosis, which pathogenesis is not completely understood. Hence, the role of the immune system has become an important fact in the trigger of inflammatory cascades in metabolic steatohepatitis and in the activation of hepatic stellate cells (HSCs). Among, the more studied immune cells in the pathogenesis of MAFLD are macrophages, T cells, natural killer and dendritic cells. In particular, hepatic dendritic cells had recently attracted a special attention, with a dual role in the pathogenesis of MAFLD. These cells have the capacity to switch from a tolerant state to active state inducing an inflammatory cascade. Furthermore, these cells play a role in the lipid storage within the liver, having, thus providing a crucial nexus between inflammation and lipid metabolism. In this review, we will discuss the current knowledge on the dual role of dendritic cells in lipid accumulation, as wells as in the triggering of hepatic inflammation and hepatocytes cell death in metabolic steatohepatitis.

Soluble and Exosome-Bound α-Galactosylceramide Mediate Preferential Proliferation of Educated NK Cells with Increased Anti-Tumor Capacity

Natural killer (NK) cells can kill target cells via the recognition of stress molecules and down-regulation of major histocompatibility complex class I (MHC-I). Some NK cells are educated to recognize and kill cells that have lost their MHC-I expression, e.g., tumor or virus-infected cells. A desired property of cancer immunotherapy is, therefore, to activate educated NK cells during anti-tumor responses in vivo. We here analyze NK cell responses to α-galactosylceramide (αGC), a potent activator of invariant NKT (iNKT) cells, or to exosomes loaded with αGC. In mouse strains which express different MHC-I alleles using an extended NK cell flow cytometry panel, we show that αGC induces a biased NK cell proliferation of educated NK cells. Importantly, iNKT cell-induced activation of NK cells selectively increased in vivo missing self-responses, leading to more effective rejection of tumor cells. Exosomes from antigen-presenting cells are attractive anti-cancer therapy tools as they may induce both innate and adaptive immune responses, thereby addressing the hurdle of tumor heterogeneity. Adding αGC to antigen-loaded dendritic-cell-derived exosomes also led to an increase in missing self-responses in addition to boosted T and B cell responses. This study manifests αGC as an attractive adjuvant in cancer immunotherapy, as it increases the functional capacity of educated NK cells and enhances the innate, missing self-based antitumor response.

Immunobiology and immunotherapy of HCC: spotlight on innate and innate-like immune cells

Immune-based therapies such as immune checkpoint inhibitors have revolutionized the systemic treatment of various cancer types. The therapeutic application of monoclonal antibodies targeting inhibitory pathways such as programmed cell death-1(PD-1)/programmed cell death ligand 1 (PD-L1) and CTLA-4 to cells of the adaptive immune system has recently been shown to generate meaningful improvement in the clinical outcome of hepatocellular carcinoma (HCC). Nevertheless, current immunotherapeutic approaches induce durable responses in only a subset of HCC patients. Since immunologic mechanisms such as chronic inflammation due to chronic viral hepatitis or alcoholic and nonalcoholic fatty liver disease play a crucial role in the initiation, development, and progression of HCC, it is important to understand the underlying mechanisms shaping the unique tumor microenvironment of liver cancer. The liver is an immunologic organ with large populations of innate and innate-like immune cells and is exposed to bacterial, viral, and fungal antigens through the gut-liver axis. Here, we summarize and highlight the role of these cells in liver cancer and propose strategies to therapeutically target them. We also discuss current immunotherapeutic strategies in HCC and outline recent advances in our understanding of how the therapeutic potential of these agents might be enhanced.

Wait, Wait … OK Now Go In: iNKT Cells Resolve Liver Inflammation

Resolution of inflammation is pivotal to restoring tissue homeostasis, yet there is limited understanding of how this process is regulated. In this issue of Immunity, Liew et al. (2017) reveal a critical role for invariant natural killer T (iNKT) cells in switching inflammation to tissue repair in an interlukin-4-dependent process.

Immune Responses in the Liver

The liver is a key, frontline immune tissue. Ideally positioned to detect pathogens entering the body via the gut, the liver appears designed to detect, capture, and clear bacteria, viruses, and macromolecules. Containing the largest collection of phagocytic cells in the body, this organ is an important barrier between us and the outside world. Importantly, as portal blood also transports a large number of foreign but harmless molecules (e.g., food antigens), the liver's default immune status is anti-inflammatory or immunotolerant; however, under appropriate conditions, the liver is able to mount a rapid and robust immune response. This balance between immunity and tolerance is essential to liver function. Excessive inflammation in the absence of infection leads to sterile liver injury, tissue damage, and remodeling; insufficient immunity allows for chronic infection and cancer. Dynamic interactions between the numerous populations of immune cells in the liver are key to maintaining this balance and overall tissue health.

The Contribution of Non-Professional Antigen-Presenting Cells to Immunity and Tolerance in the Liver

The liver represents a unique organ biased toward a tolerogenic milieu. Due to its anatomical location, it is constantly exposed to microbial and food-derived antigens from the gut and thus equipped with a complex cellular network that ensures dampening T-cell responses. Within this cellular network, parenchymal cells (hepatocytes), non-parenchymal cells (liver sinusoidal endothelial cells and hepatic stellate cells), and immune cells contribute directly or indirectly to this process. Despite this refractory bias, the liver is capable of mounting efficient T-cell responses. How the various antigen-presenting cell (APC) populations contribute to this process and how they handle danger signals determine the outcome of the generated immune responses. Importantly, liver mounted responses convey consequences not only for the local but also to systemic immunity. Here, we discuss various aspects of antigen presentation and its consequences by the non-professional APCs in the liver microenvironment.

Immunology in the liver--from homeostasis to disease

The liver is a central immunological organ with a high exposure to circulating antigens and endotoxins from the gut microbiota, particularly enriched for innate immune cells (macrophages, innate lymphoid cells, mucosal-associated invariant T (MAIT) cells). In homeostasis, many mechanisms ensure suppression of immune responses, resulting in tolerance. Tolerance is also relevant for chronic persistence of hepatotropic viruses or allograft acceptance after liver transplantation. The liver can rapidly activate immunity in response to infections or tissue damage. Depending on the underlying liver disease, such as viral hepatitis, cholestasis or NASH, different triggers mediate immune-cell activation. Conserved mechanisms such as molecular danger patterns (alarmins), Toll-like receptor signalling or inflammasome activation initiate inflammatory responses in the liver. The inflammatory activation of hepatic stellate and Kupffer cells results in the chemokine-mediated infiltration of neutrophils, monocytes, natural killer (NK) and natural killer T (NKT) cells. The ultimate outcome of the intrahepatic immune response (for example, fibrosis or resolution) depends on the functional diversity of macrophages and dendritic cells, but also on the balance between pro-inflammatory and anti-inflammatory T-cell populations. As reviewed here, tremendous progress has helped to understand the fine-tuning of immune responses in the liver from homeostasis to disease, indicating promising targets for future therapies in acute and chronic liver diseases.

The Role of Dendritic Cells in Fibrosis Progression in Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is the most frequent cause of chronic liver disease. NAFLD encompasses a wide range of pathologies, from simple steatosis to steatosis with inflammation to fibrosis. The pathogenesis of NAFLD progression has not been completely elucidated, and different liver cells could be implicated. This review focuses on the current evidence of the role of liver dendritic cells (DCs) in the progression from NAFLD to fibrosis. Liver DCs are a heterogeneous population of hepatic antigen-presenting cells; their main function is to induce T-cell mediated immunity by antigen processing and presentation to T cells. During the steady state liver DCs are immature and tolerogenic. However, in an environment of chronic inflammation, DCs are transformed to potent inducers of immune responses. There is evidence about the role of DC in liver fibrosis, but it is not clearly understood. Interestingly, there might be a link between lipid metabolism and DC function, suggesting that immunogenic DCs are associated with liver lipid storage, representing a possible pathophysiological mechanism in NAFLD development. A better understanding of the interaction between inflammatory pathways and the different cell types and the effect on the progression of NAFLD is of great relevance.

N-acetylglucosaminyltransferase V exacerbates concanavalin A-induced hepatitis in mice

N‑Acetylglucosaminyltransferase V (GnT‑V) catalyzes β1‑6 branching in asparagine‑linked oligosaccharides and is one of the most important glycosyltransferases involved in carcinogenesis, cancer metastasis and immunity. To investigate the biological functions of GnT‑V, the present study developed GnT‑V transgenic (Tg) mice and the role of GnT‑V in experimental immune‑mediated hepatitis, induced by concanavalin A (ConA), were investigated. It was found that the aberrant expression of GnT‑V exacerbated ConA‑induced hepatitis in the Tg mice compared with the wild‑type (WT) mice. The survival rate of the ConA‑induced hepatitis at a high‑dose of ConA was significantly lower in the Tg mice. Intravenously injected ConA is known to initially bind predominantly to the mannose gland of the liver sinusoidal endothelial cell (LSEC) surface and to leads to the activation of various immune cells. In the present study, the binding affinity of ConA to the LSECs did not differ between the WT and Tg mice. In addition, T cell receptor stimulation by anti‑cluster of differentiation (CD)3/CD28 antibodies produced lower levels of T helper (Th)1 cytokine (interferon‑γ) and higher levels of Th2 cytokine (interleukin‑10) in the Tg mouse splenic lymphocytes compared with WT mice. The composition of the hepatic mononuclear cells revealed that CD11b‑positive cells were significantly increased in the GnT‑V Tg mice. In addition, F4/80‑positive cells were significantly increased in the Tg mouse liver and the depletion of macrophages reduced the difference in the severity of ConA‑induced hepatitis between the WT and Tg mice. In conclusion, the present findings indicated that the aberrant expression of GnT‑V led to an increase in hepatic macrophage infiltration and enhanced ConA‑induced hepatitis. Modulation of glycosylation may be a novel therapeutic target for immunity‑associated acute hepatitis.

Pro-inflammatory activated Kupffer cells by lipids induce hepatic NKT cells deficiency through activation-induced cell death

Background

Dietary lipids play an important role in the progression of non-alcoholic fatty liver disease (NAFLD) through alternation of liver innate immune response.

Aims

The present study was to investigate the effect of lipid on Kupffer cells phenotype and function invivo and invitro. And further to investigate the impact of lipid on ability of Kupffer cell lipid antigen presentation to activate NKT cells.

Methods

Wild type male C57BL/6 mice were fed either normal or high-fat diet. Hepatic steatosis, Kupffer cell abundance, NKT cell number and cytokine gene expression were evaluated. Antigen presentation assay was performed with Kupffer cells treated with certain fatty acids invitro and co-cultured with NKT cells.

Results

High-fat diet induced hepatosteatosis, significantly increased Kupffer cells and decreased hepatic NKT cells. Lipid treatment invivo or invitro induced increase of pro-inflammatory cytokines gene expression and toll-like receptor 4 (TLR4) expression in Kupffer cells. Kupffer cells expressed high levels of CD1d on cell surface and only presented exogenous lipid antigen to activate NKT cells. Ability of Kupffer cells to present antigen and activate NKT cells was enhanced after lipid treatment. In addition, pro-inflammatory activated Kupffer cells by lipid treatment induced hepatic NKT cells activation-induced apoptosis and necrosis.

Conclusion

High-fat diet increase Kupffer cells number and induce their pro-inflammatory status. Pro-inflammatory activated Kupfffer cells by lipid promote hepatic NKT cell over-activation and cell death, which lead to further hepatic NKT cell deficiency in the development of NAFLD.

Ex vivo analysis of resident hepatic pro-inflammatory CD1d-reactive T cells and hepatocyte surface CD1d expression in hepatitis C

Hepatic CD1d-restricted and natural killer T-cell populations are heterogeneous. Classical 'type 1' α-galactosylceramide-reactive CD1d-restricted T cells express 'invariant' TCRα ('iNKT'). iNKT dominating rodent liver are implicated in inflammation, including in hepatitis models. Low levels of iNKT are detected in human liver, decreased in subjects with chronic hepatitis C (CHC). However, high levels of human hepatic CD161(±) CD56(±) noninvariant pro-inflammatory CD1d-restricted 'type 2' T cells have been identified in vitro. Unlike rodents, healthy human hepatocytes only express trace and intracellular CD1d. Total hepatic CD1d appears to be increased in CHC and primary biliary cirrhosis. Direct ex vivo analysis of human intrahepatic lymphocytes (IHL), including matched ex vivo versus in vitro expanded IHL, demonstrated detectable noninvariant CD1d reactivity in substantial proportions of HCV-positive livers and significant fractions of HCV-negative livers. However, α-galactosylceramide-reactive iNKT were detected only relatively rarely. Liver CD1d-restricted IHL produced IFNγ, variable levels of IL-10 and modest levels of Th2 cytokines IL-4 and IL-13 ex vivo. In a novel FACS assay, a major fraction (10-20%) of hepatic T cells rapidly produced IFNγ and up-regulated activation marker CD69 in response to CD1d. As previously only shown with murine iNKT, noninvariant human CD1d-specific responses were also augmented by IL-12. Interestingly, CD1d was found selectively expressed on the surface of hepatocytes in CHC, but not those CHC subjects with history of alcohol usage or resolved CHC. In contrast to hepatic iNKT, noninvariant IFNγ-producing type 2 CD1d-reactive NKT cells are commonly detected in CHC, together with cognate ligand CD1d, implicating them in CHC liver damage.

The CD1d-natural killer T cell axis in atherosclerosis

A key role for 'lipid-sensing' CD1-restricted natural killer T (NKT) cells in the pathogenesis of atherosclerosis has been suggested. However, the biology of NKT cells remains poorly characterized, as in different experimental settings their activation was reported to both stimulate and suppress innate and adaptive immune responses. Most of the data from experimental models suggest that NKT cells are proatherogenic; however, it is debated whether the increase in atherosclerosis observed following NKT cell stimulation is a consequence of the inability to induce functional NKT cells rather than the proatherogenic nature of NKT cells. CD1d-expressing antigen-presenting cells and NKT cells were detected in mouse and human atherosclerotic lesions. Furthermore, several lysophospholipids and glycosphingolipids, known to accumulate in atherosclerotic plaques, are antigenic for human NKT cell clones. Lipid transfer proteins, such as apolipoprotein E and microsomal triglyceride transfer protein, are central to NKT cell responses. All these data suggest a profound relation between lipid metabolism, CD1d-NKT cell axis activation and atherosclerosis. In this review, we summarize the advances and gaps in our knowledge of NKT cell biology in the context of atherosclerosis as well as the possibility of influencing NKT cell polarization toward an atheroprotective phenotype.

CLEC4F is an inducible C-type lectin in F4/80-positive cells and is involved in alpha-galactosylceramide presentation in liver

CLEC4F, a member of C-type lectin, was first purified from rat liver extract with high binding affinity to fucose, galactose (Gal), N-acetylgalactosamine (GalNAc), and un-sialylated glucosphingolipids with GalNAc or Gal terminus. However, the biological functions of CLEC4F have not been elucidated. To address this question, we examined the expression and distribution of murine CLEC4F, determined its binding specificity by glycan array, and investigated its function using CLEC4F knockout (Clec4f-/-) mice. We found that CLEC4F is a heavily glycosylated membrane protein co-expressed with F4/80 on Kupffer cells. In contrast to F4/80, CLEC4F is detectable in fetal livers at embryonic day 11.5 (E11.5) but not in yolk sac, suggesting the expression of CLEC4F is induced as cells migrate from yolk cells to the liver. Even though CLEC4F is not detectable in tissues outside liver, both residential Kupffer cells and infiltrating mononuclear cells surrounding liver abscesses are CLEC4F-positive upon Listeria monocytogenes (L. monocytogenes) infection. While CLEC4F has strong binding to Gal and GalNAc, terminal fucosylation inhibits CLEC4F recognition to several glycans such as Fucosyl GM1, Globo H, Bb3∼4 and other fucosyl-glycans. Moreover, CLEC4F interacts with alpha-galactosylceramide (α-GalCer) in a calcium-dependent manner and participates in the presentation of α-GalCer to natural killer T (NKT) cells. This suggests that CLEC4F is a C-type lectin with diverse binding specificity expressed on residential Kupffer cells and infiltrating monocytes in the liver, and may play an important role to modulate glycolipids presentation on Kupffer cells.

Absence of invariant natural killer T cells deteriorates liver inflammation and fibrosis in mice fed high-fat diet

BACKGROUND

Invariant natural killer T (iNKT) cells have been suggested to play critical roles in a wide range of immune responses by acting in a proinflammatory or anti-inflammatory manner. Nonalcoholic steatohepatitis (NASH) is a chronic liver disease progressing to advanced cirrhosis and hepatocellular carcinoma. Despite the abundance of iNKT cells in the liver, their role in the pathogenesis of NASH remains obscure. Here, we investigated their role in the development of diet-induced steatosis/steatohepatitis.

METHODS

We used BALB/c wild-type mice and Jα18-deficient (KO) mice lacking iNKT cells fed either a normal diet or a high-fat diet (HFD). The liver and blood were collected from these mice to examine liver inflammation, steatosis, and fibrosis at the indicated time points.

RESULTS

KO mice fed the HFD, compared with control mice fed the HFD, exhibited a clearly higher serum alanine aminotransferase level and a greater number of hepatic inflammatory foci, although there was no significant difference in hepatic lipid retention between these groups of mice. The HFD enhanced hepatic messenger RNA expression of inflammatory cytokines and chemokines in KO but not in control mice. The HFD also increased the proportion of hepatic CD4 T cells and CD8 T cells that composed hepatic inflammatory foci in KO mice, but not in the controls. Prolonged feeding with the HFD augmented liver fibrosis in KO but not in control mice.

CONCLUSIONS

These findings indicate that iNKT cells play a protective role against liver inflammation progressing to fibrosis, but not against steatosis, enhanced by dietary excess fat, suggesting a key role of these cells in NASH pathogenesis.

An expanding role for apolipoprotein E in sepsis and inflammation

BACKGROUND

Apolipoprotein E (apoE), a component of plasma lipoproteins, plays an important, but poorly defined role in sepsis. We have shown that injecting apoE increases septic mortality in a rat model of gram-negative bacterial sepsis, with concomitant hepatic natural killer T (NKT) cell proliferation and activation. The presumed mechanism for this apoE-mediated mortality is that apoE can bind and traffic antigens, presumed to include lipopolysaccharide (LPS), and promote activation of dendritic cells (DC) with subsequent NKT activation and cytokine release. Thus, we sought to prove that LPS was the antigen responsible for the increased NKT activation enhanced by the presence of apoE.

METHODS

We isolated murine marrow-derived DCs, pulsed them with lipid antigen (LPS, and positive controls alpha-galactosylceramide [alpha-GalCer] and isoglobotrihexosylceramide 3 [iGb3]) with or without apoE, and then cocultured the DCs with hybridoma NKTs. NKT activation was measured by interleukin-2 (IL-2) supernatant levels using enzyme-linked immunosorbent assay (ELISA).

RESULTS

LPS at different concentrations was a weak stimulus for NKT activation regardless of apoE presence. When apoE was present, iGb3, an endogenous ligand analog, elicited more than a 2-fold increase in IL-2 response when compared with iGb3 alone (P < .05).

CONCLUSIONS

These results indicate an endogenous ligand, not LPS, may be responsible for NKT activation. A molecular remnant similar to iGb3 could act as a damage-associated molecular pattern and play a prominent role in animal models of sepsis.

The specialized iNKT cell system recognizes glycolipid antigens and bridges the innate and acquired immune systems with potential applications for cancer therapy

Invariant NKT (iNKT) cells bridge innate and acquired immunity and play an important role in both protective and regulatory responses. The nature of the response is dictated by the initial cytokine environment: interaction with IL-10-producing cells induces negative regulatory T(h)2/regulatory T cell-type iNKT cells, while that with IL-12-producing cells results in pro-inflammatory T(h)1-type responses. Particularly, in the anti-tumor response, iNKT cells mediate adjuvant activity by their production of IFN-gamma, which in turn activates both innate and acquired immune systems. Thus, upon activation of iNKT cells, both MHC(-) and MHC(+) tumor cells can be efficiently eliminated. On the basis of these mechanisms, iNKT cell-targeted adjuvant cell therapies have been developed and have shown great promise in initial clinical trials on cancer patients.

NKT cells mediate pulmonary inflammation and dysfunction in murine sickle cell disease through production of IFN-gamma and CXCR3 chemokines

Ischemia-reperfusion injury (IRI) triggers an inflammatory cascade that is initiated by the activation of CD1d-restricted iNKT cells. In sickle cell disease (SCD), misshapen erythrocytes evoke repeated transient bouts of microvascular IRI. Compared with C57BL/6 controls, NY1DD mice have more numerous and activated (CD69(+), interferon-gamma(+) [IFN-gamma(+)]) lung, liver, and spleen iNKT cells that are hyperresponsive to hypoxia/reoxygenation. NY1DD mice have increased pulmonary levels of IFN-gamma, IFN-gamma-inducible chemokines (CXCL9, CXCL10), and elevated numbers of lymphocytes expressing the chemokine receptor CXCR3. Treating NY1DD mice with anti-CD1d antibody to inhibit iNKT cell activation reverses baseline pulmonary dysfunction manifested as elevated vascular permeability, decreased arterial oxygen saturation, and increased numbers of activated leukocytes. Anti-CD1d antibodies decrease pulmonary levels of IFN-gamma and CXCR3 chemokines. Neutralization of CXCR3 receptors ameliorates pulmonary dysfunction. Crossing NY1DD to lymphocyte-deficient Rag1(-/-) mice decreases pulmonary dysfunction. This is counteracted by the adoptive transfer of 1 million NKT cells. Like mice, people with SCD have increased numbers of activated circulating iNKT cells expressing CXCR3. Together, these data indicate that iNKT cells play a pivotal role in sustaining inflammation in SCD mice by a pathway involving IFN-gamma and production of chemotactic CXCR3 chemokines and that this mechanism may translate to human disease.

Characterization of the role of TCR gammadelta in NK cell accumulation during viral liver inflammation

Polyinosinic-polyctidylic acid (Poly I:C) is a viral RNA mimic that can induce immune responses similar to that seen during viral infection. Although poly I:C administration into mice is associated increased NK cell infiltrates in the liver, the mechanisms underlying increased hepatic NK cell accumulation in response to poly I:C administration are incompletely defined. In the current study, we have identified a novel and important role for gammadelta T cells in driving the accumulation and activation of NK cells in the liver during poly I:C-mediated viral liver infection. Specifically, NK cell accumulation but not activation in gammadelta T cell deficient mice following poly I:C administration was significantly attenuated in comparison to that seen in poly I:C-treated wildtype mice. The ability of gammadelta T cells to promote NK cell accumulation and activation in the liver may be virus-specific since NK cell accumulation in the liver was not altered by TCR gammadelta deficiency following adenovirus administration.

B7-H1 on hepatocytes facilitates priming of specific CD8 T cells but limits the specific recall of primed responses

BACKGROUND & AIMS

The requirement for costimulation of CD8 T-cell priming and restimulation by nonprofessional antigen-presenting cells is unresolved. Here, we investigated whether B7-H1 (CD274, PD-L1) on hepatocytes (HC) is involved in the specific activation of naive CD8 T cells or activated CD8 T blasts.

METHODS

Naive or activated CD8 T cells from transgenic OT-I mice were primed/restimulated by peptide-pulsed HC, and their proliferation and effector response were determined. We used blocking monoclonal antibodies against B7-H1 and HC from B7-H1-deficient mice to assign a costimulatory or coinhibitory role to B7-H1 for CD8 T-cell priming/restimulation.

RESULTS

Blockade of B7-H1 on HC down modulated interferon (IFN)-gamma production and proliferation of HC-primed CD8 T cells, indicating a costimulatory role for B7-H1 in priming CD8 T cells. In contrast, the PD-1/B7-H1 interaction inhibited proliferation and interferon-gamma release of effector/memory CD8 T blasts specifically restimulated by peptide-pulsed HC.

CONCLUSIONS

B7-H1 differentially modulates the different stages of the specific CD8 T-cell response triggered by HC, and, whereas it costimulates priming and cytokine responses of naive CD8 T cells, it coinhibits their specific local recall of effector cytokine responses. The interaction of CD8 T cells with B7-H1(+) HC can thus fine-tune proliferative and effector responses of specific CD8 T cells reacting locally to nonprofessional antigen-presenting cells infected with hepatotropic agents.

Critical role for CD1d-restricted invariant NKT cells in stimulating intrahepatic CD8 T-cell responses to liver antigen

BACKGROUND & AIMS

V alpha14 invariant natural killer T cells (iNKT) are localized in peripheral tissues such as the liver rather than lymphoid tissues. Therefore, their role in modulating the stimulation of conventional, major histocompatibility complex (MHC)-restricted T-cell responses has remained ambiguous. We here describe a role for V alpha14 iNKT cells in modulating conventional T-cell responses to antigen expressed in liver, using transferrin-mOVA (Tf-mOVA) mice.

METHODS

Naïve ovalbumin-specific class I MHC-restricted T cells (OTI) were adoptively transferred into Tf-mOVA mice in the presence or absence of iNKT-cell agonist alpha-galactosylceramide, after which OTI T-cell priming, antigen-specific cytokine production, cytotoxic killing ability, and liver damage were analyzed.

RESULTS

Transfer of OTI cells resulted in robust intrahepatic, antigen-specific proliferation of T cells. OTI T cells were activated in liver, and antigen-specific effector function was stimulated by coactivation of Valpha14 iNKT cells using alpha-galactosylceramide. This stimulation was absent in CD1d(-/-)Tf-mOVA mice, which lack V alpha14 iNKT cells, and was prevented when interferon-gamma and tumor necrosis factor-alpha production by V alpha14 iNKT cells was blocked.

CONCLUSIONS

CD1d-restricted V alpha14 iNKT cells stimulate intrahepatic CD8 T-cell effector responses to antigen expressed in liver. Our findings elucidate a previously unknown intervention point for targeted immunotherapy to autoimmune and possibly infectious liver diseases.

Activation-induced NKT cell hyporesponsiveness protects from alpha-galactosylceramide hepatitis and is independent of active transregulatory factors

NK T (NKT) cells, unique lymphocytes expressing features of NK and T lymphocytes, can specifically be activated with the glycolipid antigen alpha-galactosylceramide (alpha-GalCer). In humans and mice, this activation provokes pronounced cytokine responses. In C57BL/6 mice, alpha-GalCer injection additionally induces NKT-mediated liver injury, representing a model for immune-mediated hepatitis in humans. However, a single alpha-GalCer pretreatment of mice prevented NKT-mediated liver injury, cytokine responses (systemically and locally in the liver), and up-regulation of hepatocellular Fas upon alpha-GalCer rechallenge. As alpha-GalCer is used as a NKT cell-activating agent in clinical trials, an investigation of tolerance induction appears crucial. We demonstrate that alpha-GalCer tolerance does not depend on Kupffer cells, IL-10, Caspase-3-mediated apoptosis, or CD4+CD25+ T regulatory cells (Tregs), which are crucial in other models of immunological tolerance. Amending relevant, earlier approaches of others, we cocultivated highly purified, nontolerized and tolerized liver NKT cells ex vivo and could convincingly exclude the relevance of transdominant NKT Tregs. These results strongly suggest alpha-GalCer-induced tolerance to be exclusively caused by NKT cell intrinsic hyporesponsiveness. Tolerized mice showed specific diminishment of the intrahepatic CD4+ NKT cell subpopulation, with the CD4(-) population largely unaffected, and revealed down-modulation of alpha-GalCer-specific TCR and the NKT costimulator glucocorticoid-induced TNFR-related protein on liver NKT cells, whereas inhibitory Ly49I was increased. In conclusion, alpha-GalCer tolerance could serve as a model for the frequently observed NKT cell hyporesponsiveness in tumor patients and might help to develop strategies for their reactivation. Conversely, approaches to render NKT cells hyporesponsive may constitute new therapeutic strategies for diseases, where aberrant NKT cell activation is causally involved.

Critical role for CXC chemokine ligand 16 (SR-PSOX) in Th1 response mediated by NKT cells

The transmembrane chemokine CXCL 16 (CXCL16), which is the same molecule as the scavenger receptor that binds phosphatidylserine and oxidized lipoprotein (SR-PSOX), has been shown to mediate chemotaxis and adhesion of CXC chemokine receptor 6-expressing cells such as NKT and activated Th1 cells. We generated SR-PSOX/CXCL16-deficient mice and examined the role of this chemokine in vivo. The mutant mice showed a reduced number of liver NKT cells, and decreased production of IFN-gamma and IL-4 by administration of alpha-galactosylceramide (alphaGalCer). Of note, the alphaGalCer-induced production of IFN-gamma was more severely impaired than the production of IL-4 in SR-PSOX-deficient mice. In this context, SR-PSOX-deficient mice showed impaired sensitivity to alphaGalCer-induced anti-tumor effect mediated by IFN-gamma from NKT cells. NKT cells from wild-type mice showed impaired production of IFN-gamma, but not IL-4, after their culture with alphaGalCer and APCs from mutant mice. Moreover, Propionibacterium acnes-induced in vivo Th1 responses were severely impaired in SR-PSOX-deficient as well as NKT KO mice. Taken together, SR-PSOX/CXCL16 plays an important role in not only the production of IFN-gamma by NKT cells, but also promotion of Th1-inclined immune responses mediated by NKT cells.

New concepts in the immunopathogenesis of chronic hepatitis B: the importance of the innate immune response

Acute and chronic infection with hepatitis B virus (HBV) is associated with an increased risk of developing liver disease including cirrhosis, decompensated liver disease, and hepatocellular carcinoma. The clinical presentation and natural history of HBV infection is mediated through complex interactions between the virus and the host immune response. HBV is not directly cytopathic to heptocytes; however, the interaction between the virus and the host immune response plays a central role in the pathogenesis of necroinflammation and liver fibrosis. Emerging data from immunopathogenesis studies in animal models and in vitro studies of liver biopsies from patients with chronic hepatitis B demonstrate a potentially important interaction between hepatitis B e antigen, HBV, and components of the innate immune response including Toll-like receptors, Kupffer cells, natural killer T-cells, and dendritic cells. These findings suggest that the innate immune response has an important role in influencing the outcome of acute and chronic HBV infection. The current knowledge regarding the interaction between HBV and components of the innate immune response during acute and chronic HBV infection is reviewed.

Regulatory roles of CD1d-restricted NKT cells in the induction of toxic shock-like syndrome in an animal model of fatal ehrlichiosis

CD1d-restricted NKT cells are key players in host defense against various microbial infections. Using a murine model of fatal ehrlichiosis, we investigated the role of CD1d-restricted NKT cells in induction of toxic shock-like syndrome caused by gram-negative, lipopolysaccharide-lacking, monocytotropic Ehrlichia. Our previous studies showed that intraperitoneal infection of wild-type (WT) mice with virulent Ehrlichia (Ixodes ovatus Ehrlichia [IOE]) results in CD8+ T-cell-mediated fatal toxic shock-like syndrome marked by apoptosis of CD4+ T cells, a weak CD4+ Th1 response, overproduction of tumor necrosis factor alpha and interleukin-10, and severe liver injury. Although CD1d-/- mice succumbed to high-dose IOE infection similar to WT mice, they did not develop signs of toxic shock, as shown by elevated bacterial burdens, low serum levels of tumor necrosis factor, normal serum levels of liver enzymes, and the presence of few apoptotic hepatic cells. An absence of NKT cells restored the percentages and absolute numbers of CD4+ and CD8+ T cells and CD11b+ cells in the spleen compared to WT mice and was also associated with decreased expression of Fas on splenic CD4+ lymphocytes and granzyme B in hepatic CD8+ lymphocytes. Furthermore, our data show that NKT cells promote apoptosis of macrophages and up-regulation of the costimulatory molecule CD40 on antigen-presenting cells, including dendritic cells, B cells, and macrophages, which may contribute to the induction of pathogenic T-cell responses. In conclusion, our data suggest that NKT cells mediate Ehrlichia-induced T-cell-mediated toxic shock-like syndrome, most likely via cognate and noncognate interactions with antigen-presenting cells.

Hepatitis C virus core protein impairs in vitro priming of specific T cell responses by dendritic cells and hepatocytes

BACKGROUND/AIMS

Hepatitis C virus leads to chronic hepatitis in the majority of infected individuals. The mechanism of viral persistence is not completely understood. Hepatitis C virus core protein is produced within hepatocytes and is secreted during HCV infection. Our study characterizes the effects of core protein on T cell priming in mice.

METHODS

We used a system of antigen-specific in vitro priming of CD4(+) and CD8(+) T cells by myeloid dendritic cells, hepatoma cells or primary hepatocytes. Core protein was either added to the cultures or expressed by antigen-presenting cells.

RESULTS

Antigen-presenting cells treated with core protein showed reduced surface expression of major histocompatibility molecules. Myeloid dendritic cells showed also reduced expression of costimulatory molecules. CD4(+) and CD8(+) T cells primed by these cells showed defects in activation, proliferation, and cytokine production. Importantly, CD4(+) and also CD8(+) T cells primed in the presence of core protein showed an increase in interleukin-10 production resembling the phenotype of regulatory T cells.

CONCLUSIONS

Hepatitis C virus core protein inhibits priming of antigen-specific CD4(+) and CD8(+) T cell responses by downregulation of major histocompatibility molecules and costimulatory molecules on antigen-presenting cells and induces development of IL-10-producing T cells.

CD1 expression on antigen-presenting cells

CD1 proteins present self and microbial glycolipids to CD 1-restricted T cells, or in the case of CD1d, to NKT cells. The CD1 family in humans consists of group I proteins CDla, CDlb, CDlc, and CDle and the group II protein CDld. Rodents express only CDld, but as CD1d is broadly expressed and traffics to all endosomal compartments, this single CD1 family member is thereby able to acquire antigens in many subcellular compartments. A complete understanding of the CD 1 family requires an appreciation of which cells express CD1 and how CD1 contributes to the unique function of each cell type. While group I CD 1 expression is limited to thymocytes and professional APCs, CD1d has a wider tissue distribution and can be found on many nonhematopoietic cells. The expression and regulation of CD1 are presented here with particular emphasis on the function of CD1 in thymocytes, B cells, monocytes and macrophages, dendritic cells (DCs), and intestinal epithelial cells (IECs). Altered expression of CD 1 in cancer, autoimmunity, and infectious disease is well documented, and the implication of CD 1 expression in these diseases is discussed.

Invariant NKT cells and tolerance

Invariant natural killer T (iNKT) cells are innate cells that can bias an immune response toward inflammation or toward a negative regulatory response. iNKT cells can produce cytokines immediately on exposure to activating signals, but the role of iNKT cells in the differentiation of T regulatory (Treg) cells and peripheral tolerance was elucidated only within the past decade. The purpose of this review is to outline the current knowledge of how iNKT cells function in various tolerance paradigms. The roles of iNKT cell in anterior chamber-associated immune deviation (ACAID), oral tolerance, other tolerance systems, and autoimmune diseases is discussed.

The Pro-Th1 Cytokine IL-12 Enhances IL-4 Production by Invariant NKT Cells: Relevance for T Cell-Mediated Hepatitis

IL-12 is essential for invariant NKT (iNKT) cells because it can maintain a functionally active population and promote a cytokine profile that is assumed to be mainly of the pro-Th1 type. We used the murine concanavalin A (Con A)-induced hepatitis model, in which iNKT cells, IL-12, IL-4, and IFN-gamma are equally requisite, to reevaluate this issue. We demonstrate that IL-12 interacts directly with iNKT cells, contributes to their recruitment to the liver, and enhances their IL-4 production, which is essential for disease onset. IL-12-deficient mice were less susceptible to experimental hepatitis and their iNKT cells produced less IL-4 than their wild-type counterpart. A normal response could be restored by IL-12 injection, revealing its importance as endogenous mediator. In accordance with this observation, we found that iNKT cells expressed the IL-12R constitutively, in contrast to conventional T cells. Furthermore, the physiological relevance of our data is supported by the lower susceptibility to disease induction of NOD mice, known for their inherent functional and numerical abnormalities of iNKT cells associated with decreased iNKT cell-derived IL-4 production and low IL-12 secretion. Taken together, our findings provide the first evidence that IL-12 can enhance the immune response through increased IL-4 production by iNKT cells, underscoring once more the functional plasticity of this subset.

Type I IFN-producing CD4 Valpha14i NKT cells facilitate priming of IL-10-producing CD8 T cells by hepatocytes

Upon entering the liver CD8 T cells encounter large numbers of NKT cells patrolling the hepatocyte (HC) surface facing the perisinusoidal space. We asked whether hepatic NKT cells modulate the priming of CD8 T cells by HC. Hepatic (alpha-galactosyl-ceramide-loaded CD1d dimer binding) NKT cells produce predominantly IL-4 when stimulated with glycolipid-presenting HC but predominantly IFN-gamma when stimulated with glycolipid-presenting dendritic cells. These NKT cells prime naive CD8 T cells to a (K(b)-presented) peptide ligand if they simultaneously recognize a CD1d-binding glycolipid presented to them on the surface of the responding CD8 T cells that they prime. No IL-10-producing CD8 T cells are detected if these T cells are primed by either HC or NKT cells. In contrast, IL-10 is produced by HC-primed CD8 T cells if IFN-beta-producing NKT cells are coactivated by the same HC presenting a glycolipid (in the context of CD1d) and an antigenic peptide (in the context of K(b)). Hence, IL-10-producing CD8 T cells are generated in a type I IFN-dependent manner if the three cell types (CD8 T cells, NKT cells, and ligand-presenting HC) specifically and closely interact. IL-10-producing CD8 T cells generated under these conditions down-modulate IL-2 (and proliferative) responses of naive CD4 or CD8 T cells primed by DC. If in close proximity, NKT cells can thus locally modulate the phenotype of CD8 T cells during their priming by HC thereby limiting the local activation of proinflammatory immune effector cells and protecting the liver against immune injury.

Primary infection of C57BL/6 mice with Plasmodium yoelii induces a heterogeneous response of NKT cells

NKT cells are a population of innate-like lymphocytes that display effector functions and immunoregulatory properties. We characterized the NKT cell response induced in C57BL/6 mice during a primary infection with Plasmodium yoelii sporozoites. We observed a heterogeneous NKT cell response that differed between liver and spleen. Hepatic NKT cells found in infected livers consisted mainly of CD1d-dependent CD4+ and double-negative (DN) NKT cells, whereas CD1d-independent NKT cells exhibiting a TCR(high) CD4(high) phenotype were prominent among splenic NKT cells during the infection. Hepatic and splenic NKT cells isolated from infected mice were activated and secreted mainly gamma interferon and tumor necrosis factor alpha in response to stimulation. Finally, P. yoelii-activated hepatic DN NKT cells inhibited the parasite's liver stage in a CD1d-dependent manner in vitro. However, experiments using B6.CD1d-deficient mice showed that CD1d and CD1d-restricted NKT cells are not necessary to control the parasite's development in vivo during neither the preerythrocytic stage nor the erythrocytic stage. Thus, our results show that a primary P. yoelii infection induces a heterogeneous and organ-specific response of NKT cells and that CD1d-dependent NKT cells play a minor role in the control of the development of Plasmodium in vivo in our model.

The murine liver is a potential target organ for IL-19, IL-20 and IL-24: Type I Interferons and LPS regulate the expression of IL-20R2

BACKGROUND/AIMS

The biological functions of the recently discovered IL-10-related cytokines IL-19, IL-20, IL-22, IL-24 and their receptors IL-20R1, IL-20R2 and IL-22R are not clear. Therefore, the expression of these cytokines and their receptors in the hepatic acute phase response to LPS was analysed. Type I interferons have important immunomodulatory functions in bacterial infections. We investigated if they influence release and organ-specific expression of TNF, IL-6 and IL-10 and the responsiveness of liver to IL-10 related cytokines during the reaction to LPS in vivo.

METHODS

B6 and congenic IFNAR-/- mice were intraperitoneally injected with 5mg/kg LPS. Systemic release of cytokines was quantified by ELISA. Organ-specific expression of cytokines and their receptors was evaluated by (semi quantitative or quantitative) RT-PCR.

RESULTS

The cytokines IL-19, IL-22 and the IL-20R2 receptor subunit are up-regulated by LPS in the liver of normal mice. IFNalpha/beta enhance the secretion and expression of IL-6 and IL-10 during the response to LPS, but also the up-regulation of IL-20R2 expression.

CONCLUSIONS

We show that the liver is a potential target for IL-19, IL-20 and IL-24. During an LPS response, IFNalpha/beta influence cytokine secretion and expression and possibly the response to IL-19 and IL-24.

Murine liver plasmacytoid dendritic cells become potent immunostimulatory cells after Flt-3 ligand expansion

The liver has unique immunological properties. Although dendritic cells (DCs) are central mediators of immune regulation, little is known about liver DCs. Plasmacytoid DCs (pDCs) are a recently identified subtype of murine liver DC. We sought to define the function of freshly isolated murine liver pDCs. We found that normal liver pDCs were weak in stimulating T cells, yet they possessed a proinflammatory cytokine profile with high tumor necrosis factor-alpha and low IL-10 secretion. To facilitate the investigation of murine liver pDCs, we expanded them in vivo with fms-like tyrosine kinase 3 ligand (Flt3L). After Toll-like receptor-9 ligation, expanded liver pDCs secreted high levels of IFN-alpha and were able to stimulate NK cells, NKT cells, and antigen-specific CD8+ T cells in vitro. In addition, Flt3L expansion alone generated pDCs capable of activating antigen-specific CD8+ T cells in vivo.

CONCLUSION

Unstimulated liver pDCs exist in a latent state with the potential to become potent activators of the innate and adaptive immune systems through their interactions with other immune effectors. Our findings have implications for understanding the role of the liver in tolerance and immunity.

Functional Adaptive CD4 Foxp3 T Cells Develop in MHC Class II-Deficient Mice

CD4 Foxp3 regulatory T (T(R)) cells are well-defined regulator T cells known to develop in the thymus through positive selection by medium-to-high affinity TCR-MHC interactions. We asked whether Foxp3 T(R) cells can be generated in the complete absence of MHC class II molecules. CD4 Foxp3 T(R) cells are found in secondary lymphoid tissues (spleen and lymph nodes) and peripheral tissues (liver) but not the thymus of severely MHC class II-deficient (Aalpha(-/-) B6) mice. These T(R) cells preferentially express CD103 (but not CD25) but up-regulate CD25 surface expression to high levels in response to TCR-mediated activation. MHC class II-independent Foxp3 T(R) cells down modulate vaccine-induced, specific antiviral CD8 T cell responses of Aalpha(-/-) B6 mice in vivo. Furthermore, these T(R) cells suppress IL-2 release and proliferative responses in vitro of naive CD25(-) (CD4 or CD8) T cells from normal B6 mice primed by bead-coupled anti-CD3/anti-CD28 Ab as efficiently as CD4CD25(high) T(R) cells from congenic, normal B6 mice. MHC class II-independent CD4 Foxp3(+) T(R) cells thus preferentially express the (TGF-beta-induced) integrin molecule alpha(E) (CD103), are generated mainly in the periphery and efficiently mediate immunosuppressive effects.

Invariant NKT cells rapidly activated via immunization with diverse contact antigens collaborate in vitro with B-1 cells to initiate contact sensitivity

In cutaneous contact sensitivity there is an early elicited innate cascade of complement, mast cells, and platelets activated via IgM Abs. This response is required to initiate the elicitation of acquired classical contact sensitivity by leading to local recruitment of effector T cells. We recently performed in vivo experiments showing that collaboration is required between innate-like invariant Valpha14+ NKT cells (iNKT) and the innate-like B-1 B cell subset to induce this initiation process. Contact sensitization triggers iNKT cells to produce IL-4 to coactivate the B-1 cells along with specific Ag for production of the initiating IgM Abs. We now describe in vitro collaboration of iNKT and B-1 cells. Normal peritoneal B-1 cells, incubated in vitro with soluble Ag, and with 1-h in vivo immune iNKT cells producing IL-4, are activated to mediate the contact sensitivity-initiation cascade. The three components of this process can be activated by different Ag. Thus, 1-h iNKT cell activation, B-1 cell stimulation, and generation of immune effector T cells can be induced by sensitization with three different Ag to respectively generate IL-4 and Ag-specific IgM Abs, to recruit the Ag-specific effector T cells. These findings have relevance to allergic and autoimmune diseases in which infections can trigger exacerbation of T cell responses to allergens or to autoantigens.

Cytokine-induced killer T cells kill immature dendritic cells by TCR-independent and perforin-dependent mechanisms

Cytokine-induced killer (CIK) cells are ex vivo, expanded T cells with proven anticancer activity in vitro and in vivo. However, their functional properties with the exception of their cancer cell-killing activity are largely unclear. Here, we show that CIK T cells recognize dendritic cells (DC), and although mature DC (mDC) induce CIK T cells to produce IFN-gamma, immature DC (iDC) are killed selectively by them. Moreover, CIK T cell activation by mDC and their destruction of iDC are independent of the TCR. The cytotoxicity of CIK T cells to iDC is perforin-dependent. Our data have revealed an important regulatory role of CIK cells.

The immune response during hepatitis B virus infection

Hepatitis B virus (HBV) is a major cause of chronic liver inflammation worldwide. Recent knowledge of the virological and immunological events secondary to HBV infection has increased our understanding of the mechanisms involved in viral clearance and persistence. In this review, how the early virological and immunological events might influence the development of a coordinate activation of adaptive immunity necessary to control HBV infection is analysed. The mechanism(s) by which high levels of viral antigens, liver immunological features, regulatory cells and dendritic cell defects might maintain the HBV-specific immunological collapse, typical of chronic hepatitis B patients, is also examined.

Characterization of human liver dendritic cells in liver grafts and perfusates

It is generally accepted that donor myeloid dendritic cells (MDC) are the main instigators of acute rejection after organ transplantation. The aim of the present study was to characterize MDC in human donor livers using liver grafts and perfusates as a source. Perfusates were collected during ex vivo vascular perfusion of liver grafts pretransplantation. MDC, visualized in wedge biopsies by immunohistochemistry with anti-BDCA-1 monoclonal antibody (mAb), were predominantly observed in the portal fields. Liver MDC, isolated from liver wedge biopsies, had an immature phenotype with a low expression of CD80 and CD83. Perfusates were collected from 20 grafts; perfusate mononuclear cells (MNC) contained 1.5% (range, 0.3-6.6%) MDC with a viability of 97 +/- 2%. Perfusates were a rich source of hepatic MDC since 0.9 x 10(6) (range, 0.11-4.5 x 10(6)) MDC detached from donor livers during vascular perfusion pretransplantation. Perfusate MDC were used to further characterize hepatic MDC. Perfusate MDC expressed less DC-LAMP (P = 0.000), CD80 (P = 0.000), CD86 (P = 0.003), and CCR7 (P = 0.014) than mature hepatic lymph node (LN) MDC, and similar CD86 (P = 0.140) and CCR7 (P = 0.262) as and more DC-LAMP (P = 0.007) and CD80 (P = 0.002) than immature blood MDC. Perfusate MDC differed from blood MDC in producing significantly higher amounts of interleukin (IL)-10 in response to lipopolysaccharide (LPS), and in being able to stimulate allogeneic T-cell proliferation. In conclusion, human donor livers contain exclusively immature MDC that detach in high numbers from the liver graft during pretransplantation perfusion. These viable MDC have the capacity to stimulate allogeneic T-cells, and thus may represent a major player in the induction of acute rejection.

Invariant NKT cells are essential for the regulation of hepatic CXCL10 gene expression during Leishmania donovani infection

Gamma interferon (IFN-gamma)-regulated chemokines of the CXC family have been implicated as key regulators of a variety of T-cell-dependent inflammatory processes. However, the cellular source(s) of IFN-gamma that regulates their early expression has rarely been defined. Here, we have directly addressed this question in mice after Leishmania donovani infection. Comparison of CXCL10 mRNA accumulation in normal and IFN-gamma-deficient mice confirmed an absolute requirement for IFN-gamma for sustained (24 h) expression of CXCL10 mRNA accumulation in this model. In normal mice, IFN-gamma was produced by both CD3int NK1.1+ NKT cells and CD3- NK1.1+ NK cells, as detected by intracellular flow cytometry. Strikingly, B6.Jalpha281-/- mice lacking NKT cells that express the invariant Valpha14Jalpha18 T-cell-receptor alpha chain, although retaining a significant population of IFN-gamma-producing NK cells and NKT cells, were unable to sustain CXCL10 mRNA accumulation. These data indicate that invariant NKT cells are indispensable for the regulation of hepatic CXCL10 gene expression during L. donovani infection.