Role of CD1d-restricted NKT cells in microbial immunity

ScRNA-Seq Analyses Define the Role of GATA3 in iNKT Cell Effector Lineage Differentiation

While the transcription factor GATA-3 is well-established for its crucial role in T cell development, its specific influence on invariant natural killer T (iNKT) cells remains relatively unexplored. Using flow cytometry and single-cell transcriptomic analysis, we demonstrated that GATA-3 deficiency in mice leads to the absence of iNKT2 and iNKT17 cell subsets, as well as an altered distribution of iNKT1 cells. Thymic iNKT cells lacking GATA-3 exhibited diminished expression of PLZF and T-bet, key transcription factors involved in iNKT cell differentiation, and reduced production of Th2, Th17, and cytotoxic effector molecules. Single-cell transcriptomics revealed a comprehensive absence of iNKT17 cells, a substantial reduction in iNKT2 cells, and an increase in iNKT1 cells in GATA-3-deficient thymi. Differential expression analysis highlighted the regulatory role of GATA-3 in T cell activation signaling and altered expression of genes critical for iNKT cell differentiation, such as Icos, Cd127, Eomes, and Zbtb16. Notably, restoration of Icos, but not Cd127, expression could rescue iNKT cell development in GATA-3-deficient mice. In conclusion, our study demonstrates the pivotal role of GATA-3 in orchestrating iNKT cell effector lineage differentiation through the regulation of T cell activation pathways and Icos expression, providing insights into the molecular mechanisms governing iNKT cell development and function.

Early Activation of iNKT Cells Increased Survival Time of BALB/c Mice in a Murine Model of Melioidosis

Melioidosis is an infectious disease caused by Burkholderia pseudomallei. High interferon gamma (IFN-γ) levels in naive mice were reported to mediate protection against B. pseudomallei infection. Invariant natural killer T (iNKT) cells can produce and secrete several cytokines, including IFN-γ. When iNKT cell-knockout (KO) BALB/c mice were infected with B. pseudomallei, their survival time was significantly shorter than wild-type mice. Naive BALB/c mice pretreated intraperitoneally with α-galactosylceramide (α-GalCer), an iNKT cell activator, 24 h before infection demonstrated 62.5% survival at the early stage, with prolonged survival time compared to nonpretreated infected control mice (14 ± 1 days versus 6 ± 1 days, respectively). At 4 h after injection with α-GalCer, treated mice showed significantly higher levels of serum IFN-γ, interleukin-4 (IL-4), IL-10, and IL-12 than control mice. Interestingly, the IFN-γ levels in the α-GalCer-pretreated group were decreased at 4, 24, and 48 h after infection, while they were highly increased in the control group. At 24 h postinfection in the α-GalCer group, bacterial loads were significantly lower in blood (no growth and 1,780.00 ± 51.21, P < 0.0001), spleens (no growth and 34,300 ± 1,106.04, P < 0.0001), and livers (1,550 ± 68.72 and 13,400 ± 1,066.67, P < 0.0001) than in the control group, but not in the lungs (15,300 ± 761.10 and 1,320 ± 41.63, P < 0.0001), and almost all were negative at 48 h postinfection. This study for the first time shows that early activation of iNKT cells by α-GalCer helps clearance of B. pseudomallei and prolongs mouse survival.

Viral PB1-F2 and host IFN-γ guide ILC2 and T cell activity during influenza virus infection

The regulation of functional immune cell plasticity is poorly understood. Host environmental cues are critical, but the possible influence of pathogen-derived virulence factors has not been described. We have used reverse-engineered influenza A viruses that differ in PB1-F2 activity to analyze influenza in mice in the presence or absence of host interferon (IFN)-γ. In the absence of functional PB1-F2 and IFN-γ, lung ILC2s initiated robust IL-5 responses following viral challenge, which led to improved tissue integrity and survival. Conversely, functional PB1-F2 suppressed IL-5⁺ ILC2 responses and induced a dominant IL-13⁺ CD8 T cell response regardless of host IFN-γ. These findings demonstrate the critical interplay between the viral virulence factors and host cytokines in regulating protective pulmonary immunity during influenza virus infection.

Functional plasticity of innate lymphoid cells (ILCs) and T cells is regulated by host environmental cues, but the influence of pathogen-derived virulence factors has not been described. We now report the interplay between host interferon (IFN)-γ and viral PB1-F2 virulence protein in regulating the functions of ILC2s and T cells that lead to recovery from influenza virus infection of mice. In the absence of IFN-γ, lung ILC2s from mice challenged with the A/California/04/2009 (CA04) H1N1 virus, containing nonfunctional viral PB1-F2, initiated a robust IL-5 response, which also led to improved tissue integrity and increased survival. Conversely, challenge with Puerto Rico/8/1934 (PR8) H1N1 virus expressing fully functional PB1-F2, suppressed IL-5⁺ ILC2 responses, and induced a dominant IL-13⁺ CD8 T cell response, regardless of host IFN-γ expression. IFN-γ–deficient mice had increased survival and improved tissue integrity following challenge with lethal doses of CA04, but not PR8 virus, and increased resistance was dependent on the presence of IFN-γR⁺ ILC2s. Reverse-engineered influenza viruses differing in functional PB1-F2 activity induced ILC2 and T cell phenotypes similar to the PB1-F2 donor strains, demonstrating the potent role of viral PB1-F2 in host resistance. These results show the ability of a pathogen virulence factor together with host IFN-γ to regulate protective pulmonary immunity during influenza infection.

Immunomodulatory properties of characellide A on human peripheral blood mononuclear cells

Marine sponges and their associated microbiota are multicellular animals known to produce metabolites with interesting pharmacological properties playing a pivotal role against a plethora of pathologic disorders such as inflammation, cancer and infections. Characellide A and B belong to a novel class of glycolipopeptides isolated from the deep sea marine sponge Characella pachastrelloides. In this study, we have evaluated the effects of characellide A and B on cytokine and chemokine release from human peripheral blood mononuclear cells (PBMC). Characellide A induces a concentration- and time-dependent CXCL8, IL-6 and TNF-α release from PBMC. This production is mediated by the induction of gene transcription. Moreover, cytokine/chemokine release induced by characellide A from PBMC is CD1d-dependent because a CD1d antagonist, 1,2-bis(diphenylphosphino)ethane [DPPE]-polyethylene glycolmonomethylether [PEG], specifically inhibits characellide A-induced activation of PBMC. In conclusion, characellide A is a novel modulator of adaptative/innate immune responses. Further studies are needed to understand its potential pharmacological application.

A double-edged sword of immuno-microenvironment in cardiac homeostasis and injury repair

The response of immune cells in cardiac injury is divided into three continuous phases: inflammation, proliferation and maturation. The kinetics of the inflammatory and proliferation phases directly influence the tissue repair. In cardiac homeostasis, cardiac tissue resident macrophages (cTMs) phagocytose bacteria and apoptotic cells. Meanwhile, NK cells prevent the maturation and transport of inflammatory cells. After cardiac injury, cTMs phagocytose the dead cardiomyocytes (CMs), regulate the proliferation and angiogenesis of cardiac progenitor cells. NK cells prevent the cardiac fibrosis, and promote vascularization and angiogenesis. Type 1 macrophages trigger the cardioprotective responses and promote tissue fibrosis in the early stage. Reversely, type 2 macrophages promote cardiac remodeling and angiogenesis in the late stage. Circulating macrophages and neutrophils firstly lead to chronic inflammation by secreting proinflammatory cytokines, and then release anti-inflammatory cytokines and growth factors, which regulate cardiac remodeling. In this process, dendritic cells (DCs) mediate the regulation of monocyte and macrophage recruitment. Recruited eosinophils and Mast cells (MCs) release some mediators which contribute to coronary vasoconstriction, leukocyte recruitment, formation of new blood vessels, scar formation. In adaptive immunity, effector T cells, especially Th17 cells, lead to the pathogenesis of cardiac fibrosis, including the distal fibrosis and scar formation. CMs protectors, Treg cells, inhibit reduce the inflammatory response, then directly trigger the regeneration of local progenitor cell via IL-10. B cells reduce myocardial injury by preserving cardiac function during the resolution of inflammation.

The assembly of glycosphingolipid determines their immunomodulatory effect: A novel method for structure-based design of immunotherapy

Structure-activity relationships provide insight into the binding interactions of beta-glycosphingolipids (GSLs) with both the TCR and the CD1d molecules, as well as the subsequent immunologic response of regulatory NKT cells.

AIM

To determine the effects of synthetic GSL structures on their immune modulatory functions.

METHODS

GSLs of various structures were tested in vitro and in an animal model of Concanavalin A (ConA) immune-mediated hepatitis.

RESULTS

In vitro, using SV40 binding to live monkey CV1 cells, the l-threo stereoisomer of C8-β-LacCer inhibits caveolar internalization, reducing viral binding to the cell surface. In vivo, in the ConA model, LR172, which has a saturated C8 chain, and LR178, which has a trans double bond at C-2 in the C8 chain, suppressed the immune-mediated liver inflammation and reduced IFNγ levels in a dose dependent manner. The beneficial effects of LR172 and of LR178 are associated with suppression of liver apoptosis, increased phosphorylated STAT3 expression in the liver, and an increase in the NKT liver/spleen ratio.

SUMMARY

The assembly of GSLs determines their immunomodulatory effect and can serve as a method for structure-based design of immunotherapy.

The Squeaky Yeast Gets Greased: The Roles of Host Lipids in the Clearance of Pathogenic Fungi

Fungal infections remain a global health threat with high morbidity and mortality. The human immune system must, therefore, perpetually defend against invasive fungal infections. Phagocytosis is critical for the clearance of fungal pathogens, as this cellular process allows select immune cells to internalize and destroy invading fungal cells. While much is known about the protein players that enable phagocytosis, the various roles that lipids play during this fundamental innate immune process are still being illuminated. In this review, we describe recent discoveries that shed new light on the mechanisms by which host lipids enable the phagocytic uptake and clearance of fungal pathogens.

CD1d-dependent natural killer T cells attenuate angiotensin II-induced cardiac remodelling via IL-10 signalling in mice

Aims

CD1d is a member of the cluster of differentiation 1 (CD1) family of glycoproteins expressed on the surface of various antigen-presenting cells, which is recognized by natural killer T (NKT) cells. CD1d-dependent NKT cells play an important role in immune-mediated diseases; but the role of these cells in regulating cardiac remodelling remains unknown.

Methods and results

Cardiac remodelling was induced by angiotensin (Ang) II infusion for 2 weeks. Ang II-induced increase in hypertension, cardiac performance, hypertrophy and fibrosis, inflammatory response, and activation of the NF-kB and TGF-β1/Smad2/3 pathways was significantly aggravated in CD1d knockout (CD1dko) mice compared with wild-type (WT) mice, but these effects were markedly abrogated in WT mice treated with α-galactosylceramide (αGC), a specific activator of NKT cells. Adoptive transfer of CD1dko bone marrow cells to WT mice further confirmed the deleterious effect of CD1dko. Moreover, IL-10 expression was significantly decreased in CD1dko hearts but increased in αGC-treated mice. Co-culture experiments revealed that CD1dko dendritic cells significantly reduced IL-10 mRNA expression from NKT cells. Administration of recombinant murine IL-10 to CD1dko mice improved hypertension, cardiac performance, and adverse cardiac remodelling induced by Ang II, and its cardioprotective effect was possibly associated with activation of STAT3, and inhibition of the TGF-β1 and NF-kB pathways.

Conclusion

These findings revealed a previously undefined role for CD1d-dependent NKT cells in Ang II-induced cardiac remodelling, hence activation of NKT cells may be a novel therapeutic target for hypertensive cardiac disease.

Invariant NKT cells facilitate cytotoxic T-cell activation via direct recognition of CD1d on T cells

Invariant natural killer T (iNKT) cells are a major subset of NKT cells that recognize foreign and endogenous lipid antigens presented by CD1d. Although iNKT cells are characteristically autoreactive to self-antigens, the role of iNKT cells in the regulation of cytotoxic T lymphocytes (CTL) has been elucidated using α-galactosylceramide (α-GalCer), a strong synthetic glycolipid that is presented by professional antigen presenting cells (APCs), such as dendritic cells. Despite the well-known effects of α-GalCer and dendritic cells on lipid antigen presentation, the physiological role of endogenous antigens presented by CTLs during crosstalk with iNKT cells has not yet been addressed. In this study, we found that antigen-primed CTLs with transient CD1d upregulation could present lipid self-antigens to activate the iNKT cell production of IFN-γ. CTL-mediated iNKT cell activation in turn enhanced IFN-γ production and the proliferation and cytotoxicity of CTLs. We also found that the direct interaction of iNKT cells and CTLs enhanced the antitumor immune responses of CTLs. This partially explains the functional role of iNKT cells in CTL-mediated antitumor immunity. Our findings suggest that in the absence of exogenous iNKT cell ligands, iNKT cells enhanced the CTL production of IFN-γ and CTL proliferation and cytotoxicity via direct interaction with CD1d expressed on T cells without interacting with APCs.

Cancer-killing T cells engage in a form of molecular crosstalk with other specialized immune cells to enhance anti-tumor immune responses in mice. Se-Ho Park and colleagues from Korea University in Seoul, South Korea, studied a specialized population of immune cells known as invariant natural killer T (iNKT) cells, which serve as important mediators of tumor surveillance. They showed that iNKT cells directly interact with cancer-killing cytotoxic T cells through surface molecules and not through other immune cells. The resulting activation of iNKT cells leads to the production of a pro-inflammatory signaling molecule, which in turn enhances the proliferation and killing potential of the cytotoxic T cells, ultimately producing more potent tumor control in a mouse model of lymphoma. The findings could aid in the development of iNKT-based cancer immunotherapies.

A molecular switch in mouse CD1d modulates natural killer T cell activation by α-galactosylsphingamides

Type I natural killer T (NKT) cells are a population of innate like T lymphocytes that rapidly respond to α-GalCer presented by CD1d via the production of both pro- and anti-inflammatory cytokines. While developing novel α-GalCer analogs that were meant to be utilized as potential adjuvants because of their production of pro-inflammatory cytokines (Th1 skewers), we generated α-galactosylsphingamides (αGSA). Surprisingly, αGSAs are not potent antigens in vivo despite their strong T-cell receptor (TCR)-binding affinities. Here, using surface plasmon resonance (SPR), antigen presentation assays, and X-ray crystallography (yielding crystal structures of 19 different binary (CD1d-glycolipid) or ternary (CD1d-glycolipid-TCR) complexes at resolutions between 1.67 and 2.85 Å), we characterized the biochemical and structural details of αGSA recognition by murine NKT cells. We identified a molecular switch within murine (m)CD1d that modulates NKT cell activation by αGSAs. We found that the molecular switch involves a hydrogen bond interaction between Tyr-73 of mCD1d and the amide group oxygen of αGSAs. We further established that the length of the acyl chain controls the positioning of the amide group with respect to the molecular switch and works synergistically with Tyr-73 to control NKT cell activity. In conclusion, our findings reveal important mechanistic insights into the presentation and recognition of glycolipids with polar moieties in an otherwise apolar milieu. These observations may inform the development αGSAs as specific NKT cell antagonists to modulate immune responses.

Evidence of CD1d pathway of lipid antigen presentation in mouse primary lung epithelial cells and its up-regulation upon Mycobacterium bovis BCG infection

Presentation of a prototype lipid antigen α-Galactosylceramide (αGC) was examined on primary epithelial cells derived from mouse lungs and on bronchoalveolar lavage (BAL) cells that essentially comprise alveolar macrophages. Presence of CD1d molecules coupled to αGC was demonstrated on both types of cells pre-treated with αGC, suggesting that both cell types are equipped to present lipid antigens. Internalization of Mycobacterium bovis Bacillus Calmette–Guérin (BCG: a prototype pathogen), a pre-requisite to the processing and presentation of protein as well as lipid antigens, was clearly demonstrated in primary lung epithelial (PLE) cells as well as BAL cells. Both PLE and BAL cells expressed CD1d molecule and a significant up-regulation of its expression occurred upon infection of these cells with BCG. Besides CD1d, the expression of other important molecules that participate in lipid antigen presentation pathway (i.e. microsomal triglyceride transfer protein (MTTP), scavenger receptor B1 (SR-B1) and Saposin) was also significantly upregulated in PLE and BAL cells upon BCG infection. In situ up-regulation of CD1d expression on lung epithelial cells was also demonstrated in the lungs of mice exposed intra-tracheally to BCG. Taken together these results suggest that lung epithelial cells may have the ability to present lipid antigens and this pathway seems to get significantly upregulated in response to BCG infection.

Natural Killer T Cells and Mucosal-Associated Invariant T Cells in Lung Infections

The immune system has been traditionally divided into two arms called innate and adaptive immunity. Typically, innate immunity refers to rapid defense mechanisms that set in motion within minutes to hours following an insult. Conversely, the adaptive immune response emerges after several days and relies on the innate immune response for its initiation and subsequent outcome. However, the recent discovery of immune cells displaying merged properties indicates that this distinction is not mutually exclusive. These populations that span the innate-adaptive border of immunity comprise, among others, CD1d-restricted natural killer T cells and MR1-restricted mucosal-associated invariant T cells. These cells have the unique ability to swiftly activate in response to non-peptidic antigens through their T cell receptor and/or to activating cytokines in order to modulate many aspects of the immune response. Despite they recirculate all through the body via the bloodstream, these cells mainly establish residency at barrier sites including lungs. Here, we discuss the current knowledge into the biology of these cells during lung (viral and bacterial) infections including activation mechanisms and functions. We also discuss future strategies targeting these cell types to optimize immune responses against respiratory pathogens.

Molecular recognition of microbial lipid-based antigens by T cells

The immune system has evolved to protect hosts from pathogens. T cells represent a critical component of the immune system by their engagement in host defence mechanisms against microbial infections. Our knowledge of the molecular recognition by T cells of pathogen-derived peptidic antigens that are presented by the major histocompatibility complex glycoproteins is now well established. However, lipids represent an additional, distinct chemical class of molecules that when presented by the family of CD1 antigen-presenting molecules can serve as antigens, and be recognized by specialized subsets of T cells leading to antigen-specific activation. Over the past decades, numerous CD1-presented self- and bacterial lipid-based antigens have been isolated and characterized. However, our understanding at the molecular level of T cell immunity to CD1 molecules presenting microbial lipid-based antigens is still largely unexplored. Here, we review the insights and the molecular basis underpinning the recognition of microbial lipid-based antigens by T cells.

The Janus Face of NKT Cell Function in Autoimmunity and Infectious Diseases

Natural killer T cells (NKT) are a subset of T lymphocytes bridging innate and adaptive immunity. These cells recognize self and microbial glycolipids bound to non-polymorphic and highly conserved CD1d molecules. Three NKT cell subsets, type I, II, and NKT-like expressing different antigen receptors (TCR) were described and TCR activation promotes intracellular events leading to specific functional activities. NKT can exhibit different functions depending on the secretion of soluble molecules and the interaction with other cell types. NKT cells act as regulatory cells in the defense against infections but, on the other hand, their effector functions can be involved in the pathogenesis of several inflammatory disorders due to their exposure to different microbial or self-antigens, respectively. A deep understanding of the biology and functions of type I, II, and NKT-like cells as well as their interplay with cell types acting in innate (neuthrophils, innate lymphoid cells, machrophages, and dendritic cells) and adaptive immunity (CD4⁺,CD8⁺, and double negative T cells) should be important to design potential immunotherapies for infectious and autoimmune diseases.

Small heterodimer partner deficiency exacerbates binge drinking‑induced liver injury via modulation of natural killer T cell and neutrophil infiltration

Binge drinking among alcohol consumers is a common occurrence, and may result in the development of numerous diseases, including liver disorders. It has previously been reported that natural killer T (NKT) cells induce alcohol‑associated liver injury by promoting neutrophil infiltration. In the present study, the role of the orphan nuclear receptor small heterodimer partner (SHP), which is encoded by the NR0B2 gene, in acute binge drinking‑induced liver injury was investigated. SHP‑knockout (KO) and wild‑type (WT) control mice were intragastrically administered single doses of alcohol. The plasma concentrations of alanine aminotransferase and aspartate aminotransferase in SHP‑KO mice following alcohol treatment were significantly increased compared with WT mice. However, results of oil red O staining and 2',7'‑dichlorodihydrofluorescein diacetate staining indicated that levels of acute binge drinking‑associated hepatic lipid accumulation and oxidative stress were not significantly different between WT and SHP‑KO alcohol‑treated mice. Notably, tumor necrosis factor‑α mRNA expression in the liver of SHP‑KO mice was significantly increased following alcohol administration, compared with WT mice. Furthermore, the mRNA expression levels of C‑C motif chemokine ligand 2, C‑X‑C motif chemokine ligand 2 and interleukin‑4, which are all potent chemoattractants of NKT cells, as well as neutrophil expression levels, were significantly increased in the livers of SHP‑KO mice compared with WT mice following alcohol administration, as determined by reverse transcription‑quantitative polymerase chain reaction and flow cytometry. Enhanced infiltration of NKT cells, determined by flow cytometry, was also demonstrated in the livers of SHP‑KO mice following alcohol administration, compared with WT mice. The results of the present study indicate that SHP may be involved in liver‑associated protective mechanisms, with regards to the attenuation of damage caused by acute binge drinking, via regulation of NKT cell and neutrophil migration to the liver. The modulation of SHP may be a novel therapeutic strategy for the treatment of acute binge drinking‑induced liver injury.

Role of Granulocyte-Macrophage Colony-Stimulating Factor Production by T Cells during Mycobacterium tuberculosis Infection

Mice deficient for granulocyte-macrophage colony-stimulating factor (GM-CSF^−/−) are highly susceptible to infection with Mycobacterium tuberculosis, and clinical data have shown that anti-GM-CSF neutralizing antibodies can lead to increased susceptibility to tuberculosis in otherwise healthy people. GM-CSF activates human and murine macrophages to inhibit intracellular M. tuberculosis growth. We have previously shown that GM-CSF produced by iNKT cells inhibits growth of M. tuberculosis. However, the more general role of T cell-derived GM-CSF during infection has not been defined and how GM-CSF activates macrophages to inhibit bacterial growth is unknown. Here we demonstrate that, in addition to nonconventional T cells, conventional T cells also produce GM-CSF during M. tuberculosis infection. Early during infection, nonconventional iNKT cells and γδ T cells are the main source of GM-CSF, a role subsequently assumed by conventional CD4⁺ T cells as the infection progresses. M. tuberculosis-specific T cells producing GM-CSF are also detected in the peripheral blood of infected people. Under conditions where nonhematopoietic production of GM-CSF is deficient, T cell production of GM-CSF is protective and required for control of M. tuberculosis infection. However, GM-CSF is not required for T cell-mediated protection in settings where GM-CSF is produced by other cell types. Finally, using an in vitro macrophage infection model, we demonstrate that GM-CSF inhibition of M. tuberculosis growth requires the expression of peroxisome proliferator-activated receptor gamma (PPARγ). Thus, we identified GM-CSF production as a novel T cell effector function. These findings suggest that a strategy augmenting T cell production of GM-CSF could enhance host resistance against M. tuberculosis.

Mycobacterium tuberculosis is the bacterium that causes tuberculosis, the leading cause of death by any infection worldwide. T cells are critical components of the immune response to Mycobacterium tuberculosis. While gamma interferon (IFN-γ) is a key effector function of T cells during infection, a failed phase IIb clinical trial and other studies have revealed that IFN-γ production alone is not sufficient to control M. tuberculosis. In this study, we demonstrate that CD4⁺, CD8⁺, and nonconventional T cells produce GM-CSF during Mycobacterium tuberculosis infection in mice and in the peripheral blood of infected humans. Under conditions where other sources of GM-CSF are absent, T cell production of GM-CSF is protective and is required for control of infection. GM-CSF activation of macrophages to limit bacterial growth requires host expression of the transcription factor PPARγ. The identification of GM-CSF production as a T cell effector function may inform future host-directed therapy or vaccine designs.

Galactosylsphingamides: new α-GalCer analogues to probe the F'-pocket of CD1d

Invariant Natural Killer T-cells (iNKT-cells) are an attractive target for immune response modulation, as upon CD1d-mediated stimulation with KRN7000, a synthetic α-galactosylceramide, they produce a vast amount of cytokines. Here we present a synthesis that allows swift modification of the phytosphingosine side chain by amidation of an advanced methyl ester precursor. The resulting KRN7000 derivatives, termed α-galactosylsphingamides, were evaluated for their capacity to stimulate iNKT-cells. While introduction of the amide-motif in the phytosphingosine chain is tolerated for CD1d binding and TCR recognition, the studied α-galactosylsphingamides showed compromised antigenic properties.

Exploring the functions of nonclassical MHC class Ib genes in Xenopus laevis by the CRISPR/Cas9 system

A large family of highly related and clustered Xenopus nonclassical MHC class Ib (XNC) genes influences Xenopus laevis immunity and potentially other physiological functions. Using RNA interference (RNAi) technology, we previously demonstrated that one of XNC genes, XNC10.1, is critical for the development and function of a specialized innate T (iT) cell population. However, RNAi limitation such as a variable and unstable degree of gene silencing in F0 and F1 generations is hampering a thorough functional analysis of XNC10.1 and other XNC genes. To overcome this obstacle, we adapted the CRISPR/Cas9-mediated gene editing technique for XNC genes. We efficiently and specifically generated single gene knockouts of XNC10.1, XNC11, and XNC1 as well as double gene knockouts of XNC10.1 and XNC11 in X. laevis. In single XNC10.1 knockout X. laevis tadpoles, the absence of XNC10.1 and Vα6-Jα1.43 invariant T cell receptor rearrangement transcripts indicated XNC10.1 loss-of-function and deficiency in Vα6-Jα1.43 iT cells. Notably, targeting XNC10.1 did not affect neighboring XNC genes exhibiting high sequence similarity. Furthermore, XNC1 gene disruption induced mortality during developmental stage 47, suggesting some non-immune but essential function of this gene. These data demonstrate that the CRISPR/Cas9 system can be successfully adapted for genetic analysis in F0 generation of X. laevis.

NNKTT120, an anti-iNKT cell monoclonal antibody, produces rapid and sustained iNKT cell depletion in adults with sickle cell disease

Invariant NKT (iNKT) cells can be activated to stimulate a broad inflammatory response. In murine models of sickle cell disease (SCD), interruption of iNKT cell activity prevents tissue injury from vaso-occlusion. NKTT120 is an anti-iNKT cell monoclonal antibody that has the potential to rapidly and specifically deplete iNKT cells and, potentially, prevent vaso-occlusion. We conducted an open-label, multi-center, single-ascending-dose study of NKTT120 to determine its pharmacokinetics, pharmacodynamics and safety in steady-state patients with SCD. Doses were escalated in a 3+3 study design over a range from 0.001 mg/kg to 1.0 mg/kg. Twenty-one adults with SCD were administered NKTT120 as part of 7 dose cohorts. Plasma levels of NKTT120 predictably increased with higher doses. Median half-life of NKTT120 was 263 hours. All subjects in the higher dose cohorts (0.1 mg/kg, 0.3 mg/kg, and 1 mg/kg) demonstrated decreased iNKT cells below the lower limit of quantification within 6 hours after infusion, the earliest time point at which they were measured. In those subjects who received the two highest doses of NKTT120 (0.3, 1 mg/kg), iNKT cells were not detectable in the peripheral blood for a range of 2 to 5 months. There were no serious adverse events in the study deemed to be related to NKTT120. In adults with SCD, NKTT120 produced rapid, specific and sustained iNKT cell depletion without any infusional toxicity or attributed serious adverse events. The next step is a trial to determine NKTT120’s ability to decrease rate of vaso-occlusive pain episodes.

Trial Registration: clinicaltrials.gov NCT01783691.

Th1 and Th17 proinflammatory profile characterizes invariant natural killer T cells in virologically suppressed HIV+ patients with low CD4+/CD8+ ratio

INTRODUCTION

Scanty data exist on the phenotype and functionality of invariant natural killer T (iNKT) cells in HIV-infected (HIV+) patients.

METHODS

By flow cytometry, we studied iNKT cells from 54 HIV+ patients who started combined antiretroviral therapy and had undetectable viral load for more than 1 year. Twenty-five maintained a CD4/CD8 ratio less than 0.4, whereas 29 reached a ratio more than 1.1; 32 age-matched and sex-matched patients were healthy controls (CTR).

RESULTS

Patients with low ratio had lower percentage of CD4 iNKT cells compared with patients with high ratio and higher CD8 iNKT cell percentage; double-negative iNKT cells were lower in HIV+ patients compared with CTR. Patients with low ratio had higher percentage of CD4 and double-negative iNKT cells expressing CD38 and HLA-DR compared with patients with high ratio. CD4 iNKT cells expressing PD-1 were higher in patients with CD4/CD8 ratio less than 0.4, whereas double-negative iNKT cells expressing PD-1 were lower compared with patients with ratio more than 1.1. Patients with low ratio had higher CD4 iNKT cells producing IL-17, CD8 iNKT cells producing IFN-γ, TNF-α or IFN-γ and TNF-α, and double-negative iNKT cells producing IL-17 or IL-17 and IFN-γ compared with CTR. Activated CD4 (or CD8) T cells correlated with activated CD4 (or CD8) iNKT cells, as well as the percentages of CD4 (or CD8) T cells expressing PD-1 was correlated to that of CD4 (or CD8) iNKT cells expressing PD-1.

CONCLUSION

Low CD4/CD8 ratio despite effective combined antiretroviral therapy is associated with altered iNKT cell subsets, enhanced activation, and prominent Th1/Th17 proinflammatory profile.

Blocking of CD1d Decreases Trypanosoma cruzi-Induced Activation of CD4-CD8- T Cells and Modulates the Inflammatory Response in Patients With Chagas Heart Disease

The control of inflammatory responses to prevent the deadly cardiac pathology in human Chagas disease is a desirable and currently unattained goal. Double-negative (DN) T cells are important sources of inflammatory and antiinflammatory cytokines in patients with Chagas heart disease and those with the indeterminate clinical form of Chagas disease, respectively. Given the importance of DN T cells in immunoregulatory processes and their potential as targets for controlling inflammation-induced pathology, we studied the involvement of CD1 molecules in the activation and functional profile of Trypanosoma cruzi-specific DN T cells. We observed that parasite stimulation significantly increased the expression of CD1a, CD1b, CD1c, and CD1d by CD14(+) cells from patients with Chagas disease. Importantly, among the analyzed molecules, only CD1d expression showed an association with the activation of DN T cells, as well as with worse ventricular function in patients with Chagas disease. Blocking of CD1d-mediated antigen presentation led to a clear reduction of DN T-cell activation and a decrease in the expression of interferon γ (IFN-γ) by DN T cells. Thus, our results showed that antigen presentation via CD1d is associated with activation of DN T cells in Chagas disease and that CD1d blocking leads to downregulation of IFN-γ by DN T cells from patients with Chagas heart disease, which may be a potential target for preventing progression of inflammation-mediated dilated cardiomyopathy.

Protective and Pathogenic Roles of CD8+ T Lymphocytes in Murine Orientia tsutsugamushi Infection

T cells are known to contribute to immune protection against scrub typhus, a potentially fatal infection caused by the obligate intracellular bacterium Orientia (O.) tsutsugamushi. However, the contribution of CD8+ T cells to protection and pathogenesis during O. tsutsugamushi infection is still unknown. Using our recently developed BALB/c mouse model that is based on footpad inoculation of the human-pathogenic Karp strain, we show that activated CD8+ T cells infiltrate spleen and lung during the third week of infection. Depletion of CD8+ T cells with monoclonal antibodies resulted in uncontrolled pathogen growth and mortality. Adoptive transfer of CD8+ T cells from infected animals protected naïve BALB/c mice from lethal outcome of intraperitoneal challenge. In C57Bl/6 mice, the pulmonary lymphocyte compartment showed an increased percentage of CD8+ T cells for at least 135 days post O. tsutsugamushi infection. Depletion of CD8+ T cells at 84 days post infection caused reactivation of bacterial growth. In CD8+ T cell-deficient beta 2-microglobulin knockout mice, bacterial replication was uncontrolled, and all mice succumbed to the infection, despite higher serum IFN-γ levels and stronger macrophage responses in liver and lung. Moreover, we show that CD8+ T cells but not NKT cells were required for hepatocyte injury: elevated concentrations of serum alanine aminotransferase and infection-induced subcapsular necrotic liver lesions surrounded by macrophages were found in C57Bl/6 and CD1d-deficient mice, but not in beta 2-microglobulin knockout mice. In the lungs, peribronchial macrophage infiltrations also depended on CD8+ T cells. In summary, our results demonstrate that CD8+ T cells restrict growth of O. tsutsugamushi during acute and persistent infection, and are required to protect from lethal infections in BALB/c and C57BL/6 mice. However, they also elicit specific pathologic tissue lesions in liver and lung.

Carbohydrates as T-cell antigens with implications in health and disease

Glycosylation is arguably the most ubiquitous post-translational modification on proteins in microbial and mammalian cells. During the past few years, there has been intensive research demonstrating that carbohydrates, either in pure forms or in conjunction with proteins or lipids, evoke and modulate adaptive immune responses. We now know that carbohydrates can be directly recognized by T cells or participate in T-cell stimulation as components of T-cell epitopes. T-cell recognition of carbohydrate antigens takes place via their presentation by major histocompatibility complex pathways on antigen-presenting cells. In this review, we summarize studies on carbohydrates as T-cell antigens modulating adaptive immune responses. Through discussion of glycan-containing antigens, such as glycoproteins, glycolipids, zwitterionic polysaccharides and carbohydrate-based glycoconjugate vaccines, we will illustrate the key molecular and cellular interactions between carbohydrate antigens and T cells and the implications of these interactions in health and disease.

Recognition of Microbial Glycolipids by Natural Killer T Cells

T cells can recognize microbial antigens when presented by dedicated antigen-presenting molecules. While peptides are presented by classical members of the major histocompatibility complex (MHC) family (MHC I and II), lipids, glycolipids, and lipopeptides can be presented by the non-classical MHC member, CD1. The best studied subset of lipid-reactive T cells are type I natural killer T (iNKT) cells that recognize a variety of different antigens when presented by the non-classical MHCI homolog CD1d. iNKT cells have been shown to be important for the protection against various microbial pathogens, including B. burgdorferi, the causative agents of Lyme disease, and S. pneumoniae, which causes pneumococcal meningitis and community-acquired pneumonia. Both pathogens carry microbial glycolipids that can trigger the T cell antigen receptor (TCR), leading to iNKT cell activation. iNKT cells have an evolutionary conserved TCR alpha chain, yet retain the ability to recognize structurally diverse glycolipids. They do so using a conserved recognition mode, in which the TCR enforces a conserved binding orientation on CD1d. TCR binding is accompanied by structural changes within the TCR binding site of CD1d, as well as the glycolipid antigen itself. In addition to direct recognition of microbial antigens, iNKT cells can also be activated by a combination of cytokines (IL-12/IL-18) and TCR stimulation. Many microbes carry TLR antigens, and microbial infections can lead to TLR activation. The subsequent cytokine response in turn lower the threshold of TCR-mediated iNKT cell activation, especially when weak microbial or even self-antigens are presented during the cause of the infection. In summary, iNKT cells can be directly activated through TCR triggering of strong antigens, while cytokines produced by the innate immune response may be necessary for TCR triggering and iNKT cell activation in the presence of weak antigens. Here, we will review the molecular basis of iNKT cell recognition of glycolipids, with an emphasis on microbial glycolipids.

Invariant NKT cells promote alcohol-induced steatohepatitis through interleukin-1β in mice

BACKGROUND & AIMS

It was reported that alcohol consumption activated the NLRP3 inflammasome in Kupffer cells, leading to mature interleukin (IL)-1β release in alcoholic liver injury; however, how IL-1β promotes liver injury remains unclear.

METHODS

We investigated the role of IL-1β in alcoholic steatohepatitis by using a chronic plus single-binge ethanol consumption mouse model.

RESULTS

Here, liver steatosis was accompanied by notably increased invariant natural killer T (iNKT) cell numbers and activation, and iNKT-deficient Jα18(-/-) mice developed less alcohol-induced steatosis, with reduced liver inflammation and neutrophil infiltration. Kupffer cells and IL-1β were required for the hepatic iNKT accumulation, as either blocking IL-1β signaling with a recombinant IL-1 receptor antagonist (IL-1Ra), depleting Kupffer cells by clodronate liposomes, or specifically silencing IL-1β in Kupffer cells by nanoparticle-encapsulated siRNA, resulted in inhibited hepatic iNKT cell accumulation and activation, as well as amelioration of alcoholic fatty liver. In addition, IL-1β overexpression in hepatocytes was sufficient to compensate for Kupffer cell depletion. Increased gene and protein expression of mature IL-1β correlated with elevated expression of the NLRP3 inflammasome components NLRP3, ASC, and cleaved caspase-1 in Kupffer cells from ethanol-exposed wild-type mice. NLRP3 deficiency led to the attenuation of alcoholic steatosis, similarly as Kupffer cell depletion, almost without hepatic NKT cells.

CONCLUSIONS

After alcohol-exposure Kupffer cell-derived IL-1β triggered by NLRP3 activation, recruits and activates hepatic iNKT cells, subsequently promoting liver inflammation and neutrophil infiltration, and inducing alcoholic liver injury.

Regulation of NKT Cell Localization in Homeostasis and Infection

Natural killer T (NKT) cells are a specialized subset of T lymphocytes that regulate immune responses in the context of autoimmunity, cancer, and microbial infection. Lipid antigens derived from bacteria, parasites, and fungi can be presented by CD1d molecules and recognized by the canonical T cell receptors on NKT cells. Alternatively, NKT cells can be activated through recognition of self-lipids and/or pro-inflammatory cytokines generated during infection. Unlike conventional T cells, only a small subset of NKT cells traffic through the lymph nodes under homeostatic conditions, with the largest NKT cell populations localizing to the liver, lungs, spleen, and bone marrow. This is thought to be mediated by differences in chemokine receptor expression profiles. However, the impact of infection on the tissue localization and function of NKT remains largely unstudied. This review focuses on the mechanisms mediating the establishment of peripheral NKT cell populations during homeostasis and how tissue localization of NKT cells is affected during infection.

Highly purified mycobacterial phosphatidylinositol mannosides drive cell-mediated responses and activate NKT cells in cattle

Mycobacterial lipids play an important role in the modulation of the immune response upon contact with the host. Using novel methods, we have isolated highly purified phosphatidylinositol mannoside (PIM) molecules (phosphatidylinositol dimannoside [PIM2], acylphosphatidylinositol dimannoside [AcPIM2], diacyl-phosphatidylinositol dimannoside [Ac2PIM2], acylphosphatidylinositol hexamannoside [AcPIM6], and diacylphosphatidylinositol hexamannoside [Ac2PIM6]) from virulent Mycobacterium tuberculosis to assess their potential to stimulate peripheral blood mononuclear cell (PBMC) responses in Mycobacterium bovis-infected cattle. Of these molecules, one (AcPIM6) induced significant levels of gamma interferon (IFN-γ) in bovine PBMCs. Three PIM molecules (AcPIM6, Ac2PIM2, and Ac2PIM6) were shown to drive significant proliferation in bovine PBMCs. AcPIM6 was subsequently used to phenotype the proliferating cells by flow cytometry. This analysis demonstrated that AcPIM6 was predominantly recognized by CD3(+) CD335(+) NKT cells. In conclusion, we have identified PIM lipid molecules that interact with bovine lymphocyte populations, and these lipids may be useful as future subunit vaccines or diagnostic reagents. Further, these data demonstrate, for the first time, lipid-specific NKT activation in cattle.

T helper type 2-polarized invariant natural killer T cells reduce disease severity in acute intra-abdominal sepsis

Sepsis is characterized by a severe systemic inflammatory response to infection that is associated with high morbidity and mortality despite optimal care. Invariant natural killer T (iNK T) cells are potent regulatory lymphocytes that can produce pro- and/or anti-inflammatory cytokines, thus shaping the course and nature of immune responses; however, little is known about their role in sepsis. We demonstrate here that patients with sepsis/severe sepsis have significantly elevated proportions of iNK T cells in their peripheral blood (as a percentage of their circulating T cells) compared to non-septic patients. We therefore investigated the role of iNK T cells in a mouse model of intra-abdominal sepsis (IAS). Our data show that iNK T cells are pathogenic in IAS, and that T helper type 2 (Th2) polarization of iNK T cells using the synthetic glycolipid OCH significantly reduces mortality from IAS. This reduction in mortality is associated with the systemic elevation of the anti-inflammatory cytokine interleukin (IL)-13 and reduction of several proinflammatory cytokines within the spleen, notably interleukin (IL)-17. Finally, we show that treatment of sepsis with OCH in mice is accompanied by significantly reduced apoptosis of splenic T and B lymphocytes and macrophages, but not natural killer cells. We propose that modulation of iNK T cell responses towards a Th2 phenotype may be an effective therapeutic strategy in early sepsis.

Lipid antigen presentation through CD1d pathway in mouse lung epithelial cells, macrophages and dendritic cells and its suppression by poly-dispersed single-walled carbon nanotubes

Effect of poly-dispersed acid-functionalized single-walled carbon nanotubes (AF-SWCNTs) was examined on lipid antigen presentation through CD1d pathway on three cell lines, LA4, MHS, and JAWSII used as prototype antigen presenting cells (APCs). CD1d molecule was expressed on 80-90% MHS (prototype macrophages) and JAWSII (prototype dendritic cells) cells whereas <5% LA4 cells (lung epithelial cells, non-classical APCs) expressed CD1d. Treatment with AF-SWCNTs but not with pristine SWCNTs resulted in a significant decline in the level of CD1d mRNA as well as mRNA levels of some other intracellular proteins involved in lipid antigen presentation pathway (MTP, ApoE, prosaposin, SR-BI and LDLr). Lipid antigen presentation was assessed by first incubating the cells with a prototype lipid antigen (α-Glactosylceramide or αGC) and then staining with L363 monoclonal antibody that detects αGC bound to CD1d molecule. While 100% MHS and JAWSII cells presented αGC, only 20% LA4 cells presented the CD1d antigen. Treatment with AF-SWCNTs resulted in a 30-40% decrease in αGC antigen presentation in all three cell lines. These results show that AF-SWCNT treatment down regulated the lipid antigen presentation pathway in all three cell lines and significantly lowered the ability of these cell lines to present αGC antigen.

Role of non-conventional T lymphocytes in respiratory infections: the case of the pneumococcus

Non-conventional T lymphocytes constitute a special arm of the immune system and act as sentinels against pathogens at mucosal surfaces. These non-conventional T cells (including mucosal-associated invariant T [MAIT] cells, gamma delta [γδ] T cells, and natural killer T [NKT] cells) display several innate cell-like features and are rapidly activated by the recognition of conserved, stress-induced, self, and microbial ligands. Here, we review the role of non-conventional T cells during respiratory infections, with a particular focus on the encapsulated extracellular pathogen Streptococcus pneumoniae, the leading cause of bacterial pneumonia worldwide. We consider whether MAIT cells, γδ T cells, and NKT cells might offer opportunities for preventing and/or treating human pneumococcus infections.

All-trans-retinoic acid and CD38 ligation differentially regulate CD1d expression and α-galactosylceramide-induced immune responses

The MHC class-I like molecule CD1d presents glycolipid antigens and thereby activates invariant natural killer-T (NKT) cells. However, little is understood regarding the regulation of its expression. All-trans-retinoic acid (RA) and CD38, which is itself a target of RA, both independently regulate the differentiation of antigen presenting cells. In the current study, we treated human THP-1 cells and murine splenic cells with RA, with and without antibody-mediated ligation of cell-surface CD38. Whereas a physiological concentration (20 nM) of RA alone rapidly and markedly increased CD1d protein in THP-1 cells, there was a marked synergy between RA and ligation of CD38 with antibody to CD38. Moreover, RA and CD38 ligation differentially regulated CD1d protein distribution between the cell surface and intracellular compartments, as, whereas RA mainly increased intracellular CD1d protein, ligation of CD38 increased CD1d protein both at the cell surface and intracellularly. By confocal microscopy, CD1d was located close to the plasma membrane but only partially overlapped with LAMP1, a late endosomes/lysosomal marker. Furthermore, RA and/or CD38 ligation increased splenocyte proliferation and differentiation after treatment with the CD1 ligand α-galactosylceramide (αGalCer), evidenced by an increase in the number of splenic dendritic cells, NKT cells, and germinal center plasmacytes. RA also differentially regulated αGalCer-induced cytokine expression, increasing IL-4 and decreasing IFNγ production by total spleen cells and the NKT cell population. Our results indicate a previously unknown mechanism in which RA and CD38 differentially yet cooperatively regulate CD1d expression and antigen-presenting function, which could be important for the enhancement of immunity.

A prominent role for invariant T cells in the amphibian Xenopus laevis tadpoles

Invariant T (iT) cells expressing an invariant or semi-invariant T cell receptor (TCR) repertoire have gained attention in recent years because of their potential as specialized regulators of immune function. These iT cells are typically restricted by nonclassical MHC class I molecules (e.g., CD1d and MR1) and undergo differentiation pathways distinct from conventional T cells. While the benefit of a limited TCR repertoire may appear counterintuitive in regard to the advantage of the diversified repertoire of conventional T cells allowing for exquisite specificity to antigens, the full biological importance and evolutionary conservation of iT cells are just starting to emerge. It is generally considered that iT cells are specialized to recognize conserved antigens equivalent to pathogen-associated molecular pattern. Until recently, little was known about the evolution of iT cells. The identification of class Ib and class I-like genes in nonmammalian vertebrates, despite the heterogeneity and variable numbers of these genes among species, suggests that iT cells are also present in ectothermic vertebrates. Indeed, recent studies in the amphibian Xenopus have revealed a drastic overrepresentation of several invariant TCRs in tadpoles and identified a prominent nonclassical MHC class I-restricted iT cell subset critical for tadpole antiviral immunity. This suggests an important and perhaps even dominant role of multiple nonclassical MHC class I-restricted iT cell populations in tadpoles and, by extension, other aquatic vertebrates with rapid external development that are under pressure to produce a functional lymphocyte repertoire with small numbers of cells.

The T-Cell Response to Lipid Antigens of Mycobacterium tuberculosis

T-cells recognize lipid antigens presented by dedicated antigen-presenting molecules that belong to the CD1 family. This review discusses the structural properties of CD1 molecules, the nature of mycobacterial lipid antigens, and the phenotypic and functional properties of T-cells recognizing mycobacterial lipids. In humans, the five CD1 genes encode structurally similar glycoproteins that recycle in and thus survey different cellular endosomal compartments. The structure of the CD1-lipid-binding pockets, their mode of intracellular recycling and the type of CD1-expressing antigen-presenting cells all contribute to diversify lipid immunogenicity and presentation to T-cells. Mycobacteria produce a large variety of lipids, which form stable complexes with CD1 molecules and stimulate specific T-cells. The structures of antigenic lipids may be greatly different from each other and each lipid may induce unique T-cells capable of discriminating small lipid structural changes. The important functions of some lipid antigens within mycobacterial cells prevent the generation of negative mutants capable of escaping this type of immune response. T-cells specific for lipid antigens are stimulated in tuberculosis and exert protective functions. The mechanisms of antigen recognition, the type of effector functions and the mode of lipid-specific T-cell priming are discussed, emphasizing recent evidence of the roles of lipid-specific T-cells in tuberculosis.

Unusual evolutionary conservation and further species-specific adaptations of a large family of nonclassical MHC class Ib genes across different degrees of genome ploidy in the amphibian subfamily Xenopodinae

Nonclassical MHC class Ib (class Ib) genes are a family of highly diverse and rapidly evolving genes wherein gene numbers, organization, and expression markedly differ even among closely related species rendering class Ib phylogeny difficult to establish. Whereas among mammals there are few unambiguous class Ib gene orthologs, different amphibian species belonging to the anuran subfamily Xenopodinae exhibit an unusually high degree of conservation among multiple class Ib gene lineages. Comparative genomic analysis of class Ib gene loci of two divergent (~65 million years) Xenopodinae subfamily members Xenopus laevis (allotetraploid) and Xenopus tropicalis (diploid) shows that both species possess a large cluster of class Ib genes denoted as Xenopus/Silurana nonclassical (XNC/SNC). Our study reveals two distinct phylogenetic patterns among these genes: some gene lineages display a high degree of flexibility, as demonstrated by species-specific expansion and contractions, whereas other class Ib gene lineages have been maintained as monogenic subfamilies with very few changes in their nucleotide sequence across divergent species. In this second category, we further investigated the XNC/SNC10 gene lineage that in X. laevis is required for the development of a distinct semi-invariant T cell population. We report compelling evidence of the remarkable high degree of conservation of this gene lineage that is present in all 12 species of the Xenopodinae examined, including species with different degrees of ploidy ranging from 2, 4, 8 to 12 N. This suggests that the critical role of XNC10 during early T cell development is conserved in amphibians.

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.

Role of type 1 natural killer T cells in pulmonary immunity

Mucosal sites are populated by a multitude of innate lymphoid cells and "innate-like" T lymphocytes expressing semiconserved T-cell receptors. Among the latter group, interest in type I natural killer T (NKT) cells has gained considerable momentum over the last decade. Exposure to NKT cell antigens is likely to occur continuously at mucosal sites. For this reason, and as they rapidly respond to stress-induced environmental cytokines, NKT cells are important contributors to immune and inflammatory responses. Here, we review the dual role of mucosal NKT cells during immune responses and pathologies with a particular focus on the lungs. Their role during pulmonary acute and chronic inflammation and respiratory infections is outlined. Whether NKT cells might provide a future attractive therapeutic target for treating human respiratory diseases is discussed.

Nonclassical MHC class I-dependent invariant T cells are evolutionarily conserved and prominent from early development in amphibians

Human and murine MHC nonclassical class Ib-restricted invariant T (iT) cell subsets, such as invariant natural killer T cells (iNKT) and mucosal-associated invariant T cells, have specialized functions early in immune responses, especially in modulating subsequent adaptive immune responses. Here, we characterize a prominent iT population in the amphibian Xenopus laevis and show the requirement of the class Ib molecule, Xenopus nonclassical gene 10, in its differentiation and function. Using Xenopus nonclassical gene 10 tetramers and RNAi loss of function by transgenesis, we identified a large class Ib-dependent CD8(-)/CD4(-) iT subset in unmanipulated frogs and tadpoles. This population is critical for antiviral immunity during early larval stages when classical MHC class Ia function is suboptimal. Furthermore, in young tadpoles with low class Ia expression, deep sequencing revealed additional preponderant invariant T cell receptor (TCR)α rearrangements, implying other iT cell subsets and a predominant selection process mediated by other class Ib molecules. The restriction and requirement of class Ib molecules for development and antiviral immunity of a mammalian iNKT or mucosal-associated invariant T cell counterpart in the amphibian Xenopus show the importance of iT cells in the emergence and evolution of the adaptive immune system.

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.

Sulfatide attenuates experimental Staphylococcus aureus sepsis through a CD1d-dependent pathway

Natural killer T (NKT) lymphocytes are implicated in the early response to microbial infection. Further, sulfatide, a myelin self-glycosphingolipid, activates a type II NKT cell subset and can modulate disease in murine models. We examined the role of NKT cells and the effect of sulfatide treatment in a murine model of Staphylococcus aureus sepsis. The lack of CD1d-restricted NKT cells did not alter survival after a lethal inoculum of S. aureus. In contrast, sulfatide treatment significantly improved the survival rate of mice with S. aureus sepsis, accompanied by decreased levels of tumor necrosis factor alpha and interleukin-6 in the blood. The protective effect of sulfatide treatment depended on CD1d but not on type I NKT cells, suggesting that activation of type II NKT cells by sulfatide has beneficial effects on the outcome of S. aureus sepsis in this model.

Olea europaea pollen lipids activate invariant natural killer T cells by upregulating CD1d expression on dendritic cells

BACKGROUND

Invariant natural killer T (iNKT) cells recognize lipids presented by CD1d and have been implicated in the pathogenesis of allergic asthma. Recognition of plant pollen lipids by iNKT cells and their role in allergic responses are poorly defined.

OBJECTIVE

Our goal was to investigate whether iNKT cells can be activated by monocyte-derived dendritic cells (DCs) exposed to lipid antigens from Olea europaea.

METHODS

DCs generated in vitro were exposed to O europaea pollen grains or lipids isolated from them. Expression of lipid-presenting molecules (CD1), as well as maturation markers (HLA-DR, HLA-I, CD86, and CD80 molecules), on DCs was analyzed. iNKT cell activation after coculture with DCs was evaluated based on expansion, cytokine production, and cytotoxicity tests.

RESULTS

DCs upregulated CD1d and CD86 expression and downregulated CD1a expression after exposure to a whole extract of olive pollen lipids. CD1d and CD1a were regulated at the transcriptional level in a peroxisome proliferator-activated receptor γ activation-dependent manner. Polar lipids, diacylglycerols, free fatty acids, and triacylglycerols isolated from pollen grains upregulate CD1d. The increase in CD1d expression on the DC cell surface induced by polar lipids was not regulated at the RNA level. iNKT cells efficiently recognize DCs treated with the different lipids isolated from olive pollen grains.

CONCLUSIONS

Lipids from O europaea pollen upregulate CD1d and CD86 molecules on DCs, which are then able to activate iNKT cells through a CD1d-dependent pathway.

Dendritic cell sphingosine 1-phosphate receptor-3 regulates Th1-Th2 polarity in kidney ischemia-reperfusion injury

Dendritic cells (DCs) are central to innate and adaptive immunity of early kidney ischemia-reperfusion injury (IRI), and strategies to alter DC function may provide new therapeutic opportunities. Sphingosine 1-phosphate (S1P) modulates immunity through binding to its receptors (S1P1-5), and protection from kidney IRI occurs in S1P3-deficient mice. Through a series of experiments we determined that this protective effect was owing in part to differences between S1P3-sufficient and -deficient DCs. Mice lacking S1P3 on bone marrow cells were protected from IRI, and S1P3-deficient DCs displayed an immature phenotype. Wild-type (WT) but not S1P3-deficient DCs injected into mice depleted of DCs prior to kidney IR reconstituted injury. Adoptive transfer (i.e., i.v. injection) of glycolipid (Ag)-loaded WT but not S1P3-deficient DCs into WT mice exacerbated IRI, suggesting that WT but not S1P3-deficient DCs activated NKT cells. Whereas WT DC transfers activated the Th1/IFN-γ pathway, S1P3-deficient DCs activated the Th2/IL-4 pathway, and an IL-4-blocking Ab reversed protection from IRI, supporting the concept that IL-4 mediates the protective effect of S1P3-deficient DCs. Administration of S1P3-deficient DCs 7 d prior to or 3 h after IRI protected mice from IRI and suggests their potential use in cell-based therapy. We conclude that absence of DC S1P3 prevents DC maturation and promotes a Th2/IL-4 response. These findings highlight the importance of DC S1P3 in modulating NKT cell function and IRI and support development of selective S1P3 antagonists for tolerizing DCs for cell-based therapy or for systemic administration for the prevention and treatment of IRI and autoimmune diseases.

Polyclonal mucosa-associated invariant T cells have unique innate functions in bacterial infection

Mucosa-associated invariant T (MAIT) cells are a unique population of αβ T cells in mammals that reside preferentially in mucosal tissues and express an invariant Vα paired with limited Vβ T-cell receptor (TCR) chains. Furthermore, MAIT cell development is dependent upon the expression of the evolutionarily conserved major histocompatibility complex (MHC) class Ib molecule MR1. Using in vitro assays, recent studies have shown that mouse and human MAIT cells are activated by antigen-presenting cells (APCs) infected with diverse microbes, including numerous bacterial strains and yeasts, but not viral pathogens. However, whether MAIT cells play an important, and perhaps unique, role in controlling microbial infection has remained unclear. To probe MAIT cell function, we show here that purified polyclonal MAIT cells potently inhibit intracellular bacterial growth of Mycobacterium bovis BCG in macrophages (MΦ) in coculture assays, and this inhibitory activity was dependent upon MAIT cell selection by MR1, secretion of gamma interferon (IFN-γ), and an innate interleukin 12 (IL-12) signal from infected MΦ. Surprisingly, however, the cognate recognition of MR1 by MAIT cells on the infected MΦ was found to play only a minor role in MAIT cell effector function. We also report that MAIT cell-deficient mice had higher bacterial loads at early times after infection compared to wild-type (WT) mice, demonstrating that MAIT cells play a unique role among innate lymphocytes in protective immunity against bacterial infection.

The glycolipid exoantigen derived from Chlamydia muridarum activates invariant natural killer T cells

The chlamydial glycolipid exoantigen (GLXA), a glycolipid antigen derived from Chlamydia muridarum, has been implicated in chlamydial-host cell interaction. Although glycolipid antigens from Sphingomonas and related bacteria have been shown to activate invariant natural killer T (iNKT) cells, it is not yet known whether GLXA can activate these cells. In this study, we have for the first time investigated the role of GLXA in iNKT cell activation using in vitro as well as in vivo settings. First, we examined the effect of GLXA on iNKT cell activation in a cell-free antigen-presentation assay, and found that GLXA specifically stimulated iNKT1.4 hybridoma cell produce enhanced amounts of IL-2. Next, we analyzed the effect of pharmacological activation of iNKT cells by GLXA using iNKT cell-deficient (iNKT knockout (KO)) mice and bone marrow-derived dendritic cell (BMDC)-liver mononuclear cell (LMC) coculture system. On stimulation with GLXA, iNKT cells produced higher quantities of cytokines in a CD1d-dependent fashion. More importantly, iNKT cells from GLXA-treated, but not from cell mock-treated, mice showed higher expression of activation marker, CD69, and enhanced production of interferon (IFN)-γ and IL-4 in vivo. Cumulatively, these data provide evidence on the pharmacological ability of GLXA in specifically activating iNKT cells.

Interleukin-22 is produced by invariant natural killer T lymphocytes during influenza A virus infection: potential role in protection against lung epithelial damages

Invariant natural killer T (iNKT) cells are non-conventional lipid-reactive αβ T lymphocytes that play a key role in host responses during viral infections, in particular through the swift production of cytokines. Their beneficial role during experimental influenza A virus (IAV) infection has recently been proposed, although the mechanisms involved remain elusive. Here we show that during in vivo IAV infection, mouse pulmonary iNKT cells produce IFN-γ and IL-22, a Th17-related cytokine critical in mucosal immunity. Although permissive to viral replication, IL-22 production by iNKT cells is not due to IAV infection per se of these cells but is indirectly mediated by IAV-infected dendritic cells (DCs). We show that activation of the viral RNA sensors TLR7 and RIG-I in DCs is important for triggering IL-22 secretion by iNKT cells, whereas the NOD-like receptors NOD2 and NLRP3 are dispensable. Invariant NKT cells respond to IL-1β and IL-23 provided by infected DCs independently of the CD1d molecule to release IL-22. In vitro, IL-22 protects IAV-infected airway epithelial cells against mortality but has no role on viral replication. Finally, during early IAV infection, IL-22 plays a positive role in the control of lung epithelial damages. Overall, IAV infection of DCs activates iNKT cells, providing a rapid source of IL-22 that might be beneficial to preserve the lung epithelium integrity.

Generation of a convalescent model of virulent Francisella tularensis infection for assessment of host requirements for survival of tularemia

Francisella tularensis is a facultative intracellular bacterium and the causative agent of tularemia. Development of novel vaccines and therapeutics for tularemia has been hampered by the lack of understanding of which immune components are required to survive infection. Defining these requirements for protection against virulent F. tularensis, such as strain SchuS4, has been difficult since experimentally infected animals typically die within 5 days after exposure to as few as 10 bacteria. Such a short mean time to death typically precludes development, and therefore assessment, of immune responses directed against virulent F. tularensis. To enable identification of the components of the immune system that are required for survival of virulent F. tularensis, we developed a convalescent model of tularemia in C57Bl/6 mice using low dose antibiotic therapy in which the host immune response is ultimately responsible for clearance of the bacterium. Using this model we demonstrate αβTCR⁺ cells, γδTCR⁺ cells, and B cells are necessary to survive primary SchuS4 infection. Analysis of mice deficient in specific soluble mediators shows that IL-12p40 and IL-12p35 are essential for survival of SchuS4 infection. We also show that IFN-γ is required for survival of SchuS4 infection since mice lacking IFN-γR succumb to disease during the course of antibiotic therapy. Finally, we found that both CD4⁺ and CD8⁺ cells are the primary producers of IFN-γand that γδTCR⁺ cells and NK cells make a minimal contribution toward production of this cytokine throughout infection. Together these data provide a novel model that identifies key cells and cytokines required for survival or exacerbation of infection with virulent F. tularensis and provides evidence that this model will be a useful tool for better understanding the dynamics of tularemia infection.

Natural killer T cell based Immunotherapy

Natural killer T (NKT) cells play an important immunoregulatory role and are thought to bridge the innate and adaptive immune responses. Following activation through cognate interactions with lipid antigen presented in the context of CD1d molecules, NKT cells rapidly produce a plethora of cytokines and can also mediate cytotoxicity. Due to their potent effector functions, extensive research has been performed to increase our understanding on how to effectively modulate these cells. In fact, NKT cell agonists have been used as vaccine adjuvants to enhance antigen specific T and B cell responses to infections and malignancy. In this review, we will focus on recent advances in NKT cell-based vaccination strategies. Given the role that NKT cells play in autoimmune disease, infectious diseases, cancer, transplant immunology and dermatology, it is important to understand how to effectively guide their effector functions in order to develop novel immunotherapeutic strategies.

Prevention of NKT cell activation accelerates cutaneous wound closure and alters local inflammatory signals

We previously reported that in the absence of NKT cells, wound closure was accelerated in a murine excisional punch wound model. Here, we explored whether purposefully inhibiting NKT cell activation had similar effects on wound closure and the dermal inflammatory response to injury. We found that prevention of NKT cell activation accelerated wound closure in a dose-responsive manner. If anti-CD1d was administered before wounding, NKT cell infiltration into cutaneous wounds was diminished without quantitative changes in cellular infiltrates. Furthermore, prevention of NKT cell activation transiently enhanced the local production of a subset of chemokines, including MIP-2, MCP-1, MIP-1α, and MIP-1β, and altered the relative expression of CD69 and CXCR2 on the surface of both circulating and wound NKT cells. Taken together, these findings suggest that wounding activates NKT cells via CD1d presentation of glycolipid antigen and help further define a role for NKT cells in the regulation of wound inflammation and closure. Many soluble factors have been targeted as potential wound healing therapies, but their clinical success has been limited. Given our findings, the NKT cell may be an attractive target for wound healing therapies.