Recent advances regarding the potential roles of invariant natural killer T cells in cardiovascular diseases with immunological and inflammatory backgrounds.

Invariant natural killer T (iNKT) cells, which bear αß-type T cell antigen-receptors, recognize glycolipid antigens in a cluster of differentiation 1d (CD1d)-restricted manner. Regarding these cells, the unique modes of thymic selection and maturation elucidate innateness, irrespective of them also being members of the adaptive immune system as a T cell. iNKT cells develop and differentiate into NKT1 [interferon γ (IFN-γγ-producing], NKT2 [interleukin 4 (IL-4)/IL-13-producing], or NKT17 (IL-17-producing) subsets in the thymus. After egress, NKT10 (IL-10-producing), follicular helper NKT (NKTfh; IL-21-producing), and regulatory NKT (NKTreg) subsets emerge following stimulation in the periphery. Moreover, iNKT cells have been shown to possess several physiological or pathological roles. iNKT cells exhibit dual alleviating or aggravating roles in experimentally induced immune and/or inflammatory diseases in mice. These findings indicate that the modulation of iNKT cells can be employed for therapeutic use or prevention of human diseases. In this review, we discuss the potential roles of iNKT cells in the development of immune/inflammatory diseases of the cardiovascular system, with emphasis on atherosclerosis, aortic aneurysms, and cardiac remodeling.

Contribution of NKT cells and CD1d-expressing cells in obesity-associated adipose tissue inflammation.

Natural killer T (NKT) cell are members of the innate-like T lymphocytes and recognizes lipid antigens presented by CD1d-expressing cells. Obesity-associated inflammation in adipose tissue (AT) leads to metabolic dysfunction, including insulin resistance. When cellular communication is properly regulated among AT-residing immune cells and adipocytes during inflammation, a favorable balance of Th1 and Th2 immune responses is achieved. NKT cells play crucial roles in AT inflammation, influencing the development of diet-induced obesity and insulin resistance. NKT cells interact with CD1d-expressing cells in AT, such as adipocytes, macrophages, and dendritic cells, shaping pro-inflammatory or anti-inflammatory microenvironments with distinct characteristics depending on the antigen-presenting cells. Additionally, CD1d may be involved in the inflammatory process independently of NKT cells. In this mini-review, we provide a brief overview of the current understanding of the interaction between immune cells, focusing on NKT cells and CD1d signaling, which control AT inflammation both in the presence and absence of NKT cells. We aim to enhance our understanding of the mechanisms of obesity-associated diseases.

MR1 deficiency enhances IL-17-mediated allergic contact dermatitis.

Major histocompatibility complex (MHC) class Ib molecules present antigens to subsets of T cells primarily involved in host defense against pathogenic microbes and influence the development of immune-mediated diseases. The MHC class Ib molecule MHC-related protein 1 (MR1) functions as a platform to select MR1-restricted T cells, including mucosal-associated invariant T (MAIT) cells in the thymus, and presents ligands to them in the periphery. MAIT cells constitute an innate-like T-cell subset that recognizes microbial vitamin B2 metabolites and plays a defensive role against microbes. In this study, we investigated the function of MR1 in allergic contact dermatitis (ACD) by examining wild-type (WT) and MR1-deficient (MR1-/-) mice in which ACD was induced with 2,4-dinitrofluorobenzene (DNFB). MR1-/- mice exhibited exaggerated ACD lesions compared with WT mice. More neutrophils were recruited in the lesions in MR1-/- mice than in WT mice. WT mice contained fewer MAIT cells in their skin lesions following elicitation with DNFB, and MR1-/- mice lacking MAIT cells exhibited a significant increase in IL-17-producing αß and γδ T cells in the skin. Collectively, MR1-/- mice displayed exacerbated ACD from an early phase with an enhanced type 3 immune response, although the precise mechanism of this enhancement remains elusive.

Immunomodulatory Functions of α-GalCer and a Derivative, α-Carba-GalCer.

Certain glycolipids have immunomodulatory potential by activating natural killer T (NKT) cells, a unique T cell subset. Invariant NKT (iNKT) cells recognize α-galactosylceramide (α-GalCer) and synthetic derivatives presented by CD1d molecules and secrete large amounts of cytokines that modulate immune functions. Some iNKT cell ligands induce distinct reactions biased toward either Th1 or Th2 immune responses, while others show mixed responses. We describe the methods for activating iNKT cells by the ligands as represented by α-GalCer using in vitro assays, such as cell-free or co-culture with antigen-presenting cells. In addition, α-GalCer/CD1d multimer can be used to specifically detect iNKT cells using flow cytometry. α-GalCer is also utilized to activate systemic iNKT cells in vivo, which leads to the production of high levels of cytokines in sera. Collectively, α-GalCer and its derivatives activate iNKT cells that modulate immune balance, and we need to understand the characteristics of these ligands for developing their utility.

The microsomal prostaglandin E synthase-1/prostaglandin E2 axis induces recovery from ischaemia via recruitment of regulatory T cells.

AIMS: Microsomal prostaglandin E synthase-1 (mPGES-1)/prostaglandin E2 (PGE2) induces angiogenesis through the prostaglandin E2 receptor (EP1-4). Among immune cells, regulatory T cells (Tregs), which inhibit immune responses, have been implicated in angiogenesis, and PGE2 is known to modulate the function and differentiation of Tregs. We hypothesized that mPGES-1/PGE2-EP signalling could contribute to recovery from ischaemic conditions by promoting the accumulation of Tregs. METHODS AND RESULTS: Wild-type (WT), mPGES-1-deficient (mPges-1-/-), and EP4 receptor-deficient (Ep4-/-) male mice, 6-8 weeks old, were used. Hindlimb ischaemia was induced by femoral artery ligation. Recovery from ischaemia was suppressed in mPges-1-/- mice and compared with WT mice. The number of accumulated forkhead box protein P3 (FoxP3)+ cells in ischaemic muscle tissue was decreased in mPges-1-/- mice compared with that in WT mice. Expression levels of transforming growth factor-ß (TGF-ß) and stromal cell derived factor-1 (SDF-1) in ischaemic tissue were also suppressed in mPges-1-/- mice. The number of accumulated FoxP3+ cells and blood flow recovery were suppressed when Tregs were depleted by injecting antibody against folate receptor 4 in WT mice but not in mPges-1-/- mice. Recovery from ischaemia was significantly suppressed in Ep4-/- mice compared with that in WT mice. Furthermore, mRNA levels of Foxp3 and Tgf-ß were suppressed in Ep4-/- mice. Moreover, the number of accumulated FoxP3+ cells in ischaemic tissue was diminished in Ep4-/- mice compared with that in Ep4+/+ mice. CONCLUSION: These findings suggested that mPGES-1/PGE2 induced neovascularization from ischaemia via EP4 by promoting the accumulation of Tregs. Highly selective EP4 agonists could be useful for the treatment of peripheral artery disease.

Adipose invariant NKT cells interact with CD1d-expressing macrophages to regulate obesity-related inflammation.

Obesity is accompanied by and accelerated with chronic inflammation in adipose tissue, especially visceral adipose tissue (VAT). This low-level inflammation predisposes the host to the development of metabolic disease, most notably type 2 diabetes. We have focused on the capacity of glycolipid-reactive, CD1d-restricted natural killer T (NKT) cells to modulate obesity and its associated metabolic sequelae. We previously reported that CD1d knockout (KO) mice are partially protected against the development of obesity-associated insulin resistance, and these findings were recapitulated in mice with an adipocyte-specific CD1d deficiency, suggesting that NKT cell-adipocyte interactions play a critical role in exacerbating disease. However, many other CD1d-expressing cells contribute to the in vivo responses of NKT cells to lipid antigens. In the present study, we examined the role of CD1d expression by macrophages (Mϕ) in the development of obesity-associated metabolic inflammation using LysMcre-cd1d1f/f mice where the CD1d1 gene is disrupted in a Mϕ-specific manner. Unexpectedly, these animals contained a higher frequency of T-bet+ CD4+ T cells in VAT with increased production of Th1 cytokines that aggravated VAT inflammation. Mϕ from mutant mice displayed increased production of IL-12p40, suggesting M1 polarization. These findings indicate that interactions of CD1d on Mϕ with NKT cells play a beneficial role in obesity-associated VAT inflammation and insulin resistance with a sharp contrast to an aggravating role of CD1d in another type of antigen-presenting cell, dendritic cells.

A new approach to analysis of intracellular proteins and subcellular localization using cellprofiler and imageJ in combination.

Analytical pipeline, which is used for various analysis application, of CellProfiler, an open-source software for cell imaging analysis, is very important. In the present study, to examine whether intracellular proteins can be discriminated using a combination of CellProfiler and ImageJ, we analyzed neuroblastoma and monocytic cell lines, and disease-specific induced pluripotent stem cell (iPSC)-derived neurons. This revealed that scattered puncta of Rab7 and transferrin in neuroblastoma lines were clearly detectable by created analytical pipelines in CellProfiler. We then constructed pipelines for measuring the distance from the center of the nucleus to allow investigation of the intracellular localization of Rab7 or transferrin. Using CellProfiler and ImageJ in combination, we confirmed that our pipelines were applicable both quantitatively and objectively to analysis of membrane trafficking of proteins such as Rab proteins and transferrin. In addition, when applied to quantitative measurement of phagocytosis, our pipelines clearly detected monocytic cell lines that had engulfed bioparticles. Finally, we developed new pipelines for analysis of disease phenotype using iPSCs from a patient with familial Parkinson's disease (PD), harboring the I2020T LRRK2 mutation (PARK8). These were able to successfully detect Rab5 puncta and Rab7 puncta in PARK8 patient iPSC-derived neurons. Interestingly, in long-term culture, we found that the numbers of Rab7 puncta in a single PARK8 patient iPSC-derived neurons were lower than that of control iPSC-derived neurons. On the other hands, at 14 days in vitro, the numbers of Rab5 puncta in PARK8 patient iPSC-derived neurons were lower than those of isogenic iPSC-derived neurons, but not Rab7 puncta. Furthermore, Rab5 puncta of PARK8 patient iPSC-derived neurons exhibited distinct localization pattern relative to isogenic iPSC-derived neurons. These present results suggest that this new analytical tool can be used as a supporting method for quantification of intracellular protein.

Development of an immunochromatographic test for the detection of Mycoplasma pneumoniae GroES antigen.

Mycoplasma pneumoniae frequently causes community-acquired pneumonia in children; ß-lactam antibiotics are ineffective against this bacterium because of its lack of a cell wall. Hence, a rapid and simple detection method is required to ensure appropriate treatment. In this study, we developed a rapid and simple immunochromatography-based detection method using monoclonal antibodies that react with the co-chaperone GroES of M. pneumoniae. Mice were immunized with recombinant GroES, and hybridoma cells producing anti-GroES monoclonal antibodies were established. For the development of the immunochromatographic test, antibody pairs with superior reactivity and specificity were selected. The developed immunochromatographic test could detect 0.1 ng/mL of recombinant GroES within 20 min. Moreover, no cross-reaction was observed with other microorganisms, including six Mycoplasma species, 20 other bacterial species, and one yeast species. Macrolide-resistant and -susceptible M. pneumoniae clinical isolates were detected at approximately 104 to 105 colony-forming units/mL. The study indicates that immunochromatographic tests targeting GroES are useful for rapid and simple detection of M. pneumoniae.

Natural Killer T Cells Are Involved in Atherosclerotic Plaque Instability in Apolipoprotein-E Knockout Mice.

The infiltration and activation of macrophages as well as lymphocytes within atherosclerotic lesion contribute to the pathogenesis of plaque rupture. We have demonstrated that invariant natural killer T (iNKT) cells, a unique subset of T lymphocytes that recognize glycolipid antigens, play a crucial role in atherogenesis. However, it remained unclear whether iNKT cells are also involved in plaque instability. Apolipoprotein E (apoE) knockout mice were fed a standard diet (SD) or a high-fat diet (HFD) for 8 weeks. Moreover, the SD- and the HFD-fed mice were divided into two groups according to the intraperitoneal injection of α-galactosylceramide (αGC) that specifically activates iNKT cells or phosphate-buffered saline alone (PBS). ApoE/Jα18 double knockout mice, which lack iNKT cells, were also fed an SD or HFD. Plaque instability was assessed at the brachiocephalic artery by the histological analysis. In the HFD group, αGC significantly enhanced iNKT cell infiltration and exacerbated atherosclerotic plaque instability, whereas the depletion of iNKT cells attenuated plaque instability compared to PBS-treated mice. Real-time PCR analyses in the aortic tissues showed that αGC administration significantly increased expressional levels of inflammatory genes such as IFN-γ and MMP-2, while the depletion of iNKT cells attenuated these expression levels compared to those in the PBS-treated mice. Our findings suggested that iNKT cells are involved in the exacerbation of plaque instability via the activation of inflammatory cells and upregulation of MMP-2 in the vascular tissues.

Activation of iNKT Cells Facilitates Liver Repair After Hepatic Ischemia Reperfusion Injury Through Acceleration of Macrophage Polarization.

Macrophage polarization is critical for liver tissue repair following acute liver injury. However, the underlying mechanisms of macrophage phenotype switching are not well defined. Invariant natural killer T (iNKT) cells orchestrate tissue inflammation and tissue repair by regulating cytokine production. Herein, we examined whether iNKT cells played an important role in liver repair after hepatic ischemia-reperfusion (I/R) injury by affecting macrophage polarization. To this end, we subjected male C57BL/6 mice to hepatic I/R injury, and mice received an intraperitoneal (ip) injection of α-galactosylceramide (α-GalCer) or vehicle. Compared with that of the vehicle, α-GalCer administration resulted in the promotion of liver repair accompanied by acceleration of macrophage differentiation and by increases in the numbers of Ly6Chigh pro-inflammatory macrophages and Ly6Clow reparative macrophages. iNKT cells activated with α-GalCer produced interleukin (IL)-4 and interferon (IFN)-γ. Treatment with anti-IL-4 antibodies delayed liver repair, which was associated with an increased number of Ly6Chigh macrophages and a decreased number of Ly6Clow macrophages. Treatment with anti-IFN-γ antibodies promoted liver repair, associated with reduced the number of Ly6Chigh macrophages, but did not change the number of Ly6Clow macrophages. Bone marrow-derived macrophages up-regulated the expression of genes related to both a pro-inflammatory and a reparative phenotype when co-cultured with activated iNKT cells. Anti-IL-4 antibodies increased the levels of pro-inflammatory macrophage-related genes and decreased those of reparative macrophage-related genes in cultured macrophages, while anti-IFN-γ antibodies reversed the polarization of macrophages. Cd1d-deficient mice showed delayed liver repair and suppressed macrophage switching, compared with that in wild-type mice. These results suggest that the activation of iNKT cells by α-GalCer facilitated liver repair after hepatic I/R injury by both IL-4-and IFN-γ-mediated acceleration of macrophage polarization. Therefore, the activation of iNKT cells may represent a therapeutic tool for liver repair after hepatic I/R injury.

Activation of Invariant Natural Killer T Cells by α-Galactosylceramide Attenuates the Development of Angiotensin II-Mediated Abdominal Aortic Aneurysm in Obese ob/ob Mice.

The infiltration and activation of macrophages as well as lymphocytes within the aorta contribute to the pathogenesis of abdominal aortic aneurysm (AAA). Invariant natural killer T (iNKT) cells are unique subset of T lymphocytes and have a crucial role in atherogenesis. However, it remains unclear whether iNKT cells also impact on the development of AAA. Ob/ob mice were administered angiotensin II (AngII, 1,000 ng/kg/min) or phosphate-buffered saline (PBS) by osmotic minipumps for 4 weeks and further divided into 2 groups; α-galactosylceramide (αGC; PBS-αGC; n = 5 and AngII-αGC; n = 12), which specifically activates iNKT cells, and PBS (PBS-PBS; n = 10, and AngII-PBS; n = 6). Maximal abdominal aortic diameter was comparable between PBS-PBS and PBS-αGC, and was significantly greater in AngII-PBS than in PBS-PBS. This increase was significantly attenuated in AngII-αGC without affecting blood pressure. αGC significantly enhanced iNKT cell infiltration compared to PBS-PBS. The ratio of F4/80-positive macrophages or CD3-positive T lymphocytes area to the lesion area was significantly higher in AngII-PBS than in PBS-PBS, and was significantly decreased in AngII-αGC. Gene expression of M2-macrophage specific markers, arginase-1 and resistin-like molecule alpha, was significantly greater in aortic tissues from AngII-αGC compared to AngII-PBS 1 week after AngII administration, and this increase was diminished at 4 weeks. Activation of iNKT cells by αGC can attenuate AngII-mediated AAA in ob/ob mice via inducing anti-inflammatory M2 polarized state. Activation of iNKT cells by the bioactive lipid αGC may be a novel therapeutic target against the development of AAA.

Correction: Expression of signal-transducing adaptor protein-1 attenuates experimental autoimmune hepatitis via down-regulating activation and homeostasis of invariant natural killer T cells.

[This corrects the article DOI: 10.1371/journal.pone.0241440.].

Natural Killer Cell Group 7 Sequence in Cytotoxic Cells Optimizes Exocytosis of Lytic Granules Essential for the Perforin-Dependent, but Not Fas Ligand-Dependent, Cytolytic Pathway.

Cytotoxic cells, such as CD8+ T cells or NK cells, have been shown to eliminate virus-infected cells or transformed cells primarily via two pathways: the perforin/granzyme-dependent pathway and the Fas ligand-Fas pathway; however, the precise cytolytic mechanisms have not been clarified thoroughly. In our previous study, we demonstrated that a T-box transcription factor, Eomesodermin (Eomes), may play important roles in activating the perforin pathway besides inducing perforin and granzyme B mRNA expression. In this study, we identified natural killer cell group 7 sequence (Nkg7), a molecule induced by Eomes, to be found critical for perforin-dependent cytolysis. Nkg7 mRNA expression in leukocytes from normal mice was mainly restricted to cells with cytotoxicity such as NK cells, NKT cells, and activated CD8+ T cells. The cytolytic activity of NK cells or CD8+ CTLs from Nkg7-deficient mice against Fas-negative target cells was reduced significantly, whereas Fas ligand-mediated cytolysis by Nkg7-deficient CTLs was not impaired. Further, translocation of granule membrane protein CD107a to the cell surface upon CD3 stimulation was defective in CD8+ CTLs from Nkg7 knockout, whereas surface induction of another granule membrane protein, CD63, was almost normal. In addition, analyses of lytic granules in CTLs by electron microscopy revealed that the number of lytic granules with dense cores was significantly reduced in Nkg7-knockout CTLs. These results indicate that Nkg7 may specifically contribute to efficient cytolysis via the perforin/granzyme pathway by enhancing the exocytosis of a particular type of lytic granules.

The protective function of invariant natural killer T cells in the relapse of experimental autoimmune uveoretinitis.

Experimental autoimmune uveoretinitis (EAU) in mice provides a useful platform to study the pathogenesis and experimental therapeutics of human uveitis. One often used EAU model employs C57BL/6 (B6) mice sensitized with a peptide residue having 1 to 20 amino acids of human interphotoreceptor retinoid binding protein (hIRBP1-20). The model using the B6 background has permitted a liberal use of genetically engineered strains and has provided insights for understanding uveoretinitis. However, this is usually acute/monophasic and does not represent human uveoretinitis that is characterized as a chronic/recurrent disease. Several chronic/recurrent EAU models have been developed; of these, we employed administration of staphylococcal enterotoxin B (SEB) for relapse in the present study, and found that recurrence was induced at day 24 after primary immunization, which is thought to be the convalescent phase. We reported the activation of invariant natural killer T (iNKT)-cells upon primary immunization of the EAU model mice with the ligand RCAI-56, which was found to mitigate the disease in our previous study. Here, we first attempted to ameliorate EAU in the relapse model using a preventive regimen by activating iNKT cells at the same time relapse induction (day 24) or in a regimen after 3 days of relapse induction (day 27). The preventive as well as post-inductive regimens were successful in reducing histopathological scores by inhibiting the Ag-specific Th17-biased response. Collectively, activation of iNKT cells may be useful to mitigate the relapse response of EAU induced with SEB.

Expression of signal-transducing adaptor protein-1 attenuates experimental autoimmune hepatitis via down-regulating activation and homeostasis of invariant natural killer T cells.

OBJECTIVE: Signal-transducing adaptor protein (STAP) family members function as adaptor molecules and are involved in several events during immune responses. Notably however, the biological functions of STAP-1 in other cells are not known. We aimed to investigate the functions of STAP-1 in invariant natural killer T (iNKT) cells and iNKT cell-dependent hepatitis. METHODS: We employed concanavalin A (Con A)-induced hepatitis and α-galactosylceramide (α-GalCer)-induced hepatitis mouse models, both are models of iNKT cell-dependent autoimmune hepatitis, and STAP-1 overexpressing 2E10 cells to investigate the role of STAP-1 in iNKT cell activation in vivo an in vitro, respectively. RESULTS: After Con A- or α-GalCer-injection, hepatocyte necrotic areas and plasma alanine aminotransferase elevation were more severe in STAP-1 knockout (S1KO) mice and milder in lymphocyte-specific STAP-1 transgenic (S1Tg) mice, as compared to wild-type (WT) mice. Two events that may be related to Con A-induced and/or α-GalCer-induced hepatitis were influenced by STAP-1 manipulation. One is that iNKT cell populations in the livers and spleens were increased in S1KO mice and were decreased in S1Tg mice. The other is that Con A-induced interleukin-4 and interferon-γ production was attenuated by STAP-1 overexpression. These effects of STAP-1 were confirmed using 2E10 cells overexpressing STAP-1 that showed impairment of interleukin-4 and interferon-γ production as well as phosphorylation of Akt and mitogen-activated protein kinases in response to Con A stimulation. CONCLUSIONS: These results conclude that STAP-1 regulates iNKT cell maintenance/activation, and is involved in the pathogenesis of autoimmune hepatitis.

NF-κB-inducing kinase contributes to normal development of cortical thymic epithelial cells: its possible role in shaping a proper T-cell repertoire.

Nuclear factor (NF)-κB-inducing kinase (NIK) is known to be a critical regulator of multiple aspects of the immune response. Although the role of NIK in the development of medullary thymic epithelial cells (mTECs) has been well documented, the impact of NIK on the differentiation and function of cortical thymic epithelial cells (cTECs) remains ambiguous. To investigate the possible involvement of NIK in cTEC differentiation, we have compared the gene expression and function of cTECs from a NIK-mutant mouse, alymphoplasia (aly/aly) with those of cTECs from wild-type (WT) mice. Flow cytometric analyses revealed that expression levels of MHC class II, but not MHC class I or other TEC markers, were higher in aly/aly cells than in WT cells. Notably, the proportion of MHC class IIhi+ cTECs was elevated in aly/aly mice. We also demonstrated that expression of Ccl5 mRNA in the MHC class IIhi+ subset of aly/aly cTECs was decreased compared with that in WT cells, implying an abnormal pattern of gene expression in aly/aly cTECs. Analyses of bone marrow chimera using aly/aly or aly/+ mice as hosts suggested that Vß usage and CD5 expression on WT T-cells were altered when they matured in aly/aly thymi. These results collectively indicate that NIK may be involved in controlling the function of cTEC in selecting a proper T-cell repertoire.

Attenuation of experimental autoimmune uveoretinitis in mice by IKKß inhibitor IMD-0354.

Uveitis is a sight-threatening intraocular inflammatory disease that accounts for almost 10% of blindness worldwide. NF-κB signaling plays pivotal roles in inflammatory diseases. We have reported that IMD-0354, which inhibits NF-κB signaling via selective blockade of IKK-ß, suppresses inflammation in several ocular disease models. Here, we examined the therapeutic effect of IMD-0354 in an experimental autoimmune uveoretinitis (EAU) model, a well-established animal model for endogenous uveitis in humans. Systemic administration of IMD-0354 significantly suppressed the clinical and histological severity, inflammatory edema, and the translocation of NF-κB p65 into the nucleus of retinas in EAU mice. Furthermore, IMD-0354 treatment significantly inhibited the levels of several Th1/Th17-mediated pro-inflammatory cytokines in vitro. Our current data demonstrate that inhibition of IKKß with IMD-0354 ameliorates inflammatory responses in the mouse EAU model, suggesting that IMD-0354 may be a promising therapeutic agent for human endogenous uveitis.

The disruption of invariant natural killer T cells exacerbates cardiac hypertrophy and failure caused by pressure overload in mice.

NEW FINDINGS: What is the central question of this study? We questioned whether the disruption of invariant natural killer T (iNKT) cells exacerbates left ventricular (LV) remodelling and heart failure after transverse aortic constriction in mice. What are the main findings and their importance? Pressure overload induced by transverse aortic constriction increased the infiltration of iNKT cells in mouse hearts. The disruption of iNKT cells exacerbated LV remodelling and hastened the transition from hypertrophy to heart failure, in association with the activation of mitogen-activated protein kinase signalling. Activation of iNKT cells modulated the immunological balance in this process and played a protective role against LV remodelling and failure. ABSTRACT: Chronic inflammation is involved in the development of cardiac remodelling and heart failure (HF). Invariant natural killer T (iNKT) cells, a subset of T lymphocytes, have been shown to produce various cytokines and orchestrate tissue inflammation. The pathophysiological role of iNKT cells in HF caused by pressure overload has not been studied. In the present study, we investigated whether the disruption of iNKT cells affected this process in mice. Transverse aortic constriction (TAC) and a sham operation were performed in male C57BL/6J wild-type (WT) and iNKT cell-deficient Jα18 knockout (KO) mice. The infiltration of iNKT cells was increased after TAC. The disruption of iNKT cells exacerbated left ventricular (LV) remodelling and hastened the transition to HF after TAC. Histological examinations also revealed that the disruption of iNKT cells induced greater myocyte hypertrophy and a greater increase in interstitial fibrosis after TAC. The expressions of interleukin-10 and tumour necrosis factor-α mRNA and their ratio in the LV after TAC were decreased in the KO compared with WT mice, which might indicate that the disruption of iNKT cells leads to an imbalance between T-helper type 1 and type 2 cytokines. The phosphorylation of extracellular signal-regulated kinase was significantly increased in the KO mice. The disruption of iNKT cells exacerbated the development of cardiac remodelling and HF after TAC. The activation of iNKT cells might play a protective role against HF caused by pressure overload. Targeting the activation of iNKT cells might thus be a promising candidate as a new therapeutic strategy for HF.

Role of Natural Killer T Cells in the Development of Obesity and Insulin Resistance: Insights From Recent Progress.

Natural killer T (NKT) cells play important roles in adipose tissue inflammation, and thus influence the development of diet-induced obesity and insulin resistance. The interactions between cluster of differentiation (CD)1d and NKT T cell receptor are thought to be critical in this process, as demonstrated in two NKT cell-deficient mouse models-systemic CD1d gene knockout (KO) and prototypic Jα18 KO mice. The latter lacks some repertoires besides invariant (i)NKT cells due to manipulation of the Jα18 gene segment; therefore, the role of iNKT vs. variant NKT cells must be reinterpreted considering the availability of new Jα18 KO mice. NKT cells have varied roles in the development of obesity; indeed, studies have reported contradictory results depending on the mouse model, diet, and rearing conditions, all of which could affect the microbiome. In this mini-review, we discuss these points considering recent findings from our laboratory and others as well as the role of NKT cells in the development of obesity and insulin resistance based on data obtained from studies on conditional CD1d1 KO and new Jα18 KO mice generated through gene editing.