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Cutting edge: the ontogeny and function of Va14Ja18 natural T lymphocytes require signal processing by protein kinase C theta and NF-kappa B.
The rapid and robust immunoregulatory cytokine response of Va14Ja18 natural T (iNKT) cells to glycolipid Ags determines their diverse functions. Unlike conventional T cells, iNKT lymphocyte ontogeny absolutely requires NF-kappa B signaling. However, the precise role of NF-kappa B in iNKT cell function and the identity of upstream signals that activate NF-kappa B in this T cell subset remain unknown. Using mice in which iNKT cell ontogeny has been rescued despite inhibition of NF-kappa B signaling, we demonstrate that iNKT cell function requires NF-kappa B in a lymphocyte-intrinsic manner. Furthermore, the ontogeny of functional iNKT cells requires signaling through protein kinase C theta, which is dispensable for conventional T lymphocyte development. The unique requirement of protein kinase C theta implies that signals emanating from the TCR activate NF-kappa B during iNKT cell development and function. Thus, we conclude that NF-kappa B signaling plays a crucial role at distinct levels of iNKT cell biology.
NF-kappa B controls cell fate specification, survival, and molecular differentiation of immunoregulatory natural T lymphocytes.
Ontogenetic, homeostatic, and functional deficiencies within immunoregulatory natural T (iNKT) lymphocytes underlie various inflammatory immune disorders including autoimmunity. Signaling events that control cell fate specification and molecular differentiation of iNKT cells are only partly understood. Here we demonstrate that these processes within iNKT cells require classical NF-kappaB signaling. Inhibition of NF-kappaB signaling blocks iNKT cell ontogeny at an immature stage and reveals an apparent, novel precursor in which negative selection occurs. Most importantly, this block occurs due to a lack of survival signals, as Bcl-x(L) overexpression rescues iNKT cell ontogeny. Maturation of immature iNKT cell precursors induces Bcl-2 expression, which is defective in the absence of NF-kappaB signaling. Bcl-x(L) overexpression also rescues this maturation-induced Bcl-2 expression. Thus, antiapoptotic signals relayed by NF-kappaB critically control cell fate specification and molecular differentiation of iNKT cells and, hence, reveal a novel role for such signals within the immune system.
Commitment toward the natural T (iNKT) cell lineage occurs at the CD4+8+ stage of thymic ontogeny.
T lineage commitment occurs in a discrete, stage-specific manner during thymic ontogeny. Intrathymic precursor transfer experiments and the identification of CD4(+)8+ double-positive (DP), V alpha 14J alpha 18 natural T (iNKT) cells suggest that commitment to this lineage might occur at the DP stage. Nevertheless, this matter remains contentious because others failed to detect V alpha 14J alpha 18-positive iNKT cells that are CD4(+)8+. In resolution to this issue, we demonstrate that retinoic acid receptor-related orphan receptor gamma (ROR gamma)0/0 thymi, which accumulate immature single-positive (ISP) thymocytes that precede the DP stage, do not rearrange V alpha 14-to-J alpha 18 gene segments, suggesting that this event occurs at a post-ISP stage. Mixed radiation bone marrow chimeras revealed that RORgamma functions in an iNKT cell lineage-specific manner. Further, introgression of a Bcl-x(L) transgene into ROR gamma(0/0) mice, which promotes survival and permits secondary rearrangements of distal V alpha and J alpha gene segments at the DP stage, rescues V alpha 14-to-J alpha 18 recombination. Similarly, introgression of a rearranged V alpha 14J alpha 18 transgene into ROR gamma(0/0) mice results in functional iNKT cells. Thus, our data support the "T cell receptor-instructive (mainstream precursor) model" of iNKT cell lineage specification where V alpha 14-to-J alpha 18 rearrangement, positive selection, and iNKT cell lineage commitment occur at or after the DP stage of ontogeny.
Another view of T cell antigen recognition: cooperative engagement of glycolipid antigens by Va14Ja18 natural T(iNKT) cell receptor [corrected].
Va14Ja18 natural T (iNKT) cells rapidly elicit a robust effector response to different glycolipid Ags, with distinct functional outcomes. Biochemical parameters controlling iNKT cell function are partly defined. However, the impact of iNKT cell receptor beta-chain repertoire and how alpha-galactosylceramide (alpha-GalCer) analogues induce distinct functional responses have remained elusive. Using altered glycolipid ligands, we discovered that the Vb repertoire of iNKT cells impacts recognition and Ag avidity, and that stimulation with suboptimal avidity Ag results in preferential expansion of high-affinity iNKT cells. iNKT cell proliferation and cytokine secretion, which correlate with iNKT cell receptor down-regulation, are induced within narrow biochemical thresholds. Multimers of CD1d1-alphaGalCer- and alphaGalCer analogue-loaded complexes demonstrate cooperative engagement of the Va14Ja18 iNKT cell receptor whose structure and/or organization appear distinct from conventional alphabeta TCR. Our findings demonstrate that iNKT cell functions are controlled by affinity thresholds for glycolipid Ags and reveal a novel property of their Ag receptor apparatus that may have an important role in iNKT cell activation.
Natural killer T cells accelerate atherogenesis in mice.
We have investigated the potential role of CD1d-restricted natural killer T (NKT) cells in the development of atherosclerosis in mice. When fed an atherogenic diet (AD), NKT cell-deficient CD1d(-/-) mice had significantly smaller atherosclerotic lesions than AD-fed C57BL/6 (wild-type [WT]) mice. A significant reduction in atherosclerotic lesions was also demonstrated in AD-fed, low-density lipoprotein receptor-deficient (Ldlr(-/-)) mice reconstituted with CD1d(-/-) bone marrow cells compared with the lesions observed in Ldlr(-/-)mice reconstituted with WT marrow cells. In addition, repeated injections of alpha-GalCer or the related glycolipid OCH to apolipoprotein E knockout (apoE(-/-)) mice during the early phase of atherosclerosis significantly enlarged the lesion areas compared with mice injected with vehicle control. However, administering alpha-GalCer to apoE(-/-) mice with established lesions did not significantly increase the lesion area but considerably decreased the collagen content. Atherosclerosis development in either AD-fed WT or apoE(-/-) mice was associated with the presence of Valpha14Jalpha18 transcripts in the atherosclerotic arterial walls, indicating that NKT cells were recruited to these lesions. Thioglycolate-elicited macrophages pulsed with oxidized low-density lipoproteins expressed enhanced CD1d levels and induced NKT cells to produce interferon-gamma, a potentially proatherogenic T-helper 1 (TH1) cytokine. Collectively, we conclude that NKT cells are proatherogenic in mice.
Increase in hepatic NKT cells in leukocyte cell-derived chemotaxin 2-deficient mice contributes to severe concanavalin A-induced hepatitis.
Leukocyte cell-derived chemotaxin 2 (LECT2) was originally identified for its possible chemotactic activity against human neutrophils in vitro. It is a 16-kDa protein that is preferentially expressed in the liver. Its homologues have been widely identified in many vertebrates. Current evidence suggests that LECT2 may be a multifunctional protein like cytokines. However, the function of LECT2 in vivo remains unclear. To elucidate the role of this protein in vivo, we have generated LECT2-deficient (LECT2(-/-)) mice. We found that the proportion of NKT cells in the liver increased significantly in LECT2(-/-) mice, although those of conventional T cells, NK cells, and other cell types were comparable with those in wild-type mice. Consistent with increased hepatic NKT cell number, the production of IL-4 and IFN-gamma was augmented in LECT2(-/-) mice upon stimulation with alpha-galactosylceramide, which specifically activates Valpha14 NKT cells. In addition, NKT cell-mediated cytotoxic activity against syngeneic thymocytes increased in hepatic mononuclear cells obtained from LECT2(-/-) mice in vitro. Interestingly, the hepatic injury was exacerbated in LECT2(-/-) mice upon treatment with Con A, possibly because of the significantly higher expression of IL-4 and Fas ligand. These results suggest that LECT2 might regulate the homeostasis of NKT cells in the liver and might be involved in the pathogenesis of hepatitis.
Characterization and Functional Analysis of Mouse Semi-invariant Natural T Cells.
Semi-invariant natural killer T (iNKT) cells are CD1d-restricted innate-like lymphocytes that recognize lipid agonists. Activated iNKT cells have immunoregulatory properties. Human and mouse iNKT cell functions elicited by different glycolipid agonists are highly conserved, making the mouse an excellent animal model for understanding iNKT cell biology in vivo. This unit describes basic methods for the characterization and quantification (see Basic Protocol 1) and functional analysis of mouse iNKT cells in vivo or in vitro. This unit also contains protocols that describe enrichment and purification of iNKT cells, generation of CD1d tetramer, and lipid antigen loading onto cell-bound and soluble CD1d for activation of NKT cell hybridomas. © 2017 by John Wiley & Sons, Inc.
Activation of the Non-canonical Inflammasome in Mouse and Human Cells.
The non-canonical inflammasome is a signaling platform that allows for the detection of cytoplasmic lipopolysaccharides (LPS) in immune and non-immune cells. Upon detection of LPS, this inflammasome activates the signaling proteases caspase-4 and -5 (in humans) and caspase-11 (in mice). Inflammatory caspases activation leads to caspase self-processing and the cleavage of the pore-forming protein Gasdermin D (GSDMD). GSDMD N-terminal fragments oligomerize and form pores at the plasma membranes, leading to an inflammatory form of cell death called pyroptosis. Here, we describe a simple method to activate the non-canonical inflammasome in myeloid and epithelial cells and to measure its activity using cell death assay and immunoblotting.
Ciliary proteins specify the cell inflammatory response by tuning NFκB signaling, independently of primary cilia.
Complex inflammatory signalling cascades define the response to tissue injury but also control development and homeostasis, limiting these pathways as therapeutic targets. Primary cilia are sub-cellular regulators of cellular signalling, controlling how signalling is organized, encoded and, in some instances, driving or influencing pathogenesis. Our previous research revealed that disruption of ciliary intraflagellar transport (IFT), altered the cell response to IL-1β, supporting a putative link emerging between cilia and inflammation. Here, we show that IFT88 depletion affects specific cytokine-regulated behaviors, changing cytosolic NFκB translocation dynamics, but leaving MAPK unaffected. RNAseq analysis indicates IFT88 regulates one third of the genome-wide targets, including the pro-inflammatory genes Nos2, Il6 and Tnf. By microscopy, we find altered NFκB dynamics are independent to assembly of a ciliary axoneme. Indeed, depletion of IFT88 inhibits the inflammatory responses in the non-ciliated macrophage. We propose ciliary proteins, including IFT88, KIF3A, TTBK2 and NPHP4, act outside of the ciliary axoneme, to tune cytoplasmic NFκB signalling, and specify the downstream cell response. This is thus a non-canonical function for ciliary proteins in shaping cellular inflammation.
How Pyroptosis Contributes to Inflammation and Fibroblast-Macrophage Cross-Talk in Rheumatoid Arthritis.
About thirty years ago, a new form of pro-inflammatory lytic cell death was observed and termed pyroptosis. Only in 2015, gasdermins were defined as molecules that create pores at the plasma membrane and drive pyroptosis. Today, we know that gasdermin-mediated death is an important antimicrobial defence mechanism in bacteria, yeast and mammals as it destroys the intracellular niche for pathogen replication. However, excessive and uncontrolled cell death also contributes to immunopathology in several chronic inflammatory diseases, including arthritis. In this review, we discuss recent findings where pyroptosis contributes to tissue damage and inflammation with a main focus on injury-induced and autoimmune arthritis. We also review novel functions and regulatory mechanisms of the pyroptotic executors gasdermins. Finally, we discuss possible models of how pyroptosis may contribute to the cross-talk between fibroblast and macrophages, and also how this cross-talk may regulate inflammation by modulating inflammasome activation and pyroptosis induction.
NKT Cells Join the Two Step for Inflammasome-Independent IL-1β Release.
The cytokine interleukin-1β (IL-1β) is critical for antimicrobial defenses; the inflammasome pathway typically controls IL-1β release, but pathogens often evade this pathway. In this issue, Donado et al. (2020) describe an alternative, two-cell model, to instruct inflammasome-independent IL-1β release.
Inflammasome-Mediated Immunogenicity of Clinical and Experimental Vaccine Adjuvants.
In modern vaccines, adjuvants can be sophisticated immunological tools to promote robust and long-lasting protection against prevalent diseases. However, there is an urgent need to improve immunogenicity of vaccines in order to protect mankind from life-threatening diseases such as AIDS, malaria or, most recently, COVID-19. Therefore, it is important to understand the cellular and molecular mechanisms of action of vaccine adjuvants, which generally trigger the innate immune system to enhance signal transition to adaptive immunity, resulting in pathogen-specific protection. Thus, improved understanding of vaccine adjuvant mechanisms may aid in the design of "intelligent" vaccines to provide robust protection from pathogens. Various commonly used clinical adjuvants, such as aluminium salts, saponins or emulsions, have been identified as activators of inflammasomes - multiprotein signalling platforms that drive activation of inflammatory caspases, resulting in secretion of pro-inflammatory cytokines of the IL-1 family. Importantly, these cytokines affect the cellular and humoral arms of adaptive immunity, which indicates that inflammasomes represent a valuable target of vaccine adjuvants. In this review, we highlight the impact of different inflammasomes on vaccine adjuvant-induced immune responses regarding their mechanisms and immunogenicity. In this context, we focus on clinically relevant adjuvants that have been shown to activate the NLRP3 inflammasome and also present various experimental adjuvants that activate the NLRP3-, NLRC4-, AIM2-, pyrin-, or non-canonical inflammasomes and could have the potential to improve future vaccines. Together, we provide a comprehensive overview on vaccine adjuvants that are known, or suggested, to promote immunogenicity through inflammasome-mediated signalling.
Emulsion and liposome-based adjuvanted R21 vaccine formulations mediate protection against malaria through distinct immune mechanisms.
Adjuvanted protein vaccines offer high efficacy, yet most potent adjuvants remain proprietary. Several adjuvant compounds are being developed by the Vaccine Formulation Institute in Switzerland for global open access clinical use. In the context of the R21 malaria vaccine, in a mouse challenge model, we characterize the efficacy and mechanism of action of four Vaccine Formulation Institute adjuvants: two liposomal (LQ and LMQ) and two squalene emulsion-based adjuvants (SQ and SMQ), containing QS-21 saponin (Q) and optionally a synthetic TLR4 agonist (M). Two R21 vaccine formulations, R21/LMQ and R21/SQ, offer the highest protection (81%-100%), yet they trigger different innate sensing mechanisms in macrophages with LMQ, but not SQ, activating the NLRP3 inflammasome. The resulting in vivo adaptive responses have a different TH1/TH2 balance and engage divergent innate pathways while retaining high protective efficacy. We describe how modular changes in vaccine formulation allow for the dissection of the underlying immune pathways, enabling future mechanistically informed vaccine design.
Nur77 controls tolerance induction, terminal differentiation, and effector functions in semi-invariant natural killer T cells.
Semi-invariant natural killer T (iNKT) cells are self-reactive lymphocytes, yet how this lineage attains self-tolerance remains unknown. iNKT cells constitutively express high levels of Nr4a1-encoded Nur77, a transcription factor that integrates signal strength downstream of the T cell receptor (TCR) within activated thymocytes and peripheral T cells. The function of Nur77 in iNKT cells is unknown. Here we report that sustained Nur77 overexpression (Nur77tg) in mouse thymocytes abrogates iNKT cell development. Introgression of a rearranged Vα14-Jα18 TCR-α chain gene into the Nur77tg (Nur77tg;Vα14tg) mouse rescued iNKT cell development up to the early precursor stage, stage 0. iNKT cells in bone marrow chimeras that reconstituted thymic cellularity developed beyond stage 0 precursors and yielded IL-4-producing NKT2 cell subset but not IFN-γ-producing NKT1 cell subset. Nonetheless, the developing thymic iNKT cells that emerged in these chimeras expressed the exhaustion marker PD1 and responded poorly to a strong glycolipid agonist. Thus, Nur77 integrates signals emanating from the TCR to control thymic iNKT cell tolerance induction, terminal differentiation, and effector functions.
Posttranslational and Therapeutic Control of Gasdermin-Mediated Pyroptosis and Inflammation.
Pyroptosis is a proinflammatory form of cell death, mediated by membrane pore-forming proteins called gasdermins. Gasdermin pores allow the release of the pro-inflammatory cytokines IL-1β and IL-18 and cause cell swelling and cell lysis leading to release of other intracellular proteins that act as alarmins to perpetuate inflammation. The best characterized, gasdermin D, forms pores via its N-terminal domain, generated after the cleavage of full length gasdermin D by caspase-1 or -11 (caspase-4/5 in humans) typically upon sensing of intracellular pathogens. Thus, gasdermins were originally thought to largely contribute to pathogen-induced inflammation. We now know that gasdermin family members can also be cleaved by other proteases, such as caspase-3, caspase-8 and granzymes, and that they contribute to sterile inflammation as well as inflammation in autoinflammatory diseases or during cancer immunotherapy. Here we briefly review how and when gasdermin pores are formed, and then focus on emerging endogenous mechanisms and therapeutic approaches that could be used to control pore formation, pyroptosis and downstream inflammation.
The ion channel CALHM6 controls bacterial infection-induced cellular cross-talk at the immunological synapse.
Membrane ion channels of the calcium homeostasis modulator (CALHM) family promote cell-cell crosstalk at neuronal synapses via ATP release, where ATP acts as a neurotransmitter. CALHM6, the only CALHM highly expressed in immune cells, has been linked to the induction of natural killer (NK) cell anti-tumour activity. However, its mechanism of action and broader functions in the immune system remain unclear. Here, we generated Calhm6-/- mice and report that CALHM6 is important for the regulation of the early innate control of Listeria monocytogenes infection in vivo. We find that CALHM6 is upregulated in macrophages by pathogen-derived signals and that it relocates from the intracellular compartment to the macrophage-NK cell synapse, facilitating ATP release and controlling the kinetics of NK cell activation. Anti-inflammatory cytokines terminate CALHM6 expression. CALHM6 forms an ion channel when expressed in the plasma membrane of Xenopus oocytes, where channel opening is controlled by a conserved acidic residue, E119. In mammalian cells, CALHM6 is localised to intracellular compartments. Our results contribute to the understanding of neurotransmitter-like signal exchange between immune cells that fine-tunes the timing of innate immune responses.
Histologic assessments in ulcerative colitis: the evidence behind a new endpoint in clinical trials.
INTRODUCTION: Treatment goals for ulcerative colitis (UC) are evolving from the achievement of clinical remission to more rigorous goals defined by endoscopic and histologic healing. Achievement of deeper remission targets aims to reduce the risk of colectomy, hospitalizations, and colorectal cancer. AREAS COVERED: This review covers histologic assessments, histologic remission as a clinical trial endpoint, and the association between histologic disease activity and clinical outcomes. Future directions are also discussed, including the use of advanced imaging and artificial intelligence technologies, as well as potential future treatment targets beyond histologic remission. EXPERT OPINION: Histologic assessments are used for their sensitivity in measuring mucosal inflammatory changes in UC. Due to correlation with disease activity, histologic assessments may support clinical decision-making regarding treatment decisions as such assessments can be associated with rates of clinical relapse, hospitalization, colectomy, and neoplasia. While histologic remission is limited by varying definitions and multiple histologic indices, work is ongoing to create a consensus on the use of histologic assessments in clinical trials. As research advances, aspirational targets beyond histologic remission, such as molecular healing and disease clearance, are being explored.