Skin and peripheral lymph node invariant NKT cells are mainly retinoic acid receptor-related orphan receptor (gamma)t+ and respond preferentially under inflammatory conditions

An intestinal TH17 cell-derived subset can initiate cancer

Approximately 25% of cancers are preceded by chronic inflammation that occurs at the site of tumor development. However, whether this multifactorial oncogenic process, which commonly occurs in the intestines, can be initiated by a specific immune cell population is unclear. Here, we show that an intestinal T cell subset, derived from interleukin-17 (IL-17)-producing helper T (TH17) cells, induces the spontaneous transformation of the intestinal epithelium. This subset produces inflammatory cytokines, and its tumorigenic potential is not dependent on IL-17 production but on the transcription factors KLF6 and T-BET and interferon-γ. The development of this cell type is inhibited by transforming growth factor-β1 (TGFβ1) produced by intestinal epithelial cells. TGFβ signaling acts on the pretumorigenic TH17 cell subset, preventing its progression to the tumorigenic stage by inhibiting KLF6-dependent T-BET expression. This study therefore identifies an intestinal T cell subset initiating cancer.

Traversing the bench to bedside journey for iNKT cell therapies

Invariant natural killer T (iNKT) cells are immune cells that harness properties of both the innate and adaptive immune system and exert multiple functions critical for the control of various diseases. Prevention of graft-versus-host disease (GVHD) by iNKT cells has been demonstrated in mouse models and in correlative human studies in which high iNKT cell content in the donor graft is associated with reduced GVHD in the setting of allogeneic hematopoietic stem cell transplants. This suggests that approaches to increase the number of iNKT cells in the setting of an allogeneic transplant may reduce GVHD. iNKT cells can also induce cytolysis of tumor cells, and murine experiments demonstrate that activating iNKT cells in vivo or treating mice with ex vivo expanded iNKT cells can reduce tumor burden. More recently, research has focused on testing anti-tumor efficacy of iNKT cells genetically modified to express a chimeric antigen receptor (CAR) protein (CAR-iNKT) cells to enhance iNKT cell tumor killing. Further, several of these approaches are now being tested in clinical trials, with strong safety signals demonstrated, though efficacy remains to be established following these early phase clinical trials. Here we review the progress in the field relating to role of iNKT cells in GVHD prevention and anti- cancer efficacy. Although the iNKT field is progressing at an exciting rate, there is much to learn regarding iNKT cell subset immunophenotype and functional relationships, optimal ex vivo expansion approaches, ideal treatment protocols, need for cytokine support, and rejection risk of iNKT cells in the allogeneic setting.

invariant Natural Killer T cell therapy as a novel therapeutic approach in hematological malignancies

Invariant Natural Killer T cell therapy is an emerging platform of immunotherapy for cancer treatment. This unique cell population is a promising candidate for cell therapy for cancer treatment because of its inherent cytotoxicity against CD1d positive cancers as well as its ability to induce host CD8 T cell cross priming. Substantial evidence supports that iNKT cells can modulate myelomonocytic populations in the tumor microenvironment to ameliorate immune dysregulation to antagonize tumor progression. iNKT cells can also protect from graft-versus-host disease (GVHD) through several mechanisms, including the expansion of regulatory T cells (Treg). Ultimately, iNKT cell-based therapy can retain antitumor activity while providing protection against GVHD simultaneously. Therefore, these biological properties render iNKT cells as a promising "off-the-shelf" therapy for diverse hematological malignancies and possible solid tumors. Further the introduction of a chimeric antigen recetor (CAR) can further target iNKT cells and enhance function. We foresee that improved vector design and other strategies such as combinatorial treatments with small molecules or immune checkpoint inhibitors could improve CAR iNKT in vivo persistence, functionality and leverage anti-tumor activity along with the abatement of iNKT cell dysfunction or exhaustion.

Invariant natural killer T cells in autoimmune cholangiopathies: Mechanistic insights and therapeutic implications

Invariant natural killer T cells (iNKT cells) constitute a specialized subset of lymphocytes that bridges innate and adaptive immunity through a combination of traits characteristic of both conventional T cells and innate immune cells. iNKT cells are characterized by their invariant T cell receptors and discerning recognition of lipid antigens, which are presented by the non-classical MHC molecule, CD1d. Within the hepatic milieu, iNKT cells hold heightened prominence, contributing significantly to the orchestration of organ homeostasis. Their unique positioning to interact with diverse cellular entities, ranging from epithelial constituents like hepatocytes and cholangiocytes to immunocytes including Kupffer cells, B cells, T cells, and dendritic cells, imparts them with potent immunoregulatory abilities. Emergering knowledge of liver iNKT cells subsets enable to explore their therapeutic potential in autoimmne liver diseases. This comprehensive review navigates the landscape of iNKT cell investigations in immune-mediated cholangiopathies, with a particular focus on primary biliary cholangitis and primary sclerosing cholangitis, across murine models and human subjects to unravel the intricate involvements of iNKT cells in liver autoimmunity. Additionally, we also highlight the prospectives of iNKT cells as therapeutic targets in cholangiopathies. Modulation of the equilibrium between regulatory and proinflammatory iNKT subsets can be defining determinant in the dynamics of hepatic autoimmunity. This discernment not only enriches our foundational comprehension but also lays the groundwork for pioneering strategies to navigate the multifaceted landscape of liver autoimmunity.

The paradigm of IL-23-independent production of IL-17F and IL-17A and their role in chronic inflammatory diseases

Interleukin-17 family (IL-17s) comprises six structurally related members (IL-17A to IL-17F); sequence homology is highest between IL-17A and IL-17F, displaying certain overlapping functions. In general, IL-17A and IL-17F play important roles in chronic inflammation and autoimmunity, controlling bacterial and fungal infections, and signaling mainly through activation of the nuclear factor-kappa B (NF-κB) pathway. The role of IL-17A and IL-17F has been established in chronic immune-mediated inflammatory diseases (IMIDs), such as psoriasis (PsO), psoriatic arthritis (PsA), axial spondylarthritis (axSpA), hidradenitis suppurativa (HS), inflammatory bowel disease (IBD), multiple sclerosis (MS), and asthma. CD4+ helper T cells (Th17) activated by IL-23 are well-studied sources of IL-17A and IL-17F. However, other cellular subtypes can also produce IL-17A and IL-17F, including gamma delta (γδ) T cells, alpha beta (αβ) T cells, type 3 innate lymphoid cells (ILC3), natural killer T cells (NKT), or mucosal associated invariant T cells (MAIT). Interestingly, the production of IL-17A and IL-17F by innate and innate-like lymphocytes can take place in an IL-23 independent manner in addition to IL-23 classical pathway. This would explain the limitations of the inhibition of IL-23 in the treatment of patients with certain rheumatic immune-mediated conditions such as axSpA. Despite their coincident functions, IL-17A and IL-17F contribute independently to chronic tissue inflammation having somehow non-redundant roles. Although IL-17A has been more widely studied, both IL-17A and IL-17F are overexpressed in PsO, PsA, axSpA and HS. Therefore, dual inhibition of IL-17A and IL-17F could provide better outcomes than IL-23 or IL-17A blockade.

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 αβ 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.

Epigenetic regulation of iNKT2 cell adoptive therapy on the imbalance of iNKT cell subsets in thymus of RA mice

Epigenetic regulation affects the development and differentiation of iNKT cells. Our previous study found that the number of iNKT cells in thymus of RA mice was reduced and the ratio of subsets was unbalanced, but the related mechanism remains unclear. We adopted an adoptive infusion of iNKT2 cells with specific phenotypes and functions to RA mice and used the α-Galcer treatment group as control. The findings revealed that: 1. Adoptive treatment of iNKT cells decreased the proportion of iNKT1 and iNKT17 subsets in the thymus of RA mice, and increased the proportion of iNKT2 subsets. 2. Following treatment with iNKT cells, the expression of PLZF in thymus DP T cells was increased whereas the expression of T-bet in thymus iNKT cells was decreased in RA mice. 3. Adoptive therapy reduced the modification levels of H3Kb7me3 and H3K4me3 in the promoter regions of Zbtb16 (encoding PLZF) and Tbx21 (encoding T-bet) gene in thymus DP T cells and iNKT cells, and the reduction of H3K4me3 was particularly significant in the cell treatment group. Furthermore, adoptive therapy also upregulated the expression of UTX (histone demethylase) in thymus lymphocytes of RA mice. As a result, it is hypothesized that adoptive therapy of iNKT2 cells may affect the level of histone methylation in the promoter region of important transcription factor genes for iNKT development and differentiation, thereby directly or indirectly correcting the imbalance of iNKT subsets in the thymus of RA mice. These findings offer a fresh rationale and concept for the management of RA that targets.

Developmentally programmed early-age skin localization of iNKT cells supports local tissue development and homeostasis

Skin is exposed to various environmental assaults and undergoes morphological changes immediately after birth. Proper localization and function of immune cells in the skin is crucial for protection and establishment of skin tissue homeostasis. Here we report the discovery of a developmentally programmed process that directs preferential localization of invariant natural killer T (iNKT) cells to the skin for early local homeostatic regulation. We show that iNKT cells are programmed predominantly with a CCR10+ skin-homing phenotype during thymic development in infant and young mice. Early skin localization of iNKT cells is critical for proper commensal bacterial colonization and tissue development. Mechanistically, skin iNKT cells provide a local source of transferrin that regulates iron metabolism in hair follicle progenitor cells and helps hair follicle development. These findings provide molecular insights into the establishment and physiological functions of iNKT cells in the skin during early life.

The role of cells of the innate immune system in psoriasis

Psoriasis is an immune-mediated disease with a complex pathogenesis. The close relationship between the development of psoriasis and the adaptive immune response is already known. However, recent data have shown that innate immune cells also play an important role in the development of psoriasis. Congenital lymphoid cells, dendritic cells, T cells, NK cells, and NKT lymphocytes are activated in psoriasis, contributing to disease pathology through IL-17-dependent and independent mechanisms. During disease progression, T cells secrete proinflammatory cytokines that induce and exacerbate the course of psoriasis. T cells have memory cell properties that respond rapidly to secondary stimulation, which contributes to disease relapse. This article presents an overview of recent findings demonstrating the role of innate immunity in psoriasis.

Re-programming mouse liver-resident invariant natural killer T cells for suppressing hepatic and diabetogenic autoimmunity

Invariant NKT (iNKT) cells comprise a heterogeneous group of non-circulating, tissue-resident T lymphocytes that recognize glycolipids, including alpha-galactosylceramide (αGalCer), in the context of CD1d, but whether peripheral iNKT cell subsets are terminally differentiated remains unclear. Here we show that mouse and human liver-resident αGalCer/CD1d-binding iNKTs largely correspond to a novel Zbtb16+Tbx21+Gata3+MaflowRorc– subset that exhibits profound transcriptional, phenotypic and functional plasticity. Repetitive in vivo encounters of these liver iNKT (LiNKT) cells with intravenously delivered αGalCer/CD1d-coated nanoparticles (NP) trigger their differentiation into immunoregulatory, IL-10+IL-21-producing Zbtb16highMafhighTbx21+Gata3+Rorc– cells, termed LiNKTR1, expressing a T regulatory type 1 (TR1)-like transcriptional signature. This response is LiNKT-specific, since neither lung nor splenic tissue-resident iNKT cells from αGalCer/CD1d-NP-treated mice produce IL-10 or IL-21. Additionally, these LiNKTR1 cells suppress autoantigen presentation, and recognize CD1d expressed on conventional B cells to induce IL-10+IL-35-producing regulatory B (Breg) cells, leading to the suppression of liver and pancreas autoimmunity. Our results thus suggest that LiNKT cells are plastic for further functional diversification, with such plasticity potentially targetable for suppressing tissue-specific inflammatory phenomena.

Deconstructing iNKT cell development at single-cell resolution

Invariant natural killer T (iNKT) cells are increasingly regarded as disease biomarkers and immunotherapeutic targets. However, a greater understanding of their biology is necessary to effectively target these cells in the clinic. The discovery of iNKT1/2/17 cell effector subsets was a milestone in our understanding of iNKT cell development and function. Recent transcriptomic studies have uncovered an even greater heterogeneity and challenge our understanding of iNKT cell ontogeny and effector differentiation. We propose a refined model whereby iNKT cells differentiate through a dynamic and continuous instructive process that requires the accumulation and integration of various signals within the thymus or peripheral tissues. Within this framework, we question the existence of true iNKT2 cells and discuss the parallels between mouse and human iNKT cells.

In vivo availability of the cytokine IL-7 constrains the survival and homeostasis of peripheral iNKT cells

Understanding the homeostatic mechanism of invariant natural killer T (iNKT) cells is a critical issue in iNKT cell biology. Because interleukin (IL)-15 is required for the thymic generation of iNKT cells, IL-15 has also been considered necessary for the homeostasis of peripheral iNKT cells. Here, we delineated the in vivo cytokine requirement for iNKT cells, and we came to the surprising conclusion that IL-7, not IL-15, is the homeostatic cytokine for iNKT cells. Employing a series of experimental mouse models where the availability of IL-7 or IL-15 was manipulated in peripheral tissues, either by genetic tools or by adult thymectomy and cytokine pump installation, we demonstrate that the abundance of IL-7, and not IL-15, limits the size of the peripheral iNKT cell pool. These results redefine the cytokine requirement for iNKT cells and indicate competition for IL-7 between iNKT and conventional αβ T cells.

Identification of liver-specific CD24+ invariant NK T cells with low granzyme B production and high proliferative capacity

Invariant NK T (iNKT) cells are innate-like lymphocytes that can recognize the lipid Ag presented by MHC I like molecule CD1d. Distinct tissue distribution of iNKT cells subsets implies a contribution of these subsets to their related tissue regional immunity. iNKT cells are enriched in liver, an organ with unique immunological properties. Whether liver-specific iNKT cells exist and dedicate to the liver immunity remains elusive. Here, a liver-specific CD24⁺ iNKT subset is shown. Hepatic CD24⁺ iNKT cells show higher levels of proliferation, glucose metabolism, and mTOR activity comparing to CD24^- iNKT cells. Although CD24⁺ iNKT cells and CD24^- iNKT cells in the liver produce similar amounts of cytokines, the hepatic CD24⁺ iNKT cells exhibit lower granzyme B production. These liver-specific CD24⁺ iNKT cells are derived from thymus and differentiate into CD24⁺ iNKT in the liver microenvironment. Moreover, liver microenvironment induces the formation of CD24⁺ conventional T cells as well, and these cells exhibit higher proliferation ability but lower granzyme B production in comparison with CD24^- T cells. The results propose that liver microenvironment might induce the generation of liver-specific iNKT subset that might play an important role in maintaining liver homeostasis.

Diversity of T cells in the skin: Novel insights

T cells populate the skin to provide an effective immunosurveillance against external insults and to maintain tissue homeostasis. Most cutaneous T cells are αβ T cells, however, γδ T cells also exist although in much lower frequency. Different subsets of αβ T cells can be found in the skin, such as short-lived effector T cells, central memory T cells, effector memory T cells, and tissue-resident memory T cells. Their differential biology, function, and location provide an ample spectrum of immune responses in the skin. Foxp3+ memory regulatory T cells have a pivotal role in maintaining homeostasis in the skin and their dysregulation has been linked with different skin pathologies. The skin also contains populations of non-classical T cells, such as γδ T cells, NK T cells, and MR1-restricted T cells. Their role in skin homeostasis and response to pathogens has been well established in the past years, however, there is also growing evidence of their role in mediating allergic skin inflammation and promoting sensitization to allergens. In this review, we provide an updated overview on the different subsets of T cells that populate the skin with a specific focus on their role in allergic skin inflammation.

Early development of the skin microbiome: therapeutic opportunities

As human skin hosts a diverse microbiota in health and disease, there is an emerging consensus that dysregulated interactions between host and microbiome may contribute to chronic inflammatory disease of the skin. Neonatal skin is a unique habitat, structurally similar to the adult but with a different profile of metabolic substrates, environmental stressors, and immune activity. The surface is colonized within moments of birth with a bias toward maternal strains. Initial colonists are outcompeted as environmental exposures increase and host skin matures. Nonetheless, early life microbial acquisitions may have long-lasting effects on health through modulation of host immunity and competitive interactions between bacteria. Microbial ecology and its influence on health have been of interest to dermatologists for >50 years, and an explosion of recent interest in the microbiome has prompted ongoing investigations of several microbial therapeutics for dermatological disease. In this review, we consider how recent insight into the host and microbial factors driving development of the skin microbiome in early life offers new opportunities for therapeutic intervention. IMPACT: Advancement in understanding molecular mechanisms of bacterial competition opens new avenues of investigation into dermatological disease. Primary development of the skin microbiome is determined by immunological features of the cutaneous habitat. Understanding coordinated microbial and immunological development in the pediatric patient requires a multidisciplinary synthesis of primary literature.

Identification of Rare Thymic NKT Cell Precursors by Multiparameter Flow Cytometry

Mouse invariant natural killer T (NKT) cells are a subset of T lymphocytes which have been shown to play a significant role in innate and adaptive immune responses. Features of innate responses are attributed to these cells because they can be stimulated simultaneously with the same ligand to produce quickly and in large amount cytokines without prior immunization. Because these characteristics could be exploited for clinical applications, NKT cells have attracted considerable interest. Many studies have investigated the molecular mechanisms through which they are selected and differentiate. These studies are based on developmental models that serve as a scaffold to understand the specific roles played by various factors and to identify checkpoints during cellular development. Analysis of NKT cell precursors at the HSA^high stage, stage 0, can reveal potential selection defects, whereas analysis of NKT cells at the HSA^low stage can shed light on defects in the maturation/differentiation of the different NKT cell subsets (NKT1, 2, and 17). Unlike HSA^low NKT cell subsets, HSA^high NKT cell precursors are not accurately identified by flow cytometry because of their extreme rarity. Here, we describe an NKT cell enrichment strategy to identify unambiguously NKT cell precursors at the HSA^high stage that can be used to assess their distribution and characteristics by multicolor flow cytometry.

PLZF Acetylation Levels Regulate NKT Cell Differentiation

The transcription factor promyelocytic leukemia zinc finger (PLZF) is encoded by the BTB domain-containing 16 (Zbtb16) gene. Its repressor function regulates specific transcriptional programs. During the development of invariant NKT cells, PLZF is expressed and directs their effector program, but the detailed mechanisms underlying PLZF regulation of multistage NKT cell developmental program are not well understood. This study investigated the role of acetylation-induced PLZF activation on NKT cell development by analyzing mice expressing a mutant form of PLZF mimicking constitutive acetylation (PLZF^ON) mice. NKT populations in PLZF^ON mice were reduced in proportion and numbers of cells, and the cells present were blocked at the transition from developmental stage 1 to stage 2. NKT cell subset differentiation was also altered, with T-bet⁺ NKT1 and RORγt⁺ NKT17 subsets dramatically reduced and the emergence of a T-bet^-RORγt^- NKT cell subset with features of cells in early developmental stages rather than mature NKT2 cells. Preliminary analysis of DNA methylation patterns suggested that activated PLZF acts on the DNA methylation signature to regulate NKT cells' entry into the early stages of development while repressing maturation. In wild-type NKT cells, deacetylation of PLZF is possible, allowing subsequent NKT cell differentiation. Interestingly, development of other innate lymphoid and myeloid cells that are dependent on PLZF for their generation is not altered in PLZF^ON mice, highlighting lineage-specific regulation. Overall, we propose that specific epigenetic control of PLZF through acetylation levels is required to regulate normal NKT cell differentiation.

Drivers of Inflammation in Psoriatic Arthritis: the Old and the New

PURPOSE OF REVIEW

The recognition that IL-17 is produced by many lymphoid-like cells other than CD4+ T helper (Th17) cells raises the potential for new pathogenic pathways in IBD/psoriasis/SpA. We review recent knowledge concerning the role of unconventional and conventional lymphocytes expressing IL-17 in human PsA and axSpA.

RECENT FINDINGS

Innate-like lymphoid cells, namely gamma delta (γδ) T-cells, invariant natural killer T (iNKT) cells and mucosal-associated invariant T (MAIT) cells, together with innate lymphoid cells (ILCs) are found at sites of disease in PsA/SpA. These cells are often skewed to Type-17 profiles and may significantly contribute to IL-17 production. Non-IL-23 dependent IL-17 production pathways, utilising cytokines such as IL-7 and IL-9, also characterise these cells. Both conventional CD4 and CD8 lymphocytes show pathogenic phenotypes at sites of disease. A variety of innate-like lymphoid cells and conventional lymphocytes contribute towards IL-17-mediated pathology in PsA/SpA. The responses of these cells to non-conventional immune and non-immune stimuli may explain characteristic clinical features of these diseases and potential therapeutic mechanisms of therapies such as Jak inhibitors.

Role of the IL-23/IL-17 Pathway in Rheumatic Diseases: An Overview

Interleukin-23 (IL-23) is a pro-inflammatory cytokine composed of two subunits, IL-23A (p19) and IL-12/23B (p40), the latter shared with Interleukin-12 (IL-12). IL-23 is mainly produced by macrophages and dendritic cells, in response to exogenous or endogenous signals, and drives the differentiation and activation of T helper 17 (Th17) cells with subsequent production of IL-17A, IL-17F, IL-6, IL-22, and tumor necrosis factor α (TNF-α). Although IL-23 plays a pivotal role in the protective immune response to bacterial and fungal infections, its dysregulation has been shown to exacerbate chronic immune-mediated inflammation. Well-established experimental data support the concept that IL-23/IL-17 axis activation contributes to the development of several inflammatory diseases, such as PsA, Psoriasis, Psoriatic Arthritis; AS, Ankylosing Spondylitis; IBD, Inflammatory Bowel Disease; RA, Rheumatoid Arthritis; SS, Sjogren Syndrome; MS, Multiple Sclerosis. As a result, emerging clinical studies have focused on the blockade of this pathogenic axis as a promising therapeutic target in several autoimmune disorders; nevertheless, a greater understanding of its contribution still requires further investigation. This review aims to elucidate the most recent studies and literature data on the pathogenetic role of IL-23 and Th17 cells in inflammatory rheumatic diseases.

Innate Cells: The Alternative Source of IL-17 in Axial and Peripheral Spondyloarthritis?

Spondyloarthritis (SpA) is a chronic inflammatory rheumatism characterized by inflammation of sacroiliac joints, peripheral joints, and spine. The Assessment of SpondyloArthritis Society describes three disease forms: axial (axSpA), peripheral, and enthesitic SpA. Each may be associated with extra-articular manifestations: psoriasis, inflammatory bowel disease, and acute anterior uveitis. Genome-wide association studies performed in axSpA and psoriatic arthritis (PsA) have shown a shared genetic background, especially the interleukin 23 (IL-23)/IL-17 pathway, which suggests pathophysiological similarities. The convincing positive results of clinical trials assessing the effect of secukinumab and ixekizumab (anti-IL-17A monoclonal antibodies) in axSpA and PsA have reinforced the speculated crucial role of IL-17 in SpA. Nevertheless, and obviously unexpectedly, the differential efficacy of anti-IL-23–targeted treatments between axSpA (failure) and PsA (success) has profoundly disrupted our presumed knowledge of disease pathogeny. The cells able to secrete IL-17, their dependence on IL-23, and their respective role according to the clinical form of the disease is at the heart of the current debate to potentially explain these observed differences in efficacy of IL-23/IL-17–targeted therapy. In fact, IL-17 secretion is usually mainly related to T helper 17 lymphocytes. Nevertheless, several innate immune cells express IL-23 receptor and can produce IL-17. To what extent these alternative cell populations can produce IL-17 independent of IL-23 and their respective involvement in axSpA and PsA are the crucial scientific questions in SpA. From this viewpoint, this is a nice example of a reverse path from bedside to bench, in which the results of therapeutic trials allow for reflecting more in depth on the pathophysiology of a disease. Here we provide an overview of each innate immunity-producing IL-17 cell subset and their respective role in disease pathogeny at the current level of our knowledge.

Modulation of Immune Responses to Influenza A Virus Vaccines by Natural Killer T Cells

Influenza A viruses (IAVs) circulate widely among different mammalian and avian hosts and sometimes give rise to zoonotic infections. Vaccination is a mainstay of IAV prevention and control. However, the efficacy of IAV vaccines is often suboptimal because of insufficient cross-protection among different IAV genotypes and subtypes as well as the inability to keep up with the rapid molecular evolution of IAV strains. Much attention is focused on improving IAV vaccine efficiency using adjuvants, which are substances that can modulate and enhance immune responses to co-administered antigens. The current review is focused on a non-traditional approach of adjuvanting IAV vaccines by therapeutically targeting the immunomodulatory functions of a rare population of innate-like T lymphocytes called invariant natural killer T (iNKT) cells. These cells bridge the innate and adaptive immune systems and are capable of stimulating a wide array of immune cells that enhance vaccine-mediated immune responses. Here we discuss the factors that influence the adjuvant effects of iNKT cells for influenza vaccines as well as the obstacles that must be overcome before this novel adjuvant approach can be considered for human or veterinary use.

Characterization of the developmental landscape of murine RORγt+ iNKT cells

Invariant natural killer T (iNKT) cells expressing the retinoic acid receptor-related orphan receptor γt (RORγt) and producing IL-17 represent a minor subset of CD1d-restricted iNKT cells (iNKT17) in C57BL/6J (B6) mice. We aimed in this study to define the reasons for their low distribution and the sequence of events accompanying their normal thymic development. We found that RORγt+ iNKT cells have higher proliferation potential and a greater propensity to apoptosis than RORγt- iNKT cells. These cells do not likely reside in the thymus indicating that thymus emigration, and higher apoptosis potential, could contribute to RORγt+ iNKT cell reduced thymic distribution. Ontogeny studies suggest that mature HSAlow RORγt+ iNKT cells might develop through developmental stages defined by a differential expression of CCR6 and CD138 during which RORγt expression and IL-17 production capabilities are progressively acquired. Finally, we found that RORγt+ iNKT cells perceive a strong TCR signal that could contribute to their entry into a specific 'Th17 like' developmental program influencing their survival and migration. Overall, our study proposes a hypothetical thymic developmental sequence for iNKT17 cells, which could be of great use to study molecular mechanisms regulating this developmental program.

Role of Innate Immune Cells in Psoriasis

Psoriasis is a chronic inflammatory skin condition caused by a combination of hereditary and environmental factors. Its development is closely related to the adaptive immune response. T helper 17 cells are major IL-17-producing cells, a function that plays an important role in the pathogenesis of psoriasis. However, recent findings have demonstrated that innate immune cells also contribute to the development of psoriasis. Innate lymphoid cells, γδ T cells, natural killer T cells, and natural killer cells are activated in psoriasis, contributing to disease pathology through IL-17-dependent and -independent mechanisms. The present review provides an overview of recent findings, demonstrating a role for innate immunity in psoriasis.

Type 2 immunity in the skin and lungs

There has been extensive progress in understanding the cellular and molecular mechanisms of inflammation and immune regulation in allergic diseases of the skin and lungs during the last few years. Asthma and atopic dermatitis (AD) are typical diseases of type 2 immune responses. interleukin (IL)-25, IL-33, and thymic stromal lymphopoietin are essential cytokines of epithelial cells that are activated by allergens, pollutants, viruses, bacteria, and toxins that derive type 2 responses. Th2 cells and innate lymphoid cells (ILC) produce and secrete type 2 cytokines such as IL-4, IL-5, IL-9, and IL-13. IL-4 and IL-13 activate B cells to class-switch to IgE and also play a role in T-cell and eosinophil migration to allergic inflammatory tissues. IL-13 contributes to maturation, activation, nitric oxide production and differentiation of epithelia, production of mucus as well as smooth muscle contraction, and extracellular matrix generation. IL-4 and IL-13 open tight junction barrier and cause barrier leakiness in the skin and lungs. IL-5 acts on activation, recruitment, and survival of eosinophils. IL-9 contributes to general allergic phenotype by enhancing all of the aspects, such as IgE and eosinophilia. Type 2 ILC contribute to inflammation in AD and asthma by enhancing the activity of Th2 cells, eosinophils, and their cytokines. Currently, five biologics are licensed to suppress type 2 inflammation via IgE, IL-5 and its receptor, and IL-4 receptor alpha. Some patients with severe atopic disease have little evidence of type 2 hyperactivity and do not respond to biologics which target this pathway. Studies in responder and nonresponder patients demonstrate the complexity of these diseases. In addition, primary immune deficiency diseases related to T-cell maturation, regulatory T-cell development, and T-cell signaling, such as Omenn syndrome, severe combined immune deficiencies, immunodysregulation, polyendocrinopathy, enteropathy, X-linked syndrome, and DOCK8, STAT3, and CARD11 deficiencies, help in our understanding of the importance and redundancy of various type 2 immune components. The present review aims to highlight recent advances in type 2 immunity and discuss the cellular sources, targets, and roles of type 2 mechanisms in asthma and AD.

High Frequency of Gamma Interferon-Producing PLZFloRORγtlo Invariant Natural Killer 1 Cells Infiltrating Herpes Simplex Virus 1-Infected Corneas Is Associated with Asymptomatic Ocular Herpesvirus Infection

Invariant natural killer (iNKT) cells are among the first innate immune cells to elicit early protective immunity that controls invading viral pathogens. The role of the iNKT cell subsets iNKT1, iNKT2, and iNKT17 in herpesvirus immunity remains to be fully elucidated. In this study, we examined the protective role of cornea-resident iNKT cell subsets using the mouse model of ocular herpesvirus infection and disease. Wild-type (WT) C57BL/6 (B6) mice and CD1d knockout (KO) mice were infected ocularly with herpes simplex virus 1 (HSV-1) (strain McKrae). Cornea, spleen, and liver were harvested at 0, 2, 5, 8, and 14 days postinfection (p.i.), and the frequency and function of the three major iNKT cell subsets were analyzed and correlated with symptomatic and asymptomatic corneal herpesvirus infections. The profiles of 16 major pro- and anti-inflammatory cytokines were analyzed in corneal lysates using Western blot and Luminex assays. Early during ocular herpesvirus infection (i.e., day 2), the gamma interferon (IFN-γ)-producing PLZFloRORγtlo (promyelocytic leukemia zinc finger, retinoic acid-related orphan receptor gT) iNKT1 cell subset was the predominant iNKT cell subset in infected asymptomatic corneas. Moreover, compared to the asymptomatic corneas of HSV-1-infected WT mice, the symptomatic corneas CD1d KO mice, with iNKT cell deficiency, had increased levels of the inflammatory cytokine interleukin-6 (IL-6) and decreased levels of IL-12, IFN-γ, and the JAK1, STAT1, NF-κB, and extracellular signal-regulated kinase 1/2 (ERK1/2) pathways. Our findings suggest that IFN-γ-producing PLZFloRORγtlo iNKT1 cells play a role in the protective innate immune response against symptomatic ocular herpes.IMPORTANCE We investigated the protective role of iNKT cell subsets in asymptomatic ocular herpesvirus infection. We found that early during ocular herpesvirus infection (i.e., on day 2 postinfection), IFN-γ-producing PLZFloRORγtlo iNKT1 cells were the predominant iNKT cell subset in infected corneas of asymptomatic B6 mice (with little to no corneal herpetic disease), compared to corneas of symptomatic mice (with severe corneal herpetic disease). Moreover, compared to asymptomatic corneas of wild-type (WT) B6 mice, the symptomatic corneas of CD1d KO mice, which lack iNKT cells, showed (i) decreases in the levels of IFN-γ and IL-12, (ii) an increase in the level of the inflammatory cytokine IL-6; and (iii) downregulation of the JAK1, STAT1, NF-κB, and ERK1/2 pathways. The findings suggest that early during ocular herpesvirus infection, cornea-resident IFN-γ-producing PLZFloRORγtlo iNKT1 cells provide protection from symptomatic ocular herpes.

Pathogenesis of psoriasis in the "omic" era. Part I. Epidemiology, clinical manifestation, immunological and neuroendocrine disturbances

Psoriasis is a common, chronic, inflammatory, immune-mediated skin disease affecting about 2% of the world's population. According to current knowledge, psoriasis is a complex disease that involves various genes and environmental factors, such as stress, injuries, infections and certain medications. The chronic inflammation of psoriasis lesions develops upon epidermal infiltration, activation, and expansion of type 1 and type 17 Th cells. Despite the enormous progress in understanding the mechanisms that cause psoriasis, the target cells and antigens that drive pathogenic T cell responses in psoriatic lesions are still unproven and the autoimmune basis of psoriasis still remains hypothetical. However, since the identification of the Th17 cell subset, the IL-23/Th17 immune axis has been considered a key driver of psoriatic inflammation, which has led to the development of biologic agents that target crucial elements of this pathway. Here we present the current understanding of various aspects in psoriasis pathogenesis.

A focus on natural killer T-cell subset characterization and developmental stages

Almost 20 years ago, CD1d tetramers were developed to track invariant natural killer T (NKT) cells based on their specificity, and to define developmental steps during which differentiation markers and functional features are progressively acquired from early NKT cell precursor to fully mature NKT cell subsets. Based on these findings, a linear developmental model was proposed and subsequently used by all studies investigating the specific role of factors that control NKT cell development. More recently, based on intracellular staining patterns of lineage-specific transcription factors such as T-bet, GATA-3, promyelocytic leukemia zinc finger and RORγt, a lineage differentiation model was proposed for NKT cell development. Currently, studies on NKT cells development present lineage differentiation model data in addition to the linear maturation model. In the perspective presented here, we discuss current knowledge relating to NKT cell developmental models and particularly focus on the approaches and strategies, some of which appear nebulous, used to define NKT cell developmental stages and subsets.

Nanovaccine administration route is critical to obtain pertinent iNKt cell help for robust anti-tumor T and B cell responses

Nanovaccines, co-delivering antigen and invariant natural killer T (iNKT) cell agonists, proved to be very effective in inducing anti-tumor T cell responses due to their exceptional helper function. However, it is known that iNKT cells are not equally present in all lymphoid organs and nanoparticles do not get evenly distributed to all immune compartments. In this study, we evaluated the effect of the vaccination route on iNKT cell help to T and B cell responses for the first time in an antigen and agonist co-delivery setting. Intravenous administration of PLGA nanoparticles was mainly targeting liver and spleen where iNKT1 cells are abundant and induced the highest serum IFN-y levels, T cell cytotoxicity, and Th-1 type antibody responses. In comparison, after subcutaneous or intranodal injections, nanoparticles mostly drained or remained in regional lymph nodes where iNKT17 cells were abundant. After subcutaneous and intranodal injections, antigen-specific IgG2 c production was hampered and IFN-y production, as well as cytotoxic T cell responses, depended on sporadic systemic drainage. Therapeutic anti-tumor experiments also demonstrated a clear advantage of intravenous injection over intranodal or subcutaneous vaccinations. Moreover, tumor control could be further improved by PD-1 immune checkpoint blockade after intravenous vaccination, but not by intranodal vaccination. Anti PD-1 antibody combination mainly exerts its effect by prolonging the cytotoxicity of T cells. Nanovaccines also demonstrated synergism with anti-4-1BB agonistic antibody treatment in controlling tumor growth. We conclude that nanovaccines containing iNKT cell agonists shall be preferentially administered intravenously, to optimally reach cellular partners for inducing effective anti-tumor immune responses.

Recent advances in iNKT cell development

Recent studies suggest that murine invariant natural killer T (iNKT) cell development culminates in three terminally differentiated iNKT cell subsets denoted as NKT1, 2, and 17 cells. Although these studies corroborate the significance of the subset division model, less is known about the factors driving subset commitment in iNKT cell progenitors. In this review, we discuss the latest findings in iNKT cell development, focusing in particular on how T-cell receptor signal strength steers iNKT cell progenitors toward specific subsets and how early progenitor cells can be identified. In addition, we will discuss the essential factors for their sustenance and functionality. A picture is emerging wherein the majority of thymic iNKT cells are mature effector cells retained in the organ rather than developing precursors.

Development of Unconventional T Cells Controlled by MicroRNA

Post-transcriptional gene regulation through microRNA (miRNA) has emerged as a major control mechanism of multiple biological processes, including development and function of T cells. T cells are vital components of the immune system, with conventional T cells playing a central role in adaptive immunity and unconventional T cells having additional functions reminiscent of both innate and adaptive immunity, such as involvement in stress responses and tissue homeostasis. Unconventional T cells encompass cells expressing semi-invariant T cell receptors (TCRs), such as invariant Natural Killer T (iNKT) and Mucosal-Associated Invariant T (MAIT) cells. Additionally, some T cells with diverse TCR repertoires, including γδT cells, intraepithelial lymphocytes (IEL) and regulatory T (Treg) cells, share some functional and/or developmental features with their semi-invariant unconventional counterparts. Unconventional T cells are particularly sensitive to disruption of miRNA function, both globally and on the individual miRNA level. Here, we review the role of miRNA in the development and function of unconventional T cells from an iNKT-centric point of view. The function of single miRNAs can provide important insights into shared and individual pathways for the formation of different unconventional T cell subsets.

Pathogenic function of bystander-activated memory-like CD4+ T cells in autoimmune encephalomyelitis

T cells generate antigen-specific immune responses to their cognate antigen as a hallmark of adaptive immunity. Despite the importance of antigen-specific T cells, here we show that antigen non-related, bystander memory-like CD4⁺ T cells also significantly contribute to autoimmune pathogenesis. Transcriptome analysis demonstrates that interleukin (IL)-1β- and IL-23-prime T cells that express pathogenic T_Η17 signature genes such as RORγt, CCR6, and granulocyte macrophage colony-stimulating factor (GM-CSF). Importantly, when co-transferred with myelin-specific 2D2 TCR-transgenic naive T cells, unrelated OT-II TCR-transgenic memory-like T_H17 cells infiltrate the spinal cord and produce IL-17A, interferon (IFN)-γ, and GM-CSF, increasing the susceptibility of the recipients to experimental autoimmune encephalomyelitis in an IL-1 receptor-dependent manner. In humans, IL-1R1^high memory CD4⁺ T cells are major producers of IL-17A and IFN-γ in response to IL-1β and IL-23. Collectively, our findings reveal the innate-like pathogenic function of antigen non-related memory CD4⁺ T cells, which contributes to the development of autoimmune diseases.

T cells express specific T cell receptors (TCR) to recognise antigens and initiate adaptive immune responses. Here the authors show, in a mouse model of autoimmune encephalomyelitis, that memory-like CD4 T cells expressing unrelated TCR can also infiltrate the spinal cord and contribute to autoimmunity.

CCR7 defines a precursor for murine iNKT cells in thymus and periphery

The precise steps of iNKT subset differentiation in the thymus and periphery have been controversial. We demonstrate here that the small proportion of thymic iNKT and mucosal associated invariant T cells that express CCR7 represent a multi-potent progenitor pool that gives rise to effector subsets within the thymus. Using intra-thymic labeling, we also showed that CCR7+ iNKT cells emigrate from the thymus in a Klf2 dependent manner, and undergo further maturation after reaching the periphery. Ccr7 deficiency impaired differentiation of iNKT effector subsets and localization to the medulla. Parabiosis and intra-thymic transfer showed that thymic NKT1 and NKT17 were resident-they were not derived from and did not contribute to the peripheral pool. Finally, each thymic iNKT effector subset produces distinct factors that influence T cell development. Our findings demonstrate how the thymus is both a source of iNKT progenitors and a unique site of tissue dependent effector cell differentiation.

The interaction between invariant Natural Killer T cells and the mucosal microbiota

The surface of mammalian bodies is colonized by a multitude of microbial organisms, which under normal conditions support the host and are considered beneficial commensals. This requires, however, that the composition of the commensal microbiota is tightly controlled and regulated. The host immune system plays an important role in the maintenance of this microbiota composition. Here we focus on the contribution of one particular immune cell type, invariant Natural Killer T (iNKT) cells, in this process. The iNKT cells are a unique subset of T cells characterized by two main features. First, they express an invariant T-cell receptor that recognizes glycolipid antigens presented by CD1d, a non-polymorphic major histocompatibility complex class I-like molecule. Second, iNKT cells develop as effector/memory cells and swiftly exert effector functions, like cytokine production and cytotoxicity, after activation. We outline the influence that the mucosal microbiota can have on iNKT cells, and how iNKT cells contribute to the maintenance of the microbiota composition.

Invariant Natural Killer T Cell Subsets-More Than Just Developmental Intermediates

Invariant natural killer T (iNKT) cells are a CD1d-restricted T cell population that can respond to lipid antigenic stimulation within minutes by secreting a wide variety of cytokines. This broad functional scope has placed iNKT cells at the frontlines of many kinds of immune responses. Although the diverse functional capacities of iNKT cells have long been acknowledged, only recently have distinct iNKT cell subsets, each with a marked functional predisposition, been appreciated. Furthermore, the subsets can frequently occupy distinct niches in different tissues and sometimes establish long-term tissue residency where they can impact homeostasis and respond quickly when they sense perturbations. In this review, we discuss the developmental origins of the iNKT cell subsets, their localization patterns, and detail what is known about how different subsets specifically influence their surroundings in conditions of steady and diseased states.

Critical Contribution of NK Group 2 Member D Expressed on Invariant Natural Killer T Cells in Concanavalin A-Induced Liver Hepatitis in Mice

Natural killer group 2D (NKG2D) is a well-characterized activating receptor expressed on many immune cells, including invariant natural killer T (iNKT) cells. These cells were shown to be responsible of liver injury in the model of concanavalin A (Con A)-induced hepatitis, considered to be an experimental model of human autoimmune hepatitis. In this study, we investigated whether NKG2D plays a role in the hepatitis induced by iNKT cell-mediated immune response to Con A. By using killer cell lectin-like receptor subfamily K, member 1 deficient (Klrk1^−/−) mice, we found that the absence of NKG2D reduced the hepatic injury upon Con A administration. This was not due to an intrinsic functional defect of NKG2D-deficient iNKT cells as mice missing NKG2D have normal distribution and function of iNKT cells. Furthermore, increased resistance to Con A-induced hepatitis was confirmed using neutralizing anti-NKG2D antibodies. The reduced pathogenic effect of Con A in the absence of NKG2D correlates with a reduction in pathogenic cytokine production and FAS-Ligand (FAS-L) expression by iNKT cells. We also found that Con A administration led to an increase in the retinoic acid early inducible (RAE-1) surface expression on wild-type hepatocytes. Finally, we found that Con A has no direct action on FAS-L expression or cytokine production by iNKT cells and thus propose that NKG2D-L expression on stressed hepatocytes promote cytotoxic activity of iNKT cells via its interaction with NKG2D contributing to hepatic injury. In conclusion, our results highlight NKG2D as an essential receptor required for the activation of iNKT cells in Con A-induced hepatitis and indicate that it represents a potential drug target for prevention of autoimmune hepatitis.

Natural Killer T Cells: An Ecological Evolutionary Developmental Biology Perspective

Type I natural killer T (NKT) cells are innate-like T lymphocytes that recognize glycolipid antigens presented by the MHC class I-like protein CD1d. Agonistic activation of NKT cells leads to rapid pro-inflammatory and immune modulatory cytokine and chemokine responses. This property of NKT cells, in conjunction with their interactions with antigen-presenting cells, controls downstream innate and adaptive immune responses against cancers and infectious diseases, as well as in several inflammatory disorders. NKT cell properties are acquired during development in the thymus and by interactions with the host microbial consortium in the gut, the nature of which can be influenced by NKT cells. This latter property, together with the role of the host microbiota in cancer therapy, necessitates a new perspective. Hence, this review provides an initial approach to understanding NKT cells from an ecological evolutionary developmental biology (eco-evo-devo) perspective.

Improved Detection of Cytokines Produced by Invariant NKT Cells

Invariant Natural killer T (iNKT) cells rapidly produce copious amounts of multiple cytokines after in vivo activation, allowing for the direct detection of a number of cytokines directly ex vivo. However, for some cytokines this approach is suboptimal. Here, we report technical variations that allow the improved detection of IL-4, IL-10, IL-13 and IL-17A ex vivo. Furthermore, we describe an alternative approach for stimulation of iNKT cells in vitro that allows a significantly improved detection of cytokines produced by iNKT cells. Together, these protocols allow the detection of iNKT cell cytokines ex vivo and in vitro with increased sensitivity.

The role of IL-23 and the IL-23/TH 17 immune axis in the pathogenesis and treatment of psoriasis

Psoriasis is a chronic, immune-mediated disease affecting more than 100 million people worldwide and up to 2.2% of the UK population. The aetiology of psoriasis is thought to originate from an interplay of genetic, environmental, infectious and lifestyle factors. The manner in which genetic and environmental factors interact to contribute to the molecular disease mechanisms has remained elusive. However, the interleukin 23 (IL-23)/T-helper 17 (TH 17) immune axis has been identified as a major immune pathway in psoriasis disease pathogenesis. Central to this pathway is the cytokine IL-23, a heterodimer composed of a p40 subunit also found in IL-12 and a p19 subunit exclusive to IL-23. IL-23 is important for maintaining TH 17 responses, and levels of IL-23 are elevated in psoriatic skin compared with non-lesional skin. A number of agents that specifically inhibit IL-23p19 are currently in development for the treatment of moderate-to-severe plaque psoriasis, with recent clinical trials demonstrating efficacy with a good safety and tolerability profile. These data support the role of this cytokine in the pathogenesis of psoriasis. A better understanding of the IL-23/TH 17 immune axis is vital and will promote the development of additional targets for psoriasis and other inflammatory diseases that share similar genetic aetiology and pathogenetic pathways.

Monoclonal Invariant NKT (iNKT) Cell Mice Reveal a Role for Both Tissue of Origin and the TCR in Development of iNKT Functional Subsets

Invariant NKT (iNKT) cell functional subsets are defined by key transcription factors and output of cytokines, such as IL-4, IFN-γ, IL-17, and IL-10. To examine how TCR specificity determines iNKT function, we used somatic cell nuclear transfer to generate three lines of mice cloned from iNKT nuclei. Each line uses the invariant Vα14Jα18 TCRα paired with unique Vβ7 or Vβ8.2 subunits. We examined tissue homing, expression of PLZF, T-bet, and RORγt, and cytokine profiles and found that, although monoclonal iNKT cells differentiated into all functional subsets, the NKT17 lineage was reduced or expanded depending on the TCR expressed. We examined iNKT thymic development in limited-dilution bone marrow chimeras and show that higher TCR avidity correlates with higher PLZF and reduced T-bet expression. iNKT functional subsets showed distinct tissue distribution patterns. Although each individual monoclonal TCR showed an inherent subset distribution preference that was evident across all tissues examined, the iNKT cytokine profile differed more by tissue of origin than by TCR specificity.

CD1-Restricted T Cells at the Crossroad of Innate and Adaptive Immunity

Lipid-specific T cells comprise a group of T cells that recognize lipids bound to the MHC class I-like CD1 molecules. There are four isoforms of CD1 that are expressed at the surface of antigen presenting cells and therefore capable of presenting lipid antigens: CD1a, CD1b, CD1c, and CD1d. Each one of these isoforms has distinct structural features and cellular localizations, which promotes binding to a broad range of different types of lipids. Lipid antigens originate from either self-tissues or foreign sources, such as bacteria, fungus, or plants and their recognition by CD1-restricted T cells has important implications in infection but also in cancer and autoimmunity. In this review, we describe the characteristics of CD1 molecules and CD1-restricted lipid-specific T cells, highlighting the innate-like and adaptive-like features of different CD1-restricted T cell subtypes.

Distinct gene expression patterns correlate with developmental and functional traits of iNKT subsets

Invariant natural killer T (iNKT) cells comprise a subpopulation of innate lymphocytes developing in thymus. A new model proposes subdividing murine iNKT cells into iNKT1, 2 and 17 cells. Here, we use transcriptome analyses of iNKT1, 2 and 17 subsets isolated from BALB/c and C57BL/6 thymi to identify candidate genes that may affect iNKT cell development, migration or function. We show that Fcɛr1γ is involved in generation of iNKT1 cells and that SerpinB1 modulates frequency of iNKT17 cells. Moreover, a considerable proportion of iNKT17 cells express IL-4 and IL-17 simultaneously. The results presented not only validate the usefulness of the iNKT1/2/17-concept but also provide new insights into iNKT cell biology.

MicroRNA-133b Regulation of Th-POK Expression and Dendritic Cell Signals Affect NKT17 Cell Differentiation in the Thymus

NKT17 cells represent a functional subset of Vα14 invariant NKT (iNKT) cells with important effector functions in infections and autoimmune diseases. The mechanisms that drive NKT17 cell differentiation in the thymus are still largely unknown. The percentage of NKT17 cells has a high variability between murine strains due to differential thymic differentiation. For example, the NOD strain carries a high percentage and absolute numbers of NKT17 cells compared with other strains. In this study, we used the NOD mouse model to analyze what regulates NKT17 cell frequency in the thymus and peripheral lymphoid organs. In accordance with previous studies showing that the zinc finger transcription factor Th-POK is a key negative regulator of thymic NKT17 cell differentiation in the thymus, our data indicate that excessive NKT17 cell frequency in NOD mice correlates with defective Th-POK expression by thymic Vα14iNKT cells. Moreover, we found that Th-POK expression is under epigenetic regulation mediated by microRNA-133b whose expression is reduced in Vα14iNKT cells of NOD mice. We also demonstrated in a conditional knockout model of dendritic cell (DC) depletion (CD11cCreXDTA.B6 and CD11cCreRosa26DTA.NOD mice) that DCs play a crucial role in regulating Vα14iNKT cell maturation and their acquisition of an NKT17 cytokine secretion phenotype in the thymus. Overall, our data show that mechanisms regulating NKT17 cell differentiation are unique and completely different from those of Vα14iNKT cells. Specifically, we found that epigenetic regulation through microRNA-133b-regulated Th-POK expression and signals provided by DCs are fundamental for thymic NKT17 cell differentiation.

Migratory and adhesive cues controlling innate-like lymphocyte surveillance of the pathogen-exposed surface of the lymph node

Lymph nodes (LNs) contain innate-like lymphocytes that survey the subcapsular sinus (SCS) and associated macrophages for pathogen entry. The factors promoting this surveillance behavior have not been defined. Here, we report that IL7R^hiCcr6⁺ lymphocytes in mouse LNs rapidly produce IL17 upon bacterial and fungal challenge. We show that these innate-like lymphocytes are mostly LN resident. Ccr6 is required for their accumulation near the SCS and for efficient IL17 induction. Migration into the SCS intrinsically requires S1pr1, whereas movement from the sinus into the parenchyma involves the integrin LFA1 and its ligand ICAM1. CD169, a sialic acid-binding lectin, helps retain the cells within the sinus, preventing their loss in lymph flow. These findings establish a role for Ccr6 in augmenting innate-like lymphocyte responses to lymph-borne pathogens, and they define requirements for cell movement between parenchyma and SCS in what we speculate is a program of immune surveillance that helps achieve LN barrier immunity.

DOI:http://dx.doi.org/10.7554/eLife.18156.001

The lymphatic system is a network of vessels and a vital part of our immune system. Amongst other things, the lymphatic system carries microbes that have entered the body – for example via to a cut or mosquito bite – to small, oval-shaped organs called lymph nodes. The lymph nodes are packed with immune cells that can be activated to help fight off infections, however certain microbes actually replicate inside the lymph nodes themselves.

Lymph nodes protect themselves from these infections by having some pre-armed immune cells that are ready to respond rapidly as soon as an invading microbe is detected. These cells, referred to as innate-like lymphocytes, position themselves at the exposed surfaces of the lymph node – the locations where microbes are most likely to enter the organ. However, it was not known which cues caused these immune cells to assemble and remain at these locations.

Zhang et al. now reveal that a signaling molecule called CCL20 attracts the innate-like lymphocytes to the lymph node’s exposed surfaces, while a protein known as CD169 helps to securely attach the innate-like lymphocytes in place. Further experiments then confirmed that positioning the innate-like lymphocytes at this location made mice more able to fight off the disease-causing bacterium Staphyloccus aureus.

Unexpectedly, Zhang et al. also found that innate-like lymphocytes can move from the surfaces of lymph node through to the underlying tissue. This unusual migratory behavior might allow the lymphocytes to search a larger area for the infectious microbes, though further studies are needed to test this hypothesis. Future studies are also likely to focus on elucidating how the innate-like lymphocytes recognize different types of invaders, and how their activity keeps the lymph nodes healthy.

DOI:http://dx.doi.org/10.7554/eLife.18156.002

A mutation within the SH2 domain of slp-76 regulates the tissue distribution and cytokine production of iNKT cells in mice

TCR ligation is critical for the selection, activation, and integrin expression of T lymphocytes. Here, we explored the role of the TCR adaptor protein slp-76 on iNKT-cell biology. Compared to B6 controls, slp-76(ace/ace) mice carrying a missense mutation (Thr428Ile) within the SH2-domain of slp-76 showed an increase in iNKT cells in the thymus and lymph nodes, but a decrease in iNKT cells in spleens and livers, along with reduced ADAP expression and cytokine response. A comparable reduction in iNKT cells was observed in the livers and spleens of ADAP-deficient mice. Like ADAP(-/-) iNKT cells, slp-76(ace/ace) iNKT cells were characterized by enhanced CD11b expression, correlating with an impaired induction of the TCR immediate-early gene Nur77 and a decreased adhesion to ICAM-1. Furthermore, CD11b-intrinsic effects inhibited cytokine release, concanavalin A-mediated inflammation, and iNKT-cell accumulation in the liver. Unlike B6 and ADAP(-/-) mice, the expression of the transcription factors Id3 and PLZF was reduced, whereas NP-1-expression was enhanced in slp-76(ace/ace) mice. Blockade of NP-1 decreased the recovery of iNKT cells from peripheral lymph nodes, identifying NP-1 as an iNKT-cell-specific adhesion factor. Thus, slp-76 contributes to the regulation of the tissue distribution, PLZF, and cytokine expression of iNKT cells via ADAP-dependent and -independent mechanisms.

Innate-like functions of natural killer T cell subsets result from highly divergent gene programs

Natural killer T cells (NKT cells) have stimulatory or inhibitory effects on the immune response that can be attributed in part to the existence of functional subsets of NKT cells. These subsets have been characterized only on the basis of the differential expression of a few transcription factors and cell-surface molecules. Here we have analyzed purified populations of thymic NKT cell subsets at both the transcriptomic level and epigenomic level and by single-cell RNA sequencing. Our data indicated that despite their similar antigen specificity, the functional NKT cell subsets were highly divergent populations with many gene-expression and epigenetic differences. Therefore, the thymus 'imprints' distinct gene programs on subsets of innate-like NKT cells that probably impart differences in proliferative capacity, homing, and effector functions.

Regulatory role of natural killer T cells in diabetes

Type 1 and type 2 diabetes are growing public health problems. Despite having different pathophysiologies, both diseases are associated with defects in immune regulation. Invariant natural killer T (iNKT) cells are innate-like T cells that recognize glycolipids presented by CD1d. These cells not only play a key role in the defense against pathogens, but also exert potent immunoregulatory functions. The regulatory role of iNKT cells in the prevention of type 1 diabetes has been demonstrated in murine models and analyzed in diabetic patients. The decreased frequency of iNKT cells in non-obese diabetic mice initially suggested the regulatory role of this cell subset. Increasing the frequency or the activation of iNKT cells with agonists protects non-obese diabetic mice from the development of diabetes. Several mechanisms mediate iNKT regulatory functions. They can rapidly produce immunoregulatory cytokines, interleukin (IL)-4 and IL-10. They induce tolerogenic dendritic cells, thereby inducing the anergy of autoreactive anti-islet T cells and increasing the frequency of T regulatory cells (Treg cells). Synthetic agonists are able to activate iNKT cells and represent potential therapeutic treatment in order to prevent type 1 diabetes. Growing evidence points to a role of immune system in glucose intolerance and type 2 diabetes. iNKT cells are resident cells of adipose tissue and their local and systemic frequencies are reduced in obese patients, suggesting their involvement in local and systemic inflammation during obesity. With the discovery of potential continuity between type 1 and type 2 diabetes in some patients, the role of iNKT cells in these diseases deserves further investigation.

Development of invariant natural killer T cells

Invariant natural killer T (iNKT) cells develop into functionally distinct subsets. Each subset expresses a unique combination of transcription factors that regulate cytokine gene transcription upon activation. The tissue distribution and localization within tissues also varies between subsets. Importantly, the relative abundance of the various subsets is directly responsible for altering several immunological parameters, which subsequently affect the immune response. Here, I review recent advances in our understanding of the molecular regulation of iNKT cell subset development.