Mucosal-associated Invariant T Cells Research Articles

Mixtures of per- and poly-fluoroalkyl substances (PFAS) reduce the in vitro activation of human T cells and basophils

In the last decades, per- and poly-fluoroalkyl substances (PFAS), widely used industrial chemicals, have been in the center of attention because of their omnipotent presence in water and soils worldwide. Although efforts have been made to substitute long-chain PFAS towards safer alternatives, their persistence in humans still leads to exposure to these compounds. PFAS immunotoxicity is poorly understood as no comprehensive analyses on certain immune cell subtypes exist. Furthermore, mainly single entities and not PFAS mixtures have been assessed. In the present study we aimed to investigate the effect of PFAS (short-chain, long-chain and a mixture of both) on the in vitro activation of primary human immune cells.Our results show the ability of PFAS to reduce T cells activation. In particular, exposure to PFAS affected T helper cells, cytotoxic T cells, Natural Killer T cells, and Mucosal associated invariant T (MAIT) cells, as assessed by multi-parameter flow cytometry. Furthermore, the exposure to PFAS reduced the expression of several genes involved in MAIT cells activation, including chemokine receptors, and typical proteins of MAIT cells, such as GZMB, IFNG and TNFSF15 and transcription factors. These changes were mainly induced by the mixture of both short- and long-chain PFAS. In addition, PFAS were able to reduce basophil activation induced by anti-FcεR1α, as assessed by the decreased expression of CD63.Our data clearly show that the exposure of immune cells to a mixture of PFAS at concentrations mimicking real-life human exposure resulted in reduced cell activation and functional changes of primary innate and adaptive human immune cells.

Classic costimulatory interactions in MAIT cell responses: from gene expression to immune regulation.

Mucosa-associated invariant T (MAIT) cells are evolutionarily conserved, innate-like T lymphocytes with enormous immunomodulatory potentials. Due to their strategic localization, their invariant T cell receptor (iTCR) specificity for major histocompatibility complex-related protein 1 (MR1) ligands of commensal and pathogenic bacterial origin, and their sensitivity to infection-elicited cytokines, MAIT cells are best known for their antimicrobial characteristics. However, they are thought to also play important parts in the contexts of cancer, autoimmunity, vaccine-induced immunity, and tissue repair. While cognate MR1 ligands and cytokine cues govern MAIT cell maturation, polarization, and peripheral activation, other signal transduction pathways, including those mediated by costimulatory interactions, regulate MAIT cell responses. Activated MAIT cells exhibit cytolytic activities and secrete potent inflammatory cytokines of their own, thus transregulating the biological behaviors of several other cell types, including dendritic cells, macrophages, natural killer cells, conventional T cells, and B cells, with significant implications in health and disease. Therefore, an in-depth understanding of how costimulatory pathways control MAIT cell responses may introduce new targets for optimized MR1/MAIT cell-based interventions. Herein, we compare and contrast MAIT cells and mainstream T cells for their expression of classic costimulatory molecules belonging to the immunoglobulin superfamily and the tumor necrosis factor (TNF)/TNF receptor superfamily, based not only on the available literature but also on our transcriptomic analyses. We discuss how these molecules participate in MAIT cells' development and activities. Finally, we introduce several pressing questions vis-à-vis MAIT cell costimulation and offer new directions for future research in this area.

Effects of interleukin-23 on the activation of mucosal-associated invariant T cells from oral lichen planus.

Oral lichen planus (OLP) is a T cell-mediated inflammatory condition in the oral cavity. Mucosal-associated invariant T (MAIT) cells are gaining more relevance in immune diseases because they can be activated by cytokines without T cell receptor stimulation. Herein, we tested the effect of interleukin-23 (IL-23) on the activation status of OLP MAIT cells. Peripheral blood mononuclear cells (PBMCs) isolated from OLP patients were stimulated by IL-23 in the absence or presence of phorbol myristate acetate (PMA) and ionomycin. The activation status of MAIT cells was analyzed by flow cytometry after staining for CD3, CD4, CD8, CD161, TCR Vα7.2, and CD69. The fraction of MAIT cells in OLP peripheral blood was approximately 0.38% to 3.97%, and CD8+ subpopulations overwhelmed CD4+ cells. The mean percentages of OLP MAIT cells in PBMCs and CD8+MAIT cells in MAIT cells were approximately 40%. PMA and ionomycin significantly increased CD69 expression on OLP T cells, MAIT cells, and CD8+MAIT cells. Cells with enhanced activation had different responsiveness to exogenous IL-23, showing increased CD69 expression on OLP T cells, decreased CD69 on OLP CD8+MAIT cells, and no significant change on OLP MAIT cells. IL-23 showed different effects on the activation status of OLP MAIT cells and CD8+MAIT cells.

Single cell analysis to study the longitudinal changes in systemic tumor immune environment in cervical cancer after radiochemotherapy.

e17530 Background: Chemoradiation is the mainstay treatment for cervical cancer, which affects not only tumor immune microenvironment (TIME) but may also the systemic tumor immune microenvironment (STIE). Improved understanding of STIE beyond the tumor may enhance improving treatment strategies for cervical cancer. With these motivations, we applied single-cell RNA-sequencing (SCRNA-seq) to investigate longitudinal dynamics of a comprehensive set of immune cells in cervical cancer patients receiving chemoradiation (RCT). Methods: Two patients diagnosed with cervical squamous cell carcinoma at a locally advanced stage and received 45Gy/25f, with concurrent cisplatin, were enrolled. Peripheral blood was collected for SCRNA-seq using the 10× Genomics. Fresh blood samples were obtained at baseline 1-week, 2-week, 3-week, 5-week (end of external beam radiotherapy) and after Chemoradiation. Seurat 4.0 was used to cluster and annotate cell clusters. Results: A total of 90862 cells were clustered into 3 main subsets, including NK&T, B, and myeloid subsets. Then NK&T subset was extracted and further annotated into 10 clusters, including CD8+T naive, CD8+T effector, CD8+T effector memory, mucosal-associated invariant T (MAIT), cycling CD8+T, CD4Tem, CD4+T naive/central memory, regulatory T (Treg), natural killer (NK), and NKT cells. After plotting the dynamic changes of different cell types, MAIT and cycling CD8+T cell steadily increased with time or RT dose accumulation, suggesting that RCT could induce their proliferation. MAIT highly expressed CD69 and CXCR4 much like CD8+T effector memory cell, and cycling CD8+T cell expressed CX3CR1 like CD8+T effector cell. Besides, pseudotime analysis revealed that the differentiation process started from naive CD8+T cell towards cycling CD8+T cell passing through effector memory CD8+T cell, and effector CD8+T cell. In this process, the transcriptionally distinct MAIT cell belong to a different branch of the Pseudotime trajectory compared to the rest of the T cells, albeit mapping close to effector memory CD8+T cell, in line with their shared phenotypic identity. Enrichment was employed to explore their function and MAIT was enriched with genes involving cytokine-cytokine receptor interaction. Moreover, MAIT cell with increased antigen process and presentation function was note, and PD-1 checkpoint pathway was up-regulated during RCT. Conclusions: Chemoradiation induced the accumulation of MAIT cell which has increased antigen process and presentation features and cycling CD8+T cell with a higher PD-1 checkpoint pathway gene expression signature. Taken together, we provide insight into the peripheral immune remodeling induced by RCT, which will help optimize and improve treatment strategies for cervical cancer. Clinical trial information: NCT05061342 .

Divergent metabolic programmes control two populations of MAIT cells that protect the lung

Although mucosal-associated invariant T (MAIT) cells provide rapid, innate-like responses, they are not pre-set, and memory-like responses have been described for MAIT cells following infections. The importance of metabolism for controlling these responses, however, is unknown. Here, following pulmonary immunization with a Salmonella vaccine strain, mouse MAIT cells expanded as separate CD127−Klrg1+ and CD127+Klrg1− antigen-adapted populations that differed in terms of their transcriptome, function and localization in lung tissue. These populations remained altered from steady state for months as stable, separate MAIT cell lineages with enhanced effector programmes and divergent metabolism. CD127+ MAIT cells engaged in an energetic, mitochondrial metabolic programme, which was critical for their maintenance and IL-17A synthesis. This programme was supported by high fatty acid uptake and mitochondrial oxidation and relied on highly polarized mitochondria and autophagy. After vaccination, CD127+ MAIT cells protected mice against Streptococcus pneumoniae infection. In contrast, Klrg1+ MAIT cells had dormant but ready-to-respond mitochondria and depended instead on Hif1a-driven glycolysis to survive and produce IFN-γ. They responded antigen independently and participated in protection from influenza virus. These metabolic dependencies may enable tuning of memory-like MAIT cell responses for vaccination and immunotherapies.

Expansion of MAIT cells in the combined absence of NKT and γδ-T cells

Mucosal-associated invariant T (MAIT) cells, natural killer T (NKT) cells, and γδT cells are collectively referred to as 'unconventional T cells' due to their recognition of non-peptide antigens and restriction to non-classical MHC-I-like molecules. Though the frequencies of MAIT, NKT and γδT cells and distribution of their functional subsets vary widely between organs and individuals, the factors controlling these differences are poorly understood. Here, we show that MAIT cells are increased in mice deficient in either NKT or γδT cells and even more-so in mice deficient in both NKT and γδT cells. In addition, characterisation of the TCRα repertoire within γδT cell-deficient thymocytes revealed an altered Trav gene segment usage relative to that of WT thymocytes, highlighting a retention of the Tcra-Tcrd locus from 129 strain embryonic stem cells used to generate Tcrd-/- mice. Accordingly, this resulted in a moderate increase in distal Trav segment usage such as Trav1, potentially contributing to increased generation of Trav1-Traj33+ MAIT cells in the Tcrd-/- thymus. However, peripheral MAIT cells also underwent increased homeostatic proliferation in the absence of NKT and γδT cells and adoptively transferred MAIT cell subsets exhibited tissue-specific homing patterns. Collectively, our data reveals a shared niche for MAIT, NKT, and γδT cells, suggesting a competition for common factors that could be exploited for treating disease. Importantly, these data highlight that careful assessment of studies using NKT or γδT cell-deficient mouse models is required when investigating the role of unconventional T cells in disease.

Early activation and recruitment of invariant natural killer T cells during liver ischemia-reperfusion: the major role of the alarmin interleukin-33.

Over the past thirty years, the complexity of the αβ-T cell compartment has been enriched by the identification of innate-like T cells (ITCs), which are composed mainly of invariant natural killer T (iNKT) cells and mucosal-associated invariant T (MAIT) cells. Based on animal studies using ischemia-reperfusion (IR) models, a key role has been attributed to iNKT cells in close connection with the alarmin/cytokine interleukin (IL)-33, as early sensors of cell-stress in the initiation of acute sterile inflammation. Here we have investigated whether the new concept of a biological axis of circulating iNKT cells and IL-33 applies to humans, and may be extended to other ITC subsets, namely MAIT and γδ-T cells, in the acute sterile inflammation sequence occurring during liver transplant (LT). From a prospective biological collection of recipients, we reported that LT was accompanied by an early and preferential activation of iNKT cells, as attested by almost 40% of cells having acquired the expression of CD69 at the end of LT (i.e. 1-3 hours after portal reperfusion), as opposed to only 3-4% of conventional T cells. Early activation of iNKT cells was positively correlated with the systemic release of the alarmin IL-33 at graft reperfusion. Moreover, in a mouse model of hepatic IR, iNKT cells were activated in the periphery (spleen), and recruited in the liver in WT mice, as early as the first hour after reperfusion, whereas this phenomenon was virtually missing in IL-33-deficient mice. Although to a lesser degree than iNKT cells, MAIT and γδ-T cells also seemed targeted during LT, as attested by 30% and 10% of them acquiring CD69 expression, respectively. Like iNKT cells, and in clear contrast to γδ-T cells, activation of MAIT cells during LT was closely associated with both release of IL-33 immediately after graft reperfusion and severity of liver dysfunction occurring during the first three post-operative days. All in all, this study identifies iNKT and MAIT cells in connection with IL-33 as new key cellular factors and mechanisms of acute sterile inflammation in humans. Further investigations are required to confirm the implication of MAIT and iNKT cell subsets, and to precisely assess their functions, in the clinical course of sterile inflammation accompanying LT.

Role of MR1-driven signals and amphiregulin on the recruitment and repair function of skin MAIT cells

Abstract Epithelial repair is crucial to reestablish adequate barrier integrity and function after tissue injury. In both mice and humans, MAIT (Mucosal associated invariant T) cells involvement in tissue repair is substantiated by their upregulation of tissue repair mediators following TCR-mediated activation. Additionally, in the absence of ɣδT cells, MAIT cells were shown to promote wound healing. By using both our congenic B6-MAIT CASTstrain (10× more MAIT cells than B6 mice) and a skin excision mouse model preventing epithelial contraction (mimicking the human repair process), we sought to uncover the underlying mechanisms of MAIT cell tissue repair function. Firstly, our scRNAseq analysis revealed that steady-state skin MAIT cells readily express a repair program. Additionally, we show that MAIT cells have a pro-repair function as their presence promotes keratinocyte proliferation, thereby accelerating healing. Using parabiosis, skin graft and the Kaede models, we found that, contrary to the resident ɣδT cells, MAIT cells are rapidly recruited into the inflamed skin. Parabiosis of MR1 +and MR1 −mice and MR1 −skin grafted onto MR1 +mice, showed that this recruitment was MR1-independent (MR1: antigen presenting molecule of MAIT cells). Instead, this recruitment relied on the chemokine receptor CXCR6 and its ligand CXCL16. Lastly, using conditional knock-out mice we demonstrated that the secretion by MAIT cells of the amphiregulin growth factor promotes skin wound healing. Overall, our study provides mechanistic insights into MAIT cell biology in the context of injury. Comprehension of these processes provides clues into the biology of related innate subsets and highlights potential new therapeutic avenues for wound healing. Institut National de la Santé et de la Recherche Médicale (OL) Institut Curie (OL) Agence Nationale de la Recherche Grant MAIT ANR-16-CE15-0020-01 (OL) Agence Nationale de la Recherche Grant MAITrepair ANR-20-CE15-0028-01 (OL) Agence Nationale de la Recherche ANR-10-IDEX-0001-02 PSL (OL) European Research Council (ERC-2019-AdG-885435) (OL) Fondation pour la Recherche Médicale, grant number FDT202106013036 (AdH)

Dysregulation of circulating MAIT cell subsets in patients with hidradenitis suppurativa

Abstract Hidradenitis suppurativa (HS) is a chronic inflammatory condition characterized by painful and debilitating skin lesions. Recent reports purport HS as an autoinflammatory keratinization disease with numerous pathways and features of systemic inflammation however few studies have been conducting to characterize peripheral immune dysregulation. Mucosal associated invariant T (MAIT) cells are an invariant T cell subset responding directly to bacterial threats and their dysregulation contributes to the pathogenesis of autoimmune disorders, cancers and inflammatory skin conditions. Here, we analyzed MAIT cells in the blood of 16 HS patients and 12 healthy controls (HC) by flow cytometry. We found that the frequency of MAIT cells did not change in HS patients, but their function changed drastically. We observed a significant reduction in the frequency of IFNy+ and TNFα+ MAIT cells in the periphery of HS patients. Furthermore, we analyzed MAIT cell subsets by their CD4 surface expression. Here, we found that the frequency of CD4+MAIT cells in the periphery of HS patients is significantly increased, while the frequency of CD4-MAIT cells is significantly decreased. Furthermore, HS patients have a reduction in CD4− IFNg+ and TNFa+ MAIT cells. Overall, these findings suggest that peripheral MAIT cells are dysregulated in HS patients which may contribute to the pathogenesis of the disease. NIH/NIAMS (1R21AR079089 and 1R01AR078688) for Dr. Mi and Henry Ford Immunology Program grant (T71017 for Dr. Mi and T71016 for Di Zhou).

MR1-deficiency in neonatal mice renders protection from necrotizing enterocolitis

Abstract Necrotizing enterocolitis (NEC) is a life-threatening disease that affects ~ 7% of premature neonates. NEC maintains high morbidity/mortality and there are long term sequelae including short bowel syndrome. The risk factors of developing NEC include prematurity, very low birth weight, microbial dysbiosis and infections. Mucosal-associated invariant T (MAIT) cells are innate T cells that have both innate and adaptive immune cell characteristics and are enriched in mucosal tissues, such as intestines. MR1 is the antigen presenting molecule for MAIT cells. Therefore, MR1-knockout (MR1 KO) mice lack MAIT cells. We hypothesized that MR1/MAIT cells play a key role in the development of NEC. To test the hypothesis, NEC was induced in 5-day old B6 wild type (WT) and MR1 KO mouse pups with gavage formula feeds supplemented with LPS as well as exposure to intermittent hypoxia and hypothermia. Pups were assessed daily for clinical sickness scores. Animals were euthanized on postnatal day 9. Intestine segments were harvested and assessed for histological NEC and cytokines were measured using multiplex assay. Compared to WT mice, we found MR1 KO pups did not develop typical NEC symptoms. When compared to WT mice with NEC, MR1 KO mice undergoing the treatment for NEC, had lower clinical scores (WT=4 [3–4]; MR1 KO=0 [0–0], p<0.05) and intestinal histology scores (WT=1.5 [1–2.375]; MR1 KO=0 [0–0.3745], p<0.05). The cytokine profile of the intestines in MR1 KO NEC mice, when compared to those in WT NEC mice, showed significant differences in IL-6 and IL-10 levels. In conclusion, deletion of MR1 in mice appears to be protective in experimental NEC. Future work will focus on studying the role MR1/MAIT cells in NEC disease development.

The proliferation of human mucosal-associated invariant T cells requires a MYC-SLC7A5-glycolysis metabolic axis

Mucosal-associated invariant T (MAIT) cells are an abundant population of innate T cells that recognize bacterial ligands and play a key role in host protection against bacterial and viral pathogens. Upon activation, MAIT cells undergo proliferative expansion and increase their production of effector molecules such as cytokines. In this study, we found that both mRNA and protein abundance of the key metabolism regulator and transcription factor MYC was increased in stimulated MAIT cells. Using quantitative mass spectrometry, we identified the activation of two MYC-controlled metabolic pathways, amino acid transport and glycolysis, both of which were necessary for MAIT cell proliferation. Last, we showed that MAIT cells isolated from people with obesity showed decreased MYC mRNA abundance upon activation, which was associated with defective MAIT cell proliferation and functional responses. Collectively, our data uncover the importance of MYC-regulated metabolism for MAIT cell proliferation and provide additional insight into the molecular basis for the functional defects of MAIT cells in obesity.

Comparative transcriptomes reveal pro-survival and cytotoxic programs of mucosal-associated invariant T cells upon Bacillus Calmette-Guérin stimulation.

Mucosal-associated invariant T (MAIT) cells are protective against tuberculous and non-tuberculous mycobacterial infections with poorly understood mechanisms. Despite an innate-like nature, MAIT cell responses remain heterogeneous in bacterial infections. To comprehensively characterize MAIT activation programs responding to different bacteria, we stimulated MAIT cells with E. coli to compare with Bacillus Calmette-Guérin (BCG), which remains the only licensed vaccine and a feasible tool for investigating anti-mycobacterial immunity in humans. Upon sequencing mRNA from the activated and inactivated CD8+ MAIT cells, results demonstrated the altered MAIT cell gene profiles by each bacterium with upregulated expression of activation markers, transcription factors, cytokines, and cytolytic mediators crucial in anti-mycobacterial responses. Compared with E. coli, BCG altered more MAIT cell genes to enhance cell survival and cytolysis. Flow cytometry analyses similarly displayed a more upregulated protein expression of B-cell lymphoma 2 and T-box transcription factor Eomesodermin in BCG compared to E.coli stimulations. Thus, the transcriptomic program and protein expression of MAIT cells together displayed enhanced pro-survival and cytotoxic programs in response to BCG stimulation, supporting BCG induces cell-mediated effector responses of MAIT cells to fight mycobacterial infections.

MAIT cell inhibition promotes liver fibrosis regression via macrophage phenotype reprogramming

Recent data have shown that liver fibrosis can regress even at later stages of cirrhosis and shifting the immune response from pro-inflammatory towards a resolutive profile is considered as a promising option. The immune regulatory networks that govern the shift of the inflammatory phenotype and thus potential reversal of liver fibrosis are lesser known. Here we show that in precision-cut human liver slices obtained from patients with end-stage fibrosis and in mouse models, inhibiting Mucosal-Associated Invariant T (MAIT) cells using pharmacological or antibody-driven approaches, limits fibrosis progression and even regresses fibrosis, following chronic toxic- or non-alcoholic steatohepatitis (NASH)-induced liver injury. Mechanistic studies, combining RNA sequencing, in vivo functional studies (performed in male mice) and co-culture experiments indicate that disruption of the MAIT cell-monocyte/macrophage interaction results in resolution of fibrosis both by increasing the frequency of restorative Ly6Clo at the expenses of pro-fibrogenic Ly6Chi monocyte-derived macrophages and promoting an autophagic phenotype in both subsets. Thus, our data show that MAIT cell activation and the consequential phenotype shift of liver macrophages are important pathogenic features of liver fibrosis and could be targeted by anti-fibrogenic therapy.

MAIT cells activate dendritic cells to promote TFH cell differentiation and induce humoral immunity

Protective immune responses against respiratory pathogens, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and influenza virus, are initiated by the mucosal immune system. However, most licensed vaccines are administered parenterally and are largely ineffective at inducing mucosal immunity. The development of safe and effective mucosal vaccines has been hampered by the lack of a suitable mucosal adjuvant. In this study we explore a class of adjuvant that harnesses mucosal-associated invariant T (MAIT) cells. We show evidence that intranasal immunization of MAIT cell agonists co-administered withprotein, including the spike receptor binding domain from SARS-CoV-2 virus and hemagglutinin from influenza virus, induce protective humoral immunity and immunoglobulin A production. MAIT cell adjuvant activity is mediated by CD40L-dependent activation of dendritic cells and subsequent priming of T follicular helper cells. In summary, we show that MAIT cells are promising vaccine targets that can be utilized as cellular adjuvants in mucosal vaccines.

Control of the temporal development of Alzheimer’s disease pathology by the MR1/MAIT cell axis

BackgroundNeuroinflammation is an important feature of Alzheimer’s disease (AD). Understanding which aspects of the immune system are important in AD may lead to new therapeutic approaches. We study the major histocompatibility complex class I-related immune molecule, MR1, which is recognized by an innate-like T cell population called mucosal-associated invariant T (MAIT) cells.MethodsHaving found that MR1 gene expression is elevated in the brain tissue of AD patients by mining the Agora database, we sought to examine the role of the MR1/MAIT cell axis in AD pathology. Brain tissue from AD patients and the 5XFAD mouse model of AD were used to analyze MR1 expression through qPCR, immunofluorescence, and flow cytometry. Furthermore, mice deficient in MR1 and MAIT cells were crossed with the 5XFAD mice to produce a model to study how the loss of this innate immune axis alters AD progression. Moreover, 5XFAD mice were also used to study brain-resident MAIT cells over time.ResultsIn tissue samples from AD patients and 5XFAD mice, MR1 expression was substantially elevated in the microglia surrounding plaques vs. those that are further away (human AD: P < 0.05; 5XFAD: P < 0.001). In 5XFAD mice lacking the MR1/MAIT cell axis, the development of amyloid-beta plaque pathology occurred at a significantly slower rate than in those mice with MR1 and MAIT cells. Furthermore, in brain tissue from 5XFAD mice, there was a temporal increase in MAIT cell numbers (P < 0.01) and their activation state, the latter determined by detecting an upregulation of both CD69 (P < 0.05) and the interleukin-2 receptor alpha chain (P < 0.05) via flow cytometry.ConclusionsTogether, these data reveal a previously unknown role for the MR1/MAIT cell innate immune axis in AD pathology and its potential utility as a novel therapeutic target.

Varicella Zoster Virus infects mucosal associated Invariant T cells.

Mucosal Associated Invariant T (MAIT) cells are innate-like T cells that respond to conserved pathogen-derived vitamin B metabolites presented by the MHC class I related-1 molecule (MR1) antigen presentation pathway. Whilst viruses do not synthesize these metabolites, we have reported that varicella zoster virus (VZV) profoundly suppresses MR1 expression, implicating this virus in manipulation of the MR1:MAIT cell axis. During primary infection, the lymphotropism of VZV is likely to be instrumental in hematogenous dissemination of virus to gain access to cutaneous sites where it clinically manifests as varicella (chickenpox). However, MAIT cells, which are found in the blood and at mucosal and other organ sites, have yet to be examined in the context of VZV infection. The goal of this study was to examine any direct impact of VZV on MAIT cells. Using flow cytometry, we interrogated whether primary blood derived MAIT cells are permissive to infection by VZV whilst further analysing differential levels of infection between various MAIT cell subpopulations. Changes in cell surface extravasation, skin homing, activation and proliferation markers after VZV infection of MAIT cells was also assessed via flow cytometry. Finally the capacity of MAIT cells to transfer infectious virus was tested through an infectious center assay and imaged via fluorescence microscopy. We identify primary blood-derived MAIT cells as being permissive to VZV infection. A consequence of VZV infection of MAIT cells was their capacity to transfer infectious virus to other permissive cells, consistent with MAIT cells supporting productive infection. When subgrouping MAIT cells by their co- expression of a variety cell surface markers, there was a higher proportion of VZV infected MAIT cells co-expressing CD4+ and CD4+/CD8+ MAIT cells compared to the more phenotypically dominant CD8+ MAIT cells, whereas infection was not associated with differences in co-expression of CD56 (MAIT cell subset with enhanced responsiveness to innate cytokine stimulation), CD27 (co-stimulatory) or PD-1 (immune checkpoint). Infected MAIT cells retained high expression of CCR2, CCR5, CCR6, CLA and CCR4, indicating a potentially intact capacity for transendothelial migration, extravasation and trafficking to skin sites. Infected MAIT cells also displayed increased expression of CD69 (early activation) and CD71 (proliferation) markers. These data identify MAIT cells as being permissive to VZV infection and identify impacts of such infection on co- expressed functional markers.

High pre-transplant Mucosal Associated Invariant T Cell (MAIT) count predicts favorable course of myeloid aplasia.

Mucosal Associated Invariant T (MAIT) cells are unconventional T cells with anti-infective potential. MAIT cells detect and fight against microbes on mucosal surfaces and in peripheral tissues. Previous works suggested that MAIT cells survive exposure to cytotoxic drugs in these locations. We sought to determine if they maintain their anti-infective functions after myeloablative chemotherapy. We correlated the amount of MAIT cells (measured by flow cytometry) in the peripheral blood of 100 adult patients before the start of myeloablative conditioning plus autologous stem cell transplantation with the clinical and laboratory outcomes of aplasia. The amount of MAIT cells negatively correlated with peak C-reactive protein level and the amount of red blood cell transfusion units resulting in earlier discharge of patients with the highest amount of MAIT cells. This work suggests the anti-infectious potential of MAIT cells is maintained during myeloid aplasia.

Mucosal-associated invariant T cells in patients with axial spondyloarthritis.

Several studies implicate Th17-cells and its cytokine (IL-17) in disease pathogenesis of spondyloarthritis (SpA), with available evidence supporting a pathogenic role of CD8+ T-cells. However, data on the involvement of CD8+ mucosal-associated invariant T-cells (MAIT) and their phenotypic characterization and inflammatory function including IL-17 and Granzyme A production in a homogenous population of SpA-patients with primarily axial disease (axSpA) are lacking. Quantify and characterize the phenotype and function of circulating CD8+MAIT-cells in axSpA-patients with primarily axial disease. Blood samples were obtained from 41 axSpA-patients and 30 age- and sex-matched healthy controls (HC). Numbers and percentages of MAIT-cells (defined as CD3+CD8+CD161highTCRVα7.2 +) were determined, and production of IL-17 and Granzyme A (GrzA) by MAIT-cells were examined by flow cytometry upon in vitro stimulation. Serum IgG specific for CMV was measured by ELISA. No significant differences in numbers and percentages of circulating MAIT-cells were found between axSpA-patients and HCr zijn meer resultaten de centrale memory CD8 T cellen. cellen van patirculating MAIT cells.. Further phenotypic analysis revealed a significant decrease in numbers of central memory MAIT-cells of axSpA-patients compared to HC. The decrease in central memory MAIT-cells in axSpA patients was not attributed to an alteration in CD8 T-cell numbers, but correlated inversely with serum CMV-IgG titers. Production of IL-17 by MAIT-cells was comparable between axSpA-patients and HC, whereas a significant decrease in the production of GrzA by MAIT-cells from axSpA-patients was observed. The decrease in cytotoxic capability of circulating MAIT-cells in axSpA-patients might implicate that these cell types migrate to the inflamed tissue and therefore associate with the axial disease pathogenesis.

MAIT cells and the microbiome.

Mucosal associated invariant T (MAIT) cells are innate-like T lymphocytes, strikingly enriched at mucosal surfaces and characterized by a semi-invariant αβ T cell receptor (TCR) recognizing microbial derived intermediates of riboflavin synthesis presented by the MHC-Ib molecule MR1. At barrier sites MAIT cells occupy a prime position for interaction with commensal microorganisms, comprising the microbiota. The microbiota is a rich source of riboflavin derived antigens required in early life to promote intra-thymic MAIT cell development and sustain a life-long population of tissue resident cells. A symbiotic relationship is thought to be maintained in health whereby microbes promote maturation and homeostasis, and in turn MAIT cells can engage a TCR-dependent "tissue repair" program in the presence of commensal organisms conducive to sustaining barrier function and integrity of the microbial community. MAIT cell activation can be induced in a MR1-TCR dependent manner or through MR1-TCR independent mechanisms via pro-inflammatory cytokines interleukin (IL)-12/-15/-18 and type I interferon. MAIT cells provide immunity against bacterial, fungal and viral pathogens. However, MAIT cells may have deleterious effects through insufficient or exacerbated effector activity and have been implicated in autoimmune, inflammatory and allergic conditions in which microbial dysbiosis is a shared feature. In this review we summarize the current knowledge on the role of the microbiota in the development and maintenance of circulating and tissue resident MAIT cells. We also explore how microbial dysbiosis, alongside changes in intestinal permeability and imbalance between pro- and anti-inflammatory components of the immune response are together involved in the potential pathogenicity of MAIT cells. Whilst there have been significant improvements in our understanding of how the microbiota shapes MAIT cell function, human data are relatively lacking, and it remains unknown if MAIT cells can conversely influence the composition of the microbiota. We speculate whether, in a human population, differences in microbiomes might account for the heterogeneity observed in MAIT cell frequency across mucosal sites or between individuals, and response to therapies targeting T cells. Moreover, we speculate whether manipulation of the microbiota, or harnessing MAIT cell ligands within the gut or disease-specific sites could offer novel therapeutic strategies.

Relevant mechanisms of MAIT cells involved in the pathogenesis of periodontitis.

Mucosal-associated invariant T (MAIT) cells are a group of unconventional T cells that are abundant in the human body, recognize microbial-derived vitamin B metabolites presented by MHC class I-related protein 1 (MR1), and rapidly produce proinflammatory cytokines, which are widely involved in the immune response to various infectious diseases. In the oral mucosa, MAIT cells tend to accumulate near the mucosal basal lamina and are more inclined to secrete IL-17 when activated. Periodontitis is a group of diseases that manifests mainly as inflammation of the gums and resorption of the alveolar bone due to periodontal tissue invasion by plaque bacteria on the dental surface. The course of periodontitis is often accompanied by a T-cell-mediated immune response. This paper discussed the pathogenesis of periodontitis and the potential contribution of MAIT cells to periodontitis.