key: cord-0903518-wuku47ic
authors: Li, Yanmei; Du, Jun; Wei, Wei
title: Emerging Roles of Mucosal-Associated Invariant T Cells in Rheumatology
date: 2022-03-04
journal: Front Immunol
DOI: 10.3389/fimmu.2022.819992
sha: 50eaf32f9b9e5672827d6235fd828f729d13841c
doc_id: 903518
cord_uid: wuku47ic

Mucosal-associated invariant T (MAIT) cells are an unconventional T cell subset expressing a semi-invariant TCR and recognize microbial riboflavin metabolites presented by major histocompatibility complex class 1-related molecule (MR1). MAIT cells serve as innate-like T cells bridging innate and adaptive immunity, which have attracted increasing attention in recent years. The involvement of MAIT cells has been described in various infections, autoimmune diseases and malignancies. In this review, we first briefly introduce the biology of MAIT cells, and then summarize their roles in rheumatic diseases including systemic lupus erythematosus, rheumatoid arthritis, primary Sjögren’s syndrome, psoriatic arthritis, systemic sclerosis, vasculitis and dermatomyositis. An increased knowledge of MAIT cells will inform the development of novel biomarkers and therapeutic approaches in rheumatology.

Rheumatic diseases are a group of multisystem, immune-mediated disorders, including rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), primary Sjögren's syndrome (pSS), psoriatic arthritis (PsA), systemic sclerosis (SSc), large vessel vasculitis and systemic vasculitis. Although the pathogenesis of rheumatic diseases remains unclear, various immune cells, especially T cells, participate in the development of rheumatic diseases (1) (2) (3) (4) (5) . Mucosal-associated invariant T (MAIT) cells are innate-like T lymphocytes that express a semi-invariant T cell receptor (TCR). MAIT cells are abundant in humans and can respond to pathogens. While many studies have focused on the roles of MAIT cells in infection, it is increasingly clear that they are also involved in autoimmune diseases. In this review, we first summarize the phenotype, distribution, development, activation and function of MAIT cells, and we then describe their roles in rheumatic diseases.

Va7.2-Ja33 (TRAV1-2-TRAJ33) rearrangement was found to be enriched in human double-negative (CD4 -CD8 -, DN) a/b T cells and the phylogenetically conserved T cell population was described to express an invariant TCR combined with a limited set of Vb chains in 1990s (6, 7) . In mice, these T cells express the orthologous Va19-Ja33 (TRAV1-TRAJ33) (7) . Since 2003, the new T cell subsets were named mucosal-associated invariant T (MAIT) cells because they are present in mucosal tissues (8) . Human MAIT cell subsets are mostly CD8a + (median 79.7%) or DN (median 14.3%) with a minor subset being CD4 + cells (median 1.3%) (9) , whereas most murine MAIT cells are DN although CD4 + and CD8 + subsets are detected in lower proportions and with varied frequencies in a tissue-specific manner (10) . A recent study has found that human DN and CD8 + MAIT cells are functionally distinct subsets, and it is speculated that apoptosis-prone DN MAIT cells may be derived from the main CD8 + MAIT cell population (11) . MAIT cells recognize metabolites from the bacterial riboflavin (vitamin B2) pathway that are presented by the major histocompatibility complex class 1-related molecule (MR1) (12, 13) . MR1 tetramers have been developed for the specific identification of MAIT cells (14) . MAIT cells have high surface expression of natural killer (NK) receptors such as C-type lectin CD161, NKG2D and NKP30 (15) . The expression of surface markers, including CD45RO, CD95hi, CD27, CD26hi, CD44hi, CD122 and CD62Llo, identify MAIT cells as effector and memory phenotypes (16, 17) . MAIT cells also possess high levels of specific homing receptors, such as chemokine CC receptor (CCR)6, CCR5, CCR9, chemokine CXC receptor (CXCR)6 and CXCR3, which are involved in cell migration to peripheral tissues, particularly the liver, intestine and inflammatory tissues (10, 15) . However, the expression levels of CXCR2 (CD182), CXCR7, and lymph node homing receptor CCR7 (CD197) are low (18) . Moreover, the high surface expression of a series of cytokine receptors such as interleukin (IL)-7, IL-12, IL-18 and IL-23 receptors is of great importance to MAIT cell activation in the absence of TCR stimulation (10, 19) . In humans, the T-Box transcription factor TBX21 (T-bet), retinoicacid-related orphan receptor (ROR)gt and promyelocytic leukemia zinc finger (PLZF) transcription factors are coexpressed, suggesting the type1, type 17, and innate-like functionality of MAIT cells (10, 16, 17) (Figure 1 ).

MAIT cells are not only enriched in mucosal tissues, but are also abundant in the blood (0.1-9.2%), liver (20-40%) and peripheral lymphoid organs under physiological conditions (8, 9, 20, 21) . However, MAIT cells are less frequent in laboratory strains of mice (C57BL/6 and BALB/c) at homeostasis. The proportion is approximately 0.6% of T cells in mouse livers (10) . MAIT cells develop in a thymus-dependent manner, similar to humans and mice, and they can be divided into three stages (17) . Stage 1 MAIT cells are present only in the thymus and are mostly either double positive (DP) or CD4 + CD8thymocytes, and they lack CD161 and CD27 surface markers (CD24 + CD44in mice) (17) . A small subset of stage 1 MAIT cells express RORgt, which is attributed to vitamin B2 metabolite transferring into the thymus (22) . Stage 2 MAIT cells are present at low frequency in the periphery and are mostly CD4 + CD8cells that express CD161 -CD27 + (CD24 -CD44in mice) with a low expression of T-bet and RORgt (17) . MiRNAs may participate in the transition from stage 1 to 2, because in the absence of miR-181a/b-1, thymic MAIT cells show low expressions of ROR gt and T -bet (23) . The maturation from stage 2 to stage 3 and acquisition of effector function are PLZF dependent, and commensal bacteria along with IL-18 play an important role in the process (17) . Stage 3 MAIT cells acquire functional potential and start to migrate to peripheral organs. At stage 3, MAIT cells expressing CD161 + CD27 pos-low (CD24 -CD44 + in mice) exhibit interferon (IFN)-g-producing T-bet + (MAIT-1) sublineage or IL-17 A producing RORgt + (MAIT-17) (24) . IL-2/IL-15 receptor b chain, inducible costimulatory (ICOS), the transcription factor (TF) Bcl11b and miR-155 are involved in regulating MAIT1 and MAIT17 cells differentiation (25) (26) (27) . Recently, MAIT2 cells that express PLZF have been defined using single-cell RNA sequencing analysis, which are considered as developmental intermediates of MAIT1 and MAIT17 cells (28) . MAIT cells undergo further maturation and expansion after leaving the thymus, and microbes play an important role in regulating the number of MAIT cells in the periphery (29, 30) .

MAIT cells can be activated by two pathways as follows: via TCR signalling (MR1 dependent) or cytokine signalling alone (MR1 independent). Riboflavin derivatives presented by MR1 of antigen presenting cells (APCs) activate MAIT cells, while the folic acid product is a competitive inhibitor (31) . Because riboflavin synthesis is broadly conserved among bacteria and fungi, MAIT cells respond to a diverse array of microbes, including known commensals (32, 33) . Following MR1mediated activation, MAIT cells rapidly produce a wide range of cytokines, including interferon (IFN)-g, tumor necrosis factor (TNF), IL-17 and IL-22. These cytokines, either directly (IFN-g, TNF and IL-17) or indirectly through cell proliferation (IL-22), promote cytolysis of the infected cells, thereby leading to the control of various infections (15, 32, 34, 35) . MAIT cells can also be activated by inflammatory cytokines alone, such as IL-7, IL-12, IL-18, IL-15 and IFN-a/b, in a TCR-independent manner (19, 36, 37) . MAIT cells are activated with no known antigens, for instance, during viral infections or sterile auto-immunities. Cytokine-dependent activation of MAIT cells leads to secretion of IFN-g, TNF and granzyme B, which exert cytotoxic functions (36, 37) . Transcriptomic analysis of E. coli-and TCR-activated MAIT cells has shown distinct transcriptional reprogramming, including altered pathways, transcription factors and effector molecules, which has been validated by proteomics and metabolomics (38) . In E. coli -activated MAIT cells, the TWIST1 transcription factor has been identified as a key driver, showing high connectivity to cytokine and chemokine expression (38) .

Because MAIT cells are also involved in a number of inflammatory and autoimmune disorders as well as malignancies, they are attractive targets for therapeutic approaches (39) (40) (41) (42) (43) . The present paper aims to review the evidence indicating that MAIT cells may contribute to the pathogenesis of rheumatic diseases due to the possible role of MAIT cells in SLE, RA, PsA, ankylosing spondylitis (AS), SSc, pSS, systemic vasculitis, polymyalgia rheumatica and dermatomyositis ( Table 1) .

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease characterized by the production of autoantibodies to nuclear antigens. Blood MAIT cell frequency and absolute number are significantly lower in SLE patients than in healthy controls (HCs) (44) . Absolute MAIT cell numbers are correlated with age, lymphocyte count, and SLE disease activity index, indicating that MAIT cell levels may reflect disease activity in SLE. The percentage of IFN-g + MAIT cells is lower in SLE patients than in HCs, and IL-17 + or IL-4 + MAIT cell levels are similar between SLE patients and HCs (44) . IFN-g production by MAIT cells has been found to be mainly regulated by the nuclear factor of activated T cell (NFAT1) transcription factor, which is intrinsically defective in SLE patients. Moreover, MAIT cell frequency is significantly correlated with NKT cell frequency in SLE patients. In particular, a-GalCer-stimulated NKT cells show poor activation of MAIT cells in SLE patients in vitro, suggesting that NKT cell dysfunction influences MAIT cell dysfunction (44) . Another study has found that the reduced frequency of MAIT cells in peripheral blood is due to increased cell death, and the expression of activation marker CD69 is correlated with disease activity (45 (46) . In FcgRIIb -/-Yaa mice, an animal model of SLE, more MAIT cells are activated in the kidneys than in the spleen, and the proportions of IL-17-or IFN-g-expressing MAIT cells are higher in the kidneys than in the spleen. Furthermore, in MR1 -/lupus mice, MAIT cell deficiency results in reduced disease severity, as evidenced by decreased autoantibody production and lower glomerulonephritis scores, and these effects are accompanied by reduced germinal center responses as well as reduced T cell and innate T cell responses (46) . Researchers have also demonstrated that MAIT cells contribute to autoantibody production by B cells in vitro dependent on the CD40L-CD40 and TCR pathways (46) .

Rheumatoid arthritis (RA) is a systemic inflammatory disorder and is characterized by chronic, erosive synovitis of diarthrodial joints. Many studies have reported that the MAIT cell percentage is decreased in the peripheral blood of RA patients, and circulating absolute MAIT cell numbers can reflect disease activity in RA (44, 47, 48) . The synovial fluid of patients with RA has a higher percentage of MAIT cells than peripheral blood (44, 47) . In early, untreated RA patients, the distribution of MAIT cells shifts from CD8 + to CD4 + MAIT cells, and MAIT cells express lower levels of CD161. Furthermore, CD69 expression of MAIT cells is lower in RA patients compared to HCs, and MAIT cells are hyporesponsive as indicated by minimal upregulation of CD25 and CD69 in response to E. coli stimulation (48) . Peripheral blood and synovial fluid MAIT cells of RA patients produce more IL-17A compared to osteoarthritis (OA) patients on stimulation (49) . In a MAIT cell-deficient MR1 -/mouse model of arthritis, the disease severity of collagen-induced arthritis (CIA) is ameliorated, indicating that MAIT cells play a pathogenic role in RA (50) . In addition, MAIT cells augment arthritis mainly by enhancing inflammation in arthritis rather than by a type II collagen-specific response. In vitro, it is revealed that IL-1b induces the proliferation of MAIT cells, and IL-23 promotes the production of IL-17 by MAIT cells in the absence of TCR stimulation, indicating that cytokine-mediated MAIT cell activation contributes to the exacerbation of arthritis (50) .

Psoriatic arthritis (PsA) is a chronic inflammatory spondyloarthritis that occurs in combination with psoriasis and has related extraarticular manifestations. The frequency of MAIT cells in peripheral blood is lower in PsA patients than in OA patients, whereas a higher MAIT cell frequency is found in paired synovial fluid, suggesting that MAIT cells are recruited to joints (49) . Most MAIT cells in the synovial fluid of PsA patients are of CD8 + and the memory (CD45RO + ) phenotype. Synovial fluid MAIT cells of PsA patients produce significantly more IL-17A than those of RA and OA patients. Moreover, the expression of IL-23R in circulating MAIT cells is higher in PsA and RA patients than in OA patients and IL-23R is functionally active, as evidenced by the profound mitotic effect in the presence of rIL-23 (49) . These findings indicate that MAIT cells are likely to be part of the IL-23/IL-17 cytokine network in the pathogenesis of PsA.

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease characterized by abnormal ossification and ankylosis affecting the spine and sacroiliac joints. Peripheral blood MAIT cell frequency and number are reduced in AS patients compared with HCs; however, MAIT cell frequency does not correlate with disease activity (47, 51, 52 

Systemic sclerosis (SSc) is an immune-mediated rheumatic disease characterized by immune dysregulation and progressive fibrosis that affects the skin and internal organs. The peripheral blood MAIT cell frequency is decreased in patients with SSc compared to HCs (55) . However, the circulating MAIT cell frequency and absolute numbers do not correlate with C reactive protein (CRP), brain natriuretic protein, pulmonary involvement, median skin fibrosis scale, steroid amount or disease duration in patients with SSc.

Anti-neutrophil cytoplasmic autoantibodies (ANCA)-associated (AAV) is an autoimmune disease characterized by inflammation and necrosis of blood vessel walls, which is accompanied by the presence of ANCA antibodies in serum. AAV includes granulomatosis with polyangiitis (GPA), microscopic polyangiitis (MPA) and eosinophilic granulomatosis with polyangiitis (EGPA). The frequency of circulating MAIT cells is lower in patients with AAV compared to HCs, especially in MPA and GPA (56) . MAIT cells in peripheral blood from AAV patients in the acute and remission phases exhibit an activated phenotype as judged by their increased expression of CD69 (57) . The frequency of circulating MAIT cells that produce IFN-g is increased in MPA and GPA patients, while the frequency of TNF and IL-17-producing MAIT cells is similar in AAV patients compared to controls (57).

Giant cell arteritis (GCA) is an immune-mediated vasculitis characterized by granulomatous inflammation that affects medium-sized and large arteries. MAIT cells are present in the arterial wall of GCA patients while the percentage of circulating MAIT cells is similar between untreated GCA patients and controls (58) . The MAIT cells in GCA patients show decreased expression of CXCR3 and increased expression of IFN-g. The percentage of circulating IFN-g + MAIT cells does not decrease after glucocorticoid therapy. MAIT cells from GCA patients proliferate and produce higher amounts of IFN-g after treatment of IL-12 and IL-18, while the production of granzyme B and TNF is higher after activation of the TCR pathway. Polymyalgia rheumatica (PMR) is an inflammatory rheumatic disease characterized by pain and stiffness in the neck and pelvic girdle, which can occur independently or in association with giant cell arteritis. Among MAIT cells, the percentages of IFN-g + cells tend to be higher in PMR patients with active disease compared to patients with inactive disease, while the percentages of IL-17 + cells are comparable between the active and inactive patient groups. MAIT cells show greater activation in patients with PMR in remission than in controls and active patients as evidenced by a higher frequency of HLA-DR + CD38 + MAIT cells and CD69 + MAIT cells. Moreover, the frequency of HLA-DR + CD38 + MAIT cells is positively correlated with the PMR activity score and CRP level in patients in remission (59) .

Dermatomyositis (DM) is an inflammatory disorder, characterized by classical cutaneous manifestations and inflammation of skeletal muscle. The frequency of MAIT cells is decreased in active DM patients in comparison with HCs, and the frequency increases after treatment (60) . Reduced MAIT cell frequency is associated with increased expression of activation and exhaustion markers such as CD25, CD39 and CTLA4. There is no correlation between MAIT cell frequency and DM clinical scores or biological markers.

MAIT cells were observed to be decreased with an activated phenotype in peripheral blood in patients with rheumatic diseases; whether these changes are a cause or an effect remains to be established. Some studies have found that the frequency or the activation level of MAIT cells is consistent with disease severity (44, 51, 59) , indicating that MAIT cells may be potential biomarkers for rheumatic disease. However, longitudinal studies are needed to verify whether the MAIT cell population may recover after treatment. Homing of MAIT cells to inflamed tissues, as evidenced by high expression of chemokine receptors, and activation-induced cell death may contribute to the decrease in circulating MAIT cells. In patients with COVID-19, the frequency of pyroptotic MAIT cells rather than apoptotic MAIT cells is significantly increased, suggesting that activated MAIT cells may exhibit different forms of morbidity (61) . Furthermore, a previous study has shown that the CD3 + MR1-tetramer + MAIT cell frequency is similar in HCs and patients with RA and that CD161 is reduced in early RA patients, indicating that the gating strategy of CD3 + CD161 + Va7.2 + might be partially responsible for the reduction in MAIT cells (48) . Another study has also found CD161 is decreased in chronic HIV-1 infection and this Va7.2 + CD161population does not contain MAIT cells (62, 63) . Glucocorticoids have long been known to inhibit T cell proliferation and induce apoptosis (64) . It has been reported that circulating MAIT cell frequency is associated with oral corticosteroids in asthma patients and MAIT cells are deficient in the airways of steroid-treated chronic obstructive pulmonary disease patients (65, 66) . However, no significant correlations are found between circulating MAIT cell levels and use of steroids in SLE and GCA patients (44, 58) . This inconsistency could be attributed to different doses of glucocorticoids. More in vitro experiments and animal studies are needed to verify the effects of corticosteroids on MAIT cells. MAIT cell activation is observed in some rheumatic diseases and pro-inflammatory cytokines have been identified as potential activator of MAIT cells (45, 57, 59) . Is there the possibility that MR1 presents riboflavin derivatives or self-antigens to activate MAIT cells? The use of an inhibitory MR1 ligand to block MAIT cell activation and sterile environments may offer the potential to study the activation mechanism of MAIT cells in rheumatic diseases.

In most rheumatic diseases, IFN-g and TNF produced by circulating MAIT cells decrease, while IL-17 produced by MAIT cells increases in blood and tissues (Figure 2) , suggesting that MAIT cell proinflammatory IL-17 is biased in rheumatology similar to that in obesity and chronic liver disease (67) (68) (69) . IL-17 plays different pathological roles in some rheumatic diseases, like the promotion and perpetuation of inflammation and the damage to the affected tissues (70, 71) . Several therapeutic strategies targeting IL-17 have been approved for the treatment of PsA and AS. MAIT cells, as a source of IL-17, emerge in the mechanism of rheumatology and might be a promising therapeutic option. It remains to be determined whether MAIT cells are "friends or foes" in autoimmune responses. MAIT cells appeared with pathogenic roles in SLE and RA animal models; however, a protective role of MAIT cells in an animal model of multiple sclerosis has been observed (46, 50, 72) . In type 1 diabetes, MAIT cells show dual roles in maintaining gut barrier integrity by secreting IL-17A and IL-22 but promote b-cell death in the pancreas (73) . The effects of MAIT cells seems to be dependent on disease stages and their tissue localization, and MAIT cells may have other functions we do not yet know about due to the lack of known antigens of MAIT cells. More research is needed to further study the molecular mechanism of MAIT cells in rheumatic diseases, especially the MAIT cells recruited to affected organs. The cross-talk of MAIT cells and several immune cell subsets by secretion of cytokines and chemokines has been demonstrated (74) . Our team has found MAIT cells induce anti-inflammatory macrophage polarization by producing regulatory cytokines in nonalcoholic fatty liver disease (75) . MAIT cells increase plasmablasts and promote Ig production in vitro, and they are involved in autoantibody production by B cells in SLE (46, 76) . We speculate that these MAIT-B cell interactions may occur in B cell/autoantibody-driven disorders, such as pSS There is increasing evidence that microbiomes and metabolites play a vital role in the immunopathogenesis of rheumatic diseases (77, 78) . The reduced richness of microbial species and a reduced ratio of Firmicutes/Bacteroides in the gut are common features of rheumatic disease (79). As described above, microbiota-derived metabolites affect MAIT cell selection, expansion and function. In alcoholic liver disease, intestinal bacteria and metabolites drive selective MAIT cell depletion and dysfunction, whereas MAIT cells induce gut microbiota alterations in obesity model (80, 81) . Thus, there are a few questions to be answered. It remains unknown whether the intestinal flora and metabolites change first to cause alternation in the functions of MAIT cells, thereby contributing to the diseases. It is important to understand how microbiota affect the phenotype of MAIT cells, and how microbiota-metabolite-MAIT cell interactions shape adaptive immunity. More in-depth investigations are required to study the correlations among dysbiosis, MAIT cell responses and clinical symptoms. The relative abundance of microbiota and metabolites in diseases can be determined by metagenomic and metabolomics analysis. And it would be interesting to investigate whether fecal microbiota transplantation from rheumatic patients in mouse models results in MAIT cell activation and disease exacerbation.

In this review, we have summarized current evidence supporting the emerging roles for MAIT cells in rheumatology. It is imperative that we continue to elucidate the activation mechanisms and functions of MAIT cells to better understand pathogenesis of rhematic diseases. MAIT cell deficiency (MR1 -/-) and transgenic mice models, as wells as acetyl-6-formylpterin, a potent blocking MAIT cell molecule (82) , are the new tools to be used for further investigations. The analysis of the crosstalk between MAIT cells and other immune cells and the interactions between MAIT cells and microbiota will identify therapeutic targets and approaches for clinical intervention in the future.

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Single-Cell RNA Sequencing Reveals the Expansion of Cytotoxic CD4(+) T Lymphocytes and a Landscape of Immune Cells in Primary Sjögren's Syndrome

Analysis of T Cell Antigen Receptor (TCR) Expression by Human Peripheral Blood CD4-8-Alpha/Beta T Cells Demonstrates Preferential Use of Several V Beta Genes and an Invariant TCR Alpha Chain

An Invariant T Cell Receptor Alpha Chain Defines a Novel TAP-Independent Major Histocompatibility Complex Class Ib-Restricted Alpha/Beta T Cell Subpopulation in Mammals

Selection of Evolutionarily Conserved Mucosal-Associated Invariant T Cells by MR1

Human Blood MAIT Cell Subsets Defined Using MR1 Tetramers

Identification of Phenotypically and Functionally Heterogeneous Mouse Mucosal-Associated Invariant T Cells Using MR1 Tetramers

The CD4(-)CD8(-) MAIT Cell Subpopulation is a Functionally Distinct Subset Developmentally Related to the Main CD8(+) MAIT Cell Pool

MR1 Presents Microbial Vitamin B Metabolites to MAIT Cells

T-Cell Activation by Transitory Neo-Antigens Derived From Distinct Microbial Pathways

Antigen-Loaded MR1 Tetramers Define T Cell Receptor Heterogeneity in Mucosal-Associated Invariant T Cells

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Stepwise Development of MAIT Cells in Mouse and Human

A Three-Stage Intrathymic Development Pathway for the Mucosal-Associated Invariant T Cell Lineage

Multiple Layers of Heterogeneity and Subset Diversity in Human MAIT Cell Responses to Distinct Microorganisms and to Innate Cytokines

IL-7 Licenses Activation of Human Liver Intrasinusoidal Mucosal-Associated Invariant T Cells

CD161(int)CD8+ T Cells: A Novel Population of Highly Functional, Memory CD8+ T Cells Enriched Within the Gut

MAIT Cells Reside in the Female Genital Mucosa and are Biased Towards IL-17 and IL-22 Production in Response to Bacterial Stimulation

Microbial Metabolites Control the Thymic Development of Mucosal-Associated Invariant T Cells

MicroRNA miR-181a/B-1 Controls MAIT Cell Development

The Biology and Functional Importance of MAIT Cells

Differential Controls of MAIT Cell Effector Polarization by Mtorc1/Mtorc2 via Integrating Cytokine and Costimulatory Signals

BCL11B is Positioned Upstream of PLZF and Rorgt to Control Thymic Development of Mucosal-Associated Invariant T Cells and MAIT17 Program. iScience

MicroRNA-155 Regulates MAIT1 and MAIT17 Cell Differentiation

Single-Cell RNA Sequencing Identifies Shared Differentiation Paths of Mouse Thymic Innate T Cells

Mucosal-Associated Invariant T-Cell Activation and Accumulation After In Vivo Infection Depends on Microbial Riboflavin Synthesis and Co-Stimulatory Signals

MAIT Cell Development and Functions: The Microbial Connection

Recognition of Vitamin B Metabolites by Mucosal-Associated Invariant T Cells

MAIT Cells are Imprinted by the Microbiota in Early Life and Promote Tissue Repair

Acquisition of Innate-Like Microbial Reactivity in Mucosal Tissues During Human Fetal MAIT-Cell Development

MAIT Cells in Infectious Diseases

MAIT Cells are Activated During Human Viral Infections

CD161++ CD8+ T Cells, Including the MAIT Cell Subset, are Specifically Activated by IL-12+IL-18 in a TCR-Independent Manner

MAIT Cells in Metabolic Diseases

Mucosal-Associated Invariant T Cells in Autoimmune Diseases

Partners or Enemies in Cancer Immunotherapy? Cancers (Basel) (2021)

Mucosal-Associated Invariant T Cells and Disease

MAIT Cells in Health and Disease

Mucosal-Associated Invariant T Cell Deficiency in Systemic Lupus Erythematosus

Activation Status of Mucosal-Associated Invariant T Cells Reflects Disease Activity and Pathology of Systemic Lupus Erythematosus

A Critical Role for Mucosal-Associated Invariant T Cells as Regulators and Therapeutic Targets in Systemic Lupus Erythematosus

IL-7 Primes IL-17 in Mucosal-Associated Invariant T (MAIT) Cells, Which Contribute to the Th17-Axis in Ankylosing Spondylitis

Altered Composition and Phenotype of Mucosal-Associated Invariant T Cells in Early Untreated Rheumatoid Arthritis

Functional Significance of MAIT Cells in Psoriatic Arthritis

Mucosal-Associated Invariant T Cells Promote Inflammation and Exacerbate Disease in Murine Models of Arthritis

Involvement of Mucosal-Associated Invariant T Cells in Ankylosing Spondylitis

Increased IL-22-and IL-17a-Producing Mucosal-Associated Invariant T Cells in the Peripheral Blood of Patients With Ankylosing Spondylitis

Mucosal-Associated Invariant T Cells are Reduced and Functionally Immature in the Peripheral Blood of Primary Sjögren's Syndrome Patients

IL-17 Polarization of MAIT Cells is Derived From the Activation of Two Different Pathways

Mucosal-Associated Invariant Cells are Deficient in Systemic Sclerosis

Alterations in Circulating Lymphoid Cell Populations in Systemic Small Vessel Vasculitis are non-Specific Manifestations of Renal Injury

Persistent Deficiency of Circulating Mucosal-Associated Invariant T (MAIT) Cells in ANCA-Associated Vasculitis

Mucosal-Associated Invariant T Cells in Giant Cell Arteritis

Association of Mucosal-Associated Invariant T Cells With Different Disease Phases of Polymyalgia Rheumatica

Single-Cell Transcriptomic Profiling of MAIT Cells in Patients With COVID-19

Activation, Exhaustion, and Persistent Decline of the Antimicrobial MR1-Restricted MAIT-Cell Population in Chronic HIV-1 Infection

Cells are Depleted Early But Retain Functional Cytokine Expression in HIV Infection

Analysis of Susceptibility of Mature Human T Lymphocytes to Dexamethasone-Induced Apoptosis

Steroid-Induced Deficiency of Mucosal-Associated Invariant T Cells in the Chronic Obstructive Pulmonary Disease Lung. Implications for Nontypeable Haemophilus Influenzae Infection

Innate and Adaptive T Cells in Asthmatic Patients: Relationship to Severity and Disease Mechanisms

Altered Distribution and Increased IL-17 Production by Mucosal-Associated Invariant T Cells in Adult and Childhood Obesity

Mucosal-Associated Invariant T Cells are a Profibrogenic Immune Cell Population in the Liver

MAIT Cells are Chronically Activated in Patients With Autoimmune Liver Disease and Promote Profibrogenic Hepatic Stellate Cell Activation

The IL-23-IL-17 Axis in Inflammatory Arthritis

Blocking IL-17: A Promising Strategy in the Treatment of Systemic Rheumatic Diseases

Invariant V (alpha)19i T Cells Regulate Autoimmune Inflammation

Cytotoxic and Regulatory Roles of Mucosal-Associated Invariant T Cells in Type 1 Diabetes

The Immune Modulating Properties of Mucosal-Associated Invariant T Cells

Mucosal-Associated Invariant T Cells Improve Nonalcoholic Fatty Liver Disease Through Regulating Macrophage Polarization

Human Mucosal-Associated Invariant T (MAIT) Cells Possess Capacity for B Cell Help

The Metabolic Role of the Gut Microbiota in Health and Rheumatic Disease: Mechanisms and Interventions

The Microbiome in Autoimmune Rheumatic Disease

MAIT Cells and Microbiota in Multiple Sclerosis and Other Autoimmune Diseases

Mucosa-Associated Invariant T Cells Link Intestinal Immunity With Antibacterial Immune Defects in Alcoholic Liver Disease

Mucosal-Associated Invariant T Cells Promote Inflammation and Intestinal Dysbiosis Leading to Metabolic Dysfunction During Obesity

A Molecular Basis Underpinning the T Cell Receptor Heterogeneity of Mucosal-Associated Invariant T Cells

Conflict of Interest: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest

YL and JD wrote the manuscript. WW provided the feedback. All authors contributed to the article and approved the submitted version.