MAIT cells and pathogen defense

Fluoride induces immunotoxicity by regulating riboflavin transport and metabolism partly through IL-17A in the spleen

The impairment of the immune system by fluoride is a public health concern worldwide, yet the underlying mechanism is unclear. Both riboflavin and IL-17A are closely related to immune function and regulate the testicular toxicity of fluoride. However, whether riboflavin or IL-17A is involved in fluoride-induced immunotoxicity is unknown. Here, we first established a male ICR mouse model by treating mice with sodium fluoride (NaF) (100 mg/L) via the drinking water for 91 days. The results showed that fluoride increased the expression of the proinflammatory factors IL-1β and IL-17A, which led to splenic inflammation and morphological injury. Moreover, the expression levels of the riboflavin transporters SLC52A2 and SLC52A3; the transformation-related enzymes RFK and FLAD1; and the key mitochondrial functional determinants SDH, COX, and ATP in the spleen were measured via real-time PCR, Western blotting, and ELISA. The results revealed that fluoride disrupted riboflavin transport, transformation, metabolism, and mitochondrial function. Furthermore, wild-type (WT) and IL-17A knockout (IL-17A-/-) C57BL/6 J male mice of the same age were treated with NaF (24 mg/kg·bw, equivalent to 100 mg/L) and/or riboflavin sodium phosphate (5 mg/kg·bw) via gavage for 91 days. Similar parameters were evaluated as above. The results confirmed that fluoride increased riboflavin metabolism through RFK but not through FLAD1. Fluoride also affected mitochondrial function and activated neutrophils (marked with Ly6g) and macrophages (marked with CD68) in the spleen. Interestingly, IL-17A partly mediated fluoride-induced riboflavin metabolism disorder and immunotoxicity in the spleen. This work not only reveals a novel toxic mechanism for fluoride but also provides new clues for exploring the physiological function of riboflavin and for diagnosing and treating the toxic effects of fluoride in the environment.

Navigating ESKAPE Pathogens: Considerations and Caveats for Animal Infection Models Development

The misuse of antibiotics has led to the global spread of drug-resistant bacteria, especially multi-drug-resistant (MDR) ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). These opportunistic bacteria pose a significant threat, in particular within hospitals, where they cause nosocomial infections, leading to substantial morbidity and mortality. To comprehensively explore ESKAPE pathogenesis, virulence, host immune response, diagnostics, and therapeutics, researchers increasingly rely on necessitate suitable animal infection models. However, no single model can fully replicate all aspects of infectious diseases. Notably when studying opportunistic pathogens in immunocompetent hosts, rapid clearance by the host immune system can limit the expression of characteristic disease symptoms. In this study, we examine the critical role of animal infection models in understanding ESKAPE pathogens, addressing limitations and research gaps. We discuss applications and highlight key considerations for effective models. Thoughtful decisions on disease replication, parameter monitoring, and data collection are crucial for model reliability. By meticulously replicating human diseases and addressing limitations, researchers maximize the potential of animal infection models. This aids in targeted therapeutic development, bridges knowledge gaps, and helps combat MDR ESKAPE pathogens, safeguarding public health.

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.

Characterization of Mucosal-Associated Invariant T Cells in Oral Lichen Planus

Oral lichen planus (OLP) is an inflammatory condition of unknown cause that has been associated with concurrent candidal infection. Mucosal-associated invariant T (MAIT) cells express the T cell receptor TCRVα7.2 and are activated by riboflavin intermediates produced by microbes. The interaction between MAIT cells, Candida, and OLP is unknown. This study aimed to determine mucosal-associated T cell presence in OLP and whether the abundance of these cells changed due to the presence of either Candida or symptoms, using multiplex immunohistochemistry (mIHC). Ninety formalin fixed-paraffin-embedded (FFPE) tissue samples were assessed using mIHC for the cellular markers CD3, interleukin 18 receptor one (IL18R1), TCRVα7.2, CD161, CD8, and major histocompatibility complex class I-related (MR-1) protein. The samples were stratified into five groups on the basis of clinical (presence/absence of symptoms) and microbiological (presence/absence of Candida) criteria. Results demonstrated the presence of MAIT cell phenotypes in OLP inflammatory infiltrate within the connective tissue. Significant differences existed between different OLP groups with the percentage of log(CD3+ CD161+) and log(CD3+ TCRVα7.2+) positive cells (p < 0.001 and p = 0.005 respectively). Significant differences also existed with the relative abundance of triple-stained log(CD3+ CD161+ IL18R1+) cells (p = 0.004). A reduction in log(CD3+ CD161+ IL18R1+) cells was observed in lesional tissue of patients with symptomatic OLP with and without Candida when compared to controls. When present in OLP, MAIT cells were identified within the connective tissue. This study demonstrates that mIHC can be used to identify MAIT cell phenotypes in OLP. Reduced percentage of log(CD3+ CD161+ IL18R1+) cells seen in symptomatic OLP with and without Candida suggests a role for these cells in OLP pathogenesis.

Innate immunity and early liver inflammation

The innate system constitutes a first-line defence mechanism against pathogens. 80% of the blood supply entering the human liver arrives from the splanchnic circulation through the portal vein, so it is constantly exposed to immunologically active substances and pathogens from the gastrointestinal tract. Rapid neutralization of pathogens and toxins is an essential function of the liver, but so too is avoidance of harmful and unnecessary immune reactions. This delicate balance of reactivity and tolerance is orchestrated by a diverse repertoire of hepatic immune cells. In particular, the human liver is enriched in many innate immune cell subsets, including Kupffer cells (KCs), innate lymphoid cells (ILCs) like Natural Killer (NK) cells and ILC-like unconventional T cells - namely Natural Killer T cells (NKT), γδ T cells and Mucosal-associated Invariant T cells (MAIT). These cells reside in the liver in a memory-effector state, so they respond quickly to trigger appropriate responses. The contribution of aberrant innate immunity to inflammatory liver diseases is now being better understood. In particular, we are beginning to understand how specific innate immune subsets trigger chronic liver inflammation, which ultimately results in hepatic fibrosis. In this review, we consider the roles of specific innate immune cell subsets in early inflammation in human liver disease.

The relationship between nutrition and the immune system

Nutrition plays an essential role in the regulation of optimal immunological response, by providing adequate nutrients in sufficient concentrations to immune cells. There are a large number of micronutrients, such as minerals, and vitamins, as well as some macronutrients such as some amino acids, cholesterol and fatty acids demonstrated to exert a very important and specific impact on appropriate immune activity. This review aims to summarize at some extent the large amount of data accrued to date related to the modulation of immune function by certain micro and macronutrients and to emphasize their importance in maintaining human health. Thus, among many, some relevant case in point examples are brought and discussed: (1) The role of vitamin A/all-trans-retinoic-acids (ATRA) in acute promyelocytic leukemia, being this vitamin utilized as a very efficient therapeutic agent via effective modulation of the immune function (2) The involvement of vitamin C in the fight against tumor cells via the increase of the number of active NK cells. (3) The stimulation of apoptosis, the suppression of cancer cell proliferation, and delayed tumor development mediated by calcitriol/vitamin D by means of immunity regulation (4) The use of selenium as a cofactor to reach more effective immune response to COVID vaccination (5). The crucial role of cholesterol to regulate the immune function, which is demonstrated to be very sensitive to the variations of this macronutrient concentration. Other important examples are reviewed as well.

MAIT cells ameliorate liver fibrosis by enhancing the cytotoxicity of NK cells in cholestatic murine models

BACKGROUND AND AIMS

Mucosal-associated invariant T (MAIT) cells are innate-like lymphocytes that display a critical role in various liver diseases. However, the role of MAIT cells in cholestatic liver fibrogenesis remains obscure. Our study aims to assess the contribution of MAIT cells and underlying mechanisms during this process.

METHODS

Cholestatic murine models using MAIT cell-deficient (MR1^- /^- ) and wild-type (WT) mice were established by feeding a 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC)-enriched diet or bile duct ligation (BDL). Liver samples were collected to determine the severity of fibrosis. Lymphocytes of the liver were isolated for analysing the phenotype and function of MAIT cells. Cell co-culture experiments were performed to investigate the cross-talk between MAIT and NK cells.

RESULTS

Liver MAIT cells were more activated with increased cytokines in cholestatic mice models than in control mice, although their frequency was decreased. MAIT cell deficiency led to severe liver inflammation and fibrosis with more activated HSCs in cholestatic mice. In addition, MR1^- /^- mice had an increased frequency of NK cells with higher expression of stimulatory receptors relative to WT mice. Paradoxically, activated MAIT cells significantly promoted the anti-fibrotic ability of NK cells by enhancing their cytotoxicity against HSCs in co-culture experiments. Importantly, this effect depended on direct cell-cell contact and TNF-α produced by MAIT cells.

CONCLUSION

Our findings indicate that MAIT cells ameliorate cholestatic liver fibrosis by enhancing the cytotoxicity of NK cells against HSCs. An in-depth understanding of the MAIT cell-mediated regulatory effect will provide more valuable immunotherapy strategies to treat liver fibrosis.

Exploring the Immune-Boosting Functions of Vitamins and Minerals as Nutritional Food Bioactive Compounds: A Comprehensive Review

Food components have long been recognized to play a fundamental role in the growth and development of the human body, conferring protective functionalities against foreign matter that can be severe public health problems. Micronutrients such as vitamins and minerals are essential to the human body, and individuals must meet their daily requirements through dietary sources. Micronutrients act as immunomodulators and protect the host immune response, thus preventing immune evasion by pathogenic organisms. Several experimental investigations have been undertaken to appraise the immunomodulatory functions of vitamins and minerals. Based on these experimental findings, this review describes the immune-boosting functionalities of micronutrients and the mechanisms of action through which these functions are mediated. Deficiencies of vitamins and minerals in plasma concentrations can lead to a reduction in the performance of the immune system functioning, representing a key contributor to unfavorable immunological states. This review provides a descriptive overview of the characteristics of the immune system and the utilization of micronutrients (vitamins and minerals) in preventative strategies designed to reduce morbidity and mortality among patients suffering from immune invasions or autoimmune disorders.

Monkeying around with MAIT Cells: Studying the Role of MAIT Cells in SIV and Mtb Co-Infection

There were an estimated 10 million new cases of tuberculosis (TB) disease in 2019. While over 90% of individuals successfully control Mycobacterium tuberculosis (Mtb) infection, which causes TB disease, HIV co-infection often leads to active TB disease. Despite the co-endemic nature of HIV and TB, knowledge of the immune mechanisms contributing to the loss of control of Mtb replication during HIV infection is lacking. Mucosal-associated invariant T (MAIT) cells are innate-like T cells that target and destroy bacterially-infected cells and may contribute to the control of Mtb infection. Studies examining MAIT cells in human Mtb infection are commonly performed using peripheral blood samples. However, because Mtb infection occurs primarily in lung tissue and lung-associated lymph nodes, these studies may not be fully translatable to the tissues. Additionally, studies longitudinally examining MAIT cell dynamics during HIV/Mtb co-infection are rare, and lung and lymph node tissue samples from HIV+ patients are typically unavailable. Nonhuman primates (NHP) provide a model system to characterize MAIT cell activity during Mtb infection, both in Simian Immunodeficiency Virus (SIV)-infected and SIV-naïve animals. Using NHPs allows for a more comprehensive understanding of tissue-based MAIT cell dynamics during infection with both pathogens. NHP SIV and Mtb infection is similar to human HIV and Mtb infection, and MAIT cells are phenotypically similar in humans and NHPs. Here, we discuss current knowledge surrounding MAIT cells in SIV and Mtb infection, how SIV infection impairs MAIT cell function during Mtb co-infection, and knowledge gaps to address.

Human endometrial MAIT cells are transiently tissue resident and respond to Neisseria gonorrhoeae

Mucosa-associated invariant T (MAIT) cells are non-classical T cells important in the mucosal defense against microbes. Despite an increasing interest in the immunobiology of the endometrial mucosa, little is known regarding human MAIT cells in this compartment. The potential role of MAIT cells as a tissue-resident local defense against microbes in the endometrium is largely unexplored. Here, we performed a high-dimensional flow cytometry characterization of MAIT cells in endometrium from pre- and postmenopausal women, and in decidua from first-trimester pregnancies. Furthermore, we assessed MAIT cell function by stimulation with Neisseria gonorrhoeae (N. gonorrhoeae). Endometrial MAIT (eMAIT) cells represented a stable endometrial immune cell population as limited dynamic changes were observed during the menstrual cycle, post menopause, or in response to pregnancy. Furthermore, eMAIT cells exhibited an activated tissue-resident phenotype. Despite expressing CD69 and CD103, eMAIT cells were replenished over time by circulating MAIT cells, as assessed using human uterus transplantation as a model. Finally, functional experiments revealed the capability of MAIT cells to respond to the sexually transmitted and tissue-relevant pathogen, N. gonorrhoeae. In conclusion, our study provides novel insight into human MAIT cell dynamics and anti-microbial properties in the human uterus.

Adults from Kisumu, Kenya have robust γδ T cell responses to Schistosoma mansoni, which are modulated by tuberculosis

Schistosoma mansoni (SM) is a parasitic helminth that infects over 200 million people and causes severe morbidity. It undergoes a multi-stage life cycle in human hosts and as such stimulates a stage-specific immune response. The human T cell response to SM is complex and varies throughout the life cycle of SM. Relative to the wealth of information regarding the immune response to SM eggs, little is known about the immune response to the adult worm. In addition, while a great deal of research has uncovered mechanisms by which co-infection with helminths modulates immunity to other pathogens, there is a paucity of data on the effect of pathogens on immunity to helminths. As such, we sought to characterize the breadth of the T cell response to SM and determine whether co-infection with Mycobacterium tuberculosis (Mtb) modifies SM-specific T cell responses in a cohort of HIV-uninfected adults in Kisumu, Kenya. SM-infected individuals were categorized into three groups by Mtb infection status: active TB (TB), Interferon-γ Release Assay positive (IGRA+), and Interferon-γ Release Assay negative (IGRA-). U.S. adults that were seronegative for SM antibodies served as naïve controls. We utilized flow cytometry to characterize the T cell repertoire to SM egg and worm antigens. We found that T cells had significantly higher proliferation and cytokine production in response to worm antigen than to egg antigen. The T cell response to SM was dominated by γδ T cells that produced TNFα and IFNγ. Furthermore, we found that in individuals infected with Mtb, γδ T cells proliferated less in response to SM worm antigens and had higher IL-4 production compared to naïve controls. Together these data demonstrate that γδ T cells respond robustly to SM worm antigens and that Mtb infection modifies the γδ T cell response to SM.

Schistosomiasis, a disease caused by parasitic helminths including Schistosoma mansoni (SM), affects hundreds of millions of people globally. SM undergoes a complex life cycle within humans resulting in adult worm pairs that release eggs into the circulatory system. The human immune response to SM, especially to adult worms, is not well characterized. In addition, the impact of co-infections, which are common in SM endemic regions, on the immune response to SM is unknown. In this study, we first sought to characterize the T cell response to different stages of the SM life cycle. We next evaluated whether T cell responses to SM were altered in the setting of co-infection with Mycobacterium tuberculosis, the bacteria that causes tuberculosis. We determined that human T cell responses to SM adult worm antigen are more robust than to SM egg antigen. This response is dominated by a non-classical T cell subset of γδ T cells producing IFNγ and TNFα. Lastly, we found that the ability of γδ T cells to proliferate in response to SM worm was lower in individuals with tuberculosis compared to naïve controls. This study provides novel insights into the immune response to SM and how tuberculosis may impair SM immunity.

MAIT cell subtypes in multiple sclerosis

In patients with multiple sclerosis (MS) and healthy controls (HC) we studied circulating MAIT cells and MAIT cell subtypes expressing CXCR3 and CCR6 by flow cytometry. Absolute numbers of MAIT cells and specifically Tc17-like MAIT cells were lower in patients with primary progressive MS (PPMS) than in controls. Low numbers of Tc17-like MAIT cells were associated with smoking and high concentrations of myelin basic protein in the cerebrospinal fluid. Treatment with alemtuzumab and dimethyl fumarate decreased MAIT cell frequencies. Altogether, we have identified specific MAIT cell subtypes related to PPMS, smoking and demyelination, and MAIT cell effects of MS therapies.

Microbiota of MR1 deficient mice confer resistance against Clostridium difficile infection

Clostridium difficile (Cd) infection (CDI) typically occurs after antibiotic usage perturbs the gut microbiota. Mucosa-associated invariant T cells (MAIT) are found in the gut and their development is dependent on Major histocompatibility complex-related protein 1 (MR1) and the host microbiome. Here we were interested in determining whether the absence of MR1 impacts resistance to CDI. To this end, wild-type (WT) and MR1-/- mice were treated with antibiotics and then infected with Cd spores. Surprisingly, MR1-/- mice exhibited resistance to Cd colonization. 16S rRNA gene sequencing of feces revealed inherent differences in microbial composition. This colonization resistance was transferred from MR1-/- to WT mice via fecal microbiota transplantation, suggesting that MR1-dependent factors influence the microbiota, leading to CDI susceptibility.

The immunopathogenesis of oral lichen planus-Is there a role for mucosal associated invariant T cells?

Oral lichen planus (OLP) is a chronic, T-cell-mediated, immune condition of unknown cause. OLP may present with painful symptoms requiring treatment, as well as lesions outside the oral cavity. It is likely that what initiates the OLP disease process is a complex interaction of host susceptibility and environmental triggers. While it is possible that OLP represents a true autoimmune condition against an epithelial autoantigen, the mechanisms that lead to this immune dysregulation are still poorly understood. In this review article, we discuss current concepts relating to the immunopathogenesis of OLP, as well as the potential contributory roles the oral microbiota and mucosal-associated invariant T (MAIT) cells.

Differences in the molecular signatures of mucosal-associated invariant T cells and conventional T cells

Mucosal-associated invariant T (MAIT) cells exhibit different characteristics from those of TCRα7.2⁻ conventional T cells. They play important roles in various inflammatory diseases, including rheumatoid arthritis and inflammatory bowel disease. MAIT cells express a single T cell receptor alpha chain, TCRα7.2 segment associated with Jα33 and CDR3 with fixed length, which recognizes bacteria-derived vitamin B metabolites. However, the characteristics of MAIT cells and TCRα7.2⁺ CD161⁻ T cells have never been compared. Here, we performed RNA sequencing to compare the properties of MAIT cells, TCRα7.2⁻ conventional T cells and TCRα7.2⁺ CD161⁻ T cells. Genome-wide transcriptomes of MAIT cells, TCRα7.2⁻ conventional T cells, and TCRα7.2⁺ CD161⁻ T cells were compared and analyzed using causal network analysis. This is the first report comparing the transcriptomes of MAIT cells, TCRα7.2⁻ conventional T cells and TCRα7.2⁺ CD161⁻ T cells. We also identified the predominant signaling pathways of MAIT cells, which differed from those of TCRα7.2⁻ conventional T cells and TCRα7.2⁺ CD161⁻ T cells, through a gene set enrichment test and upstream regulator analysis and identified the genes responsible for the characteristic MAIT cell phenotypes. Our study advances the complete understanding of MAIT biology.

Immunomodulation by food: impact on gut immunity and immune cell function

Recent studies have revealed that various food components affect the immune response. These components act on various immune cells, and their effects are mediated through the intestinal immune system and, in some cases, the intestinal microbiota. In this review, we describe the immunomodulating effects of various food components, including probiotics, prebiotics, polysaccharides, vitamins, minerals, fatty acids, peptides, amino acids and polyphenols. Some of these components enhance immune responses, leading to host defense against infection, whereas others inhibit immune responses, thus suppressing allergy and inflammation.

Role of MAIT cells in the immunopathogenesis of inflammatory diseases: New players in old game

Current advances in immunology have led to the identification of a population of novel innate immune T cells, called mucosa-associated invariant T (MAIT) cells. The cells in humans express an invariant TCRα chain (Vα7.2-Jα33) paired with a limited subset of TCRβ chains (Vβ2, 13 and 22), are restricted by the MHC class I (MH1)-related (MR)-1, and recognize molecules that are produced in the bacterial riboflavin (vitamin B2) biosynthetic pathway. They are present in the circulation, liver and at various mucosal sites (i.e. intestine, lungs and female reproductive tract, etc.). They kill host cells infected with bacteria and yeast, and secrete soluble mediators such as TNF-α, IFN-γ, IL-17, etc. The cells regulate immune responses and inflammation associated with a wide spectrum of acute and chronic diseases in humans. Since their discovery in 1993, significant advances have been made in understanding biology of MAIT cells and the potential role of these cells in the pathogenesis of autoimmune, inflammatory and infectious diseases as well as cancer in humans. The purpose of this review is to provide a current state of our knowledge about MAIT cell biology and delineate their role in autoimmune and inflammatory diseases (sterile or caused by infectious agents) and cancer in humans. A better understanding of the role of MAIT cells in human diseases may lead to novel ways of immunotherapies.

Animal Models of Tuberculosis: An Overview

This article provides an overview of the animal models currently used in tuberculosis research, both for understanding the basic science of the disease process and also for practical issues such as testing new vaccine candidates and evaluating the activity of potential new drugs. Animals range in size, from zebrafish to cattle, and in degrees of similarity to the human disease from both an immunological and pathologic perspective. These models have provided a great wealth of information (impossible to obtain simply from observing infected humans), but we emphasize here that one must use care in interpreting or applying this information, and indeed the true art of animal modeling is in deciding what is pertinent information and what might not be. These ideas are discussed in the context of current approaches in vaccine and drug development, including a discussion of certain limitations the field is currently facing in such studies.

Stabilizing short-lived Schiff base derivatives of 5-aminouracils that activate mucosal-associated invariant T cells

Mucosal-associated invariant T (MAIT) cells are activated by unstable antigens formed by reactions of 5-amino-6-D-ribitylaminouracil (a vitamin B2 biosynthetic intermediate) with glycolysis metabolites such as methylglyoxal. Here we show superior preparations of antigens in dimethylsulfoxide, avoiding their rapid decomposition in water (t_1/2 1.5 h, 37 °C). Antigen solution structures, MAIT cell activation potencies (EC₅₀ 3–500 pM), and chemical stabilities are described. Computer analyses of antigen structures reveal stereochemical and energetic influences on MAIT cell activation, enabling design of a water stable synthetic antigen (EC₅₀ 2 nM). Like native antigens, this antigen preparation induces MR1 refolding and upregulates surface expression of human MR1, forms MR1 tetramers that detect MAIT cells in human PBMCs, and stimulates cytokine expression (IFNγ, TNF) by human MAIT cells. These antigens also induce MAIT cell accumulation in mouse lungs after administration with a co-stimulant. These chemical and immunological findings provide new insights into antigen properties and MAIT cell activation.

MAIT cells are activated by MR1 restricted antigens derived from riboflavin biosynthesis. Here the authors characterize MAIT cell antigenicity and synthesize a water stable antigen that activates human MAIT cells in vitro and mouse MAIT cells in vivo.

The Specific Roles of Vitamins in the Regulation of Immunosurveillance and Maintenance of Immunologic Homeostasis in the Gut

Vitamins are micronutrients which are essential for the maintenance of biological responses including immune system. Hence, vitamin deficiency increases a risk of infectious, allergic, and inflammatory diseases. Accumulating evidence has recently revealed the molecular and cellular mechanisms of vitamin-mediated regulation in the active and quiescent immune responses. In this review, we focus on the immunologic roles of vitamins in the regulation of homeostasis and surveillance in the gut.

The effects of vitamin B on the immune/cytokine network and their involvement in depression

Increasing evidence indicates that there are various interactions between the nervous system and the immune system, and that the immune system plays an important role in the pathogenesis of depression. Pro-inflammatory cytokines (such as IL-1, IL-6, TNF-α) have been implicated in the neurobiological manifestations of depression. The immune/cytokine network has a powerful influence on the brain. In addition, deficiency in B vitamins has been linked to depression. Hence, greater knowledge of how immune cells change in the presence of vitamin B derivatives could improve understanding of how immune changes may correlate with depression, all of which are discussed herein.

MAIT cells promote inflammatory monocyte differentiation into dendritic cells during pulmonary intracellular infection

Cowley and Meierovics show that mucosa-associated invariant T (MAIT) cells promote the differentiation of monocytes into monocyte-derived dendritic cells during Francisella tularensis LVS pulmonary infection.

Mucosa-associated invariant T (MAIT) cells are a unique innate T cell subset that is necessary for rapid recruitment of activated CD4⁺ T cells to the lungs after pulmonary F. tularensis LVS infection. Here, we investigated the mechanisms behind this effect. We provide evidence to show that MAIT cells promote early differentiation of CCR2-dependent monocytes into monocyte-derived DCs (Mo-DCs) in the lungs after F. tularensis LVS pulmonary infection. Adoptive transfer of Mo-DCs to MAIT cell–deficient mice (MR1^−/− mice) rescued their defect in the recruitment of activated CD4⁺ T cells to the lungs. We further demonstrate that MAIT cell–dependent GM-CSF production stimulated monocyte differentiation in vitro, and that in vivo production of GM-CSF was delayed in the lungs of MR1^−/− mice. Finally, GM-CSF–deficient mice exhibited a defect in monocyte differentiation into Mo-DCs that was phenotypically similar to MR1^−/− mice. Overall, our data demonstrate that MAIT cells promote early pulmonary GM-CSF production, which drives the differentiation of inflammatory monocytes into Mo-DCs. Further, this delayed differentiation of Mo-DCs in MR1^−/− mice was responsible for the delayed recruitment of activated CD4⁺ T cells to the lungs. These findings establish a novel mechanism by which MAIT cells function to promote both innate and adaptive immune responses.

The role of mucosal-associated invariant T cells in infectious diseases

Mucosal-associated invariant T (MAIT) cells are donor-unrestricted lymphocytes that are surprisingly abundant in humans, representing 1-10% of circulating T cells and further enriched in mucosal tissues. MAIT cells recognize and are activated by small molecule ligands produced by microbes and presented by MR1, a highly conserved MHC-related antigen-presenting protein that is ubiquitously expressed in human cells. Increasing evidence suggests that MAIT cells play a protective role in anti-bacterial immunity at mucosal interfaces. Some fungi are known to produce MAIT-activating ligands, but the role of MAIT cells in fungal infections has not yet been investigated. In viral infections, specifically HIV, which has received the most study, MAIT cell biology is clearly altered, but the mechanisms explaining these alterations and their clinical significance are not yet understood. Many questions remain unanswered about the potential of MAIT cells for protection or pathogenesis in infectious diseases. Because they interact with the universal, donor-unrestricted ligand-presenting MR1 molecule, MAIT cells may be attractive immunotherapy or vaccine targets. New tools, including the development of MR1-ligand tetramers and next-generation T-cell receptor sequencing, have the potential to accelerate MAIT cell research and lead to new insights into the role of this unique set of lymphocytes in infectious diseases.

Circulating and tumor-infiltrating mucosal associated invariant T (MAIT) cells in colorectal cancer patients

Mucosal associated invariant T (MAIT) cells are important for immune defense against infectious pathogens and regulate the pathogenesis of various inflammatory diseases. However, their roles in the development of colorectal cancer (CRC) are still unclear. This study examined the phenotype, distribution, clinical relevance and potential function of MAIT cells in CRC patients. We found that the percentages of circulating memory CD8⁺ MAIT cells were significantly reduced while tumor infiltrating MAIT cells were increased, especially in patients with advanced CRC. The serum CEA levels were positively correlated with the percentages of tumor infiltrating MAIT cells in CRC patients, but negatively correlated with the percentages of circulating MAIT in advanced CRC patients. Activated circulating MAIT cells from CRC patients produced lower IFN-γ, but higher IL-17. Furthermore, higher levels of Vα7.2-Jα33, IFN-γ and IL-17A were expressed in the CRC tissues. Co-culture of activated MAIT cells with HCT116 cells enhanced IL-17 expression and induced HCT116 cell cycle arrest at G2/M phase in a contact- and dose-dependent manner, which was abrogated by treatment with anti-MR1. Therefore, MAIT cells preferably infiltrate into the solid tumor in CRC patients and may participate in the immune surveillance of CRC.

Mucosal-Associated Invariant T Cells in the Human Gastric Mucosa and Blood: Role in Helicobacter pylori Infection

Mucosal-associated invariant T (MAIT) cells represent a class of antimicrobial innate-like T cells that have been characterized in human blood, liver, lungs, and intestine. Here, we investigated, for the first time, the presence of MAIT cells in the stomach of children, adults, and the elderly undergoing routine endoscopy and assessed their reactivity to Helicobacter pylori (H. pylori – Hp), a major gastric pathogen. We observed that MAIT cells are present in the lamina propria compartment of the stomach and display a similar memory phenotype to blood MAIT cells. We then demonstrated that gastric and blood MAIT cells are able to recognize H. pylori. We found that CD8⁺ and CD4⁻CD8⁻ (double negative) MAIT cell subsets respond to H. pylori-infected macrophages stimulation in a MR-1 restrictive manner by producing cytokines (IFN-γ, TNF-α, IL-17A) and exhibiting cytotoxic activity. Interestingly, we observed that blood MAIT cell frequency in Hp^+ve individuals was significantly lower than in Hp^−ve individuals. However, gastric MAIT cell frequency was not significantly different between Hp^+ve and Hp^−ve individuals, demonstrating a dichotomy between blood and gastric tissues. Further, we observed that the majority of gastric MAIT cells (>80%) expressed tissue-resident markers (CD69⁺ CD103⁺), which were only marginally present on PBMC MAIT cells (<3%), suggesting that gastric MAIT cells are readily available to respond quickly to pathogens. These results contribute important new information to the understanding of MAIT cells function on peripheral and mucosal tissues and its possible implications in the host response to H. pylori.

Vaccines to prevent tuberculosis infection rather than disease: Physiological and immunological aspects

There is increasing enthusiasm and optimism that a vaccine could be developed that prevents infection rather than disease. In this article I discuss the fact that despite this optimism nothing has been produced so far that seems to have this capability, and moreover even the borderline between when infection ends and disease begins has not even been defined. To be effective such a vaccine, or at least the immunity it would generate, would have to work within the confines of the pulmonary physiological systems, which are complex. To date much of the emphasis here has turned away from T cell mediated immunity and towards establishing specific antibodies in the lungs. Here, I argue that with the exception of a possible exclusionary function, most claims of a protective role of antibody are completely over-blown. Finally, even if we had a potential "anti-infection" vaccine, how would we test and validate it?