Obesity Reduces mTORC1 Activity in Mucosal-Associated Invariant T Cells, Driving Defective Metabolic and Functional Responses

Diet switch pre-vaccination improves immune response and metabolic status in formerly obese mice

Metabolic disease is epidemiologically linked to severe complications upon influenza virus infection, thus vaccination is a priority in this high-risk population. Yet, vaccine responses are less effective in these same hosts. Here we examined how the timing of diet switching from a high-fat diet to a control diet affected influenza vaccine efficacy in diet-induced obese mice. Our results demonstrate that the systemic meta-inflammation generated by high-fat diet exposure limited T cell maturation to the memory compartment at the time of vaccination, impacting the recall of effector memory T cells upon viral challenge. This was not improved with a diet switch post-vaccination. However, the metabolic dysfunction of T cells was reversed if weight loss occurred 4 weeks before vaccination, restoring a functional recall response. This corresponded with changes in the systemic obesity-related biomarkers leptin and adiponectin, highlighting the systemic and specific effects of diet on influenza vaccine immunogenicity.

Pretreatment circulating MAIT cells, neutrophils, and periostin predicted the real-world response after 1-year mepolizumab treatment in asthmatics

BACKGROUND

Mepolizumab treatment improves symptom control and quality of life and reduces exacerbations in patients with severe eosinophilic asthma. However, biomarkers that predict therapeutic effectiveness must be determined for use in precision medicine. Herein, we elucidated the dynamics of various parameters before and after treatment as well as patient characteristics predictive of clinical responsiveness to mepolizumab after 1-year treatment.

METHODS

Twenty-seven patients with severe asthma were treated with mepolizumab for one year. Asthma control test scores, pulmonary function tests, fractional exhaled nitric oxide levels, and blood samples were evaluated. Additionally, we explored the role of CD69-positive mucosal-associated invariant T (MAIT) cells as a candidate biomarker for predicting treatment effectiveness by evaluating an OVA-induced asthma murine model using MR1 knockout mice, where MAIT cells were absent.

RESULTS

The frequencies of CD69-positive group 1 innate lymphoid cells, group 3 innate lymphoid cells, natural killer cells, and MAIT cells decreased after mepolizumab treatment. The frequency of CD69-positive MAIT cells and neutrophils was lower and serum periostin levels were higher in responders than in non-responders. In the OVA-induced asthma murine model, CD69-positive MAIT cell count in the whole mouse lung was significantly higher than that in the control mice. Moreover, OVA-induced eosinophilic airway inflammation was exacerbated in the MAIT cell-deficient MR1 knockout mice.

CONCLUSIONS

This study shows that circulating CD69-positive MAIT cells, neutrophils, and serum periostin might predict the real-world response after 1-year mepolizumab treatment. Furthermore, MAIT cells potentially have a protective role against type 2 airway inflammation.

The paradox of aging: Aging-related shifts in T cell function and metabolism

T cell survival, differentiation after stimulation, and function are intrinsically linked to distinct cellular metabolic states. The ability of T cells to readily transition between metabolic states enables flexibility to meet the changing energy demands defined by distinct effector states or T cell lineages. Immune aging is characterized, in part, by the loss of naïve T cells, accumulation of senescent T cells, severe dysfunction in memory phenotype T cells in particular, and elevated levels of inflammatory cytokines, or 'inflammaging'. Here, we review our current understanding of the phenotypic and functional changes that occur with aging in T cells, and how they relate to metabolic changes in the steady state and after T cell activation. We discuss the apparent contradictions in the aging T cell phenotype - where enhanced differentiation states and metabolic profiles in the steady state can correspond to a diminished capacity to adapt metabolically and functionally after T cell activation. Finally, we discuss key recent studies that indicate the enormous potential for aged T cell metabolism to induce systemic inflammaging and organism-wide multimorbidity, resulting in premature death.

Multifaceted roles of T cells in obesity and obesity-related complications: A narrative review

Obesity is characterized by chronic low-grade inflammatory responses in the adipose tissue, accompanied by pronounced insulin resistance and metabolic anomalies. It affects almost all body organs and eventually leads to diseases such as fatty liver disease, type 2 diabetes mellitus, and atherosclerosis. Recently, T cells have emerged as interesting therapeutic targets because the dysfunction of T cells and their cytokines in the adipose tissue is implicated in obesity-induced inflammation and their complicated onset. Although several recent narrative reviews have provided a brief overview of related evidence in this area, they have mainly focused on either obesity-associated T cell metabolism or modulation of T cell activation in obesity. Moreover, at present, no published review has reported on the multifaceted roles of T cells in obesity and obesity-related complications, even though there has been a significant increase in studies on this topic since 2019. Therefore, this narrative review aims to comprehensively summarize current advances in the mechanistic roles of T cells in the development of obesity and its related complications. Further, we aim to discuss relevant drugs for weight loss as well as the contradictory role of T cells in the same disease so as to highlight key findings regarding this topic and provide a valid basis for future treatment strategies.

NK cells vs. obesity: A tale of dysfunction & redemption

Natural killer (NK) cells are critical in protecting the body against infection and cancer. NK cells can rapidly respond to these threats by directly targeting the infected or transformed cell using their cytotoxic machinery or by initiating and amplifying the immune response via their production of cytokines. Additionally, NK cells are resident across many tissues including adipose, were their role extends from host protection to tissue homeostasis. Adipose resident NK cells can control macrophage polarization via cytokine production, whilst also regulating stressed adipocyte fate using their cytotoxic machinery. Obesity is strongly associated with increased rates of cancer and a heightened susceptibility to severe infections. This is in part due to significant obesity-related immune dysregulation, including defects in both peripheral and adipose tissue NK cells. In this review, we detail the literature to date on NK cells in the setting of obesity - outlining the consequences, mechanisms and therapeutic interventions.

CD83+ B cells alleviate uveitis through inhibiting DCs by sCD83

Soluble CD83 (sCD83) exerts immunosuppressive functions in many autoimmune diseases, including experimental autoimmune uveitis (EAU), but the cells and mechanisms involved are unclear. This study showed that CD83+ B cells were the main sources of sCD83. They alleviated the symptoms of EAU and decreased the percentage of T cells and DCs in the eyes and lymph nodes. These CD83+ B cells decreased IL-1β, IL-18 and IFN-γ secretion by DCs through sCD83. sCD83 interacted with GTPase Ras-related protein (Rab1a) in DCs to promote Rab1a accumulation in autolysosomes and inhibit mTORC1 phosphorylation and NLRP3 expression. Hence, CD83+ B cells play a regulatory role in EAU by secreting sCD83. The lack of regulation of CD83+ B cells might be an important factor leading to hyperimmune activation in patients with autoimmune uveitis. CD83+ B cells suppress activated DCs in uveitis, indicating the potential therapeutic role of CD83+ B cells in uveitis.

Glucagon-like peptide-1 therapy in people with obesity restores natural killer cell metabolism and effector function

OBJECTIVE

People with obesity (PWO) have functionally defective natural killer (NK) cells, with a decreased capacity to produce cytokines and kill target cells, underpinned by defective cellular metabolism. It is plausible that the changes in peripheral NK cell activity are contributing to the multimorbidity in PWO, which includes an increased risk of cancer. This study investigated whether therapy with long-acting glucagon-like peptide-1 (GLP-1) analogues, which are an effective treatment for obesity, could restore NK cell functionality in PWO.

METHODS

In a cohort of 20 PWO, this study investigated whether 6 months of once weekly GLP-1 therapy (semaglutide) could restore human NK cell function and metabolism using multicolor flow cytometry, enzyme-linked immunosorbent assays, and cytotoxicity assays.

RESULTS

These data demonstrate that PWO who received GLP-1 therapy have improved NK cell function, as measured by cytotoxicity and interferon-γ/granzyme B production. In addition, the study demonstrates increases in a CD98-mTOR-glycolysis metabolic axis, which is critical for NK cell cytokine production. Finally, it shows that the reported improvements in NK cell function appear to be independent of weight loss.

CONCLUSIONS

The restoration, by GLP-1 therapy, of NK cell functionality in PWO may be contributing to the overall benefits being seen with this class of medication.

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.

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.

MAITabolism2 - the emerging understanding of MAIT cell metabolism and their role in metabolic disease

Mucosal associated invariant T (MAIT) cells are a population of unconventional innate T cells due to their non-MHC restriction and rapid effector responses. MAIT cells can recognise bacterial derived antigens presented on the MHC-like protein via their semi-restricted T cell receptor (TCR). Upon TCR triggering MAIT cells rapidly produce a range of effector molecules including cytokines, lytic granules and chemokines. This rapid and robust effector response makes MAIT cells critical in host responses against many bacterial pathogens. MAIT cells can also respond independent of their TCR via innate cytokines such as interleukin (IL)-18, triggering cytokine production, and are important in anti-viral responses. In addition to their protective role, MAIT cells have been implicated in numerous inflammatory diseases, including metabolic diseases often contributing to the pathogenesis via their robust cytokine production. Effector cells such as MAIT cells require significant amounts of energy to support their potent responses, and the type of nutrients available can dictate the functionality of the cell. Although data on MAIT cell metabolism is just emerging, several recent studies are starting to define the intrinsic metabolic requirements and regulators of MAIT cells. In this review we will outline our current understanding of MAIT cell metabolism, and outline their role in metabolic disease, and how disease-related changes in extrinsic metabolism can alter MAIT cell responses.

Enhancing Mucosal-Associated Invariant T Cell Function and Expansion with Human Selective Serum

Mucosal-associated invariant T (MAIT) cells are promising innate-like lymphocytes with potential for use in anti-tumor immunotherapy. Existing MAIT cell expansion protocols are associated with potentially decremental phenotypic changes, including increased frequency of CD4+ MAIT cells and higher inhibitory receptor expression. In this study, we compared the effect on expansion of human MAIT cells of a serum replacement, Physiologix XF SR (Phx), with traditional serum FBS for supplementing RPMI 1640 media. Using flow cytometry, we found that Phx supported a significantly higher proliferative capacity for MAIT cells and resulted in a lower frequency of CD4+ MAIT cells, which have been associated with reduced Th1 effector and cytolytic functions. We saw that culturing MAIT cells in Phx led to better survival of MAIT cells and lower frequency of PD-1+ MAIT cells than FBS-supplemented media. Functionally, we saw that Phx supplementation was associated with a higher frequency of IFN-γ+ MAIT cells after stimulation with Escherichia coli than FBS-supplemented RPMI. In conclusion, we show that MAIT cells cultured in Phx have higher proliferative capacity, lower expression of inhibitory receptors, and higher capacity to produce IFN-γ after E. coli stimulation than FBS-supplemented RPMI. This work shows that expanding MAIT cells with Phx compared with FBS-supplemented RPMI results in a more functionally desirable MAIT cell for future anti-tumor immunotherapy.

T-cell Metabolism as Interpreted in Obesity-associated Inflammation

The appreciation of metabolic regulation of T-cell function has exploded over the past decade, as has our understanding of how inflammation fuels comorbidities of obesity, including type 2 diabetes. The likelihood that obesity fundamentally alters T-cell metabolism and thus chronic obesity-associated inflammation is high, but studies testing causal relationships remain underrepresented. We searched PubMed for key words including mitochondria, obesity, T cell, type 2 diabetes, cristae, fission, fusion, redox, and reactive oxygen species to identify foundational and more recent studies that address these topics or cite foundational work. We investigated primary papers cited by reviews found in these searches and highlighted recent work with >100 citations to illustrate the state of the art in understanding mechanisms that control metabolism and thus function of various T-cell subsets in obesity. However, "popularity" of a paper over the first 5 years after publication cannot assess long-term impact; thus, some likely important work with fewer citations is also highlighted. We feature studies of human cells, supplementing with studies from animal models that suggest future directions for human cell research. This approach identified gaps in the literature that will need to be filled before we can estimate efficacy of mitochondria-targeted drugs in clinical trials to alleviate pathogenesis of obesity-associated inflammation.

Obesity-Mediated Immune Modulation: One Step Forward, (Th)2 Steps Back

Over the past decades, the relationship between the immune system and metabolism has become a major research focus. In this arena of immunometabolism the capacity of adipose tissue to secrete immunomodulatory molecules, including adipokines, within the underlying low-grade inflammation during obesity brought attention to the impact obesity has on the immune system. Adipokines, such as leptin and adiponectin, influence T cell differentiation into different T helper subsets and their activation during immune responses. Furthermore, within the cellular milieu of adipose tissue nutrient availability regulates differentiation and activation of T cells and changes in cellular metabolic pathways. Upon activation, T cells shift from oxidative phosphorylation to oxidative glycolysis, while the differential signaling of the kinase mammalian target of rapamycin (mTOR) and the nuclear receptor PPARγ, amongst others, drive the subsequent T cell differentiation. While the mechanisms leading to a shift from the typical type 2-dominated milieu in lean people to a Th1-biased pro-inflammatory environment during obesity are the subject of extensive research, insights on its impact on peripheral Th2-dominated immune responses become more evident. In this review, we will summarize recent findings of how Th2 cells are metabolically regulated during obesity and malnutrition, and how these states affect local and systemic Th2-biased immune responses.

Hallmarks of Severe COVID-19 Pathogenesis: A Pas de Deux Between Viral and Host Factors

Two years into Coronavirus Disease 2019 (COVID-19) pandemic, a comprehensive characterization of the pathogenesis of severe and critical forms of COVID-19 is still missing. While a deep dysregulation of both the magnitude and functionality of innate and adaptive immune responses have been described in severe COVID-19, the mechanisms underlying such dysregulations are still a matter of scientific debate, in turn hampering the identification of new therapies and of subgroups of patients that would most benefit from individual clinical interventions. Here we review the current understanding of viral and host factors that contribute to immune dysregulation associated with COVID-19 severity in the attempt to unfold and broaden the comprehension of COVID-19 pathogenesis and to define correlates of protection to further inform strategies of targeted therapeutic interventions.

Mucosal-associated invariant T cells are associated with insulin resistance in childhood obesity, and disrupt insulin signalling via IL-17

AIMS/HYPOTHESIS

Mucosal-associated invariant T cells (MAIT cells) are an abundant population of innate T cells. When activated, MAIT cells rapidly produce a range of cytokines, including IFNγ, TNF-α and IL-17. Several studies have implicated MAIT cells in the development of metabolic dysfunction, but the mechanisms through which this occurs are not fully understood. We hypothesised that MAIT cells are associated with insulin resistance in children with obesity, and affect insulin signalling through their production of IL-17.

METHODS

In a cross-sectional observational study, we investigated MAIT cell cytokine profiles in a cohort of 30 children with obesity and 30 healthy control participants, of similar age, using flow cytometry. We then used a cell-based model to determine the direct effect of MAIT cells and IL-17 on insulin signalling and glucose uptake.

RESULTS

Children with obesity display increased MAIT cell frequencies (2.2% vs 2.8%, p=0.047), and, once activated, these produced elevated levels of both TNF-α (39% vs 28%, p=0.03) and IL-17 (1.25% vs 0.5%, p=0.008). The IL-17-producing MAIT cells were associated with an elevated HOMA-IR (r=0.65, p=0.001). The MAIT cell secretome from adults with obesity resulted in reduced glucose uptake when compared with the secretome from healthy adult control (1.31 vs 0.96, p=0.0002), a defect that could be blocked by neutralising IL-17. Finally, we demonstrated that recombinant IL-17 blocked insulin-mediated glucose uptake via inhibition of phosphorylated Akt and extracellular signal-regulated kinase.

CONCLUSIONS/INTERPRETATIONS

Collectively, these studies provide further support for the role of MAIT cells in the development of metabolic dysfunction, and suggest that an IL-17-mediated effect on intracellular insulin signalling is responsible.

Differential Effects of Dietary versus Exercise Intervention on Intrahepatic MAIT Cells and Histological Features of NAFLD

Background: Mucosal-associated invariant T (MAIT) cells promote inflammation in obesity and are implicated in the progression of non-alcoholic fatty liver disease (NAFLD). However, as the intrahepatic MAIT cell response to lifestyle intervention in NAFLD has not been investigated, this work aimed to examine circulating and intrahepatic MAIT cell populations in patients with NAFLD, after either 12 weeks of dietary intervention (DI) or aerobic exercise intervention (EI). Methods: Multicolour flow cytometry was used to immunophenotype circulating and intrahepatic MAIT cells and measure MAIT cell expression (median fluorescence intensity, MFI) of the activation marker CD69 and apoptotic marker CD95. Liver histology, clinical parameters, and MAIT cell populations were assessed at baseline (T0) and following completion (T1) of DI or EI. Results: Forty-five patients completed the study. DI participants showed decreased median (interquartile range) expression of the activation marker CD69 on circulating MAIT cells (T0: 104 (134) versus T1 27 (114) MFI; p = 0.0353) and improvements in histological steatosis grade post-intervention. EI participants showed increased expression of the apoptotic marker CD95, both in circulating (T0: 1549 (888) versus T1: 2563 (1371) MFI; p = 0.0043) and intrahepatic MAIT cells (T0: 2724 (862) versus T1: 3117 (1622) MFI; p = 0.0269). Moreover, the percentage of intrahepatic MAIT cells significantly decreased after EI (T0: 11.1 (14.4) versus T1: 5.3 (9.3)%; p = 0.0029), in conjunction with significant improvements in fibrosis stage and hepatocyte ballooning. Conclusions: These data demonstrate independent benefits from dietary and exercise intervention and suggest a role for intrahepatic MAIT cells in the observed histological improvements in NAFLD.

Characterization of cord blood CD3+ TCRVα7.2+ CD161high T and innate lymphoid cells in the pregnancies with gestational diabetes, morbidly adherent placenta, and pregnancy hypertension diseases

PROBLEM

Although pregnant women with gestational diabetes (GD), morbidly adherent placenta (MAP), and pregnancy hypertension (pHT) diseases lead to intrauterine growth restriction (IUGR), little is known about their effect on mucosal-associated invariant T (MAIT) and innate lymphoid cells (ILC) in the umbilical cord. This study aimed to quantify and characterize MAIT cells and ILCs in the cord blood of pregnant women with GD, MAP, and pHT diseases.

METHOD OF STUDY

Cord blood mononuclear cells (CBMCs) were isolated by Ficoll-Paque gradient. CD3⁺ TCRVα7.2⁺ CD161^high cells and ILC subsets were quantified by flow cytometry. CBMCs were stimulated with PMA/Ionomycin and Golgi Plug for 4 h and stained for IFN-γ, TNF-α, and granzyme B. The stained cells were analyzed on FACS ARIA III.

RESULTS

Compared with healthy pregnancies, in the cord blood of the pHT group, elevated number of lymphocytes was observed. Moreover, the absolute number of IFN-γ producing CD4⁺ or CD4^- subsets of CD3⁺ TCRVα7.2⁺ CD161^high cells as well as those producing granzyme B were significantly elevated in the pHT group compared to healthy controls suggesting increased MAIT cell activity in the pHT cord blood. Similarly, in the MAP group, the absolute number of total CD3⁺ TCRVα7.2⁺ CD161^high cells, but not individual CD4⁺ or negative subsets, were significantly increased compared with healthy controls' cord blood. Absolute numbers of total CD3⁺ TCRVα7.2⁺ CD161^high cells and their subsets were comparable in the cord blood of the GD group compared with healthy controls. Finally, the absolute number of total ILCs and ILC3 subset were significantly elevated in only pHT cord blood compared with healthy controls. Our data also reveal that IFN-γ⁺ or granzyme B⁺ cell numbers negatively correlated with fetal birth weight.

CONCLUSIONS

CD3⁺ TCRVα7.2⁺ CD161^high cells and ILCs show unique expansion and activity in the cord blood of pregnant women with distinct diseases causing IUGR and may play roles in fetal growth restriction.

Amino Acid Solute Carrier Transporters in Inflammation and Autoimmunity

The past decade exposed the importance of many homeostasis and metabolism related proteins in autoimmunity disease and inflammation. Solute carriers (SLCs) are a group of membrane channels that can transport amino acids, the building blocks of proteins, nutrients, and neurotransmitters. This review summarizes the role of SLCs amino acid transporters in inflammation and autoimmunity disease. In detail, the importance of Glutamate transporters SLC1A1, SLC1A2, and SLC1A3, mainly expressed in the brain where they help prevent glutamate excitotoxicity, is discussed in the context of central nervous system disorders such as multiple sclerosis. Similarly, the cationic amino acid transporter SLC7A1 (CAT1), which is an important arginine transporter for T cells, and SLC7A2 (CAT2), essential for innate immunity. SLC3 family proteins, which bind with light chains from the SLC7 family (SLC7A5, SLC7A7 and SLC7A11) to form heteromeric amino acid transporters, are also explored to describe their roles in T cells, NK cells, macrophages and tumor immunotherapies. Altogether, the link between SLC amino acid transporters with inflammation and autoimmunity may contribute to a better understanding of underlying mechanism of disease and provide novel potential therapeutic avenues. Significance Statement SIGNIFICANCE STATEMENT In this review, we summarize the link between SLC amino acid transporters and inflammation and immune responses, specially SLC1 family members and SLC7 members. Studying the link may contribute to a better understanding of related diseases and provide potential therapeutic targets and useful to the researchers who have interest in the involvement of amino acids in immunity.

Cytokine-induced natural killer cell training is dependent on cellular metabolism and is defective in obesity

NK cell cytokine training is dependent on glycolysis, oxidative phosphorylation, and the metabolic regulator Srebp.

NK cell cytokine training is defective in PWO.

Natural killer (NK) cells are a population of innate immune cells that can rapidly kill cancer cells and produce cytokines such as interferon-γ. A key feature of NK cells is their ability to respond without prior sensitization; however, it is now well established that NK cells can possess memory-like features. After activation with cytokines, NK cells demonstrate enhanced effector functions upon restimulation days or weeks later. This demonstrates that NK cells may be trained to be more effective killers and harnessed as more potent cancer immunotherapy agents. We have previously demonstrated that cellular metabolism is essential for NK cell responses, with NK cells upregulating both glycolysis and oxidative phosphorylation upon cytokine stimulation. Limiting NK cell metabolism results in reduced cytotoxicity and cytokine production. We have also demonstrated that defective NK cell responses in obesity are linked to defective cellular metabolism. In the current study, we investigated if cellular metabolism is required during the initial period of NK cell cytokine training and if NK cells from people with obesity (PWO) can be effectively trained. We show that increased flux through glycolysis and oxidative phosphorylation during the initial cytokine activation period is essential for NK cell training, as is the metabolic signaling factor Srebp. We show that NK cells from PWO, which are metabolically defective, display impaired NK cell training, which may have implications for immunotherapy in this particularly vulnerable group.

Mucosal-Associated Invariant T Cell Response to Acute Exercise and Exercise Training in Older Obese Women

(1) Background: Obesity is a major global public health concern as it is associated with many of the leading causes of preventable deaths. Exercise reduces obesity-induced inflammation; however, it is unknown how exercise training may impact mucosal associated invariant T (MAIT) cells in overweight/obese (OW) post-menopausal women. Therefore, the purpose of this study was to investigate (i) circulating MAIT-cells at rest in OW vs. Lean women, (ii) the response of MAIT-cells to a single bout of combined aerobic and resistance exercise, and (iii) the effects of 12 weeks of exercise training (EX) or educational program (ED) on the MAIT-cell response in OW. (2) Methods: OW completed an acute exercise session or sitting control, underwent 12 weeks of exercise training or received educational materials, and then repeated the exercise session/sitting control. Lean post-menopausal women provided a baseline comparison. (3) Results: OW had lower circulating MAIT-cells at rest than Lean prior to exercise training; however, after training EX displayed improved MAIT-cell frequency. Additionally, prior to training EX did not exhibit MAIT-cell mobilization/egress, however, both improved after training. (4) Conclusions: Reduced MAIT-cell frequency and ability to mobilize/egress were potentially partially rescued in EX after 12 weeks of exercise training; however, further research is needed to elucidate age or obesity-induced attenuations in MAIT-cells.

The Importance of Metabolism for Immune Homeostasis in Allergic Diseases

There is increasing evidence that the metabolic status of T cells and macrophages is associated with severe phenotypes of chronic inflammation, including allergic inflammation. Metabolic changes in immune cells have a crucial role in their inflammatory or regulatory responses. This notion is reinforced by metabolic diseases influencing global energy metabolism, such as diabetes or obesity, which are known risk factors of severity in inflammatory conditions, due to the metabolic-associated inflammation present in these patients. Since several metabolic pathways are closely tied to T cell and macrophage differentiation, a better understanding of metabolic alterations in immune disorders could help to restore and modulate immune cell functions. This link between energy metabolism and inflammation can be studied employing animal, human or cellular models. Analytical approaches rank from classic immunological studies to integrated analysis of metabolomics, transcriptomics, and proteomics. This review summarizes the main metabolic pathways of the cells involved in the allergic reaction with a focus on T cells and macrophages and describes different models and platforms of analysis used to study the immune system and its relationship with metabolism.

Regulation and Functions of Protumoral Unconventional T Cells in Solid Tumors

The vast majority of studies on T cell biology in tumor immunity have focused on peptide-reactive conventional T cells that are restricted to polymorphic major histocompatibility complex molecules. However, emerging evidence indicated that unconventional T cells, including γδ T cells, natural killer T (NKT) cells and mucosal-associated invariant T (MAIT) cells are also involved in tumor immunity. Unconventional T cells span the innate-adaptive continuum and possess the unique ability to rapidly react to nonpeptide antigens via their conserved T cell receptors (TCRs) and/or to activating cytokines to orchestrate many aspects of the immune response. Since unconventional T cell lineages comprise discrete functional subsets, they can mediate both anti- and protumoral activities. Here, we review the current understanding of the functions and regulatory mechanisms of protumoral unconventional T cell subsets in the tumor environment. We also discuss the therapeutic potential of these deleterious subsets in solid cancers and why further feasibility studies are warranted.

Mucosal-Associated Invariant T Cell Effector Function Is an Intrinsic Cell Property That Can Be Augmented by the Metabolic Cofactor α-Ketoglutarate

Mucosal-associated invariant T (MAIT) cells are an innate-like population of unconventional T cells that respond rapidly to microbial metabolite Ags or cytokine stimulation. Because of this reactivity and surface expression of CD45RO⁺, CD45RA^-, and CD127⁺, they are described as effector memory cells. Yet, there is heterogeneity in MAIT cell effector response. It is unclear what factors control MAIT cell effector capacity, whether it is fixed or can be modified and if this differs based on whether activation is TCR dependent or independent. To address this, we have taken a systematic approach to examine human MAIT cell effector capacity across healthy individuals in response to ligand and cytokine stimulation. We demonstrate the heterogenous nature of MAIT cell effector capacity and that the ability to produce an effector response is not directly attributable to TCR clonotype or coreceptor expression. Global gene transcription analysis revealed that the MAIT cell effector capacity produced in response to TCR stimulation is associated with increased expression of the epigenetic regulator lysine demethylase 6B (KDM6B). Addition of a KDM6B inhibitor did not alter MAIT cell effector function to Ag or cytokine stimulation. However, addition of the KDM6B cofactor α-ketoglutarate greatly enhanced MAIT cell effector capacity to TCR-dependent stimulation in a partially KDM6B-dependent manner. These results demonstrate that the TCR-dependent effector response of MAIT cells is epigenetically regulated and dependent on the availability of metabolic cofactors.

Differential controls of MAIT cell effector polarization by mTORC1/mTORC2 via integrating cytokine and costimulatory signals

Mucosal-associated invariant T (MAIT) cells have important functions in immune responses against pathogens and in diseases, but mechanisms controlling MAIT cell development and effector lineage differentiation remain unclear. Here, we report that IL-2/IL-15 receptor β chain and inducible costimulatory (ICOS) not only serve as lineage-specific markers for IFN-γ-producing MAIT1 and IL-17A-producing MAIT17 cells, but are also important for their differentiation, respectively. Both IL-2 and IL-15 induce mTOR activation, T-bet upregulation, and subsequent MAIT cell, especially MAIT1 cell, expansion. By contrast, IL-1β induces more MAIT17 than MAIT1 cells, while IL-23 alone promotes MAIT17 cell proliferation and survival, but synergizes with IL-1β to induce strong MAIT17 cell expansion in an mTOR-dependent manner. Moreover, mTOR is dispensable for early MAIT cell development, yet pivotal for MAIT cell effector differentiation. Our results thus show that mTORC2 integrates signals from ICOS and IL-1βR/IL-23R to exert a crucial role for MAIT17 differentiation, while the IL-2/IL-15R-mTORC1-T-bet axis ensures MAIT1 differentiation.

Mucosal Associated Invariant T Cells in Cancer-Friend or Foe?

Mucosal associated invariant T (MAIT) cells are a population of unconventional T cells which can bridge the innate and adaptive immune systems. Well-described roles for MAIT cells include host protection against invading bacteria, fungi and viruses. Upon activation, MAIT cells become prolific effector cells, capable of producing a range of cytokines and lytic molecules. In addition to their anti-microbial role, MAIT cells have been implicated in immune responses to cancer, with opposing beneficial and pathogenic roles reported. On the one hand, MAIT cells can home to the site of the tumour in many human cancers and can produce anti-tumour molecules. On the other, MAIT cells can display defective phenotypes in certain cancers and produce pro-tumour molecules. In this review, we discuss the current literature on the diverse roles for MAIT cells in cancer, outlining their frequencies, functions and associations with N staging and prognosis. We also discuss potential mechanisms underpinning cancer-related alterations in MAIT cells and highlight therapeutic approaches to harness or target MAIT cells in cancer.

Role of MAIT cells in metabolic diseases

MAIT cells are innate-like T cells that are enriched in mucosal sites and tissues including adipose tissue and liver. They play an important role in immunity against microbial pathogens. Recently, it has been reported that MAIT cells could also be important in metabolic diseases and can be involved in setting up and maintaining chronic inflammation. In this review, we give an overview of recent advances in understanding MAIT cells role in the ethology of this diseases.

Obesity and immune status in children

PURPOSE OF REVIEW

Childhood obesity, with persistent chronic inflammation, is a worldwide epidemic. Obesity causes dysregulation throughout the immune system, affecting the balance and levels of cytokines, adipokines, and innate and adaptive immune cells. The present review focuses on the impact of obesity on immune function in children: altering the baseline activation state of immune cells and affecting the ability of the host to combat pathogens and malignancy and respond appropriately to vaccination.

RECENT FINDINGS

Obesity causes dysregulation of the immune system. Single-cell RNA-sequencing of adipose tissue and resident immune cells is quantifying the impact of obesity on the frequency of immune cell subsets and their states. The system-wide alterations in immune function in obesity are most evident upon perturbation, including the response to infection (e.g. increased risk of severe COVID-19 in the ongoing pandemic), vaccination, and malignancy. However, mechanistic research in pediatric obesity is limited and this impacts our ability to care for these children.

SUMMARY

We must better understand baseline and perturbed immune health in obese children to determine how to account for altered frequency and function of humoral and cellular immune components in acute infection, during vaccine design and when considering therapeutic options for this complex, medically vulnerable group.

MAIT Cells in Barrier Tissues: Lessons from Immediate Neighbors

Mucosal-associated invariant T (MAIT) cells are innate-like T cells present at considerable frequencies in human blood and barrier tissues, armed with an expanding array of effector functions in response to homeostatic perturbations. Analogous to other barrier immune cells, their phenotype and function is driven by crosstalk with host and dynamic environmental factors, most pertinently the microbiome. Given their distribution, they must function in diverse extracellular milieus. Tissue-specific and adapted functions of barrier immune cells are shaped by transcriptional programs and regulated through a blend of local cellular, inflammatory, physiological, and metabolic mediators unique to each microenvironment. This review compares the phenotype and function of MAIT cells with other barrier immune cells, highlighting potential areas for future exploration. Appreciation of MAIT cell biology within tissues is crucial to understanding their niche in health and disease.

Review of the Correlation of LAT1 With Diseases: Mechanism and Treatment

LAT1 is a member of the system L transporter family. The main role of the LAT1 is to transport specific amino acids through cell membranes to provide nutrients to cells and participate in several metabolic pathways. It also contributes to the transport of hormones and some drugs, which are essential for the development and treatment of some diseases. In recent years, many studies have shown that LAT1 is related to cancer, obesity, diabetes, and other diseases. However, the specific mechanism underlying the influence of LAT1 on such conditions remains unclear. Through the increasing number of studies on LAT1, we have obtained a preliminary understanding on the function of LAT1 in diseases. These studies also provide a theoretical basis for finding treatments for LAT1-related diseases, such as cancer. This review summarizes the function and mechanism of LAT1 in different diseases and the treatment of LAT1-related diseases. It also provides support for the development of novel and reliable disease treatments.

Expression Pattern of the SARS-CoV-2 Entry Genes ACE2 and TMPRSS2 in the Respiratory Tract

To address the expression pattern of the SARS-CoV-2 receptor ACE2 and the viral priming protease TMPRSS2 in the respiratory tract, this study investigated RNA sequencing transcriptome profiling of samples of airway and oral mucosa. As shown, ACE2 has medium levels of expression in both small airway epithelium and masticatory mucosa, and high levels of expression in nasal epithelium. The expression of ACE2 is low in mucosal-associated invariant T (MAIT) cells and cannot be detected in alveolar macrophages. TMPRSS2 is highly expressed in small airway epithelium and nasal epithelium and has lower expression in masticatory mucosa. Our results provide the molecular basis that the nasal mucosa is the most susceptible locus in the respiratory tract for SARS-CoV-2 infection and consequently for subsequent droplet transmission and should be the focus for protection against SARS-CoV-2 infection.

Expression Pattern of the SARS-CoV-2 Entry Genes ACE2 and TMPRSS2 in the Respiratory Tract

To address the expression pattern of the SARS-CoV-2 receptor ACE2 and the viral priming protease TMPRSS2 in the respiratory tract, this study investigated RNA sequencing transcriptome profiling of samples of airway and oral mucosa. As shown, ACE2 has medium levels of expression in both small airway epithelium and masticatory mucosa, and high levels of expression in nasal epithelium. The expression of ACE2 is low in mucosal-associated invariant T (MAIT) cells and cannot be detected in alveolar macrophages. TMPRSS2 is highly expressed in small airway epithelium and nasal epithelium and has lower expression in masticatory mucosa. Our results provide the molecular basis that the nasal mucosa is the most susceptible locus in the respiratory tract for SARS-CoV-2 infection and consequently for subsequent droplet transmission and should be the focus for protection against SARS-CoV-2 infection.

Diverse Immunoregulatory Roles of Oxysterols-The Oxidized Cholesterol Metabolites

Intermediates of both cholesterol synthesis and cholesterol metabolism can have diverse roles in the control of cellular processes that go beyond the control of cholesterol homeostasis. For example, oxidized forms of cholesterol, called oxysterols have functions ranging from the control of gene expression, signal transduction and cell migration. This is of particular interest in the context of immunology and immunometabolism where we now know that metabolic processes are key towards shaping the nature of immune responses. Equally, aberrant metabolic processes including altered cholesterol homeostasis contribute to immune dysregulation and dysfunction in pathological situations. This review article brings together our current understanding of how oxysterols affect the control of immune responses in diverse immunological settings.

Single Cell Glucose Uptake Assays: A Cautionary Tale

Assays to monitor the metabolic state or nutrient uptake capacity of immune cells at a single cell level are increasingly in demand. One assay, used by many immunologists, employs 2-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)Amino)-2-Deoxyglucose (2-NBDG), a fluorescent analogue of 2-deoxyglucose (2DG), as a substrate for glucose transporters. This molecule has been validated as a substrate for the glucose transporter Glut2 (Slc2a2) in mammalian cells but 2-NDBG selectivity for the glucose transporters expressed by T cells, Glut1 (Slc2a1) and Glut3 (Slc2a3), has never been explored. Nor has the possibility that 2-NBDG might bind to T cells that do not express glucose transporters been assessed. In this technical commentary we interrogate the specificity of 2-NBBG labelling as a readout for glucose transport in T lymphocytes. We compare flow cytometric 2-NBDG staining against well validated radiolabelled glucose transport assays in murine T cells. Our data show there can be a large discordance between glucose transport capacity and 2-NBDG labelling in T cells. We also find that 2-NBDG uptake into murine T cells is not inhibited by competitive substrates or facilitative glucose transporter inhibitors, nor can 2-NBDG competitively block glucose uptake in T cells. Collectively, these data argue that 2-NBDG uptake alone is not a reliable tool for the assessment of cellular glucose transport capacity.

Mitogen-Activated Protein Kinase (MAPK) and Obesity-Related Cancer

Obesity is a major public health concern worldwide. The increased risk of certain types of cancer is now an established deleterious consequence of obesity, although the molecular mechanisms of this are not completely understood. In this review, we aim to explore the links between MAPK signalling and obesity-related cancer. We focus mostly on p38 and JNK MAPK, as the role of ERK remains unclear. These links are seen through the implication of MAPK in obesity-related immune paralysis as well as through effects on the endoplasmic reticulum stress response and activation of aromatase. By way of example, we highlight areas of interest and possibilities for future research in endometrioid endometrial cancer and hepatocellular carcinoma associated with non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH) and MAPK.

IL-17 production by tissue-resident MAIT cells is locally induced in children with pneumonia

Community-acquired pneumonia (CAP) contributes substantially to morbidity and mortality in children under the age of 5 years. In examining bronchoalveolar lavages (BALs) of children with CAP, we found that interleukin-17 (IL-17) production was significantly increased in severe CAP. Immune profiling showed that mucosal-associated invariant T (MAIT) cells from the BALs, but not blood, of CAP patients actively produced IL-17 (MAIT17). Single-cell RNA-sequencing revealed that MAIT17 resided in a BAL-resident PLZF^hiCD103⁺ MAIT subset with high expression of hypoxia-inducible factor 1α (HIF-1α), reflecting the hypoxic state of the inflamed tissue. CAP BALs also contained a T-bet⁺ MAIT1 subset and a novel DDIT3⁺ (DNA damage-inducible transcript 3-positive) MAIT subset with low expression of HIF1A. Furthermore, MAIT17 differed from T-helper type 17 (Th17) cells in the expression of genes related to tissue location, innateness, and cytotoxicity. Finally, we showed that BAL monocytes were hyper-inflammatory and elicited differentiation of MAIT17. Thus, tissue-resident MAIT17 cells are induced at the infected respiratory mucosa, likely influenced by inflammatory monocytes, and contribute to IL-17-mediated inflammation during CAP.

MAIT Cells in Health and Disease

Mucosal-associated invariant T (MAIT) cells are a newly described subset of T cells that are found in the blood and are enriched in many tissues, particularly in the liver. MAIT cells express a semi-invariant T cell receptor restricted by the MHC class I-related (MR1) molecule. MAIT cells are activated in a MR1-dependent manner in response to microbial-derived riboflavin metabolites which leads to rapid effector functions, but they can also be activated in a MR1-independent manner by cytokines and viruses. The use of mice models and MR1 tetramers, among other recent methodological advances, have provided more insight into the development, mode of activation, characterization in different diseases and tissues of MAIT cells. In this chapter, we provide an overview of MAIT cells and yet remaining questions about their potential therapeutic role.

Mucosal-Associated Invariant T cell in liver diseases

Mucosal-associated invariant T cells (MAIT cells) are a new population of innate immune cells, which are abundant in the liver and play complex roles in various liver diseases. In this review, we summarize MAIT cells in the liver diseases in recent studies, figure out the role of MAIT cells in various liver disease, including Alcoholic liver disease, Non-alcoholic liver disease, Autoimmune liver diseases, Viral hepatitis and Liver Cancer. Briefly, MAIT cells are involved in anti-bacteria responses in the alcoholic liver diseases. Besides, the activated MAIT cells promote the liver inflammation by secreting inflammatory cytokines and produce regulatory cytokines, which induces anti-inflammatory macrophage polarization. MAIT cells participate in the liver fibrosis via enhancing hepatic stellate cell activation. In viral hepatitis, MAIT cells exhibit a flawed and exhausted phenotype, which results in little effect on controlling the virus and bacteria. In liver cancer, MAIT cells indicate the disease progression and the outcome of therapy. In summary, MAIT cells are attractive biomarkers and therapeutic targets for liver disease.

Immunometabolism of Phagocytes During Mycobacterium tuberculosis Infection

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) remains as a leading killer among infectious diseases worldwide. The nature of the host immune response dictates whether the initial Mtb infection is cleared or progresses toward active disease, and is ultimately determined by intricate host-pathogen interactions that are yet to be fully understood. The early immune response to infection is mediated by innate immune cells, including macrophages and neutrophils that can phagocytose Mtb and mount an antimicrobial response. However, Mtb can exploit these innate immune cells for its survival and dissemination. Recently, it has become clear that the immune response and metabolic remodeling are interconnected, which is highlighted by the rapid evolution of the interdisciplinary field of immunometabolism. It has been proposed that the net outcome to Mtb infection—clearance or chronic disease—is likely a result of combined immunologic and metabolic activities of the immune cells. Indeed, host cells activated by Mtb infection have strikingly different metabolic requirements than naïve/non-infected cells. Macrophages activated by Mtb-derived molecules or upon phagocytosis acquire a phenotype similar to M1 with elevated production of pro-inflammatory molecules and rely on glycolysis and pentose phosphate pathway to meet their bioenergetic and metabolic requirements. In these macrophages, oxidative phosphorylation and fatty acid oxidation are dampened. However, the non-infected/naive, M2-type macrophages are anti-inflammatory and derive their energy from oxidative phosphorylation and fatty acid oxidation. Similar metabolic adaptations also occur in other phagocytes, including dendritic cells, neutrophils upon Mtb infection. This metabolic reprogramming of innate immune cells during Mtb infection can differentially regulate their effector functions, such as the production of cytokines and chemokines, and antimicrobial response, all of which can ultimately determine the outcome of Mtb-host interactions within the granulomas. In this review, we describe key immune cells bolstering host innate response and discuss the metabolic reprogramming in these phagocytes during Mtb infection. We focused on the major phagocytes, including macrophages, dendritic cells and neutrophils and the key regulators involved in metabolic reprogramming, such as hypoxia-inducible factor-1, mammalian target of rapamycin, the cellular myelocytomatosis, peroxisome proliferator-activator receptors, sirtuins, arginases, inducible nitric acid synthase and sphingolipids.