Foxp3(+) T cells expressing RORγt represent a stable regulatory T-cell effector lineage with enhanced suppressive capacity during intestinal inflammation

Limosilactobacillus reuteri - a probiotic gut commensal with contextual impact on immunity

The gut microbiome plays a key role in human health, influencing various biological processes and disease outcomes. The historical roots of probiotics are traced back to Nobel Laureate Élie Metchnikoff, who linked the longevity of Bulgarian villagers to their consumption of sour milk fermented by Lactobacilli. His pioneering work led to the global recognition of probiotics as beneficial supplements, now a multibillion-dollar industry. Modern probiotics have been extensively studied for their immunomodulatory effects. Limosilactobacillus reuteri (L. reuteri), a widely used probiotic, has garnered significant attention for its systemic immune-regulatory properties, particularly in relation to autoimmunity and cancer. This review delves into the role of L. reuteri in modulating immune responses, with a focus on its impact on systemic diseases.

Thetis cells: regulators of intestinal immune tolerance

Our body's mucosal surfaces interface with the external environment and are potential sites of entry for pathogens as well as noxious substances. Yet, these barrier sites are also colonized with symbiotic microbes and are in contact with harmless environmental antigens. Different barrier epithelia harbor distinct microbial communities that shape both the epithelial layer and local immune cells that maintain tissue homeostasis and tolerance to symbiotic microbes. This seemingly paradoxical peaceful co-existence of immune cells and microbes has fascinated immunologists for decades: how does the immune system balance inflammatory and tolerogenic responses? The mechanisms underlying peripheral immune tolerance to harmless foreign antigens have been most widely studied within the intestine, where the immune system must establish and maintain tolerance to harmless food and commensal antigens. Dysregulated immune responses to these antigens are linked to several human diseases, including inflammatory bowel disease, celiac disease, and food allergy. Understanding the cellular and molecular cues that promote intestinal immune tolerance is key to the development of effective therapeutic strategies for these pathologies. Here, we review recent insights into mechanisms of intestinal tolerance with a focus on recently identified RORγt+ antigen-presenting cells.

Rorγt-positive dendritic cells are required for the induction of peripheral regulatory T cells in response to oral antigens

The intestinal immune system maintains tolerance to harmless food proteins and gut microbiota through peripherally derived RORγt+ Tregs (pTregs), which prevent food intolerance and inflammatory bowel disease. Recent studies suggested that RORγt+ antigen-presenting cells (APCs), which encompass rare dendritic cell (DC) subsets and type 3 innate lymphoid cells (ILC3s), are key to pTreg induction. Here, we developed a mouse with reduced RORγt+ APCs by deleting a specific cis-regulatory element of Rorc encoding RORγt. Single-cell RNA sequencing and flow cytometry analyses confirmed the depletion of a RORγt+ DC subset and ILC3s. These mice showed a secondary reduction in pTregs, impaired tolerance to oral antigens, and an increase in T helper (Th)2 cells. Conversely, ILC3-deficient mice showed no pTregs or Th2 cell abnormalities. Lineage tracing revealed that RORγt+ DCs share a lymphoid origin with ILC3s, consistent with their similar phenotypic traits. These findings highlight the role of lymphoid RORγt+ DCs in maintaining intestinal immune balance and preventing conditions like food allergies.

Neuroimmune interactions: The bridge between inflammatory bowel disease and the gut microbiota

BACKGROUND

The multidimensional regulatory mechanism of the gut-brain-immune axis in the context of inflammatory bowel disease (IBD) has garnered significant attention, particularly regarding how intestinal microbiota finely regulates immune responses through immune cells and sensory neurons.

MAIN BODY

Metabolites produced by intestinal microbiota influence the phenotype switching of immune cells via complex signalling pathways, thereby modulating their anti-inflammatory and pro-inflammatory functions during intestinal inflammation. Furthermore, sensory neurons exhibit heightened sensitivity to microbial-derived signals, which is essential for preserving intestinal balance and controlling pathological inflammation by integrating peripheral environmental signals with local immune responses. The dynamic equilibrium between immune cells and the neuroimmunoregulation mediated by sensory neurons collectively sustains immune homeostasis within the intestine. However, this coordination mechanism is markedly disrupted under the pathological conditions associated with IBD.

CONCLUSION

An in-depth exploration of the interactions among immune cells, gut microbiota and sensory neurons may yield significant insights into the pathological mechanisms underlying IBD and guide the creation of new treatment approaches.

KEY POINTS

The gut microbiota regulates the gut-brain-immune axis, modulating neuroimmune interactions in IBD. Microbiota-derived metabolites influence immune cells, thereby affecting neurons. Neurons secrete mediators, enabling bidirectional neuroimmune communication essential for intestinal homeostasis. Disruptions contribute to IBD, offering therapeutic targets.

Independent and temporally separated dynamics for RORγt and Foxp3 during Th17 differentiation

T helper 17 and Regulatory T cells (Th17 and Treg, respectively) are two well-described lymphocyte subsets with opposing actions. The divergent fates of Th17 and Treg cells are accounted for, at least in part, by molecular antagonism that occurs between their respective specific transcription factors, RORγt and Foxp3. An imbalance between Th17 and Treg cells may lead to tissue inflammation and is associated with certain types of autoimmunity. In order to understand the heterogeneity and dynamics of the differentiation process, we studied Th17/Treg cell differentiation of naïve cells in vitro, using RORγtGFPFoxp3RFP dual-reporter mouse. Flow cytometry revealed the consistent emergence of a population of double positive RORγt+Foxp3+ (DP) cells during the early stages of Th17 cell differentiation. These DP cells are closely related to RORγt+ single positive (SPR) cells in terms of global gene expression. Nevertheless, for some genes, DP cells share an expression pattern with Foxp3+ single positive (SPF) Treg cells, most importantly by reducing IL17 levels. Using time-lapse microscopy, we could delineate the expression dynamics of RORγt and Foxp3 at a clonal level. While the RORγt expression level elevates early during differentiation, Foxp3 rises later and is more stable upon environmental changes. These distinct expression profiles are independent of each other. During differentiation and proliferation, individual cells transit between SPR, DP, and SPF states. Nevertheless, the differentiation of sister cells within a clone progeny was highly correlated. We further demonstrated that sorted SPR and DP populations were not significantly affected by changes in their environment, suggesting that the correlated fate decision emerged at early time points before the first division. Overall, this study provides the first quantitative analysis of differentiation dynamics during the generation of DP RORγt+Foxp3+ cells. Characterizing these dynamics and the differentiation trajectory could provide a profound understanding and be used to better define the distinct fates of T cells, critical mediators of the immune response.

ACC1 is a dual metabolic-epigenetic regulator of Treg stability and immune tolerance

OBJECTIVE

Regulatory T cells (Tregs) are essential in maintaining immune tolerance and controlling inflammation. Treg stability relies on transcriptional and post-translational mechanisms, including histone acetylation at the Foxp3 locus and FoxP3 protein acetylation. Additionally, Tregs depend on specific metabolic programs for differentiation, yet the underlying molecular mechanisms remain elusive. We aimed to investigate the role of acetyl-CoA carboxylase 1 (ACC1) in the differentiation, stability, and function of regulatory T cells (Tregs).

METHODS

We used either T cell-specific ACC1 knockout mice or ACC1 inhibition via a pharmacological agent to examine the effects on Treg differentiation and stability. The impact of ACC1 inhibition on Treg function was assessed in vivo through adoptive transfer models of Th1/Th17-driven inflammatory diseases.

RESULTS

Inhibition or genetic deletion of ACC1 led to an increase in acetyl-CoA availability, promoting enhanced histone and protein acetylation, and sustained FoxP3 transcription even under inflammatory conditions. Mice with T cell-specific ACC1 deletion exhibited an enrichment of double positive RORγt+FoxP3+ cells. Moreover, Tregs treated with an ACC1 inhibitor demonstrated superior long-term stability and an enhanced capacity to suppress Th1/Th17-driven inflammatory diseases in adoptive transfer models.

CONCLUSIONS

We identified ACC1 as a metabolic checkpoint in Treg biology. Our data demonstrate that ACC1 inhibition promotes Treg differentiation and long-term stability in vitro and in vivo. Thus, ACC1 serves as a dual metabolic and epigenetic hub, regulating immune tolerance and inflammation by balancing de novo lipid synthesis and protein acetylation.

Dual neutralization of TGF-β and IL-21 regulates Th17/Treg balance by suppressing inflammatory signalling in the splenic lymphocytes of Staphylococcus aureus infection-induced septic arthritic mice

Septic arthritis (SA) caused by Staphylococcus aureus is a severe inflammatory joint disease, characterized by synovitis accompanied with cartilage destruction and bone erosion. The available antibiotic treatment alone is insufficient to resolve the inflammation that leads to high rates of morbidity and mortality. Among the CD4+ T helper lymphocytes, the Th17 and Tregs are key regulators of immune homeostasis. A high Th17 could lead to autoimmunity, whereas an increase in Tregs indicates immunosuppression. Depending on the external cytokine milieu, naïve CD4+ T cells transform into either Th17 or Treg cell lineage. TGF-β in the presence of IL-21 produces Th17 cells and drives the inflammatory cascade of reactions. We studied the effects of in vivo neutralization of TGF-β and IL-21 in septic arthritic mice to control arthritic inflammation, which has not been studied before. The arthritic index showed maximum severity in the SA group which substantially reduced in the Ab-treated groups. Flow cytometric analyses of peripheral blood collected from mice at 9DPI revealed the highest Th17/Treg ratio in the SA group but least in the combined-antibody-treated group. TGF-β1 and IL-21 cytokine production from serum, spleen, and synovial tissue homogenates was significantly reduced in the dual Ab-treated group than in the untreated SA group. From the Western blot analyses obtained from splenic lymphocytes at 9 DPI, we elucidated the possible underlying mechanism of interplay in downstream signalling involving the interaction between different STAT proteins and SOCS, NF-κB, RANKL, mTOR, iNOS, and COX-2 in regulating inflammation and osteoclastogenesis. On endogenous blockade with TGF-β and IL-21, the Th17/Treg ratio and resultant arthritic inflammation in SA were found to be reduced. Therefore, maintaining the Th17/Treg balance is critical to eradicate infection as well as suppress excessive inflammation and neutralization of TGF-β and IL-21 could provide a novel therapeutic strategy to treat staphylococcal SA.

Interactions of human milk oligosaccharides with the immune system

Human milk oligosaccharides (HMOs) are abundant, diverse and complex sugars present in human breast milk. HMOs are well-characterized barriers to microbial infection and by modulating the human microbiome they are also thought to be nutritionally beneficial to the infant. The structural variety of over 200 HMOs, including neutral, fucosylated and sialylated forms, allows them to interact with the immune system in various ways. Clinically, HMOs impact allergic diseases, reducing autoimmune and inflammatory responses, and offer beneficial support to the preterm infant immune health. This review examines the HMO composition and associated immunomodulatory effects, including interactions with immune cell receptors and gut-associated immune responses. These immunomodulatory properties highlight the potential for HMO use in early stage immune development and for use as novel immunotherapeutics. HMO research is rapidly evolving and promises innovative treatments for immune-related conditions and improved health outcomes.

Translational characterization of immune pathways in inflammatory bowel disease: insights for targeted treatments

INTRODUCTION

The pathogenesis of inflammatory bowel disease (IBD) involves the dysregulation of multiple inflammatory pathways. The understanding of these mechanisms allows their selective targeting for therapeutic purposes. The discovery of Tumor Necrosis Factor-alpha's (TNF-α) role in mucosal inflammation ushered an exciting new era of drug development which now comprises agents targeting multiple pro-inflammatory signaling pathways, integrins, and leukocyte trafficking regulators.

AREA COVERED

This review provides an overview of the main molecular players of IBD, their translation into therapeutic targets and the successful development of the advanced agents modulating them. We combine basic science with clinical trials data to present a critical review of both the successful and failed drug development programs. A PubMed literature search was conducted to delve into the available literature and clinical trials.

EXPERT OPINION

The treatment landscape for IBD has rapidly expanded, particularly with the development of biologics targeting TNF-α, integrins, and S1P modulators, as well as newer agents such as IL-12/IL-23 inhibitors and JAK inhibitors, offering robust efficacy and safety profiles. However, challenges persist in understanding and effectively treating difficult-to-treat IBD, highlighting the need for continued research to uncover novel therapeutic targets and optimize patient outcomes.

The IL-23R and Its Genetic Variants: A Hitherto Unforeseen Bridge Between the Immune System and Cancer Development

IL-23R (interleukin-23 receptor), found on the surface of several immune cells, plays a key role in the immune system. Indeed, this process is not limited to the inflammatory response but also plays a role in the adaptive immune response. The binding between IL-23R and its specific ligand, the interleukin 23, initiates a number of specific signals by modulating both properties and behavior of immune cells. In particular, it is critical for the regulation of T helper 17 cells (Th17). Th17s are a subset of T cells involved in autoimmune and inflammatory diseases, as well as in cancer. The clinical relevance of IL-23R is underscored by its association with an elevated susceptibility or diminished vulnerability to a spectrum of diseases, including psoriasis, ankylosing spondylitis, and inflammatory bowel disease (IBD). Evidence has emerged that suggests it may also serve to predict both tumor progression and therapeutic responsiveness. It is noteworthy that the IL-23/IL-23R pathway is emerging as a promising therapeutic target. A number of biologic drugs, such as monoclonal antibodies, are currently developing with the aim of blocking this interaction, thus reducing inflammation. This represents a significant advancement in the field of medicine, offering new hope for pursuing more effective and personalized treatments. Recent studies have also investigated the role of such a pathway in autoimmune diseases, and its potential impact on infections as well as in carcinogenesis. The aim of this review is to focus on the role of IL-23R in immune genetics and its potential for modulating the natural history of neoplastic disease.

The IL-2 SYNTHORIN molecule promotes functionally adapted Tregs in a preclinical model of type 1 diabetes

Deficits in IL-2 signaling can precipitate autoimmunity by altering the function and survival of FoxP3+ regulatory T cells (Tregs) while high concentrations of IL-2 fuel inflammatory responses. Recently, we showed that the non-beta IL-2 SYNTHORIN molecule SAR444336 (SAR'336) can bypass the induction of autoimmune and inflammatory responses by increasing its reliance on IL-2 receptor α chain subunit (CD25) to provide a bona fide IL-2 signal selectively to Tregs, making it an attractive approach for the control of autoimmunity. In this report, we further demonstrate that SAR'336 can support non-beta IL-2 signaling in murine Tregs and limit NK and CD8+ T cells' proliferation and function. Using a murine model of spontaneous type 1 diabetes, we showed that the administration of SAR'336 slows the development of disease in mice by decreasing the degree of insulitis through the expansion of antigen-specific Tregs over Th1 cells in pancreatic islets. Specifically, SAR'336 promoted the differentiation of IL-33-responsive (ST2+), IL-10-producing GATA3+ Tregs over other Treg subsets in the pancreas, demonstrating the ability of this molecule to further orchestrate Treg adaptation. These results offer insight into the capacity of SAR'336 to generate highly specialized, tissue-localized Tregs that promote restoration of homeostasis during ongoing autoimmune disease.

Interleukin-2 receptor signaling acts as a checkpoint that influences the distribution of regulatory T cell subsets

Regulatory T cells (Tregs) require IL-2 for survival in the periphery, yet how IL-2 shapes Treg heterogeneity remains poorly defined. Here we show that inhibition of IL-2R signaling in post-thymic Tregs leads to a preferential early loss of circulating Tregs (cTregs). Gene expression of cTregs was more dependent on IL-2R signaling than effector Tregs (eTregs). Unexpectedly, ablation of IL-2R signaling in cTregs resulted in increased proliferation, expression of eTreg genes, and enhanced capacity to develop into eTregs. Thus, IL-2R signaling normally acts as a checkpoint to maintain cTreg homeostasis while restraining their development into eTregs. Loss of IL-2R signaling also alters the distribution of eTreg subsets, with increased IFNγR1+ eTregs and CXCR5+ PD-1+ T follicular regulatory (TFR) cells but decreased intestinal RORγt+ TR17 cells. These changes lower eTreg suppressive function supporting expansion of IFNγ-secreting T effector cells. Thus, IL-2R signaling also safeguards Treg function and licenses differentiation of specialized eTregs.

Metabolic drives affecting Th17/Treg gene expression changes and differentiation: impact on immune-microenvironment regulation

The CD4+ T-cell population plays a vital role in the adaptive immune system by coordinating the immune response against different pathogens. A significant transformation occurs in CD4+ cells during an immune response, as they shift from a dormant state to an active state. This transformation leads to extensive proliferation, differentiation, and cytokine production, which contribute to regulating and coordinating the immune response. Th17 and Treg cells are among the most intriguing CD4+ T-cell subpopulations in terms of genetics and metabolism. Gene expression modulation processes rely on and are linked to metabolic changes in cells. Lactylation is a new model that combines metabolism and gene modulation to drive Th17/Treg differentiation and functional processes. The focus of this review is on the metabolic pathways that impact lymphocyte gene modulation in a functionally relevant manner.

Dysregulation of T cell response in the pathogenesis of inflammatory bowel disease

Inflammatory bowel disease (IBD), comprised of Crohn's disease (CD) and ulcerative colitis (UC), are gut inflammatory diseases that were earlier prevalent in the Western Hemisphere but now are on the rise in the East, with India standing second highest in the incidence rate in the world. Inflammation in IBD is a cause of dysregulated immune response, wherein helper T (Th) cell subsets and their cytokines play a major role in the pathogenesis of IBD. In addition, gut microbiota, environmental factors such as dietary factors and host genetics influence the outcome and severity of IBD. Dysregulation between effector and regulatory T cells drives gut inflammation, as effector T cells like Th1, Th17 and Th9 subsets Th cell lineages were found to be increased in IBD patients. In this review, we attempted to discuss the role of different Th cell subsets together with other T cells like CD8+ T cells, NKT and γδT cells in the outcome of gut inflammation in IBD. We also highlighted the potential therapeutic candidates for IBD.

Neutralization of TLR2 in combination with either TNF-α or IL-1β antibody reduces the severity of septic arthritis through STAT3/mTOR signalling in lymphocytes

Staphylococcus aureus induced Septic arthritis is considered a medical concern. S.aureus binds TLR2 to induce an array of inflammatory responses. Generation of pro-inflammatory cytokines induces T cell responses and control Th17/Treg cell balance. Regulation of T cell-mediated immunity in response to inflammation is significantly influenced by mTOR. Presence of elevated TNF-α, IL-1β decreases Treg cell activity through STAT3/mTOR, promoting proliferation of T cells towards Th17 cells. Therefore, we postulated, neutralizing TLR2 with either TNF-α or IL-1β in combination could be useful in modifying Th17/Treg cell ratio in order to treat septic arthritis by suppressing expression of mTOR/STAT3. To date, no studies have reported effects of neutralization of TLR2 along with either TNF-α or IL-1β on amelioration of arthritis correlating with mTOR/STAT3 expression. Contribution of T lymphocytes collected from blood, spleen, synovial tissues, their derived cytokines IFN-γ, IL-6, IL-17, TGF-β, IL-10 were noted. Expression of TLR2, TNFR1, TNFR2, NF-κB along with mTOR/STAT3 also recorded. Neutralization of TLR2 along with TNF-α and IL-1β were able to shift Th17 cells into immunosuppressive Treg cells. Furthermore,elevated expression of IL-10, TNFR2 and demoted expression of mTOR/ STAT3 along with NF-κB in lymphocytes confirms its role in resolution of arthritis. It was also effective in reducing oxidative stress via increasing expression of the antioxidant enzymes. As a result, it can be inferred that Treg-derived IL-10, which may mitigate inflammatory effects of septic arthritis by influencing the mTOR/STAT3 interaction in lymphocytes, may be selected as a different therapeutic strategy for reducing the impact of septic arthritis.

How bile acids and the microbiota interact to shape host immunity

Bile acids are increasingly appearing in the spotlight owing to their novel impacts on various host processes. Similarly, there is growing attention on members of the microbiota that are responsible for bile acid modifications. With recent advances in technology enabling the discovery and continued identification of microbially conjugated bile acids, the chemical complexity of the bile acid landscape in the body is increasing at a rapid pace. In this Review, we summarize our current understanding of how bile acids and the gut microbiota interact to modulate immune responses during homeostasis and disease, with a particular focus on the gut.

Lymphotoxins from distinct types of lymphoid cells differentially contribute to neuroinflammation

Lymphotoxin α and lymphotoxin β (LTs), TNF superfamily members, are expressed in either soluble (LTα3) or membrane-bound (LTα1β2 or LTα2β1) forms. In the pathological context, LT-mediated signaling is known to exacerbate autoimmunity by perpetuating inflammation and promoting the formation of tertiary lymphoid organs. Despite this understanding, the exact roles of LTα and LTβ in the pathogenesis of the murine model of multiple sclerosis, and experimental autoimmune encephalomyelitis (EAE), remain controversial. Here, we employed a panel of gene-modified mice with cell-type restricted ablation of LTα (targeting both membrane-bound and soluble forms of LTs) to unravel the contributions of LTs from various lymphoid cells, namely T cells, type 3 innate lymphoid cells (ILC3) and B cells, in EAE. We found that the effects of LTα deletion were dependent on the cellular source. ILC3-derived lymphotoxins exerted a protective role in EAE by regulating the accumulation of IFN-ɣ- and GM-CSF-producing TH cells in the CNS. In contrast, T-cell-derived lymphotoxins promoted IL-17A- and GM-CSF-mediated TH responses in the periphery, whereas B-cell-derived lymphotoxins were pathogenic only in the autoantibody-mediated EAE model. Collectively, our findings unveil the multifaceted involvement of lymphotoxins in EAE pathogenesis and challenge the view that lymphotoxins play a solely pathogenic role in neuroinflammation.

Multistability and predominant hybrid phenotypes in a four node mutually repressive network of Th1/Th2/Th17/Treg differentiation

Elucidating the emergent dynamics of cellular differentiation networks is crucial to understanding cell-fate decisions. Toggle switch - a network of mutually repressive lineage-specific transcription factors A and B - enables two phenotypes from a common progenitor: (high A, low B) and (low A, high B). However, the dynamics of networks enabling differentiation of more than two phenotypes from a progenitor cell has not been well-studied. Here, we investigate the dynamics of a four-node network A, B, C, and D inhibiting each other, forming a toggle tetrahedron. Our simulations show that this network is multistable and predominantly allows for the co-existence of six hybrid phenotypes where two of the nodes are expressed relatively high as compared to the remaining two, for instance (high A, high B, low C, low D). Finally, we apply our results to understand naïve CD4+ T cell differentiation into Th1, Th2, Th17 and Treg subsets, suggesting Th1/Th2/Th17/Treg decision-making to be a two-step process.

Gut Microbiota Defines Functional Direction of Colonic Regulatory T Cells with Unique TCR Repertoires

Intestinal microbiota and selected strains of commensal bacteria influence regulatory T (Treg) cell functionality in the colon. Nevertheless, whether and how microbiota changes the transcriptome profile and TCR specificities of colonic Tregs remain to be precisely defined. In this study, we have employed single-cell RNA sequencing and comparatively analyzed colonic Tregs from specific pathogen-free and germ-free (GF) mice. We found that microbiota shifts the activation trajectory of colonic Tregs toward a distinct phenotypic subset enriched in specific pathogen-free but not in GF mice. Moreover, microbiota induced the expansion of specific Treg clonotypes with shared transcriptional specificities. The microbiota-induced subset of colonic Tregs, identified as PD-1- CXCR3+ Tregs, displayed enhanced suppressive capabilities compared with colonic Tregs derived from GF mice, enhanced production of IL-10, and were the primary regulators of enteric inflammation in dextran sodium sulfate-induced colitis. These findings identify a hitherto unknown gut microbiota and immune cell interaction module that could contribute to the development of a therapeutic modality for intestinal inflammatory diseases.

Interleukin-2 immunotherapy reveals human regulatory T cell subsets with distinct functional and tissue-homing characteristics

Due to its stimulatory potential for immunomodulatory CD4+ regulatory T (Treg) cells, low-dose interleukin-2 (IL-2) immunotherapy has gained considerable attention for the treatment of autoimmune diseases. In this investigator-initiated single-arm non-placebo-controlled phase-2 clinical trial of low-dose IL-2 immunotherapy in systemic lupus erythematosus (SLE) patients, we generated a comprehensive atlas of in vivo human immune responses to low-dose IL-2. We performed an in-depth study of circulating and cutaneous immune cells by imaging mass cytometry, high-parameter flow cytometry, transcriptomics, and targeted serum proteomics. Low-dose IL-2 stimulated various circulating immune cells, including Treg cells with a skin-homing phenotype that appeared in the skin of SLE patients in close interaction with endothelial cells. Analysis of surface proteins and transcriptomes revealed different IL-2-driven Treg cell activation programs, including gut-homing CD38+, skin-homing HLA-DR+, and highly proliferative inflammation-homing CD38+ HLA-DR+ Treg cells. Collectively, these data define the distinct human Treg cell subsets that are responsive to IL-2 immunotherapy.

DNA methylation profiling identifies TBKBP1 as potent amplifier of cytotoxic activity in CMV-specific human CD8+ T cells

Epigenetic mechanisms stabilize gene expression patterns during CD8+ T cell differentiation. Although adoptive transfer of virus-specific T cells is clinically applied to reduce the risk of virus infection or reactivation in immunocompromised individuals, the DNA methylation pattern of virus-specific CD8+ T cells is largely unknown. Hence, we here performed whole-genome bisulfite sequencing of cytomegalovirus-specific human CD8+ T cells and found that they display a unique DNA methylation pattern consisting of 79 differentially methylated regions (DMRs) when compared to memory CD8+ T cells. Among the top demethylated DMRs in cytomegalovirus-specific CD8+ T cells was TBKBP1, coding for TBK-binding protein 1 that can interact with TANK-binding kinase 1 (TBK1) and mediate pro-inflammatory responses in innate immune cells downstream of intracellular virus sensing. Since TBKBP1 has not yet been reported in T cells, we aimed to unravel its role in virus-specific CD8+ T cells. TBKBP1 demethylation in terminal effector CD8+ T cells correlated with higher TBKBP1 expression at both mRNA and protein level, independent of alternative splicing of TBKBP1 transcripts. Notably, the distinct DNA methylation patterns in CD8+ T cell subsets was stable upon long-term in vitro culture. TBKBP1 overexpression resulted in enhanced TBK1 phosphorylation upon stimulation of CD8+ T cells and significantly improved their virus neutralization capacity. Collectively, our data demonstrate that TBKBP1 modulates virus-specific CD8+ T cell responses and could be exploited as therapeutic target to improve adoptive T cell therapies.

Crucial role of dendritic cells in the generation of anti-tumor T-cell responses and immunogenic tumor microenvironment to suppress tumor development

Dendritic cells (DCs) are known as unique professional antigen (Ag)-presenting cells (APCs) to prime naïve T cells for the initiation of adaptive immunity. While DCs are believed to play a pivotal role in generating anti-tumor T-cell responses, the importance of DCs in the protection from the progression of tumors remains elusive. Here, we show how the constitutive deficiency of CD11chi DCs influences the progression of tumors with the use of binary transgenic mice with constitutive loss of CD11chi DCs. Constitutive loss of CD11chi DCs not only enhances the progression of tumors but also reduces the responses of Ag-specific T cells. Furthermore, the congenital deficiency of CD11chi DCs generates the immunosuppressive tumor microenvironment (TME) that correlates with the marked accumulation of myeloid-derived suppressor cells (MDSCs) and the prominent productions of immunosuppressive mediators. Thus, our findings suggest that CD11chi DCs are crucial for generating anti-tumor T-cell responses and immunogenic TME to suppress the development of tumors.

The atypical IκB family member Bcl3 determines differentiation and fate of intestinal RORγt+ regulatory T-cell subsets

Peripherally-induced regulatory T cells (pTregs) expressing the retinoic acid receptor-related orphan-receptor gamma t (RORγt) are indispensable for intestinal immune homeostasis. Nuclear factor kappa family members regulate the differentiation of thymic Tregs and promote their survival in the periphery. However, the Treg intrinsic molecular mechanisms controlling the size of the pTregs in the intestine and associated lymphoid organs remain unclear. Here, we provide direct evidence that B-cell lymphoma 3 (Bcl3) limits the development of pTregs in a T cell-intrinsic manner. Moreover, the absence of Bcl3 allowed for the formation of an unusual intestinal Treg population co-expressing the transcription factors Helios and RORγt. The expanded RORγt+ Treg populations in the absence of Bcl3 displayed an activated phenotype and secreted high levels of the anti-inflammatory cytokines interleukin (IL)-10 and transforming growth factor beta. They were fully capable of suppressing effector T cells in a transfer colitis model despite an intrinsic bias to trans-differentiate toward T helper 17-like cells. Finally, we provide a Bcl3-dependent gene signature in pTregs including altered responsiveness to the cytokines IL-2, IL-6, and tumor necrosis factor alpha. Our results demonstrate that Bcl3 acts as a molecular switch to limit the expansion of different intestinal Treg subsets and may thus serve as a novel therapeutic target for inflammatory bowel disease by restoring intestinal immune tolerance.

Venetoclax Induces BCL-2-Dependent Treg to TH17 Plasticity to Enhance the Antitumor Efficacy of Anti-PD-1 Checkpoint Blockade

The specific BCL-2 small molecule inhibitor venetoclax induces apoptosis in a wide range of malignancies, which has led to rapid clinical expansion in its use alone and in combination with chemotherapy and immune-based therapies against a myriad of cancer types. While lymphocytes, and T cells in particular, rely heavily on BCL-2 for survival and function, the effects of small molecule blockade of the BCL-2 family on surviving immune cells is not fully understood. We aimed to better understand the effect of systemic treatment with venetoclax on regulatory T cells (Treg), which are relatively resistant to cell death induced by specific drugging of BCL-2 compared to other T cells. We found that BCL-2 blockade altered Treg transcriptional profiles and mediated Treg plasticity toward a TH17-like Treg phenotype, resulting in increased IL17A production in lymphoid organs and within the tumor microenvironment. Aligned with previously described augmented antitumor effects observed when combining venetoclax with anti-PD-1 checkpoint inhibition, we also demonstrated that Treg-specific genetic BCL-2 knockout combined with anti-PD-1 induced tumor regression and conferred overlapping genetic changes with venetoclax-treated Tregs. As long-term combination therapies using venetoclax gain more traction in the clinic, an improved understanding of the immune-modulatory effects caused by venetoclax may allow expansion of its use against malignancies and immune-related diseases.

Stress and the gut-brain axis: an inflammatory perspective

The gut-brain axis (GBA) plays a dominant role in maintaining homeostasis as well as contributes to mental health maintenance. The pathways that underpin the axis expand from macroscopic interactions with the nervous system, to the molecular signals that include microbial metabolites, tight junction protein expression, or cytokines released during inflammation. The dysfunctional GBA has been repeatedly linked to the occurrence of anxiety- and depressive-like behaviors development. The importance of the inflammatory aspects of the altered GBA has recently been highlighted in the literature. Here we summarize current reports on GBA signaling which involves the immune response within the intestinal and blood-brain barrier (BBB). We also emphasize the effect of stress response on altering barriers' permeability, and the therapeutic potential of microbiota restoration by probiotic administration or microbiota transplantation, based on the latest animal studies. Most research performed on various stress models showed an association between anxiety- and depressive-like behaviors, dysbiosis of gut microbiota, and disruption of intestinal permeability with simultaneous changes in BBB integrity. It could be postulated that under stress conditions impaired communication across BBB may therefore represent a significant mechanism allowing the gut microbiota to affect brain functions.

The regulation and differentiation of regulatory T cells and their dysfunction in autoimmune diseases

The discovery of FOXP3+ regulatory T (Treg) cells as a distinct cell lineage with a central role in regulating immune responses provided a deeper understanding of self-tolerance. The transcription factor FOXP3 serves a key role in Treg cell lineage determination and maintenance, but is not sufficient to enable the full potential of Treg cell suppression, indicating that other factors orchestrate the fine-tuning of Treg cell function. Moreover, FOXP3-independent mechanisms have recently been shown to contribute to Treg cell dysfunction. FOXP3 mutations in humans cause lethal fulminant systemic autoinflammation (IPEX syndrome). However, it remains unclear to what degree Treg cell dysfunction is contributing to the pathophysiology of common autoimmune diseases. In this Review, we discuss the origins of Treg cells in the periphery and the multilayered mechanisms by which Treg cells are induced, as well as the FOXP3-dependent and FOXP3-independent cellular programmes that maintain the suppressive function of Treg cells in humans and mice. Further, we examine evidence for Treg cell dysfunction in the context of common autoimmune diseases such as multiple sclerosis, inflammatory bowel disease, systemic lupus erythematosus and rheumatoid arthritis.

Stability and plasticity of regulatory T cells in health and disease

The mechanisms that negatively regulate inflammation upon a pathogenic stimulus are crucial for the maintenance of tissue integrity and organ function. T regulatory cells are one of the main drivers in controlling inflammation. The ability of T regulatory cells to adapt to different inflammatory cues and suppress inflammation is one of the relevant features of T regulatory cells. During this process, T regulatory cells express different transcription factors associated with their counterparts, Th helper cells, including Tbx21, GATA-3, Bcl6, and Rorc. The acquisition of this transcription factor helps the T regulatory cells to suppress and migrate to the different inflamed tissues. Additionally, the T regulatory cells have different mechanisms that preserve stability while acquiring a particular T regulatory cell subtype. This review focuses on describing T regulatory cell subtypes and the mechanisms that maintain their identity in health and diseases.

Long noncoding RNA LIRIL2R modulates FOXP3 levels and suppressive function of human CD4+ regulatory T cells by regulating IL2RA

Regulatory T cells (Tregs) are central in controlling immune responses, and dysregulation of their function can lead to autoimmune disorders or cancer. Despite extensive studies on Tregs, the basis of epigenetic regulation of human Treg development and function is incompletely understood. Long intergenic noncoding RNAs (lincRNA)s are important for shaping and maintaining the epigenetic landscape in different cell types. In this study, we identified a gene on the chromosome 6p25.3 locus, encoding a lincRNA, that was up-regulated during early differentiation of human Tregs. The lincRNA regulated the expression of interleukin-2 receptor alpha (IL2RA), and we named it the lincRNA regulator of IL2RA (LIRIL2R). Through transcriptomics, epigenomics, and proteomics analysis of LIRIL2R-deficient Tregs, coupled with global profiling of LIRIL2R binding sites using chromatin isolation by RNA purification, followed by sequencing, we identified IL2RA as a target of LIRIL2R. This nuclear lincRNA binds upstream of the IL2RA locus and regulates its epigenetic landscape and transcription. CRISPR-mediated deletion of the LIRIL2R-bound region at the IL2RA locus resulted in reduced IL2RA expression. Notably, LIRIL2R deficiency led to reduced expression of Treg-signature genes (e.g., FOXP3, CTLA4, and PDCD1), upregulation of genes associated with effector T cells (e.g., SATB1 and GATA3), and loss of Treg-mediated suppression.

Sialyl Lewis X Defines an Activated and Functional Regulatory T Cell Subpopulation in Mice

Attempts have been made to elucidate the functional markers of regulatory T cells (Tregs), CD4+Foxp3+ T cells with an immunosuppressive function. Sialyl Lewis X (sLex), a tetrasaccharide Ag, is involved in leukocyte trafficking as selectin ligands and is a marker of highly differentiated Tregs in humans. However, the importance of sLex in murine Tregs remains unknown. In this study, we report that sLex defines the activated and functional subset of murine Tregs. The contact hypersensitivity model showed that murine Tregs strongly express sLex upon activation, accompanied by functional Treg marker elevation, such as Foxp3, CD25, CD103, CD39, and granzyme B. RNA sequencing analysis revealed sLex-positive (sLex+) Tregs expressed genes involved in Treg function at a higher level than sLex-negative (sLex-) Tregs. Using an in vitro suppression assay, we found that sLex+ Tregs could more efficiently suppress naive CD4+ T cell proliferation than sLex- Tregs. In the murine contact hypersensitivity elicitation model, the topical sLex+ Treg injection into the ears suppressed ear inflammation more efficiently than that of sLex- Tregs. Our results indicate that sLex could serve as a unique surface marker of activated and functional Tregs with immunosuppressive functions in mice.

The histone lysine methyltransferase MLL1 regulates the activation and functional specialization of regulatory T cells

The activation and specialization of regulatory T cells (Tregs) are crucial for maintaining immune self-tolerance; however, the regulation of these processes by histone modifications is not fully understood. Here, we show that T cell-specific deletion of the lysine methyltransferase MLL1 results in a spontaneous lymphocyte proliferation phenotype in aged mice without disturbing the development of conventional T cells and Tregs. Treg-specific MLL1 ablation leads to a systemic autoimmune disease associated with Treg dysfunction. Moreover, RNA sequencing demonstrates that the induction of multiple genes involved in Treg activation, functional specialization, and tissue immigration is defective in MLL1-deficient Tregs. This dysregulation is associated with defects in H3K4 trimethylation at these genes' transcription start sites. Finally, using a T-bet fate-mapping mouse system, we determine that MLL1 is required to establish stable Th1-type Tregs. Thus, MLL1 is essential in optimal Treg function by providing a coordinated chromatin context for activation and specialization.

Microbial dysbiosis in systemic lupus erythematosus: a scientometric study

Introduction

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease. Mounting evidence suggests microbiota dysbiosis augment autoimmune response. This study aims to provide a systematic overview of this research field in SLE through a bibliometric analysis.

Methods

We conducted a comprehensive search and retrieval of literature related to microbial researches in SLE from the Web of Science Core Collection (WOSCC) database. The retrieved articles were subjected to bibliometric analysis using VOSviewer and Bibliometricx to explore annual publication output, collaborative patterns, research hotspots, current research status, and emerging trends.

Results

In this study, we conducted a comprehensive analysis of 218 research articles and 118 review articles. The quantity of publications rises annually, notably surging in 2015 and 2018. The United States and China emerged as the leading contributors in microbial research of SLE. Mashhad University of Medical Sciences had the highest publication outputs among the institutions. Frontiers in Immunology published the most papers. Luo XM and Margolles A were the most prolific and highly cited contributors among individual authors. Microbial research in SLE primarily focused on changes in microbial composition, particularly gut microbiota, as well as the mechanisms and practical applications in SLE. Recent trends emphasize "metabolites," "metabolomics," "fatty acids," "T cells," "lactobacillus," and "dietary supplementation," indicating a growing emphasis on microbial metabolism and interventions in SLE.

Conclusion

This study provides a thorough analysis of the research landscape concerning microbiota in SLE. The microbial research in SLE mainly focused on three aspects: microbial dysbiosis, mechanism studies and translational studies (microbiota-based therapeutics). It identifies current research trends and focal points, offering valuable guidance for scholars in the field.

Functional characterization of helminth-associated Clostridiales reveals covariates of Treg differentiation

BACKGROUND

Parasitic helminths influence the composition of the gut microbiome. However, the microbiomes of individuals living in helminth-endemic regions are understudied. The Orang Asli, an indigenous population in Malaysia with high burdens of the helminth Trichuris trichiura, display microbiotas enriched in Clostridiales, an order of spore-forming obligate anaerobes with immunogenic properties. We previously isolated novel Clostridiales that were enriched in these individuals and found that a subset promoted the Trichuris life cycle. In this study, we aimed to further characterize the functional properties of these bacteria.

RESULTS

Clostridiales isolates were profiled for their ability to perform 57 enzymatic reactions and produce short-chain fatty acids (SCFAs) and hydrogen sulfide, revealing that these bacteria were capable of a range of activities associated with metabolism and host response. Consistent with this finding, monocolonization of mice with individual isolates identified bacteria that were potent inducers of regulatory T-cell (Treg) differentiation in the colon. Comparisons between variables revealed by these studies identified enzymatic properties correlated with Treg induction and Trichuris egg hatching.

CONCLUSION

We identified Clostridiales species that are sufficient to induce high levels of Tregs. We also identified a set of metabolic activities linked with Treg differentiation and Trichuris egg hatching mediated by these newly isolated bacteria. Altogether, this study provides functional insights into the microbiotas of individuals residing in a helminth-endemic region. Video Abstract.

A serine-conjugated butyrate prodrug with high oral bioavailability suppresses autoimmune arthritis and neuroinflammation in mice

Butyrate-a metabolite produced by commensal bacteria-has been extensively studied for its immunomodulatory effects on immune cells, including regulatory T cells, macrophages and dendritic cells. However, the development of butyrate as a drug has been hindered by butyrate's poor oral bioavailability, owing to its rapid metabolism in the gut, its low potency (hence, necessitating high dosing), and its foul smell and taste. Here we report that the oral bioavailability of butyrate can be increased by esterifying it to serine, an amino acid transporter that aids the escape of the resulting odourless and tasteless prodrug (O-butyryl-L-serine, which we named SerBut) from the gut, enhancing its systemic uptake. In mice with collagen-antibody-induced arthritis (a model of rheumatoid arthritis) and with experimental autoimmune encephalomyelitis (a model of multiple sclerosis), we show that SerBut substantially ameliorated disease severity, modulated key immune cell populations systemically and in disease-associated tissues, and reduced inflammatory responses without compromising the global immune response to vaccination. SerBut may become a promising therapeutic for autoimmune and inflammatory diseases.

Decoding the potential role of regulatory T cells in sepsis-induced immunosuppression

Sepsis, a multiorgan dysfunction with high incidence and mortality, is caused by an imbalanced host-to-infection immune response. Organ-support therapy improves the early survival rate of sepsis patients. In the long term, those who survive the "cytokine storm" and its secondary damage usually show higher susceptibility to secondary infections and sepsis-induced immunosuppression, in which regulatory T cells (Tregs) are evidenced to play an essential role. However, the potential role and mechanism of Tregs in sepsis-induced immunosuppression remains elusive. In this review, we elucidate the role of different functional subpopulations of Tregs during sepsis and then review the mechanism of sepsis-induced immunosuppression from the aspects of regulatory characteristics, epigenetic modification, and immunometabolism of Tregs. Thoroughly understanding how Tregs impact the immune system during sepsis may shed light on preclinical research and help improve the translational value of sepsis immunotherapy.

Bile acid metabolism and signaling in health and disease: molecular mechanisms and therapeutic targets

Bile acids, once considered mere dietary surfactants, now emerge as critical modulators of macronutrient (lipid, carbohydrate, protein) metabolism and the systemic pro-inflammatory/anti-inflammatory balance. Bile acid metabolism and signaling pathways play a crucial role in protecting against, or if aberrant, inducing cardiometabolic, inflammatory, and neoplastic conditions, strongly influencing health and disease. No curative treatment exists for any bile acid influenced disease, while the most promising and well-developed bile acid therapeutic was recently rejected by the FDA. Here, we provide a bottom-up approach on bile acids, mechanistically explaining their biochemistry, physiology, and pharmacology at canonical and non-canonical receptors. Using this mechanistic model of bile acids, we explain how abnormal bile acid physiology drives disease pathogenesis, emphasizing how ceramide synthesis may serve as a unifying pathogenic feature for cardiometabolic diseases. We provide an in-depth summary on pre-existing bile acid receptor modulators, explain their shortcomings, and propose solutions for how they may be remedied. Lastly, we rationalize novel targets for further translational drug discovery and provide future perspectives. Rather than dismissing bile acid therapeutics due to recent setbacks, we believe that there is immense clinical potential and a high likelihood for the future success of bile acid therapeutics.

Core fucosylation of maternal milk N-glycans imparts early-life immune tolerance through gut microbiota-dependent regulation in RORγt+ Treg cells

Milk glycans play key roles in shaping and maintaining a healthy infant gut microbiota. Core fucosylation catalyzed by fucosyltransferase (Fut8) is the major glycosylation pattern on human milk N-glycan, which was crucial for promoting the colonization and dominant growth of Bifidobacterium and Lactobacillus spp. in neonates. However, the influence of core-fucose in breast milk on the establishment of early-life immune tolerance remains poorly characterized. In this study, we found that the deficiency of core-fucose in the milk of maternal mice caused by Fut8 gene heterozygosity (Fut8+/-) resulted in poor immune tolerance towards the ovalbumin (OVA) challenge, accompanied by a reduced proportion of intestinal RORγt+ Treg cells and the abundance of Lactobacillus spp., especially L. reuteri and L. johnsonii, in their breast-fed neonates. The administration of the L. reuteri and L. johnsonii mixture to neonatal mice compromised the OVA-induced allergy and up-regulated the intestinal RORγt+ Treg cell proportions. However, Lactobacillus mixture supplementation did not alleviate allergic responses in RORγt+ Treg cell-deficient mice caused by Rorc gene heterozygosity (Rorc+/-) post OVA challenge, indicating that the intervention effects depend on the RORγt+ Treg cells. Interestingly, instead of L. reuteri and L. johnsonii, we found that the relative abundance of another Lactobacillus spp., L. murinus, in the gut of the offspring mice was significantly promoted by intervention, which showed enhancing effects on the proliferation of splenic and intestinal RORγt+ Treg cells in in vitro studies. The above results indicate that core fucosylation of breast milk N-glycans is beneficial for the establishment of RORγt+ Treg cell mediated early-life immune tolerance through the manipulation of symbiotic bacteria in mice.

Opposing diet, microbiome, and metabolite mechanisms regulate inflammatory bowel disease in a genetically susceptible host

Inflammatory bowel diseases (IBDs) are chronic conditions characterized by periods of spontaneous intestinal inflammation and are increasing in industrialized populations. Combined with host genetics, diet and gut bacteria are thought to contribute prominently to IBDs, but mechanisms are still emerging. In mice lacking the IBD-associated cytokine, interleukin-10, we show that a fiber-deprived gut microbiota promotes the deterioration of colonic mucus, leading to lethal colitis. Inflammation starts with the expansion of natural killer cells and altered immunoglobulin-A coating of some bacteria. Lethal colitis is then driven by Th1 immune responses to increased activities of mucin-degrading bacteria that cause inflammation first in regions with thinner mucus. A fiber-free exclusive enteral nutrition diet also induces mucus erosion but inhibits inflammation by simultaneously increasing an anti-inflammatory bacterial metabolite, isobutyrate. Our findings underscore the importance of focusing on microbial functions-not taxa-contributing to IBDs and that some diet-mediated functions can oppose those that promote disease.

Fecal microbiota transplantation stimulates type 2 and tolerogenic immune responses in a mouse model

OBJECTIVES

Clostridioides difficile infection (CDI) is the leading hospital-acquired infection in North America. While previous work on fecal microbiota transplantation (FMT), a highly effective treatment for CDI, has focused on colonization resistance mounted against C. difficile by FMT-delivered commensals, the effects of FMT on host gene expression are relatively unexplored. This study aims to identify transcriptional changes associated with FMT, particularly changes associated with protective immune responses.

METHODS

Gene expression was assessed on day 2 and day 7 after FMT in mice after antibiotic-induced dysbiosis. Flow cytometry was also performed on colon and mesenteric lymph nodes at day 7 to investigate changes in immune cell populations.

RESULTS

FMT administration after antibiotic-induced dysbiosis successfully restored microbial alpha diversity to levels of donor mice by day 7 post-FMT. Bulk RNA sequencing of cecal tissue at day 2 identified immune genes, including both pro-inflammatory and Type 2 immune pathways as upregulated after FMT. RNA sequencing was repeated on day 7 post-FMT, and expression of these immune genes was decreased along with upregulation of genes associated with restoration of intestinal homeostasis. Immunoprofiling on day 7 identified increased colonic CD45+ immune cells that exhibited dampened Type 1 and heightened regulatory and Type 2 responses. These include an increased abundance of eosinophils, alternatively activated macrophages, Th2, and T regulatory cell populations.

CONCLUSION

These results highlight the impact of FMT on host gene expression, providing evidence that FMT restores intestinal homeostasis after antibiotic treatment and facilitates tolerogenic and Type 2 immune responses.

Deciphering the developmental trajectory of tissue-resident Foxp3+ regulatory T cells

Foxp3+ TREG cells have been at the focus of intense investigation for their recognized roles in preventing autoimmunity, facilitating tissue recuperation following injury, and orchestrating a tolerance to innocuous non-self-antigens. To perform these critical tasks, TREG cells undergo deep epigenetic, transcriptional, and post-transcriptional changes that allow them to adapt to conditions found in tissues both at steady-state and during inflammation. The path leading TREG cells to express these tissue-specialized phenotypes begins during thymic development, and is further driven by epigenetic and transcriptional modifications following TCR engagement and polarizing signals in the periphery. However, this process is highly regulated and requires TREG cells to adopt strategies to avoid losing their regulatory program altogether. Here, we review the origins of tissue-resident TREG cells, from their thymic and peripheral development to the transcriptional regulators involved in their tissue residency program. In addition, we discuss the distinct signalling pathways that engage the inflammatory adaptation of tissue-resident TREG cells, and how they relate to their ability to recognize tissue and pathogen-derived danger signals.

IRF4-mediated Treg phenotype switching can aggravate hyperoxia-induced alveolar epithelial cell injury

Bronchopulmonary dysplasia (BPD) is characterized by alveolar dysplasia, and evidence indicates that interferon regulatory factor 4 (IRF4) is involved in the pathogenesis of various inflammatory lung diseases. Nonetheless, the significance and mechanism of IRF4 in BPD remain unelucidated. Consequently, we established a mouse model of BPD through hyperoxia exposure, and ELISA was employed to measure interleukin-17 A (IL-17 A) and interleukin-6 (IL-6) expression levels in lung tissues. Western blotting was adopted to determine the expression of IRF4, surfactant protein C (SP-C), and podoplanin (T1α) in lung tissues. Flow cytometry was utilized for analyzing the percentages of FOXP3+ regulatory T cells (Tregs) and FOXP3+RORγt+ Tregs in CD4+ T cells in lung tissues to clarify the underlying mechanism. Our findings revealed that BPD mice exhibited disordered lung tissue structure, elevated IRF4 expression, decreased SP-C and T1α expression, increased IL-17 A and IL-6 levels, reduced proportion of FOXP3+ Tregs, and increased proportion of FOXP3+RORγt+ Tregs. For the purpose of further elucidating the effect of IRF4 on Treg phenotype switching induced by hyperoxia in lung tissues, we exposed neonatal mice with IRF4 knockout to hyperoxia. These mice exhibited regular lung tissue structure, increased proportion of FOXP3+ Tregs, reduced proportion of FOXP3+RORγt+ Tregs, elevated SP-C and T1α expression, and decreased IL-17 A and IL-6 levels. In conclusion, our findings demonstrate that IRF4-mediated Treg phenotype switching in lung tissues exacerbates alveolar epithelial cell injury under hyperoxia exposure.

The dynamic shifts of IL-10-producing Th17 and IL-17-producing Treg in health and disease: a crosstalk between ancient "Yin-Yang" theory and modern immunology

The changes in T regulatory cell (Treg) and T helper cell (Th) 17 ratios holds paramount importance in ensuring internal homeostasis and disease progression. Recently, novel subsets of Treg and Th17, namely IL-17-producing Treg and IL-10-producing Th17 have been identified. IL-17-producing Treg and IL-10-producing Th17 are widely considered as the intermediates during Treg/Th17 transformation. These "bi-functional" cells exhibit plasticity and have been demonstrated with important roles in multiple physiological functions and disease processes. Yin and Yang represent opposing aspects of phenomena according to the ancient Chinese philosophy "Yin-Yang" theory. Furthermore, Yin can transform into Yang, and vice versa, under specific conditions. This theory has been widely used to describe the contrasting functions of immune cells and molecules. Therefore, immune-activating populations (Th17, M1 macrophage, etc.) and immune overreaction (inflammation, autoimmunity) can be considered Yang, while immunosuppressive populations (Treg, M2 macrophage, etc.) and immunosuppression (tumor, immunodeficiency) can be considered Yin. However, another important connotation of "Yin-Yang" theory, the conversion between Yin and Yang, has been rarely documented in immune studies. The discovery of IL-17-producing Treg and IL-10-producing Th17 enriches the meaning of "Yin-Yang" theory and further promotes the relationship between ancient "Yin-Yang" theory and modern immunology. Besides, illustrating the functions of IL-17-producing Treg and IL-10-producing Th17 and mechanisms governing their differentiation provides valuable insights into the mechanisms underlying the dynamically changing statement of immune statement in health and diseases.

Gastric coinfection with thiopeptide-positive Cutibacterium acnes decreases FOXM1 and pro-inflammatory biomarker expression in a murine model of Helicobacter pylori-induced gastric cancer

IMPORTANCE

H. pylori infects half of the world population and is the leading cause of gastric cancer. We previously demonstrated that gastric cancer risk is associated with gastric microbiota. Specifically, gastric urease-positive Staphylococcus epidermidis and Streptococcus salivarius had contrasting effects on H. pylori-associated gastric pathology and immune responses in germ-free INS-GAS mice. As gastritis progresses to gastric cancer, the oncogenic transcription factor Foxm1 becomes increasingly expressed. In this study, we evaluated the gastric commensal C. acnes, certain strains of which produce thiopeptides that directly inhibit FOXM1. Thiopeptide-positive C. acnes was isolated from Nicaraguan patient gastric biopsies and inoculated into germ-free INS-GAS mice with H. pylori. We, therefore, asked whether coinfection with C. acnes expressing thiopeptide and H. pylori would decrease gastric Foxm1 expression and pro-inflammatory cytokine mRNA and protein levels. Our study supports the growing literature that specific non-H. pylori gastric bacteria affect inflammatory and cancer biomarkers in H. pylori pathogenesis.

Eosinophils Contribute to Oral Tolerance via Induction of RORγt-Positive Antigen-Presenting Cells and RORγt-Positive Regulatory T Cells

Oral tolerance has been defined as the specific suppression of immune responses to an antigen by prior oral administration of the antigen. It has been thought to serve to suppress food allergy. Previous studies have shown that dendritic cells (DCs) and regulatory T cells (Tregs) are involved in the induction of oral tolerance. However, the detailed mechanisms of Treg induction in oral tolerance remain largely unknown. Eosinophils have been recognized as effector cells in allergic diseases, but in recent years, the diverse functions of tissue-resident eosinophils have been reported. Eosinophils in the intestine have been reported to induce Tregs by releasing TGF-β, but the role of eosinophils in oral tolerance is still controversial. In this study, we analyzed the roles of eosinophils in oral tolerance using eosinophil-deficient ΔdblGATA mice (mice lacking a high-affinity GATA-binding site in the GATA1 promoter). ΔdblGATA mice showed impaired antigen-induced oral tolerance compared to wild-type mice. The induction of RORγt+ Tregs in mesenteric lymph nodes (MLNs) by oral tolerance induction was impaired in ΔdblGATA mice compared to wild-type mice. An increase in RORγt+ antigen-presenting cells (APCs), which are involved in RORγt+ Treg differentiation, in the intestine and MLNs was not seen in ΔdblGATA mice. Notably, the expansion of group 3 innate lymphoid cells (ILC3s), a subset of RORγt+ APCs, by oral tolerance induction was seen in wild-type mice but not ΔdblGATA mice. These results suggest that eosinophils are crucial in the induction of oral tolerance, possibly via the induction of RORγt+ APCs and RORγt+ Tregs.

Regulatory T cells in dominant immunologic tolerance

Regulatory T cells expressing the transcription factor forkhead box protein 3 mediate peripheral immune tolerance both to self-antigens and to the commensal flora. Their defective function due to inborn errors of immunity or acquired insults is associated with a broad range of autoimmune and immune dysregulatory diseases. Although their function in suppressing autoimmunity and enforcing commensalism is established, a broader role for regulatory T cells in tissue repair and metabolic regulation has emerged, enabled by unique programs of tissue adaptability and specialization. In this review, we focus on the myriad roles played by regulatory T cells in immunologic tolerance and host homeostasis and the potential to harness these cells in novel therapeutic approaches to human diseases.

Interleukin 23 receptor: Expression and regulation in immune cells

The importance of IL-23 and its specific receptor, IL-23R, in the pathogenesis of several chronic inflammatory diseases has been established, but the underlying pathological mechanisms are not fully understood. This review focuses on IL-23R expression and regulation in immune cells.

Oral tolerance to systemic vaccination remains intact without RORγt expression in regulatory T cells

Many promising vaccine candidates and licensed vaccines lead to variable immune responses within humans. Studies suggest that environmental exposures in the gastrointestinal tract could contribute to a reduction in vaccine efficacy via immune tolerance at this site; this is partly achieved by a high abundance of regulatory T cells (Tregs). It is unclear if Treg subsets regulate systemic vaccine responses following oral antigen pre-exposure. Here, we implemented a conditional knock-out mouse model of RORγt+ Tregs to examine the role of these cells in mediating this process. Following oral exposure to the model antigen ovalbumin (OVA) prior to immunization, we found similar induction of vaccine-induced antibody responses in mice lacking RORγt expression in Tregs compared to sufficient controls. Use of various adjuvants led to distinct findings. Our data suggest that expression of RORγt+ within Tregs is not required to regulate tolerance to systemic vaccination following oral antigen exposure.

Homeostatic, repertoire and transcriptional relationships between colon T regulatory cell subsets

Foxp3+ regulatory T cells (Tregs) in the colon are key to promoting peaceful coexistence with symbiotic microbes. Differentiated in either thymic or peripheral locations, and modulated by microbes and other cellular influencers, colonic Treg subsets have been identified through key transcription factors (TFs; Helios, Rorγ, Gata3, and cMaf), but their interrelationships are unclear. Applying a multimodal array of immunologic, genomic, and microbiological assays, we find more overlap than expected between populations. The key TFs (Rorγ, Helios, Gata3, and cMaf) play different roles, some essential for subset identity, others driving functional gene signatures. Functional divergence was clearest under challenge. Single-cell genomics revealed a spectrum of phenotypes between the Helios+ and Rorγ+ poles, different Treg-inducing bacteria inducing the same Treg phenotypes to varying degrees, not distinct populations. TCR repertoires in monocolonized mice revealed that Helios+ and Rorγ+ Tregs are related and cannot be uniquely equated to tTreg and pTreg. Comparison of spleen and colon repertoires revealed that 2 to 5% of clonotypes are shared between the locations. We propose that rather than the origin of their differentiation, tissue-specific cues dictate the spectrum of colonic Treg phenotypes.

Alterations of milk oligosaccharides in mothers with gestational diabetes mellitus impede colonization of beneficial bacteria and development of RORγt+ Treg cell-mediated immune tolerance in neonates

Gestational diabetes mellitus (GDM) is an increasing public health concern that significantly increases the risk of early childhood allergic diseases. Altered maternal milk glycobiome may strongly affect gut microbiota and enteric-specific Treg cell-mediated development of immune tolerance in GDM infants. In this study, we found that, compared with healthy Chinese mothers, mothers with GDM had significantly lower levels of total and specific human milk oligosaccharides (HMOs) in their colostrum that subsequently increased with extension of lactation. This alteration in HMO profiles significantly delayed colonization of Lactobacillus and Bifidobacterium spp. in their breast-fed infants, resulting in a distinct gut microbial structure and metabolome. Further experiments in GDM mouse models indicated that decreased contents of milk oligosaccharides, mainly 3'-sialyllactose (3'-SL), in GDM maternal mice reduced colonization of bacteria, such as L. reuteri and L. johnsonii, in the neonatal gut, which impeded development of RORγt+ regulatory T (Treg) cell-mediated immune tolerance. Treatment of GDM neonates with 3'-SL, Lactobacillus reuteri (L. reuteri) and L. johnsonii promoted the proliferation of enteric Treg cells and expression of transcription factor RORγt, which may have contributed to compromising ovalbumin (OVA)-induced allergic responses. In vitro experiments showed that 3'-SL, metabolites of L. johnsonii, and lysates of L. reuteri stimulated differentiation of mouse RORγt+ Treg cells through multiple regulatory effects on Toll-like receptor, MAPK, p53, and NOD-like receptor signaling pathways. This study provides new ideas for the development of gut microbiota and immune tolerance in GDM newborns.

The interplay between the microbiota, diet and T regulatory cells in the preservation of the gut barrier in inflammatory bowel disease

Inflammatory bowel disease (IBD) is becoming more common in the Western world due to changes in diet-related microbial dysbiosis, genetics and lifestyle. Incidences of gut permeability can predate IBD and continued gut barrier disruptions increase the exposure of bacterial antigens to the immune system thereby perpetuating chronic inflammation. Currently, most of the approved IBD therapies target individual pro-inflammatory cytokines and pathways. However, they fail in approximately 50% of patients due to their inability to overcome the redundant pro inflammatory immune responses. There is increasing interest in the therapeutic potential of T regulatory cells (Tregs) in inflammatory conditions due to their widespread capability to dampen inflammation, promote tolerance of intestinal bacteria, facilitate healing of the mucosal barrier and ability to be engineered for more targeted therapy. Intestinal Treg populations are inherently shaped by dietary molecules and gut microbiota-derived metabolites. Thus, understanding how these molecules influence Treg-mediated preservation of the intestinal barrier will provide insights into immune tolerance-mediated mucosal homeostasis. This review comprehensively explores the interplay between diet, gut microbiota, and immune system in influencing the intestinal barrier function to attenuate the progression of colitis.

The mycobiome in atopic diseases: Inducers and triggers

Atopic diseases are characterized by type 2 inflammation, with high levels of allergen-specific TH2 cell immune responses and elevated production of IgE. These common disorders have increased in incidence around the world, which is partly explained by detrimental disturbances to the early-life intestinal microbiome. Although most studies have focused exclusively on bacterial members of the microbiome, intestinal fungi have started to be recognized for their impact on host immune development and atopy pathogenesis. From this perspective, we review recent findings demonstrating the strong interactions between members of the mycobiome and the host immune system early in life, leading to immune tolerance during eubiosis or inducing sensitization and overt TH2 cell responses during dysbiosis. Current evidence places intestinal fungi as central players in the development of allergic diseases and potential targets for atopy prevention and treatments.