In vivo equilibrium of proinflammatory IL-17+ and regulatory IL-10+ Foxp3+ RORgamma t+ T cells

RIPK3 and caspase-8 interpret cytokine signals to regulate ILC3 survival in the gut

Group 3 innate lymphoid cells (ILC3s) are abundant in the developing or healthy intestine to critically support tissue homeostasis in response to microbial colonization. However, intestinal ILC3s are reduced during chronic infections, colorectal cancer, or inflammatory bowel disease (IBD), and the mechanisms driving these alterations remain poorly understood. Here we employed RNA sequencing of ILC3s from IBD patients and observed a significant upregulation of RIPK3, the central regulator of necroptosis, during intestinal inflammation. This was modeled in mice where we found that intestinal ILC3s express RIPK3, with conventional (c)ILC3s exhibiting high RIPK3 and low levels of pro-survival genes relative to lymphoid tissue inducer (LTi)-like ILC3s. ILC3-specific RIPK3 is promoted by gut microbiota, further upregulated following enteric infection, and dependent upon IL-23R and STAT3 signaling. However, lineage-specific deletion of RIPK3 revealed a redundant role in ILC3 survival, due to a blockade of RIPK3-mediated necroptosis by caspase 8, which was also activated in response to enteric infection. In contrast, lineage-specific deletion of caspase 8 resulted in loss of cILC3s from the healthy intestine and all ILC3 subsets during enteric infection, which increased pathogen burdens and gut inflammation. This function of caspase 8 required catalytic activity induced by TNF or TL1A and was dispensable if RIPK3 was simultaneously deleted. Caspase 8 activation and cell death were associated with increased Fas on ILC3s, and the Fas-FasL pathway was upregulated by cILC3s during enteric infection, which could restrain the abundance of intestinal ILC3s. Collectively, these data reveal that interpretation of key cytokine signals controls ILC3 survival following microbial challenge, and that an imbalance of these pathways, such as in IBD or across ILC3 subsets, provokes depletion of tissue-protective ILC3s from the inflamed intestine.

Chronic skin damage induces small intestinal damage via IL-13-induced apoptosis

The gut-skin axis has recently been widely recognized, and both the gut and skin have been found to affect each other through a bidirectional connection; however, the precise mechanisms remain to be elucidated. Therefore, we aimed to investigate the effects of chronic skin damage (CSD) on mouse intestines. Following the CSD model, 4% sodium dodecyl sulfate was applied to the back-shaved murine skin six times for 2 weeks after tape stripping. The small and large intestines were analyzed histologically and immunologically, respectively. Intestinal permeability was measured using fluorescein isothiocyanate-conjugated-dextran. The role of interleukin-13 (IL-13) in the ileum was investigated using an anti-IL-13 antibody. Apoptotic intestinal cells were analyzed using TUNEL staining. Villus atrophy was observed in the small intestine in the CSD model, along with increased permeability. Mast cells, but not T cells, eosinophils, or innate lymph cell-2, were increased in the intestinal mucosa. However, no significant changes were observed in the large intestine. mRNA expression of IL-13 was increased only in the ileum of the CSD model. Apoptotic intestinal epithelial cells were significantly increased in the ileum of the CSD model. Administration of an anti-IL-13 antibody ameliorated the intestinal damage caused by CSD, along with decreased apoptotic cells and mast cell infiltration. Skin damage causes morphological changes in the small intestine, accompanied by increased intestinal permeability, possibly through the IL-13-induced apoptosis of mast cells in the epithelium. Surfactant-mediated mechanical skin damage can cause a leaky gut.

RORγt-dependent antigen-presenting cells direct regulatory T cell-mediated tolerance to food antigen

The gastrointestinal tract is continuously exposed to foreign antigens in food and commensal microbes with potential to induce adaptive immune responses. Peripherally induced T regulatory (pTreg) cells are essential for mitigating inflammatory responses to these agents1-4. While RORγt+ antigen-presenting cells (RORγt-APCs) were shown to program gut microbiota-specific pTregs5-7, understanding of their characteristics remains incomplete, and the APC subset responsible for food tolerance has remained elusive. Here, we demonstrate that RORγt-APCs are similarly required for differentiation of food antigen-specific pTregs and establishment of oral tolerance. The ability of these cells to direct both food and microbiota-specific pTreg cell differentiation is contingent on expression of RORγt and on a unique cis-regulatory element within the Rorc gene locus (Rorc(t) +7kb). Absent this +7kb element, there was a notable increase in food antigen-specific T helper 2 (Th2) cells in lieu of pTregs, leading to compromised tolerance in a mouse asthma model. By employing single-cell analyses across these models, as well as freshly resected mesenteric lymph nodes from a human organ donor, we identified a rare subset of evolutionarily conserved APCs that are dependent on RORγt, uniquely express the Prdm16 transcription factor, and are endowed with essential mediators for inducing pTreg cell differentiation. Our findings suggest that a better understanding of how RORγt-APCs develop and how they regulate T cell responses to food and microbial antigens could offer new insights into developing therapeutic strategies for autoimmune and allergic diseases as well as organ transplant tolerance.

Perinatal thymic-derived CD8αβ-expressing γδ T cells are innate IFN-γ producers that expand in IL-7R-STAT5B-driven neoplasms

The contribution of γδ T cells to immune responses is associated with rapid secretion of interferon-γ (IFN-γ). Here, we show a perinatal thymic wave of innate IFN-γ-producing γδ T cells that express CD8αβ heterodimers and expand in preclinical models of infection and cancer. Optimal CD8αβ+ γδ T cell development is directed by low T cell receptor signaling and through provision of interleukin (IL)-4 and IL-7. This population is pathologically relevant as overactive, or constitutive, IL-7R-STAT5B signaling promotes a supraphysiological accumulation of CD8αβ+ γδ T cells in the thymus and peripheral lymphoid organs in two mouse models of T cell neoplasia. Likewise, CD8αβ+ γδ T cells define a distinct subset of human T cell acute lymphoblastic leukemia pediatric patients. This work characterizes the normal and malignant development of CD8αβ+ γδ T cells that are enriched in early life and contribute to innate IFN-γ responses to infection and cancer.

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.

CTLA-4-expressing ILC3s restrain interleukin-23-mediated inflammation

Interleukin (IL-)23 is a major mediator and therapeutic target in chronic inflammatory diseases that also elicits tissue protection in the intestine at homeostasis or following acute infection1-4. However, the mechanisms that shape these beneficial versus pathological outcomes remain poorly understood. To address this gap in knowledge, we performed single-cell RNA sequencing on all IL-23 receptor-expressing cells in the intestine and their acute response to IL-23, revealing a dominance of T cells and group 3 innate lymphoid cells (ILC3s). Unexpectedly, we identified potent upregulation of the immunoregulatory checkpoint molecule cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) on ILC3s. This pathway was activated by gut microbes and IL-23 in a FOXO1- and STAT3-dependent manner. Mice lacking CTLA-4 on ILC3s exhibited reduced regulatory T cells, elevated inflammatory T cells and more-severe intestinal inflammation. IL-23 induction of CTLA-4+ ILC3s was necessary and sufficient to reduce co-stimulatory molecules and increase PD-L1 bioavailability on intestinal myeloid cells. Finally, human ILC3s upregulated CTLA-4 in response to IL-23 or gut inflammation and correlated with immunoregulation in inflammatory bowel disease. These results reveal ILC3-intrinsic CTLA-4 as an essential checkpoint that restrains the pathological outcomes of IL-23, suggesting that disruption of these lymphocytes, which occurs in inflammatory bowel disease5-7, contributes to chronic inflammation.

Regulatory role of PI16 in autoimmune arthritis and intestinal inflammation: implications for Treg cell differentiation and function

BACKGROUND

Regulatory T cells (Tregs) are crucial in maintaining immune homeostasis and preventing autoimmunity and inflammation. A proportion of Treg cells can lose Foxp3 expression and become unstable under inflammation conditions. The precise mechanisms underlying this phenomenon remain unclear.

METHODS

The PI16 gene knockout mice (PI16fl/flFoxp3Cre) in Treg were constructed, and the genotypes were identified. The proportion and phenotypic differences of immune cells in 8-week-old mice were detected by cell counter and flow cytometry. Two groups of mouse Naïve CD4+T cells were induced to differentiate into iTreg cells to observe the effect of PI16 on the differentiation and proliferation of iTreg cells, CD4+CD25+Treg and CD4+CD25- effector T cells (Teff) were selected and co-cultured with antigen presenting cells (APC) to observe the effect of PI16 on the inhibitory ability of Treg cells in vitro. The effects of directed knockout of PI16 in Treg cells on inflammatory symptoms, histopathological changes and immune cell expression in mice with enteritis and autoimmune arthritis were observed by constructing the model of antigen-induced arthritis (AIA) and colitis induced by dextran sulfate sodium salt (DSS).

RESULTS

We identified peptidase inhibitor 16 (PI16) as a negative regulator of Treg cells. Our findings demonstrate that conditional knock-out of PI16 in Tregs significantly enhances their differentiation and suppressive functions. The conditional knockout of the PI16 gene resulted in a significantly higher abundance of Foxp3 expression (35.12 ± 5.71% vs. 20.00 ± 1.61%, p = 0.034) in iTreg cells induced in vitro compared to wild-type mice. Mice with Treg cell-specific PI16 ablation are protected from autoimmune arthritis (AIA) and dextran sulfate sodium (DSS)-induced colitis development. The AIA model of PI16CKO is characterized by the reduction of joint structure and the attenuation of synovial inflammation and in DSS-induced colitis model, conditional knockout of the PI16 reduce intestinal structural damage. Additionally, we found that the deletion of the PI16 gene in Treg can increase the proportion of Treg (1.46 ± 0.14% vs. 0.64 ± 0.07%, p < 0.0001) and decrease the proportion of Th17 (1.00 ± 0.12% vs. 3.84 ± 0.64%, p = 0.001). This change will enhance the shift of Th17/Treg toward Treg cells in AIA arthritis model (0.71 ± 0.06% vs. 8.07 ± 1.98%, p = 0.003). In DSS-induced colitis model of PI16CKO, the proportion of Treg in spleen was significantly increased (1.40 ± 0.15% vs. 0.50 ± 0.11%, p = 0.003), Th17 (2.18 ± 0.55% vs. 6.42 ± 1.47%, p = 0.017), Th1 (3.42 ± 0.19% vs. 6.59 ± 1.28%, p = 0.028) and Th2 (1.52 ± 0.27% vs. 2.76 ± 0.38%, p = 0.018) in spleen was significantly decreased and the Th17/Treg balance swift toward Treg cells (1.44 ± 0.50% vs. 24.09 ± 7.18%, p = 0.012).

CONCLUSION

PI16 plays an essential role in inhibiting Treg cell differentiation and function. Conditional knock out PI16 gene in Treg can promote the Treg/Th17 balance towards Treg dominance, thereby alleviating the condition. Targeting PI16 may facilitate Treg cell-based therapies for preventing autoimmune diseases and inflammatory diseases. The research provides us with novel insights and future research avenues for the treatment of autoimmune diseases, particularly arthritis and colitis.

Antimicrobial peptides in bone regeneration: mechanism and potential

INTRODUCTION

Antimicrobial peptides (AMPs) are small-molecule peptides with a unique antimicrobial mechanism. Other notable biological activities of AMPs, including anti-inflammatory, angiogenesis, and bone formation effects, have recently received widespread attention. These remarkable bioactivities, combined with the unique antimicrobial mechanism of action of AMPs, have led to their increasingly important role in bone regeneration.

AREAS COVERED

In this review, on the one hand, we aimed to summarize information about the AMPs that are currently used for bone regeneration by reviewing published literature in the PubMed database. On the other hand, we also highlight some AMPs with potential roles in bone regeneration and their possible mechanisms of action.

EXPERT OPINION

The translation of AMPs to the clinic still faces many problems, but their unique antimicrobial mechanisms and other conspicuous biological activities suggest great potential. An in-depth understanding of the structure and mechanism of action of AMPs will help us to subsequently combine AMPs with different carrier systems and perform structural modifications to reduce toxicity and achieve stable release, which may be a key strategy for facilitating the translation of AMPs to the clinic.

γδ T Cells Mediate a Requisite Portion of a Wound Healing Response Triggered by Cutaneous Poxvirus Infection

Infection at barrier sites, e.g., skin, activates local immune defenses that limit pathogen spread, while preserving tissue integrity. Phenotypically distinct γδ T cell populations reside in skin, where they shape immunity to cutaneous infection prior to onset of an adaptive immune response by conventional αβ CD4+ (TCD4+) and CD8+ (TCD8+) T cells. To examine the mechanisms used by γδ T cells to control cutaneous virus replication and tissue pathology, we examined γδ T cells after infection with vaccinia virus (VACV). Resident γδ T cells expanded and combined with recruited γδ T cells to control pathology after VACV infection. However, γδ T cells did not play a role in control of local virus replication or blockade of systemic virus spread. We identified a unique wound healing signature that has features common to, but also features that antagonize, the sterile cutaneous wound healing response. Tissue repair generally occurs after clearance of a pathogen, but viral wound healing started prior to the peak of virus replication in the skin. γδ T cells contributed to wound healing through induction of multiple cytokines/growth factors required for efficient wound closure. Therefore, γδ T cells modulate the wound healing response following cutaneous virus infection, maintaining skin barrier function to prevent secondary bacterial infection.

A conserved transcriptional program for MAIT cells across mammalian evolution

Mucosal-associated invariant T (MAIT) cells harbor evolutionarily conserved TCRs, suggesting important functions. As human and mouse MAIT functional programs appear distinct, the evolutionarily conserved MAIT functional features remain unidentified. Using species-specific tetramers coupled to single-cell RNA sequencing, we characterized MAIT cell development in six species spanning 110 million years of evolution. Cross-species analyses revealed conserved transcriptional events underlying MAIT cell maturation, marked by ZBTB16 induction in all species. MAIT cells in human, sheep, cattle, and opossum acquired a shared type-1/17 transcriptional program, reflecting ancestral features. This program was also acquired by human iNKT cells, indicating common differentiation for innate-like T cells. Distinct type-1 and type-17 MAIT subsets developed in rodents, including pet mice and genetically diverse mouse strains. However, MAIT cells further matured in mouse intestines to acquire a remarkably conserved program characterized by concomitant expression of type-1, type-17, cytotoxicity, and tissue-repair genes. Altogether, the study provides a unifying view of the transcriptional features of innate-like T cells across evolution.

Multimodal profiling reveals site-specific adaptation and tissue residency hallmarks of γδ T cells across organs in mice

γδ T cells perform heterogeneous functions in homeostasis and disease across tissues. However, it is unclear whether these roles correspond to distinct γδ subsets or to a homogeneous population of cells exerting context-dependent functions. Here, by cross-organ multimodal single-cell profiling, we reveal that various mouse tissues harbor unique site-adapted γδ subsets. Epidermal and intestinal intraepithelial γδ T cells are transcriptionally homogeneous and exhibit epigenetic hallmarks of functional diversity. Through parabiosis experiments, we uncovered cellular states associated with cytotoxicity, innate-like rapid interferon-γ production and tissue repair functions displaying tissue residency hallmarks. Notably, our observations add nuance to the link between interleukin-17-producing γδ T cells and tissue residency. Moreover, transcriptional programs associated with tissue-resident γδ T cells are analogous to those of CD8+ tissue-resident memory T cells. Altogether, this study provides a multimodal landscape of tissue-adapted γδ T cells, revealing heterogeneity, lineage relationships and their tissue residency program.

Bi-directional signaling between the intestinal epithelium and type-3 innate lymphoid cells regulates secretory dynamics and interleukin-22

Type-3 innate lymphoid cells (ILC3) respond to localized environmental cues to regulate homeostasis and orchestrate immunity in the intestine. The intestinal epithelium is an important upstream regulator and downstream target of ILC3 signaling, however, the complexity of mucosal tissues can hinder efforts to define specific interactions between these two compartments. Here, we employ a reductionist co-culture system of murine epithelial small intestinal organoids (SIO) with ILC3 to uncover bi-directional signaling mechanisms that underlie intestinal homeostasis. We report that ILC3 induce global transcriptional changes in intestinal epithelial cells, driving the enrichment of secretory goblet cell signatures. We find that SIO enriched for goblet cells promote NKp46+ ILC3 and interleukin (IL)-22 expression, which can feedback to induce IL-22-mediated epithelial transcriptional signatures. However, we show that epithelial regulation of ILC3 in this system is contact-dependent and demonstrate a role for epithelial Delta-Like-Canonical-Notch-Ligand (Dll) in driving IL-22 production by ILC3, via subset-specific Notch1-mediated activation of T-bet+ ILC3. Finally, by interfering with Notch ligand-receptor dynamics, ILC3 appear to upregulate epithelial Atoh1 to skew secretory lineage determination in SIO-ILC3 co-cultures. This research outlines two complimentary bi-directional signaling modules between the intestinal epithelium and ILC3, which may be relevant in intestinal homeostasis and disease.

Beyond FOXP3: a 20-year journey unravelling human regulatory T-cell heterogeneity

The initial idea of a distinct group of T-cells responsible for suppressing immune responses was first postulated half a century ago. However, it is only in the last three decades that we have identified what we now term regulatory T-cells (Tregs), and subsequently elucidated and crystallized our understanding of them. Human Tregs have emerged as essential to immune tolerance and the prevention of autoimmune diseases and are typically contemporaneously characterized by their CD3+CD4+CD25high CD127lowFOXP3+ phenotype. It is important to note that FOXP3+ Tregs exhibit substantial diversity in their origin, phenotypic characteristics, and function. Identifying reliable markers is crucial to the accurate identification, quantification, and assessment of Tregs in health and disease, as well as the enrichment and expansion of viable cells for adoptive cell therapy. In our comprehensive review, we address the contributions of various markers identified in the last two decades since the master transcriptional factor FOXP3 was identified in establishing and enriching purity, lineage stability, tissue homing and suppressive proficiency in CD4+ Tregs. Additionally, our review delves into recent breakthroughs in innovative Treg-based therapies, underscoring the significance of distinct markers in their therapeutic utilization. Understanding Treg subsets holds the key to effectively harnessing human Tregs for immunotherapeutic approaches.

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.

The emerging family of RORγt+ antigen-presenting cells

Antigen-presenting cells (APCs) are master regulators of the immune response by directly interacting with T cells to orchestrate distinct functional outcomes. Several types of professional APC exist, including conventional dendritic cells, B cells and macrophages, and numerous other cell types have non-classical roles in antigen presentation, such as thymic epithelial cells, endothelial cells and granulocytes. Accumulating evidence indicates the presence of a new family of APCs marked by the lineage-specifying transcription factor retinoic acid receptor-related orphan receptor-γt (RORγt) and demonstrates that these APCs have key roles in shaping immunity, inflammation and tolerance, particularly in the context of host-microorganism interactions. These RORγt+ APCs include subsets of group 3 innate lymphoid cells, extrathymic autoimmune regulator-expressing cells and, potentially, other emerging populations. Here, we summarize the major findings that led to the discovery of these RORγt+ APCs and their associated functions. We discuss discordance in recent reports and identify gaps in our knowledge in this burgeoning field, which has tremendous potential to advance our understanding of fundamental immune concepts.

Deficiency of Complement C3a and C5a receptors Does Not Prevent Angiotensin II-Induced Hypertension and Hypertensive End-Organ Damage

BACKGROUND

Complement may drive the pathology of hypertension through effects on innate and adaptive immune responses. Recently an injurious role for the anaphylatoxin receptors C3aR (complement component 3a receptor) and C5aR1 (complement component 5a receptor) in the development of hypertension was shown through downregulation of Foxp3+ (forkhead box protein 3) regulatory T cells. Here, we deepen our understanding of the therapeutic potential of targeting both receptors in hypertension.

METHODS

Data from the European Renal cDNA Bank, single cell sequencing and immunohistochemistry were examined in hypertensive patients. The effect of C3aR or C3aR/C5aR1 double deficiency was assessed in two models of Ang II (angiotensin II)-induced hypertension in knockout mice.

RESULTS

We found increased expression of C3aR, C5aR1 and Foxp3 cells in kidney biopsies of patients with hypertensive nephropathy. Expression of both receptors was mainly found in myeloid cells. No differences in blood pressure, renal injury (albuminuria, glomerular filtration rate, glomerular and tubulointerstitial injury, inflammation) or cardiac injury (cardiac fibrosis, heart weight, gene expression) between control and mutant mice was discerned in C3aR-/- as well as C3aR/C5aR1-/- double knockout mice. The number of renal Tregs was not decreased in Ang II as well as in DOCA salt induced hypertension.

CONCLUSIONS

Hypertensive nephropathy in mice and men is characterized by an increase of renal regulatory T cells and enhanced expression of anaphylatoxin receptors. Our investigations do not corroborate a role for C3aR/C5aR1 axis in Ang II-induced hypertension hence challenging the concept of anaphylatoxin receptor targeting in the treatment of hypertensive disease.

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.

The gut ecosystem and immune tolerance

The gastrointestinal tract is home to the largest microbial population in the human body. The gut microbiota plays significant roles in the development of the gut immune system and has a substantial impact on the maintenance of immune tolerance beginning in early life. These microbes interact with the immune system in a dynamic and interdependent manner. They generate immune signals by presenting a vast repertoire of antigenic determinants and microbial metabolites that influence the development, maturation and maintenance of immunological function and homeostasis. At the same time, both the innate and adaptive immune systems are involved in modulating a stable microbial ecosystem between the commensal and pathogenic microorganisms. Hence, the gut microbial population and the host immune system work together to maintain immune homeostasis synergistically. In susceptible hosts, disruption of such a harmonious state can greatly affect human health and lead to various auto-inflammatory and autoimmune disorders. In this review, we discuss our current understanding of the interactions between the gut microbiota and immunity with an emphasis on: a) important players of gut innate and adaptive immunity; b) the contribution of gut microbial metabolites; and c) the effect of disruption of innate and adaptive immunity as well as alteration of gut microbiome on the molecular mechanisms driving autoimmunity in various autoimmune diseases.

The role of transcription factors in shaping regulatory T cell identity

Forkhead box protein 3-expressing (FOXP3+) regulatory T cells (Treg cells) suppress conventional T cells and are essential for immunological tolerance. FOXP3, the master transcription factor of Treg cells, controls the expression of multiples genes to guide Treg cell differentiation and function. However, only a small fraction (<10%) of Treg cell-associated genes are directly bound by FOXP3, and FOXP3 alone is insufficient to fully specify the Treg cell programme, indicating a role for other accessory transcription factors operating upstream, downstream and/or concurrently with FOXP3 to direct Treg cell specification and specialized functions. Indeed, the heterogeneity of Treg cells can be at least partially attributed to differential expression of transcription factors that fine-tune their trafficking, survival and functional properties, some of which are niche-specific. In this Review, we discuss the emerging roles of accessory transcription factors in controlling Treg cell identity. We specifically focus on members of the basic helix-loop-helix family (AHR), basic leucine zipper family (BACH2, NFIL3 and BATF), CUT homeobox family (SATB1), zinc-finger domain family (BLIMP1, Ikaros and BCL-11B) and interferon regulatory factor family (IRF4), as well as lineage-defining transcription factors (T-bet, GATA3, RORγt and BCL-6). Understanding the imprinting of Treg cell identity and specialized function will be key to unravelling basic mechanisms of autoimmunity and identifying novel targets for drug development.

T-helper cells flexibility: the possibility of reprogramming T cells fate

Various disciplines cooperate to find novel approaches to cure impaired body functions by repairing, replacing, or regenerating cells, tissues, or organs. The possibility that a stable differentiated cell can reprogram itself opens the door to new therapeutic strategies against a multitude of diseases caused by the loss or dysfunction of essential, irreparable, and specific cells. One approach to cell therapy is to induce reprogramming of adult cells into other functionally active cells. Understanding the factors that cause or contribute to T cell plasticity is not only of clinical importance but also expands the knowledge of the factors that induce cells to differentiate and improves the understanding of normal developmental biology. The present review focuses on the advances in the conversion of peripheral CD4+ T cells, the conditions of their reprogramming, and the methods proposed to control such cell differentiation.

Intestinal factors promoting the development of RORγt+ cells and oral tolerance

The gastrointestinal tract has to harmonize the two seemingly opposite functions of fulfilling nutritional needs and avoiding the entry of pathogens, toxins and agents that can cause physical damage. This balance requires a constant adjustment of absorptive and defending functions by sensing environmental changes or noxious substances and initiating adaptive or protective mechanisms against them through a complex network of receptors integrated with the central nervous system that communicate with cells of the innate and adaptive immune system. Effective homeostatic processes at barrier sites take the responsibility for oral tolerance, which protects from adverse reactions to food that cause allergic diseases. During a very specific time interval in early life, the establishment of a stable microbiota in the large intestine is sufficient to prevent pathological events in adulthood towards a much larger bacterial community and provide tolerance towards diverse food antigens encountered later in life. The beneficial effects of the microbiome are mainly exerted by innate and adaptive cells that express the transcription factor RORγt, in whose generation, mediated by different bacterial metabolites, retinoic acid signalling plays a predominant role. In addition, recent investigations indicate that food antigens also contribute, analogously to microbial-derived signals, to educating innate immune cells and instructing the development and function of RORγt+ cells in the small intestine, complementing and expanding the tolerogenic effect of the microbiome in the colon. This review addresses the mechanisms through which microbiota-produced metabolites and dietary antigens maintain intestinal homeostasis, highlighting the complementarity and redundancy between their functions.

Zfp362 potentiates murine colonic inflammation by constraining Treg cell function rather than promoting Th17 cell differentiation

Mucosal barrier integrity and pathogen clearance is a complex process influenced by both Th17 and Treg cells. Previously, we had described the DNA methylation profile of Th17 cells and identified Zinc finger protein (Zfp)362 to be uniquely demethylated. Here, we generated Zfp362-/- mice to unravel the role of Zfp362 for Th17 cell biology. Zfp362-/- mice appeared clinically normal, showed no phenotypic alterations in the T-cell compartment, and upon colonization with segmented filamentous bacteria, no effect of Zfp362 deficiency on Th17 cell differentiation was observed. By contrast, Zfp362 deletion resulted in increased frequencies of colonic Foxp3+ Treg cells and IL-10+ and RORγt+ Treg cell subsets in mesenteric lymph nodes. Adoptive transfer of naïve CD4+ T cells from Zfp362-/- mice into Rag2-/- mice resulted in a significantly lower weight loss when compared with controls receiving cells from Zfp362+/+ littermates. However, this attenuated weight loss did not correlate with alterations of Th17 cells but instead was associated with an increase of effector Treg cells in mesenteric lymph nodes. Together, these results suggest that Zfp362 plays an important role in promoting colonic inflammation; however, this function is derived from constraining the effector function of Treg cells rather than directly promoting Th17 cell differentiation.

IL-17a-producing γδT cells and NKG2D signaling mediate bacterial endotoxin-induced neonatal lung injury: implications for bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease in preterm birth survivors characterized by inflammation, impaired alveolarization and dysmorphic vasculature. Activated IL-17A+ lymphocytes are key drivers of inflammation in preterm infants. We have shown that in immature mice chronic airway exposure to lipopolysaccharide (LPS) induces pulmonary inflammation, increased IL-17a expression, and hypoalveolarization, a BPD-like phenotype. The source of IL-17a and contribution to lung pathology is unknown. The natural-killer group 2, member D (NKG2D) receptor mediates activation and IL-17a production in γδ T cells by binding to stress molecules. LPS induces NKG2D ligand expression, including Rae-1 and MULT1. We hypothesized that IL-17a+ γδ T cells and NKG2D signaling mediate neonatal LPS-induced lung injury. Immature C57BL/6J (wild type), Nkg2d-/- or Tcrd-/- (lacking γδ T cells) mice were inoculated with 3ug/10ul of LPS from E. coli O26:B6 or 10ul of PBS intranasally on day of life 3, 5, 7, and 10. Selected mice were treated with neutralizing antibodies against IL-17a, or NKG2D intraperitoneally. Lung immune cells were assessed by flow cytometry and gene expression was analyzed by qPCR. Alveolar growth was assessed by lung morphometry. We established that anti-IL-17a antibody treatment attenuated LPS-induced hypoalveolarization. We found that LPS induced the fraction of IL-17a+NKG2D+ γδ T cells, a major source of IL-17a in the neonatal lung. LPS also induced lung mRNA expression of NKG2D, Rae-1, MULT1, and the DNA damage regulator p53. Anti-NKG2D treatment attenuated the effect of LPS on γδ T cell IL-17a expression, immune cell infiltration and hypoalveolarization. LPS-induced hypoalveolarization was also attenuated in Nkg2d-/- and Tcrd-/- mice. In tracheal aspirates of preterm infants IL-17A and its upstream regulator IL-23 were higher in infants who later developed BPD. Also, human ligands of NKG2D, MICA and MICB were present in the aspirates and MICA correlated with median FiO2. Our novel findings demonstrate a central role for activated IL-17a+ γδ T cells and NKG2D signaling in neonatal LPS-induced lung injury. Future studies will determine the role of NKG2D ligands and effectors, other NKG2D+ cells in early-life endotoxin-induced lung injury and inflammation with a long-term goal to understand how inflammation contributes to BPD pathogenesis.

Factors impacting the benefits and pathogenicity of Th17 cells in the tumor microenvironment

Tumor development is closely associated with a complex tumor microenvironment, which is composed of tumor cells, blood vessels, tumor stromal cells, infiltrating immune cells, and associated effector molecules. T helper type 17 (Th17) cells, which are a subset of CD4+ T cells and are renowned for their ability to combat bacterial and fungal infections and mediate inflammatory responses, exhibit context-dependent effector functions. Within the tumor microenvironment, different molecular signals regulate the proliferation, differentiation, metabolic reprogramming, and phenotypic conversion of Th17 cells. Consequently, Th17 cells exert dual effects on tumor progression and can promote or inhibit tumor growth. This review aimed to investigate the impact of various alterations in the tumor microenvironment on the antitumor and protumor effects of Th17 cells to provide valuable clues for the exploration of additional tumor immunotherapy strategies.

Differentiation, regulation and function of regulatory T cells in non-lymphoid tissues and tumors

Regulatory T cells (Tregs) play a substantial role in inhibiting excessive immune response. A large number of studies have focused on the tissue homeostasis maintenance and remodeling characteristics of Tregs in non-lymphoid tissues, such as the skin, colon, lung, brain, muscle, and adipose tissues. Herein, we overview the kinetics of Treg migration to non-lymphoid tissues and adaptation to the specific tissue microenvironment through the development of tissue-specific chemokine receptors, transcription factors, and phenotypes. Additionally, tumor-infiltrating Tregs (Ti-Tregs) play an important role in tumor generation and immunotherapy resistance. The phenotypes of Ti-Tregs are related to the histological location of the tumor and there is a large overlap between the transcripts of Ti-Tregs and those of tissue-specific Tregs. We recapitulate the molecular underpinnings of tissue-specific Tregs, which might shed new light on Treg-based therapeutic targets and biomarkers for inflammatory diseases and cancer.

The CCR6/CCL20 axis expands RORγt+ Tregs to protect from glomerulonephritis

Previous studies have identified a unique Treg population, which expresses the Th17 characteristic transcription factor RORγt. These RORγt+ Tregs possess enhanced immunosuppressive capacity, which endows them with great therapeutic potential. However, as a caveat, they are also capable of secreting pro-inflammatory IL-17A. Since the sum function of RORγt+ Tregs in glomerulonephritis (GN) remains unknown, we studied the effects of their absence. Purified CD4+ T cell populations, containing or lacking RORγt+ Tregs, were transferred into immunocompromised RAG1 knockout mice and the nephrotoxic nephritis model of GN was induced. Absence of RORγt+ Tregs significantly aggravated kidney injury, demonstrating overall kidney-protective properties. Analyses of immune responses showed that RORγt+ Tregs were broadly immunosuppressive with no preference for a particular type of T cell response. Further characterization revealed a distinct functional and transcriptional profile, including enhanced production of IL-10. Expression of the chemokine receptor CCR6 marked a particularly potent subset, whose absence significantly worsened GN. As an underlying mechanism, we found that chemokine CCL20 acting through receptor CCR6 signaling mediated expansion and activation of RORγt+ Tregs. Finally, we also detected an increase of CCR6+ Tregs in kidney biopsies, as well as enhanced secretion of chemokine CCL20 in 21 patients with anti-neutrophil cytoplasmic antibody associated GN compared to that of 31 healthy living donors, indicating clinical relevance. Thus, our data characterize RORγt+ Tregs as anti-inflammatory mediators of GN and identify them as promising target for Treg directed therapies.

Dysfunction of Foxp3+ Regulatory T Cells Induces Dysbiosis of Gut Microbiota via Aberrant Binding of Immunoglobulins to Microbes in the Intestinal Lumen

Foxp3⁺ regulatory T (Treg) cells prevent excessive immune responses against dietary antigens and commensal bacteria in the intestine. Moreover, Treg cells contribute to the establishment of a symbiotic relationship between the host and gut microbes, partly through immunoglobulin A. However, the mechanism by which Treg cell dysfunction disturbs the balanced intestinal microbiota remains unclear. In this study, we used Foxp3 conditional knockout mice to conditionally ablate the Foxp3 gene in adult mice and examine the relationship between Treg cells and intestinal bacterial communities. Deletion of Foxp3 reduced the relative abundance of Clostridia, suggesting that Treg cells have a role in maintaining Treg-inducing microbes. Additionally, the knockout increased the levels of fecal immunoglobulins and immunoglobulin-coated bacteria. This increase was due to immunoglobulin leakage into the gut lumen as a result of loss of mucosal integrity, which is dependent on the gut microbiota. Our findings suggest that Treg cell dysfunction leads to gut dysbiosis via aberrant antibody binding to the intestinal microbes.

Group 2 innate lymphoid cells constrain type 3/17 lymphocytes in shared stromal niches to restrict liver fibrosis

Group 2 innate lymphoid cells (ILC2s) cooperate with adaptive Th2 cells as key organizers of tissue type 2 immune responses, while a spectrum of innate and adaptive lymphocytes coordinate early type 3/17 immunity. Both type 2 and type 3/17 lymphocyte associated cytokines are linked to tissue fibrosis, but how their dynamic and spatial topographies may direct beneficial or pathologic organ remodelling is unclear. Here we used volumetric imaging in models of liver fibrosis, finding accumulation of periportal and fibrotic tract IL-5 + lymphocytes, predominantly ILC2s, in close proximity to expanded type 3/17 lymphocytes and IL-33 high niche fibroblasts. Ablation of IL-5 + lymphocytes worsened carbon tetrachloride-and bile duct ligation-induced liver fibrosis with increased niche IL-17A + type 3/17 lymphocytes, predominantly γδ T cells. In contrast, concurrent ablation of IL-5 + and IL-17A + lymphocytes reduced this progressive liver fibrosis, suggesting a cross-regulation of type 2 and type 3 lymphocytes at specialized fibroblast niches that tunes hepatic fibrosis.

Breast milk microRNAs: Potential players in oral tolerance development

Breast milk is an essential source of nutrition and hydration for the infant. In addition, this highly complex biological fluid contains numerous immunologically active factors such as microorganisms, immunoglobulins, cytokines and microRNAs (miRNAs). Here, we set out to predict the function of the top 10 expressed miRNAs in human breast milk, focusing on their relevance in oral tolerance development and allergy prevention in the infant. The top expressed miRNAs in human breast milk were identified on basis of previous peer-reviewed studies gathered from a recent systematic review and an updated literature search. The miRNAs with the highest expression levels in each study were used to identify the 10 most common miRNAs or miRNA families across studies and these were selected for subsequent target prediction. The predictions were performed using TargetScan in combination with the Database for Annotation, Visualization and Integrated Discovery. The ten top expressed miRNAs were: let-7-5p family, miR-148a-3p, miR-30-5p family, miR-200a-3p + miR-141-3p, miR-22-3p, miR-181-5p family, miR-146b-5p, miR-378a-3p, miR-29-3p family, miR-200b/c-3p and miR-429-3p. The target prediction identified 3,588 potential target genes and 127 Kyoto Encyclopedia of Genes and Genomes pathways; several connected to the immune system, including TGF-b and T cell receptor signaling and T-helper cell differentiation. This review highlights the role of breast milk miRNAs and their potential contribution to infant immune maturation. Indeed, breast milk miRNAs seem to be involved in several pathways that influence oral tolerance development.

Principles of regulatory T cell function

Regulatory T (Treg) cells represent a distinct lineage of cells of the adaptive immune system indispensable for forestalling fatal autoimmune and inflammatory pathologies. The role of Treg cells as principal guardians of the immune system can be attributed to their ability to restrain all currently recognized major types of inflammatory responses through modulating the activity of a wide range of cells of the innate and adaptive immune system. This broad purview over immunity and inflammation is afforded by the multiple modes of action Treg cells exert upon their diverse molecular and cellular targets. Beyond the suppression of autoimmunity for which they were originally recognized, Treg cells have been implicated in tissue maintenance, repair, and regeneration under physiologic and pathologic conditions. Herein, we discuss the current and emerging understanding of Treg cell effector mechanisms in the context of the basic properties of Treg cells that endow them with such functional versatility.

Regulatory T-cell stability and functional plasticity in health and disease

FOXP3-expressing regulatory T cells (T_reg ) are indispensable for immune homeostasis and tolerance, and in addition tissue-resident T_reg have been found to perform noncanonical, tissue-specific functions. For optimal tolerogenic function during inflammatory disease, T_reg are equipped with mechanisms that assure lineage stability. T_reg lineage stability is closely linked to the installation and maintenance of a lineage-specific epigenetic landscape, specifically a T_reg -specific DNA demethylation pattern. At the same time, for local and directed immune regulation T_reg must possess a level of functional plasticity that requires them to partially acquire T helper cell (T_H ) transcriptional programs-then referred to as T_H -like T_reg . Unleashing T_H programs in T_reg , however, is not without risk and may threaten the epigenetic stability of T_reg with consequently pathogenic ex-T_reg contributing to (auto-) inflammatory conditions. Here, we review how the T_reg -stabilizing epigenetic landscape is installed and maintained, and further discuss the development, necessity and lineage instability risks of T_H 1-, T_H 2-, T_H 17-like T_reg and follicular T_reg .

γδT cells in oral tissue immune surveillance and pathology

The oral mucosa's immune system is composed of tissue-resident and specifically recruited leukocytes that could effectively tolerate a wide range of microbial and mechanical assaults. Shortly after CD4⁺ helper T cells (TH17 cells) that produce interleukin 17 (IL-17) were identified, it was discovered that γδT cells could also induce substantial levels of this pro-inflammatory cytokine. In the past decades, it has become clear that due to a complicated thymic program of development, γδT cells frequently serve as the primary sources of IL-17 in numerous models of inflammatory diseases while also assisting in the maintenance of tissue homeostasis in the skin and intestine. But it wasn't until recently that we took thorough insight into the complex features of γδT cells in the oral mucosa. Most gingival intraepithelial γδT cells reside in the junctional epithelium adjacent to the dental biofilm, suggesting their potential role in regulating oral microbiota. However, inconsistent results have been published in this regard. Similarly, recent findings showed contradictory data about the role of γδT lymphocytes in experimental periodontitis based on different models. In addition, conflicting findings were presented in terms of alveolar bone physiology and pathology underlying the oral mucosa. This review provided an overview of current knowledge and viewpoints regarding the complex roles played by oral-resident γδT cells in host-microbiota interactions, gingivitis and periodontitis, bone physiology and pathology.

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

Tissue repair processes maintain proper organ function following mechanical or infection-related damage. In addition to antibacterial properties, mucosal associated invariant T (MAIT) cells express a tissue repair transcriptomic program and promote skin wound healing when expanded. Herein, we use a human-like mouse model of full-thickness skin excision to assess the underlying mechanisms of MAIT cell tissue repair function. Single-cell RNA sequencing analysis suggested that skin MAIT cells already express a repair program at steady state. Following skin excision, MAIT cells promoted keratinocyte proliferation, thereby accelerating healing. Using skin grafts, parabiosis, and adoptive transfer experiments, we show that MAIT cells migrated into the wound in a T cell receptor (TCR)-independent but CXCR6 chemokine receptor-dependent manner. Amphiregulin secreted by MAIT cells following excision promoted wound healing. Expression of the repair function was probably independent of sustained TCR stimulation. Overall, our study provides mechanistic insights into MAIT cell wound healing function in the skin.

CD200R1 promotes interleukin-17 production by group 3 innate lymphoid cells by enhancing signal transducer and activator of transcription 3 activation

Psoriasis is a common chronic inflammatory skin disease with no cure. It is driven by the interleukin (IL)-23/IL-17A axis and type 17 T helper cells; however, recently, group 3 innate lymphoid cells (ILC3s) have also been implicated. Despite being the focus of much research, factors regulating the activity of ILC3s remain incompletely understood. Immune regulatory pathways are particularly important at barrier sites, such as the skin, gut, and lungs, which are exposed to environmental substances and microbes. CD200R1 is an immune regulatory cell surface receptor that inhibits proinflammatory cytokine production in myeloid cells. CD200R1 is also highly expressed on ILCs, where its function remains largely unexplored. We previously observed reduced CD200R1 signaling in psoriasis-affected skin, suggesting that dysregulation may promote disease. Here, we show that contrary to this, psoriasis models are less severe in CD200R1-deficient mice due to reduced IL-17 production. Here, we uncover a key cell-intrinsic role for CD200R1 in promoting IL-23-driven IL-17A production by ILC3s by promoting signal transducer and activator of transcription 3 activation. Therefore, contrary to its inhibitory role in myeloid cells, CD200R1 is required on ILC3 to promote IL-23-stimulated signal transducer and activator of transcription 3 activation, triggering optimal IL-17 production.

Differential regulation of lineage-determining transcription factor expression in innate lymphoid cell and adaptive T helper cell subsets

CD4 T helper (Th) cell subsets, including Th1, Th2 and Th17 cells, and their innate counterparts innate lymphoid cell (ILC) subsets consisting of ILC1s, ILC2s and ILC3s, display similar effector cytokine-producing capabilities during pro-inflammatory immune responses. These lymphoid cell subsets utilize the same set of lineage-determining transcription factors (LDTFs) for their differentiation, development and functions. The distinct ontogeny and developmental niches between Th cells and ILCs indicate that they may adopt different external signals for the induction of LDTF during lineage commitment. Increasing evidence demonstrates that many conserved cis-regulatory elements at the gene loci of LDTFs are often preferentially utilized for the induction of LDTF expression during Th cell differentiation and ILC development at different stages. In this review, we discuss the functions of lineage-related cis-regulatory elements in inducing T-bet, GATA3 or RORγt expression based on the genetic evidence provided in recent publications. We also review and compare the upstream signals involved in LDTF induction in Th cells and ILCs both in vitro and in vivo. Finally, we discuss the possible mechanisms and physiological importance of regulating LDTF dynamic expression during ILC development and activation.

The role of γδ T17 cells in cardiovascular disease

Due to the ability of γδ T cells to bridge adaptive and innate immunity, γδ T cells can respond to a variety of molecular cues and acquire the ability to induce a variety of cytokines such as IL-17 family, IFN-γ, IL-4, and IL-10. IL-17⁺ γδ T cells (γδ T17 cells) populations have recently received considerable interest as they are the major early source of IL-17A in many immune response models. However, the exact mechanism of γδ T17 cells is still poorly understood, especially in the context of cardiovascular disease (CVD). CVD is the leading cause of death in the world, and it tends to be younger. Here, we offer a review of the cardiovascular inflammatory and immune functions of γδ T17 cells in order to understand their role in CVD, which may be the key to developing new clinical applications.

Alteration of Gut Immunity and Microbiome in Mixed Granulocytic Asthma

Growing evidence suggests that there is an essential link between the gut and lungs. Asthma is a common chronic inflammatory disease and is considered a heterogeneous disease. While it has been documented that eosinophilic asthma affects gut immunity and the microbiome, the effect of other types of asthma on the gut environment has not been examined. In this study, we utilized an OVA/poly I:C-induced mixed granulocytic asthma model and found increased Tregs without significant changes in other inflammatory cells in the colon. Interestingly, an altered gut microbiome has been observed in a mixed granulocytic asthma model. We observed an increase in the relative abundance of the Faecalibaculum genus and Erysipelotrichaceae family, with a concomitant decrease in the relative abundance of the genera Candidatus arthromitus and Streptococcus. The altered gut microbiome leads to changes in the abundance of genes associated with microbial metabolism, such as glycolysis. We found that mixed granulocytic asthma mainly affects the gut microbial composition and metabolism, which may have important implications in the severity and development of asthma and gut immune homeostasis. This suggests that altered gut microbial metabolism may be a potential therapeutic target for patients with mixed granulocytic asthma.

Mining the microbiota to identify gut commensals modulating neuroinflammation in a mouse model of multiple sclerosis

BACKGROUND

The gut microbiome plays an important role in autoimmunity including multiple sclerosis and its mouse model called experimental autoimmune encephalomyelitis (EAE). Prior studies have demonstrated that the multiple sclerosis gut microbiota can contribute to disease, hence making it a potential therapeutic target. In addition, antibiotic treatment has been shown to ameliorate disease in the EAE mouse model of multiple sclerosis. Yet, to this date, the mechanisms mediating these antibiotic effects are not understood. Furthermore, there is no consensus on the gut-derived bacterial strains that drive neuroinflammation in multiple sclerosis.

RESULTS

Here, we characterized the gut microbiome of untreated and vancomycin-treated EAE mice over time to identify bacteria with neuroimmunomodulatory potential. We observed alterations in the gut microbiota composition following EAE induction. We found that vancomycin treatment ameliorates EAE, and that this protective effect is mediated via the microbiota. Notably, we observed increased abundance of bacteria known to be strong inducers of regulatory T cells, including members of Clostridium clusters XIVa and XVIII in vancomycin-treated mice during the presymptomatic phase of EAE, as well as at disease peak. We identified 50 bacterial taxa that correlate with EAE severity. Interestingly, several of these taxa exist in the human gut, and some of them have been implicated in multiple sclerosis including Anaerotruncus colihominis, a butyrate producer, which had a positive correlation with disease severity. We found that Anaerotruncus colihominis ameliorates EAE, and this is associated with induction of RORγt⁺ regulatory T cells in the mesenteric lymph nodes.

CONCLUSIONS

We identified vancomycin as a potent modulator of the gut-brain axis by promoting the proliferation of bacterial species that induce regulatory T cells. In addition, our findings reveal 50 gut commensals as regulator of the gut-brain axis that can be used to further characterize pathogenic and beneficial host-microbiota interactions in multiple sclerosis patients. Our findings suggest that elevated Anaerotruncus colihominis in multiple sclerosis patients may represent a protective mechanism associated with recovery from the disease. Video Abstract.

Profiling of epigenetic marker regions in murine ILCs under homeostatic and inflammatory conditions

Epigenetic modifications such as DNA methylation play an essential role in imprinting specific transcriptional patterns in cells. We performed genome-wide DNA methylation profiling of murine lymph node–derived ILCs, which led to the identification of differentially methylated regions (DMRs) and the definition of epigenetic marker regions in ILCs. Marker regions were located in genes with a described function for ILCs, such as Tbx21, Gata3, or Il23r, but also in genes that have not been related to ILC biology. Methylation levels of the marker regions and expression of the associated genes were strongly correlated, indicating their functional relevance. Comparison with T helper cell methylomes revealed clear lineage differences, despite partial similarities in the methylation of specific ILC marker regions. IL-33–mediated challenge affected methylation of ILC2 epigenetic marker regions in the liver, while remaining relatively stable in the lung. In our study, we identified a set of epigenetic markers that can serve as a tool to study phenotypic and functional properties of ILCs.

A RORγt+ cell instructs gut microbiota-specific Treg cell differentiation

The mutualistic relationship of gut-resident microbiota and the host immune system promotes homeostasis that ensures maintenance of the microbial community and of a largely non-aggressive immune cell compartment^1,2. The consequences of disturbing this balance include proximal inflammatory conditions, such as Crohn's disease, and systemic illnesses. This equilibrium is achieved in part through the induction of both effector and suppressor arms of the adaptive immune system. Helicobacter species induce T regulatory (T_reg) and T follicular helper (T_FH) cells under homeostatic conditions, but induce inflammatory T helper 17 (T_H17) cells when induced T_reg (iT_reg) cells are compromised^3,4. How Helicobacter and other gut bacteria direct T cells to adopt distinct functions remains poorly understood. Here we investigated the cells and molecular components required for iT_reg cell differentiation. We found that antigen presentation by cells expressing RORγt, rather than by classical dendritic cells, was required and sufficient for induction of T_reg cells. These RORγt⁺ cells-probably type 3 innate lymphoid cells and/or Janus cells⁵-require the antigen-presentation machinery, the chemokine receptor CCR7 and the TGFβ activator α_v integrin. In the absence of any of these factors, there was expansion of pathogenic T_H17 cells instead of iT_reg cells, induced by CCR7-independent antigen-presenting cells. Thus, intestinal commensal microbes and their products target multiple antigen-presenting cells with pre-determined features suited to directing appropriate T cell differentiation programmes, rather than a common antigen-presenting cell that they endow with appropriate functions.

ILC3s select microbiota-specific regulatory T cells to establish tolerance in the gut

Microbial colonization of the mammalian intestine elicits inflammatory or tolerogenic T cell responses, but the mechanisms controlling these distinct outcomes remain poorly understood, and accumulating evidence indicates that aberrant immunity to intestinal microbiota is causally associated with infectious, inflammatory and malignant diseases1-8. Here we define a critical pathway controlling the fate of inflammatory versus tolerogenic T cells that respond to the microbiota and express the transcription factor RORγt. We profiled all RORγt+ immune cells at single-cell resolution from the intestine-draining lymph nodes of mice and reveal a dominant presence of T regulatory (Treg) cells and lymphoid tissue inducer-like group 3 innate lymphoid cells (ILC3s), which co-localize at interfollicular regions. These ILC3s are distinct from extrathymic AIRE-expressing cells, abundantly express major histocompatibility complex class II, and are necessary and sufficient to promote microbiota-specific RORγt+ Treg cells and prevent their expansion as inflammatory T helper 17 cells. This occurs through ILC3-mediated antigen presentation, αV integrin and competition for interleukin-2. Finally, single-cell analyses suggest that interactions between ILC3s and RORγt+ Treg cells are impaired in inflammatory bowel disease. Our results define a paradigm whereby ILC3s select for antigen-specific RORγt+ Treg cells, and against T helper 17 cells, to establish immune tolerance to the microbiota and intestinal health.

Metabolic regulation and function of T helper cells in neuroinflammation

Neuroinflammatory conditions such as multiple sclerosis (MS) are initiated by pathogenic immune cells invading the central nervous system (CNS). Autoreactive CD4⁺ T helper cells are critical players that orchestrate the immune response both in MS and in other neuroinflammatory autoimmune diseases including animal models that have been developed for MS. T helper cells are classically categorized into different subsets, but heterogeneity exists within these subsets. Untangling the more complex regulation of these subsets will clarify their functional roles in neuroinflammation. Here, we will discuss how differentiation, immune checkpoint pathways, transcriptional regulation and metabolic factors determine the function of CD4⁺ T cell subsets in CNS autoimmunity. T cells rely on metabolic reprogramming for their activation and proliferation to meet bioenergetic demands. This includes changes in glycolysis, glutamine metabolism and polyamine metabolism. Importantly, these pathways were recently also implicated in the fine tuning of T cell fate decisions during neuroinflammation. A particular focus of this review will be on the Th17/Treg balance and intra-subset functional states that can either promote or dampen autoimmune responses in the CNS and thus affect disease outcome. An increased understanding of factors that could tip CD4⁺ T cell subsets and populations towards an anti-inflammatory phenotype will be critical to better understand neuroinflammatory diseases and pave the way for novel treatment paradigms.

Organoids capture tissue-specific innate lymphoid cell development in mice and humans

Organoid-based models of murine and human innate lymphoid cell precursor (ILCP) maturation are presented. First, murine intestinal and pulmonary organoids are harnessed to demonstrate that the epithelial niche is sufficient to drive tissue-specific maturation of all innate lymphoid cell (ILC) groups in parallel, without requiring subset-specific cytokine supplementation. Then, more complex human induced pluripotent stem cell (hiPSC)-based gut and lung organoid models are used to demonstrate that human epithelial cells recapitulate maturation of ILC from a stringent systemic human ILCP population, but only when the organoid-associated stromal cells are depleted. These systems offer versatile and reductionist models to dissect the impact of environmental and mucosal niche cues on ILC maturation. In the future, these could provide insight into how ILC activity and development might become dysregulated in chronic inflammatory diseases.

Continuous activation of the IL-17F driven inflammatory pathway in acute and chronic digital dermatitis lesions in dairy cattle

Objectives of the present study were to get a deeper insight into the course of the inflammatory pathways of digital dermatitis lesions in dairy cattle by investigating the gene expression patterns throughout the different clinical stages (M0 to M4.1) of the disease. Normal skin samples (M0) were used as a reference for comparing the gene expression levels in the other M-stages through RNA Seq-technology. Principal component analysis revealed a distinct gene expression pattern associated with digital dermatitis lesions in comparison to healthy skin with a further clustering of the acute M1, M2 and M4.1 stages versus the chronic M3 and M4 stages. The majority of the up-and downregulated genes in the acute and chronic stages can be placed into a common 'core' set of genes involved in inflammation, such as A2ML1, PI3, CCL11 and elafin-like protein, whereas the most downregulated genes included keratins and anti-inflammatory molecules such as SCGB1D and MGC151921. Pathway analysis indicated the activation of the pro-inflammatory IL-17 signaling pathway in all the M stages through the upregulation of IL-17F. These results indicate that digital dermatitis is associated with an excessive inflammatory immune response concomitant with a disrupted skin barrier and impaired wound repair mechanism. Importantly, despite their macroscopically healed appearance, a significant inflammatory response (Padj < 0.05) was still measurable in the M3 and M4 lesions, potentially explaining the frequent re-activation of such lesions.

Vitamin A, systemic T-cells, and the eye: Focus on degenerative retinal disease

The first discovered vitamin, vitamin A, exists in a range of forms, primarily retinoids and provitamin carotenoids. The bioactive forms of vitamin A, retinol and retinoic acid, have many critical functions in body systems including the eye and immune system. Vitamin A deficiency is associated with dysfunctional immunity, and presents clinically as a characteristic ocular syndrome, xerophthalmia. The immune functions of vitamin A extend to the gut, where microbiome interactions and nutritional retinoids and carotenoids contribute to the balance of T cell differentiation, thereby determining immune status and contributing to inflammatory disease around the whole body. In the eye, degenerative conditions affecting the retina and uvea are influenced by vitamin A. Stargardt's disease (STGD1; MIM 248200) is characterised by bisretinoid deposits such as lipofuscin, produced by retinal photoreceptors as they use and recycle a vitamin A-derived chromophore. Age-related macular degeneration features comparable retinal deposits, such as drusen featuring lipofuscin accumulation; and is characterised by parainflammatory processes. We hypothesise that local parainflammatory processes secondary to lipofuscin deposition in the retina are mediated by T cells interacting with dietary vitamin A derivatives and the gut microbiome, and outline the current evidence for this. No cures exist for Stargardt's or age-related macular degeneration, but many vitamin A-based therapeutic approaches have been or are being trialled. The relationship between vitamin A's functions in systemic immunology and the eye could be further exploited, and further research may seek to leverage the interactions of the gut-eye immunological axis.

Inflammation, Immune Senescence, and Dysregulated Immune Regulation in the Elderly

An optimal immune response requires the appropriate interaction between the innate and the adaptive arms of the immune system as well as a proper balance of activation and regulation. After decades of life, the aging immune system is continuously exposed to immune stressors and inflammatory assaults that lead to immune senescence. In this review, we will discuss inflammaging in the elderly, specifically concentrating on IL-6 and IL-1b in the context of T lymphocytes, and how inflammation is related to mortality and morbidities, specifically cardiovascular disease and cancer. Although a number of studies suggests that the anti-inflammatory cytokine TGF-b is elevated in the elderly, heightened inflammation persists. Thus, the regulation of the immune response and the ability to return the immune system to homeostasis is also important. Therefore, we will discuss cellular alterations in aging, concentrating on senescent T cells and CD4+ CD25+ FOXP3+ regulatory T cells (Tregs) in aging

Acetyl-CoA-Carboxylase 1-mediated de novo fatty acid synthesis sustains Lgr5+ intestinal stem cell function

Basic processes of the fatty acid metabolism have an important impact on the function of intestinal epithelial cells (IEC). However, while the role of cellular fatty acid oxidation is well appreciated, it is not clear how de novo fatty acid synthesis (FAS) influences the biology of IECs. We report here that interfering with de novo FAS by deletion of the enzyme Acetyl-CoA-Carboxylase (ACC)1 in IECs results in the loss of epithelial crypt structures and a specific decline in Lgr5⁺ intestinal epithelial stem cells (ISC). Mechanistically, ACC1-mediated de novo FAS supports the formation of intestinal organoids and the differentiation of complex crypt structures by sustaining the nuclear accumulation of PPARδ/β-catenin in ISCs. The dependency of ISCs on cellular de novo FAS is tuned by the availability of environmental lipids, as an excess delivery of external fatty acids is sufficient to rescue the defect in crypt formation. Finally, inhibition of ACC1 reduces the formation of tumors in colitis-associated colon cancer, together highlighting the importance of cellular lipogenesis for sustaining ISC function and providing a potential perspective to colon cancer therapy.

Here the authors report that inhibition of de novo fatty acid synthesis by deleting the enzyme Acetyl-CoA-Carboxylase 1 in the intestinal epithelium results in the loss of crypt structures and a specific decline in Lgr5+ intestinal epithelial stem cells.

Physicochemical Characteristics and Antidiabetic Properties of the Polysaccharides from Pseudostellaria heterophylla

This study aimed to investigate the Pseudostellaria heterophylla polysaccharides (PF40) physicochemical and antidiabetic characteristics. The ultraviolet–visible (UV) spectra, Fourier transform infrared radiation (FT-IR) spectra, nuclear magnetic resonance (NMR) spectra, zeta potential, surface characteristics, and conformational and thermal stability properties of PF40 were characterized. X-ray diffraction (XRD) and scanning electron microscopy (SEM), combined with Congo red test, revealed that PF40 powder has mainly existed in amorphous form with triple-helix conformation. The single-molecular structure of PF40 exhibited a multi-branched structure extending from the center to the periphery by scanning probe microscopy (SPM) scanning. The monosaccharide residue of PF40 was an α-pyranoid ring and exhibits good stability below 168 °C. Experimental studies on antidiabetic characteristics found that PF40 could significantly improve STZ-induced intestinal mucosal damage and reduce the apoptosis of villus epithelial cells. PF40 combined with metformin could significantly improve the symptoms of insulin resistance in type 2 diabetes mellitus (T2DM) rats, the molecular mechanism might be through inhibiting the expression of RORγ protein and increasing Foxp3 protein in the jejunum of T2DM rats, and then restoring the STZ-induced imbalance of T helper 17(Th17)/ regulatory T cells (Treg) cells, thereby maintaining intestinal immune homeostasis. Results identified in this study provided important information regarding the structure and antidiabetic characteristics of Pseudostellaria heterophylla polysaccharides, which can contribute to the development of Pseudostellaria heterophylla polysaccharides for industrial purposes in the future.

Regulation of Treg Cell Metabolism and Function in Non-Lymphoid Tissues

Regulator T cells (Tregs) play pivotal roles in maintaining immune tolerance and regulating immune responses against pathogens and tumors. Reprogramming of cellular metabolism has been determined as a crucial process that connects microenvironmental cues and signaling networks to influence homeostasis and function of tissue Tregs. In adaptation to a variety of non-lymphoid tissues, Tregs coordinate local immune signals and signaling networks to rewire cellular metabolic programs to sustain their suppressive function. Altered Treg metabolism in turn shapes Treg activation and function. In light of the advanced understanding of immunometabolism, manipulation of systemic metabolites has been emerging as an attractive strategy aiming to modulate metabolism and function of tissue Tregs and improve the treatment of immune-related diseases. In this review, we summarize key immune signals and metabolic programs involved in the regulation of tissue Tregs, review the mechanisms underlying the differentiation and function of Tregs in various non-lymphoid tissues, and discuss therapeutic intervention of metabolic modulators of tissue Tregs for the treatment of autoimmune diseases and cancer.