The alarmins IL-1 and IL-33 differentially regulate the functional specialisation of Foxp3(+) regulatory T cells during mucosal inflammation

Inbred Mouse Models in Cryptococcus neoformans Research

Animal models are frequently used as surrogates to understand human disease. In the fungal pathogen Cryptococcus species complex, several variations of a mouse model of disease were developed that recapitulate different aspects of human disease. These mouse models have been implemented using various inbred and outbred mouse backgrounds, many of which have genetic differences that can influence host response and disease outcome. In this review, we will discuss the most commonly used inbred mouse backgrounds in C. neoformans infection models.

Pathogenic role of different phenotypes of immune cells in airway allergic diseases: a study based on Mendelian randomization

Background

Airway allergic disease (AAD) is a class of autoimmune diseases with predominantly Th2-type inflammation, mainly including allergic rhinitis (AR), allergic asthma (AS), and chronic sinusitis (CRS). There are very complex regulatory mechanisms between immune cells and AAD; however, previous reports found that the functions of the same immune cells in AAD are not identical.

Objective

The aim of this study was to explore the causal relationship between different phenotypic immune cells and their association with AAD.

Method

Utilizing the publicly available Genome-Wide Association Studies (GWAS) database, this study conducted a bidirectional Mendelian randomization (MR) to assess the causal relationship between immune cells of 731 different immunophenotypes and AAD. The primary assessment methods included inverse variance weighting, weighted median, and MR Egger. Additionally, sensitivity analyses such as MR-PRESSO, leave-one-out, and scatter plots were employed to eliminate the interference of heterogeneity and pleiotropy, ensuring the stability of the causal inference.

Result

A total of 38 immune cells with different immunophenotypes were found to be positively and causally associated with AR, of which 26 were protective factors and 12 were risk factors. Positive associations were found between 33 immune cells and AS, of which 14 were protective factors and 19 were risk factors, as well as between 39 immune cells and CRS, of which 22 were protective factors and 17 were risk factors. Finally, the results of all relevant immune cells for the three diseases were taken and intersected, and it was found that CD3 on CD39+-activated Treg (IVWAR = 0.001, IVWCRS = 0.043, IVWAS = 0.027) may be the key immune cell that inhibits the development of AAD (ORAR = 0.940, ORAS = 0.967, ORCRS = 0.976).

Conclusion

This study reveals that different immune phenotypes of immune cells are closely related to AAD at the genetic level, which provides a theoretical basis for future clinical studies.

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.

Role of Treg cell subsets in cardiovascular disease pathogenesis and potential therapeutic targets

In the genesis and progression of cardiovascular diseases involving both innate and adaptive immune responses, inflammation plays a pivotal and dual role. Studies in experimental animals indicate that certain immune responses are protective, while others exacerbate the disease. T-helper (Th) 1 cell immune responses are recognized as key drivers of inflammatory progression in cardiovascular diseases. Consequently, the CD4+CD25+FOXP3+ regulatory T cells (Tregs) are gaining increasing attention for their roles in inflammation and immune regulation. Given the critical role of Tregs in maintaining immune-inflammatory balance and homeostasis, abnormalities in their generation or function might lead to aberrant immune responses, thereby initiating pathological changes. Numerous preclinical studies and clinical trials have unveiled the central role of Tregs in cardiovascular diseases, such as atherosclerosis. Here, we review the roles and mechanisms of Treg subsets in cardiovascular conditions like atherosclerosis, hypertension, myocardial infarction and remodeling, myocarditis, dilated cardiomyopathy, and heart failure. While the precise molecular mechanisms of Tregs in cardiac protection remain elusive, therapeutic strategies targeting Tregs present a promising new direction for the prevention and treatment of cardiovascular diseases.

Sodium as an Important Regulator of Immunometabolism

Salt sensitivity concerns blood pressure alterations after a change in salt intake (sodium chloride). The heart is a pump, and vessels are tubes; sodium can affect both. A high salt intake increases cardiac output, promotes vascular dysfunction and capillary rarefaction, and chronically leads to increased systemic vascular resistance. More recent findings suggest that sodium also acts as an important second messenger regulating energy metabolism and cellular functions. Besides endothelial cells and fibroblasts, sodium also affects innate and adaptive immunometabolism, immune cell function, and influences certain microbes and microbiota-derived metabolites. We propose the idea that the definition of salt sensitivity should be expanded beyond high blood pressure to cellular and molecular salt sensitivity.

The dichotomic role of single cytokines: Fine-tuning immune responses

Cytokines are known for their pleiotropic effects. They can be classified by their function as pro-inflammatory, such as tumor necrosis factor (TNF), interleukin (IL) 1 and IL-12, or anti-inflammatory, like IL-10, IL-35 and transforming growth factor β (TGF-β). Though this type of classification is an important simplification for the understanding of the general cytokine's role, it can be misleading. Here, we discuss recent studies that show a dichotomic role of the so-called pro and anti-inflammatory cytokines, highlighting that their function can be dependent on the microenvironment and their concentrations. Furthermore, we discuss how the back-and-forth interplay between cytokines and immunometabolism can influence the dichotomic role of inflammatory responses as an important target to complement cytokine-based therapies.

TRAF4 is crucial for ST2+ memory Th2 cell expansion in IL-33-driven airway inflammation

Tumor necrosis factor receptor-associated factor 4 (TRAF4) is an important regulator of type 2 responses in the airway; however, the underlying cellular and molecular mechanisms remain elusive. Herein, we generated T cell-specific TRAF4-deficient (CD4-cre Traf4fl/fl) mice and investigated the role of TRAF4 in memory Th2 cells expressing IL-33 receptor (ST2, suppression of tumorigenicity 2) (ST2+ mTh2 cells) in IL-33-mediated type 2 airway inflammation. We found that in vitro-polarized TRAF4-deficient (CD4-cre Traf4fl/fl) ST2+ mTh2 cells exhibited decreased IL-33-induced proliferation as compared with TRAF4-sufficient (Traf4fl/fl) cells. Moreover, CD4-cre Traf4fl/fl mice showed less ST2+ mTh2 cell proliferation and eosinophilic infiltration in the lungs than Traf4fl/fl mice in the preclinical models of IL-33-mediated type 2 airway inflammation. Mechanistically, we discovered that TRAF4 was required for the activation of AKT/mTOR and ERK1/2 signaling pathways as well as the expression of transcription factor Myc and nutrient transporters (Slc2a1, Slc7a1, and Slc7a5), signature genes involved in T cell growth and proliferation, in ST2+ mTh2 cells stimulated by IL-33. Taken together, the current study reveals a role of TRAF4 in ST2+ mTh2 cells in IL-33-mediated type 2 pulmonary inflammation, opening up avenues for the development of new therapeutic strategies.

Xenomake: a pipeline for processing and sorting xenograft reads from spatial transcriptomic experiments

Xenograft models are attractive models that mimic human tumor biology and permit one to perturb the tumor microenvironment and study its drug response. Spatially resolved transcriptomics (SRT) provide a powerful way to study the organization of xenograft models, but currently there is a lack of specialized pipeline for processing xenograft reads originated from SRT experiments. Xenomake is a standalone pipeline for the automated handling of spatial xenograft reads. Xenomake handles read processing, alignment, xenograft read sorting, quantification, and connects well with downstream spatial analysis packages. We additionally show that Xenomake can correctly assign organism specific reads, reduce sparsity of data by increasing gene counts, while maintaining biological relevance for studies.

The functional adaptation of effector Foxp3+ regulatory T cells to pulmonary inflammation

During infections, the timings of effector differentiation of pulmonary immune responses are of paramount importance, as pathogen persistence and unsuppressed inflammation can rapidly lead to a loss of function, increased frailty, and death. Thus, both an efficient clearance of the danger and a rapid resolution of inflammation are critical to host survival. We now know that tissue-localized FoxP3+ regulatory T cells, a subset of CD4+ T cells, are highly attuned to the type of immune response, acquiring unique phenotypic characteristics that allow them to adapt their suppressive functions with the nature of inflammatory cells. To achieve this, activated effector TREG cells acquire specialized TH 1, TH 2, and TH 17-like characteristics that allow them to migrate, survive, and time their function(s) through refined mechanisms. Herein, we describe how this process requires a unique developmental path that includes the acquisition of master transcription factors and the expression of receptors adapted to sense local danger signals that are found during pulmonary inflammation. In turn, we offer an overview of how these characteristics promote the capacity of local effector TREG cells to proliferate, survive, and display suppressive strategies to resolve lung injury.

Foxp3+ regulatory T cells in the central nervous system and other nonlymphoid tissues

Foxp3+ regulatory T (Treg) cells are indispensable for the maintenance of immunologic self-tolerance as well as for the confinement of autoimmune inflammation after the breach of self-tolerance. In order to fulfill these tasks, Treg cells operate in secondary lymphoid tissues and nonlymphoid tissues. The conditions for Treg cell stability and for their modes of action are different according to their compartment of residence. In addition, Treg cells initiate residency programs to inhabit niches in nonlympoid tissues (NLT) in steady state and after re-establishment of previously deflected homeostasis for extended periods of time. These NLT Treg cells are different from lymphoid tissue residing Treg cells and are functionally specialized to subserve not only immune functions but support intrinsic functions of their tissue of residence. This review will highlight current ideas about the functional specialization of NLT Treg cells in particular in the central nervous system (CNS) and discuss challenges that we are facing in an effort to exploit the power of NLT Treg cells for maintenance of tissue homeostasis and perhaps also tissue regeneration.

IL-18 is required for the TH1-adaptation of TREG cells and the selective suppression of TH17 responses in acute and chronic infections

Interleukin (IL)-18, a member of the IL-1 family of alarmins, is abundantly released in the lungs following influenza A (IAV) infections yet its role in orchestrating the local adaptive immune response remains ill defined. Through genetic disruption of the IL-18 receptor, we demonstrate that IL-18 not only promotes pulmonary TH1 responses but also influences regulatory T cells (TREG) function in the infected lungs. As the response unfolds, TREG cells accumulating in the lungs express Helios, T-bet, CXCR3, and IL-18R1 and produce interferon γ in the presence of IL-12. During IAV, IL-18R1 is required for TREG cells to control TH17, but not TH1, responses and promote a return to lung homeostasis, revealing a novel mechanism of selective suppression. Moreover, this observation was not limited to the lungs, as skin-localized TREG cells require an IL-18 signal to specifically suppress IL-17A production by TH17 and γδ T cells in a model of chronic cutaneous Leishmania major infection. Overall, these results uncover how IL-18 orchestrates the tissue adaptation of TREG cells to selectively favor TH1 over TH17 responses during TH1-driven immune responses and provide a novel perspective into how IL-18 dictates the immune response during viral and parasitic infections.

The eIF4EBP-eIF4E axis regulates CD4+ T cell differentiation through modulation of T cell activation and metabolism

CD4⁺ T cells are critical for adaptive immunity, differentiating into distinct effector and regulatory subsets. Although the transcriptional programs underlying their differentiation are known, recent research has highlighted the importance of mRNA translation in determining protein abundance. We previously conducted genome-wide analysis of translation in CD4⁺ T cells revealing distinct translational signatures distinguishing these subsets, identifying eIF4E as a central differentially translated transcript. As eIF4E is vital for eukaryotic translation, we examined how altered eIF4E activity affected T cell function using mice lacking eIF4E-binding proteins (BP^-/-). BP^-/- effector T cells showed elevated Th1 responses ex vivo and upon viral challenge with enhanced Th1 differentiation observed in vitro. This was accompanied by increased TCR activation and elevated glycolytic activity. This study highlights how regulating T cell-intrinsic eIF4E activity can influence T cell activation and differentiation, suggesting the eIF4EBP-eIF4E axis as a potential therapeutic target for controlling aberrant T cell responses.

Adaptive immunology of Cryptococcus neoformans infections-an update

The fungal genus Cryptococcus comprises a group of pathogens with considerable phenotypic and genotypic diversity that can lead to cryptococcosis in both healthy and immunocompromised individuals. With the emergence of the HIV pandemic, cryptococcosis, mainly meningoencephalitis, afflicts HIV-infected patients with severe dysfunction of T cells. It has also been reported in recipients of solid organ transplantation and in patients with autoimmune diseases who take immunosuppressive agents long-term, as well as in those with unidentified immunodeficiency. The clinical outcome of the disease is primarily determined by the immune response resulting from the interplay between the host immune system and the pathogen. Most human infections are caused by Cryptococcus neoformans, and nearly all immunological studies have focused on C. neoformans. This review provides an updated understanding of the role of adaptive immunity during infection with C. neoformans in human and animal models over the past half-decade.

Interleukin-23 receptor signaling impairs the stability and function of colonic regulatory T cells

The cytokine interleukin-23 (IL-23) is involved in the pathogenesis of inflammatory and autoimmune conditions including inflammatory bowel disease (IBD). IL23R is enriched in intestinal Tregs, yet whether IL-23 modulates intestinal Tregs remains unknown. Here, investigating IL-23R signaling in Tregs specifically, we show that colonic Tregs highly express Il23r compared with Tregs from other compartments and their frequency is reduced upon IL-23 administration and impairs Treg suppressive function. Similarly, colonic Treg frequency is increased in mice lacking Il23r specifically in Tregs and exhibits a competitive advantage over IL-23R-sufficient Tregs during inflammation. Finally, IL-23 antagonizes liver X receptor pathway, cellular cholesterol transporter Abca1, and increases Treg apoptosis. Our results show that IL-23R signaling regulates intestinal Tregs by increasing cell turnover, antagonizing suppression, and decreasing cholesterol efflux. These results suggest that IL-23 negatively regulates Tregs in the intestine with potential implications for promoting chronic inflammation in patients with IBD.

Autoreactive T-Cells in Psoriasis: Are They Spoiled Tregs and Can Therapies Restore Their Functions?

Psoriasis is a chronic inflammatory skin disease, which affects 2-4% of the population worldwide. T-cell derived factors such as Th17 and Th1 cytokines or cytokines such as IL-23, which favors Th17-expansion/differentiation, dominate in the disease. Therapies targeting these factors have been developed over the years. An autoimmune component is present, as autoreactive T-cells specific for keratins, the antimicrobial peptide LL37 and ADAMTSL5 have been described. Both autoreactive CD4 and CD8 T-cells exist, produce pathogenic cytokines, and correlate with disease activity. Along with the assumption that psoriasis is a T-cell-driven disease, Tregs have been studied extensively over the years, both in the skin and in circulation. This narrative review resumes the main findings about Tregs in psoriasis. We discuss how Tregs increase in psoriasis but are impaired in their regulatory/suppressive function. We debate the possibility that Tregs convert into T-effector cells under inflammatory conditions; for instance, they may turn into Th17-cells. We put particular emphasis on therapies that seem to counteract this conversion. We have enriched this review with an experimental section analyzing T-cells specific for the autoantigen LL37 in a healthy subject, suggesting that a shared specificity may exist between Tregs and autoreactive responder T-cells. This suggests that successful psoriasis treatments may, among other effects, restore Tregs numbers and functions.

A comparative study of IL-33 and its receptor ST2 in a C57BL/6 J mouse model of pulmonary Cryptococcus neoformans infection

It has been reported that IL-33 receptor ST2 deficiency mitigates Cryptococcus neoformans (C. neoformans) pulmonary infection in BALB/c mice. IL-33 may modulate immune responses in ST2-dependent and ST2-independent manners. The host genetic background (i.e., BALB/c, C57BL/6 J) influences immune responses against C. neoformans. In the present study, we aimed to explore the roles of IL-33 and ST2 in pulmonary C. neoformans-infected mice on a C57BL/6 J genetic background. C. neoformans infection increased IL-33 expression in lung tissues. IL-33 deficiency but not ST2 deficiency significantly extended the survival time of C. neoformans-infected mice. In contrast, either IL-33 or ST2 deficiency reduced fungal burdens in lung, spleen and brain tissues from the mice following C. neoformans intratracheal inoculation. Similarly, inflammatory responses in the lung tissues were more pronounced in both the IL-33^-/- and ST2^-/- infected mice. However, mucus production was decreased in IL-33^-/- infected mice alone, and the level of IL-5 in bronchoalveolar lavage fluid (BALF) was substantially decreased in the IL-33^-/- infected mice but not ST2^-/- infected mice. Moreover, IL-33 deficiency but not ST2 deficiency increased iNOS-positive macrophages. At the early stage of infection, the reduced pulmonary fungal burden in the IL-33^-/- and ST2^-/- mice was accompanied by increased neutrophil infiltration. Collectively, IL-33 regulated pulmonary C. neoformans infection in an ST2-dependent and ST2-independent manner in C57BL/6 J mice.

Knowledge mapping and research trends of IL-33 from 2004 to 2022: a bibliometric analysis

Background

IL-33 has been studied widely but its comprehensive and systematic bibliometric analysis is yet available. The present study is to summarize the research progress of IL-33 through bibliometric analysis.

Methods

The publications related to IL-33 were identified and selected from the Web of Science Core Collection (WoSCC) database on 7 December 2022. The downloaded data was analyzed with bibliometric package in R software. CiteSpace and VOSviewer were used to conduct IL-33 bibliometric and knowledge mapping analysis.

Results

From 1 January 2004 to 7 December 2022, 4711 articles on IL-33 research published in 1009 academic journals by 24652 authors in 483 institutions from 89 countries were identified. The number of articles had grown steadily over this period. The United States of America(USA) and China are the major contributors in the field of research while University of Tokyo and University of Glasgow are the most active institutions. The most prolific journal is Frontiers in Immunology, while the Journal of Immunity is the top 1 co-cited journal. Andrew N. J. Mckenzie published the most significant number of articles and Jochen Schmitz was co-cited most. The major fields of these publications are immunology, cell biology, and biochemistry & molecular biology. After analysis, the high-frequency keywords of IL-33 research related to molecular biology (sST2, IL-1), immunological effects (type 2 immunity, Th2 cells), and diseases (asthma, cancer, cardiovascular diseases). Among these, the involvement of IL-33 in the regulation of type 2 inflammation has strong research potential and is a current research hotspot.

Conclusion

The present study quantifies and identifies the current research status and trends of IL-33 using bibliometric and knowledge mapping analysis. This study may offer the direction of IL-33-related research for scholars.

Implications of regulatory T cells in non-lymphoid tissue physiology and pathophysiology

Treg cells have been initially described as gatekeepers for the control of autoimmunity, as they can actively suppress the activity of other immune cells. However, their role goes beyond this as Treg cells further control immune responses during infections and tumor development. Furthermore, Treg cells can acquire additional properties for e.g., the control of tissue homeostasis. This is instructed by a specific differentiation program and the acquisition of effector properties unique to Treg cells in non-lymphoid tissues. These tissue Treg cells can further adapt to their tissue environment and acquire distinct functional properties through specific transcription factors activated by a combination of tissue derived factors, including tissue-specific antigens and cytokines. In this review, we will focus on recent findings extending our current understanding of the role and differentiation of these tissue Treg cells. As such we will highlight the importance of tissue Treg cells for tissue maintenance, regeneration, and repair in adipose tissue, muscle, CNS, liver, kidney, reproductive organs, and the lung.

Tregs in Autoimmunity: Insights Into Intrinsic Brake Mechanism Driving Pathogenesis and Immune Homeostasis

CD4⁺CD25^highFoxp3⁺ regulatory T-cells (Tregs) are functionally characterized for their ability to suppress the activation of multiple immune cell types and are indispensable for maintaining immune homeostasis and tolerance. Disruption of this intrinsic brake system assessed by loss of suppressive capacity, cell numbers, and Foxp3 expression, leads to uncontrolled immune responses and tissue damage. The conversion of Tregs to a pathogenic pro-inflammatory phenotype is widely observed in immune mediated diseases. However, the molecular mechanisms that underpin the control of Treg stability and suppressive capacity are incompletely understood. This review summarizes the concepts of T_reg cell stability and T_reg cell plasticity highlighting underlying mechanisms including translational and epigenetic regulators that may enable translation to new therapeutic strategies. Our enhanced understanding of molecular mechanism controlling Tregs will have important implications into immune homeostasis and therapeutic potential for the treatment of immune-mediated diseases.

Extricating human tumour immune alterations from tissue inflammation

Immunotherapies have achieved remarkable successes in the treatment of cancer, but major challenges remain1,2. An inherent weakness of current treatment approaches is that therapeutically targeted pathways are not restricted to tumours, but are also found in other tissue microenvironments, complicating treatment3,4. Despite great efforts to define inflammatory processes in the tumour microenvironment, the understanding of tumour-unique immune alterations is limited by a knowledge gap regarding the immune cell populations in inflamed human tissues. Here, in an effort to identify such tumour-enriched immune alterations, we used complementary single-cell analysis approaches to interrogate the immune infiltrate in human head and neck squamous cell carcinomas and site-matched non-malignant, inflamed tissues. Our analysis revealed a large overlap in the composition and phenotype of immune cells in tumour and inflamed tissues. Computational analysis identified tumour-enriched immune cell interactions, one of which yields a large population of regulatory T (Treg) cells that is highly enriched in the tumour and uniquely identified among all haematopoietically-derived cells in blood and tissue by co-expression of ICOS and IL-1 receptor type 1 (IL1R1). We provide evidence that these intratumoural IL1R1+ Treg cells had responded to antigen recently and demonstrate that they are clonally expanded with superior suppressive function compared with IL1R1- Treg cells. In addition to identifying extensive immunological congruence between inflamed tissues and tumours as well as tumour-specific changes with direct disease relevance, our work also provides a blueprint for extricating disease-specific changes from general inflammation-associated patterns.

Foxo3a tempers excessive glutaminolysis in activated T cells to prevent fatal gut inflammation in the murine IL-10-/- model of colitis

Mutations in susceptibility alleles correlate with gut-inflammatory diseases, such as Crohn's disease; however, this does not often impact the disease progression indicating the existence of compensatory genes. We show that a reduction in Foxo3a expression in IL-10-deficient mice results in a spontaneous and aggressive Crohn's- like disease with 100% penetrance, which is rescued by deletion of myeloid cells, T cells and inhibition of mTORC1. In Foxo3a^-/- IL-10^-/- mice, there is poor cell death of myeloid cells in the gut, leading to increased accumulation of myeloid and T cells in the gut. Myeloid cells express high levels of inflammatory cytokines, and regulatory T cells are dysfunctional despite increased abundance. Foxo3a signaling represses the transcription of glutaminase (GLS/GLS2) to prevent over-consumption of glutamine by activated T cells and its conversion to glutamate that contributes to the TCA cycle and mTORC1 activation. Finally, we show that Foxo3a restricts the abundance of colitogenic microbiota in IL-10-deficient mice. Thus, by suppressing glutaminolysis in activated T cells Foxo3a mediates a critical checkpoint that prevents the development of fulminant gut inflammatory disease.

Emerging Functions of IL-33 in Homeostasis and Immunity

Our understanding of the functions of the IL-1 superfamily cytokine and damage-associated molecular pattern IL-33 continues to evolve with our understanding of homeostasis and immunity. The early findings that IL-33 is a potent driver of type 2 immune responses promoting parasite expulsion, but also inflammatory diseases like allergy and asthma, have been further supported. Yet, as the importance of a type 2 response in tissue repair and homeostasis has emerged, so has the fundamental importance of IL-33 to these processes. In this review, we outline an evolving understanding of IL-33 immunobiology, paying particular attention to how IL-33 directs a network of ST2+ regulatory T cells, reparative and regulatory macrophages, and type 2 innate lymphoid cells that are fundamental to tissue development, homeostasis, and repair.

Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

The fellowship of regulatory and tissue-resident memory cells

T cells located in non-lymphoid tissues have come to prominence in recent years. CD8⁺ tissue-resident memory (Trm) cells are important for tissue immune surveillance, provide an important line of defence against invading pathogens and show promise in cancer therapies. These cells differ in phenotype from other memory populations, are adapted to the tissue they home to where they found their cognate antigen and have different metabolic requirements for survival and activation. CD4⁺ Foxp3⁺ regulatory T (Treg) cells also consist of specialised populations, found in non-lymphoid tissues, with distinct transcriptional programmes. These cells have equally adapted to function in the tissue they made their home. Both Trm and Treg cells have functions beyond immune defence, involving tissue homeostasis, repair and turnover. They are part of a multicellular communication network. Intriguingly, occupying the same niche, Treg cells are important in the establishment of Trm cells, which may have implications to harness the immune surveillance and tissue homeostasis properties of Trm cells for future therapies.

Acsbg1-dependent mitochondrial fitness is a metabolic checkpoint for tissue Treg cell homeostasis

Regulatory T (Treg) cells are critical for immunological tolerance and immune homeostasis. Treg cells strongly rely on mitochondrial metabolism and show a lower level of glycolysis. However, little is known about the role of lipid metabolism in the regulation of Treg cell homeostasis. Some members of the ACSL family of acyl-coenzyme A (CoA) synthases are expressed in T cells, but their function remains unclear. A combination of RNA-sequencing and proteome analyses shows that Acsbg1, a member of ACSL, is selectively expressed in Treg cells. We show that the genetic deletion of Acsbg1 not only causes mitochondrial dysfunction, but it also dampens other metabolic pathways. The extrinsic supplementation of Acsbg1-deficient Treg cells with oleoyl-CoA restores the phenotype of the Treg metabolic signature. Furthermore, this pathway in ST2+ effector Treg cells enhances immunosuppressive capacity in airway inflammation. Thus, Acsbg1 serves as a metabolic checkpoint governing Treg cell homeostasis and the resolution of lung inflammation.

Phenotypic and Functional Diversity in Regulatory T Cells

The concept that a subset of T cells exists that specifically suppresses immune responses was originally proposed over 50 years ago. It then took the next 30 years to solidify the concept of regulatory T cells (Tregs) into the paradigm we understand today – namely a subset of CD4+ FOXP3+ T-cells that are critical for controlling immune responses to self and commensal or environmental antigens that also play key roles in promoting tissue homeostasis and repair. Expression of the transcription factor FOXP3 is a defining feature of Tregs, while the cytokine IL2 is necessary for robust Treg development and function. While our initial conception of Tregs was as a monomorphic lineage required to suppress all types of immune responses, recent work has demonstrated extensive phenotypic and functional diversity within the Treg population. In this review we address the ontogeny, phenotype, and function of the large number of distinct effector Treg subsets that have been defined over the last 15 years.

Regulation of T Cell Responses by Ionic Salt Signals

T helper cell responses are tailored to their respective antigens and adapted to their specific tissue microenvironment. While a great proportion of T cells acquire a resident identity, a significant proportion of T cells continue circulating, thus encountering changing microenvironmental signals during immune surveillance. One signal, which has previously been largely overlooked, is sodium chloride. It has been proposed to have potent effects on T cell responses in the context of autoimmune, allergic and infectious tissue inflammation in mouse models and humans. Sodium chloride is stringently regulated in the blood by the kidneys but displays differential deposition patterns in peripheral tissues. Sodium chloride accumulation might furthermore be regulated by dietary intake and thus by intentional behavior. Together, these results make sodium chloride an interesting but still controversial signal for immune modulation. Its downstream cellular activities represent a potential therapeutic target given its effects on T cell cytokine production. In this review article, we provide an overview and critical evaluation of the impact of this ionic signal on T helper cell polarization and T helper cell effector functions. In addition, the impact of sodium chloride from the tissue microenvironment is assessed for human health and disease and for its therapeutic potential.

Intestinal Regulatory T Cells as Specialized Tissue-Restricted Immune Cells in Intestinal Immune Homeostasis and Disease

FOXP3+ regulatory T cells (Treg cells) are a specialized population of CD4+ T cells that restrict immune activation and are essential to prevent systemic autoimmunity. In the intestine, the major function of Treg cells is to regulate inflammation as shown by a wide array of mechanistic studies in mice. While Treg cells originating from the thymus can home to the intestine, the majority of Treg cells residing in the intestine are induced from FOXP3neg conventional CD4+ T cells to elicit tolerogenic responses to microbiota and food antigens. This process largely takes place in the gut draining lymph nodes via interaction with antigen-presenting cells that convert circulating naïve T cells into Treg cells. Notably, dysregulation of Treg cells leads to a number of chronic inflammatory disorders, including inflammatory bowel disease. Thus, understanding intestinal Treg cell biology in settings of inflammation and homeostasis has the potential to improve therapeutic options for patients with inflammatory bowel disease. Here, the induction, maintenance, trafficking, and function of intestinal Treg cells is reviewed in the context of intestinal inflammation and inflammatory bowel disease. In this review we propose intestinal Treg cells do not compose fixed Treg cell subsets, but rather (like T helper cells), are plastic and can adopt different programs depending on microenvironmental cues.

IL-1β-driven osteoclastogenic T regulatory cells accelerate bone erosion in arthritis

IL-1β is a pro-inflammatory mediator with roles in innate and adaptive immunity. Here we show that IL-1β contributes to autoimmune arthritis by inducing osteoclastogenic capacity in T regulatory cells (Tregs). Using mice with joint inflammation arising through deficiency of the IL-1 receptor antagonist (Il1rn-/-), we observed that IL-1β blockade attenuated disease more effectively in early arthritis than in established arthritis, especially with respect to bone erosion. Protection was accompanied by a reduction in synovial CD4+Foxp3+ Tregs that displayed preserved suppressive capacity and aerobic metabolism but aberrant expression of RANKL and a striking capacity to drive RANKL-dependent osteoclast differentiation. Both Il1rn-/- Tregs and wild-type Tregs differentiated with IL-1β accelerated bone erosion upon adoptive transfer. Human Tregs exhibited analogous differentiation, and corresponding RANKLhiFoxp3+ T cells could be identified in rheumatoid arthritis synovial tissue. Together, these findings identify IL-1β-induced osteoclastogenic Tregs (O-Tregs) as a contributor to bone erosion in arthritis.

Mechanisms of exTreg induction

CD4+ CD25+ Foxp3+ Tregs play an important role in the maintenance of the immune system by regulating immune responses and resolving inflammation. Tregs exert their function by suppressing other immune cells and mediating peripheral self-tolerance. Under homeostatic conditions, Tregs are stable T-cell populations. However, under inflammatory environments, Tregs are converted to CD4+ CD25low Foxp3low cells. These cells are termed "exTreg" or "exFoxp3" cells. The molecular mechanism of Treg transition to exTregs remains incompletely understood. Uncertainties might be explained by a lack of consensus of biological markers to define Treg subsets in general and exTregs in particular. In this review, we summarize known markers of Tregs and factors responsible for exTreg generation including cytokines, signaling pathways, transcription factors, and epigenetic mechanisms. We also identify studies demonstrating the presence of exTregs in various diseases and sources of exTregs. Understanding the biology of Treg transition to exTregs will help in designing Treg-based therapeutic approaches.

Host-microbiome intestinal interactions during early life: considerations for atopy and asthma development

PURPOSE OF REVIEW

The body's largest microbial community, the gut microbiome, is in contact with mucosal surfaces populated with epithelial, immune, endocrine and nerve cells, all of which sense and respond to microbial signals. These mutual interactions have led to a functional coevolution between the microbes and human physiology. Examples of coadaptation are anaerobes Bifidobacteria and Bacteroides, which have adjusted their metabolism to dietary components of human milk, and infant immune development, which has evolved to become reliant on the presence of beneficial microbes. Current research suggests that specific composition of the early-life gut microbiome aligns with the maturation of host immunity. Disruptions of natural microbial succession patterns during gut colonization are a consistent feature of immune-mediated diseases, including atopy and asthma.

RECENT FINDINGS

Here, we catalog recent birth cohorts documenting associations between immune dysregulation and microbial alterations, and summarize the evidence supporting the role of the gut microbiome as an etiological determinant of immune-mediated allergic diseases.

SUMMARY

Ecological concepts that describe microbial dynamics in the context of the host environment, and a portray of immune and neuroendocrine signaling induced by host-microbiome interactions, have become indispensable in describing the molecular role of early-life microbiome in atopy and asthma susceptibility.

Recruitment and Expansion of Tregs Cells in the Tumor Environment-How to Target Them?

Simple Summary

The immune response against cancer is generated by effector T cells, among them cytotoxic CD8⁺ T cells that destroy cancer cells and helper CD4⁺ T cells that mediate and support the immune response. This antitumor function of T cells is tightly regulated by a particular subset of CD4⁺ T cells, named regulatory T cells (Tregs), through different mechanisms. Even if the complete inhibition of Tregs would be extremely harmful due to their tolerogenic role in impeding autoimmune diseases in the periphery, the targeted blockade of their accumulation at tumor sites or their targeted depletion represent a major therapeutic challenge. This review focuses on the mechanisms favoring Treg recruitment, expansion and stabilization in the tumor microenvironment and the therapeutic strategies developed to block these mechanisms.

Abstract

Regulatory T cells (Tregs) are present in a large majority of solid tumors and are mainly associated with a poor prognosis, as their major function is to inhibit the antitumor immune response contributing to immunosuppression. In this review, we will investigate the mechanisms involved in the recruitment, amplification and stability of Tregs in the tumor microenvironment (TME). We will also review the strategies currently developed to inhibit Tregs’ deleterious impact in the TME by either inhibiting their recruitment, blocking their expansion, favoring their plastic transformation into other CD4⁺ T-cell subsets, blocking their suppressive function or depleting them specifically in the TME to avoid severe deleterious effects associated with Treg neutralization/depletion in the periphery and normal tissues.

Elevated Extracellular cGMP Produced after Exposure to Enterotoxigenic Escherichia coli Heat-Stable Toxin Induces Epithelial IL-33 Release and Alters Intestinal Immunity

Enterotoxigenic Escherichia coli (ETEC) is a major diarrheal pathogen in children in low- to middle-income countries. Previous studies identified heat-stable enterotoxin (ST)-producing ETEC as a prevalent diarrheal pathogen in children younger than 5 years.

Enterotoxigenic Escherichia coli (ETEC) is a major diarrheal pathogen in children in low- to middle-income countries. Previous studies identified heat-stable enterotoxin (ST)-producing ETEC as a prevalent diarrheal pathogen in children younger than 5 years. While many studies have evaluated the interaction of ETEC heat-labile enterotoxin (LT) with host epithelium and immunity, few investigations have attempted similar studies with ST. To further understand ST pathogenesis, we examined the impact of ST on cGMP localization, epithelial cell cytokine production, and antibody development following immunization. In addition to robust intracellular cGMP in T84 cells in the presence of phosphodiesterase inhibitors (PDEis) that prevent the breakdown of cyclic nucleotides, we found that prolonged ST intoxication induced extracellular cGMP accumulation in the presence or absence of PDEis. Further, ST intoxication induced luminal cGMP in vivo in mice, suggesting that secreted cGMP may have other cellular functions. Using transcriptome sequencing (RNA-seq) and quantitative PCR (qPCR), we demonstrated that ST intoxication, or treatment with the clinically used ST mimic linaclotide, altered inflammatory cytokine gene expression, including the interleukin 1 (IL-1) family member IL-33, which could also be induced by cell-permeative 8-Br-cGMP. Finally, when present during immunization, ST suppressed induction of antibodies to specific antigens. In conclusion, our studies indicate that ST modulates epithelial cell physiology and the interplay between the epithelial and immune compartments.

Role for IL-1 Family Cytokines in Fungal Infections

Fungal pathogens kill approximately 1.5 million individuals per year and represent a severe disease burden worldwide. It is estimated over 150 million people have serious fungal disease such as recurrent mucosal infections or life-threatening systemic infections. Disease can ensue from commensal fungi or new infection and involves different fungal morphologies and the expression of virulence factors. Therefore, anti-fungal immunity is complex and requires coordination between multiple facets of the immune system. IL-1 family cytokines are associated with acute and chronic inflammation and are essential for the innate response to infection. Recent research indicates IL-1 cytokines play a key role mediating immunity against different fungal infections. During mucosal disease, IL-1R and IL-36R are required for neutrophil recruitment and protective Th17 responses, but function through different mechanisms. During systemic disease, IL-18 drives protective Th1 responses, while IL-33 promotes Th2 and suppresses Th1 immunity. The IL-1 family represents an attractive anti-fungal immunotherapy target. There is a need for novel anti-fungal therapeutics, as current therapies are ineffective, toxic and encounter resistance, and no anti-fungal vaccine exists. Furthering our understanding of the IL-1 family cytokines and their complex role during fungal infection may aid the development of novel therapies. As such, this review will discuss the role for IL-1 family cytokines in fungal infections.

Interleukin-33 signaling exacerbates experimental infectious colitis by enhancing gut permeability and inhibiting protective Th17 immunity

A wide range of microbial pathogens is capable of entering the gastrointestinal tract, causing infectious diarrhea and colitis. A finely tuned balance between different cytokines is necessary to eradicate the microbial threat and to avoid infection complications. The current study identified IL-33 as a critical regulator of the immune response to the enteric pathogen Citrobacter rodentium. We observed that deficiency of the IL-33 signaling pathway attenuates bacterial-induced colitis. Conversely, boosting this pathway strongly aggravates the inflammatory response and makes the mice prone to systemic infection. Mechanistically, IL-33 mediates its detrimental effect by enhancing gut permeability and by limiting the induction of protective T helper 17 cells at the site of infection, thus impairing host defense mechanisms against the enteric pathogen. Importantly, IL-33-treated infected mice supplemented with IL-17A are able to resist the otherwise strong systemic spreading of the pathogen. These findings reveal a novel IL-33/IL-17A crosstalk that controls the pathogenesis of Citrobacter rodentium-driven infectious colitis. Manipulating the dynamics of cytokines may offer new therapeutic strategies to treat specific intestinal infections.

Molecular Insights Into Regulatory T-Cell Adaptation to Self, Environment, and Host Tissues: Plasticity or Loss of Function in Autoimmune Disease

There has been much interest in the ability of regulatory T cells (Treg) to switch function in vivo, either as a result of genetic risk of disease or in response to environmental and metabolic cues. The relationship between levels of FOXP3 and functional fitness plays a significant part in this plasticity. There is an emerging role for Treg in tissue repair that may be less dependent on FOXP3, and the molecular mechanisms underpinning this are not fully understood. As a result of detailed, high-resolution functional genomics, the gene regulatory networks and key functional mediators of Treg phenotype downstream of FOXP3 have been mapped, enabling a mechanistic insight into Treg function. This transcription factor-driven programming of T-cell function to generate Treg requires the switching on and off of key genes that form part of the Treg gene regulatory network and raises the possibility that this is reversible. It is plausible that subtle shifts in expression levels of specific genes, including transcription factors and non-coding RNAs, change the regulation of the Treg gene network. The subtle skewing of gene expression initiates changes in function, with the potential to promote chronic disease and/or to license appropriate inflammatory responses. In the case of autoimmunity, there is an underlying genetic risk, and the interplay of genetic and environmental cues is complex and impacts gene regulation networks frequently involving promoters and enhancers, the regulatory elements that control gene expression levels and responsiveness. These promoter–enhancer interactions can operate over long distances and are highly cell type specific. In autoimmunity, the genetic risk can result in changes in these enhancer/promoter interactions, and this mainly impacts genes which are expressed in T cells and hence impacts Treg/conventional T-cell (Tconv) function. Genetic risk may cause the subtle alterations to the responsiveness of gene regulatory networks which are controlled by or control FOXP3 and its target genes, and the application of assays of the 3D organization of chromatin, enabling the connection of non-coding regulatory regions to the genes they control, is revealing the direct impact of environmental/metabolic/genetic risk on T-cell function and is providing mechanistic insight into susceptibility to inflammatory and autoimmune conditions.

Animal Models of Cryptococcus neoformans in Identifying Immune Parameters Associated With Primary Infection and Reactivation of Latent Infection

Cryptococcus species are environmental fungal pathogens and the causative agents of cryptococcosis. Infection occurs upon inhalation of infectious particles, which proliferate in the lung causing a primary infection. From this primary lung infection, fungal cells can eventually disseminate to other organs, particularly the brain, causing lethal meningoencephalitis. However, in most cases, the primary infection resolves with the formation of a lung granuloma. Upon severe immunodeficiency, dormant cryptococcal cells will start proliferating in the lung granuloma and eventually will disseminate to the brain. Many investigators have sought to study the protective host immune response to this pathogen in search of host parameters that keep the proliferation of cryptococcal cells under control. The majority of the work assimilates research carried out using the primary infection animal model, mainly because a reactivation model has been available only very recently. This review will focus on anti-cryptococcal immunity in both the primary and reactivation models. An understanding of the differences in host immunity between the primary and reactivation models will help to define the key host parameters that control the infections and are important for the research and development of new therapeutic and vaccine strategies against cryptococcosis.

Molecular mechanism for impaired suppressive function of Tregs in autoimmune diseases: A summary of cell-intrinsic and cell-extrinsic factors

Regulatory T (Treg) cells are responsible for maintaining immune homeostasis and preventing autoimmunity. In immune homeostasis condition, Tregs exert their suppressive function through inhibiting the proliferation of effector T cells. In response to environmental signals, Tregs display phenotypic heterogeneity and altered stability, which endows their suppressive function in a context-dependent manner. Compelling evidence indicates deficiency of Treg suppressive function is related to the immunopathogenesis of various autoimmune diseases. Consequently, it is vital to further our understanding of the molecular mechanism accounting for the regulation of Treg suppressive functions. In this review, we outline the current knowledge that highlights how cell-intrinsic factors, such as inflammatory cytokines, transcription factors, signalling pathways, post-translational modification (PTM), miRNAs, protein and protein complex, and cell-extrinsic factors orchestrate the suppressive function of Tregs. Improved understanding of the molecular mechanism related to the suppressive functional property of Tregs should provide new insights into autoimmunity and disease pathogenesis, which offers opportunity for identifying new therapeutic targets for Treg-related autoimmune diseases and cancers.

PTX3 Predicts Myocardial Damage and Fibrosis in Duchenne Muscular Dystrophy

Pentraxin 3 (PTX3) is a main component of the innate immune system by inducing complement pathway activation, acting as an inflammatory mediator, coordinating the functions of macrophages/dendritic cells and promoting apoptosis/necrosis. Additionally, it has been found in fibrotic regions co-localizing with collagen. In this work, we wanted to investigate the predictive role of PTX3 in myocardial damage and fibrosis of Duchenne muscular dystrophy (DMD). DMD is an X-linked recessive disease caused by mutations of the dystrophin gene that affects muscular functions and strength and accompanying dilated cardiomyopathy. Here, we expound the correlation of PTX3 cardiac expression with age and Toll-like receptors (TLRs)/interleukin-1 receptor (IL-1R)-MyD88 inflammatory markers and its modulation by the so-called alarmins IL-33, high-mobility group box 1 (HMGB1), and S100β. These findings suggest that cardiac levels of PTX3 might have prognostic value and potential in guiding therapy for DMD cardiomyopathy.

Mechanisms of TREG cell adaptation to inflammation

Inflammation is an important defense mechanism. In this complex and dynamic process, drastic changes in the tissue micro-environment play key roles in dictating the nature of the evolving immune response. However, uncontrolled inflammation is detrimental, leading to unwanted cellular damage, loss of physiological functions, and even death. As such, the immune system possesses tools to limit inflammation while ensuring rapid and effective clearance of the inflammatory trigger. Foxp3⁺ regulatory T (T_REG ) cells, a potently immunosuppressive CD4⁺ T cell subset, play a crucial role in immune tolerance by controlling the extent of the response to self and non-self Ags, all-the-while promoting a quick return to immune homeostasis. T_REG cells adapt to changes in the local micro-environment enabling them to migrate, proliferate, survive, differentiate, and tailor their suppressive ability at inflamed sites. Several inflammation-associated factors can impact T_REG cell functional adaptation in situ including locally released alarmins, oxygen availability, tissue acidity and osmolarity and nutrient availability. Here, we review some of these key signals and pathways that control the adaptation of T_REG cell function in inflammatory settings.

Alarmins in Osteoporosis, RAGE, IL-1, and IL-33 Pathways: A Literature Review

Alarmins are endogenous mediators released by cells following insults or cell death to alert the host’s innate immune system of a situation of danger or harm. Many of these, such as high-mobility group box-1 and 2 (HMGB1, HMGB2) and S100 (calgranulin proteins), act through RAGE (receptor for advanced glycation end products), whereas the IL-1 and IL-33 cytokines bind the IL-1 receptors type I and II, and the cellular receptor ST2, respectively. The alarmin family and their signal pathways share many similarities of cellular and tissue localization, functions, and involvement in various physiological processes and inflammatory diseases including osteoporosis. The aim of the review was to evaluate the role of alarmins in osteoporosis. A bibliographic search of the published scientific literature regarding the role of alarmins in osteoporosis was organized independently by two researchers in the following scientific databases: Pubmed, Scopus, and Web of Science. The keywords used were combined as follows: “alarmins and osteoporosis”, “RAGE and osteoporosis”, “HMGB1 and osteoporosis”, “IL-1 and osteoporosis”, “IL 33 and osteopororsis”, “S100s protein and osteoporosis”. The information was summarized and organized in the present review. We highlight the emerging roles of alarmins in various bone remodeling processes involved in the onset and development of osteoporosis, as well as their potential role as biomarkers of osteoporosis severity and progression. Findings of the research suggest a potential use of alarmins as pharmacological targets in future therapeutic strategies aimed at preventing bone loss and fragility fractures induced by aging and inflammatory diseases.

Salt Sensing by Serum/Glucocorticoid-Regulated Kinase 1 Promotes Th17-like Inflammatory Adaptation of Foxp3+ Regulatory T Cells

Regulatory T (Treg) cells integrate diverse environmental signals to modulate their function for optimal suppression. Translational regulation represents a favorable mechanism for Treg cell environmental sensing and adaptation. In this study, we carry out an unbiased screen of the Treg cell translatome and identify serum/glucocorticoid-regulated kinase 1 (SGK1), a known salt sensor in T cells, as being preferentially translated in activated Treg cells. We show that high salt (HS) drives thymic Treg cells to adopt a T helper type 17 (Th17)-like phenotype and enhances generation of Th17-like induced Treg cells in a SGK1-dependent manner, all the while maintaining suppressive function. Salt-mediated Th17-like differentiation of Treg cells was evident in mice fed with HS diet or injected with HS-preconditioned T cells. Overall, SGK1 enables Treg cells to adapt their function in response to environmental cues. By understanding these environmental-sensing mechanisms, we envision targeted approaches to fine-tune Treg cell function for better control of inflammation.

Inhibition of miR-378a-3p by Inflammation Enhances IL-33 Levels: A Novel Mechanism of Alarmin Modulation in Ulcerative Colitis

Ulcerative colitis (UC) is an inflammatory bowel disease (IBD) characterized by mucosa damage associated with an uncontrolled inflammatory response. This immunological impairment leads to altered inflammatory mediators such as IL-33, which is shown to increase in the mucosa of active UC (aUC) patients. MicroRNAs present a distorted feature in inflamed colonic mucosa and are potential IL-33 regulating candidates in UC. Therefore, we studied the microRNA and mRNA profiles in inflamed colonic samples of UC patients, evaluating the effect of a microRNA (selected by in silico analysis and its expression in UC patients), on IL-33 under inflammatory conditions. We found that inflamed mucosa (n = 8) showed increased expression of 40 microRNAs and 2,120 mRNAs, while 49 microRNAs and 1,734 mRNAs were decreased, as determined by microarrays. In particular, IL-33 mRNA showed a 3.8-fold increase and eight members of a microRNA family (miR-378), which targets IL-33 mRNA in the 3'UTR, were decreased (-3.9 to -3.0 times). We selected three members of the miR-378 family (miR-378a-3p, miR-422a, and miR-378c) according to background information and interaction energy analysis, for further correlation analyses with IL-33 expression through qPCR and ELISA, respectively. We determined that aUC (n = 24) showed high IL-33 levels, and decreased expression of miR-378a-3p and miR-422a compared to inactive UC (n = 10) and controls (n = 6). Moreover, both microRNAs were inversely correlated with IL-33 expression, while miR-378c does not show a significant difference. To evaluate the effect of TNFα on the studied microRNAs, aUC patients with anti-TNF therapy were compared to aUC receiving other treatments. The levels of miR-378a-3p and miR-378c were higher in aUC patients with anti-TNF. Based on these findings, we selected miR-378a-3p to exploring the molecular mechanism involved by in vitro assays, showing that over-expression of miR-378a-3p decreased the levels of an IL-33 target sequence β-gal-reporter gene in HEK293 cells. Stable miR-378a-3p over-expression/inhibition inversely modulated IL-33 content and altered viability of HT-29 cells. Additionally, in an inflammatory context, TNFα decreased miR-378a-3p levels in HT-29 cells enhancing IL-33 expression. Together, our results propose a regulatory mechanism of IL-33 expression exerted by miR-378a-3p in an inflammatory environment, contributing to the understanding of UC pathogenesis.

Foxp3 Post-translational Modifications and Treg Suppressive Activity

Regulatory T cells (Tregs) are engaged in maintaining immune homeostasis and preventing autoimmunity. Treg cells include thymic Treg cells and peripheral Treg cells, both of which can suppress the immune response via multiple distinct mechanisms. The differentiation, proliferation, suppressive function and survival of Treg cells are affected by distinct energy metabolic programs. Tissue-resident Treg cells hold unique features in comparison with the lymphoid organ Treg cells. Foxp3 transcription factor is a lineage master regulator for Treg cell development and suppressive activity. Accumulating evidence indicates that the activity of Foxp3 protein is modulated by various post-translational modifications (PTMs), including phosphorylation, O-GlcNAcylation, acetylation, ubiquitylation and methylation. These modifications affect multiple aspects of Foxp3 function. In this review, we define features of Treg cells and roles of Foxp3 in Treg biology, and summarize current research in PTMs of Foxp3 protein involved in modulating Treg function. This review also attempts to define Foxp3 dimer modifications relevant to mediating Foxp3 activity and Treg suppression. Understanding Foxp3 protein features and modulation mechanisms may help in the design of rational therapies for immune diseases and cancer.

Rebalancing Immune Homeostasis to Treat Autoimmune Diseases

During homeostasis, interactions between tolerogenic dendritic cells (DCs), self-reactive T cells, and T regulatory cells (Tregs) contribute to maintaining mammalian immune tolerance. In response to infection, immunogenic DCs promote the generation of proinflammatory effector T cell subsets. When complex homeostatic mechanisms maintaining the balance between regulatory and effector functions become impaired, autoimmune diseases can develop. We discuss some of the newest advances on the mechanisms of physiopathologic homeostasis that can be employed to develop strategies to restore a dysregulated immune equilibrium. Some of these designs are based on selectively activating regulators of immunity and inflammation instead of broadly suppressing these processes. Promising approaches include the use of nanoparticles (NPs) to restore Treg control over self-reactive cells, aiming to achieve long-term disease remission, and potentially to prevent autoimmunity in susceptible individuals.

Fibro-Adipogenic Progenitors Cross-Talk in Skeletal Muscle: The Social Network

Skeletal muscle is composed of a large and heterogeneous assortment of cell populations that interact with each other to maintain muscle homeostasis and orchestrate regeneration. Although satellite cells (SCs) – which are muscle stem cells – are the protagonists of functional muscle repair following damage, several other cells such as inflammatory, vascular, and mesenchymal cells coordinate muscle regeneration in a finely tuned process. Fibro–adipogenic progenitors (FAPs) are a muscle interstitial mesenchymal cell population, which supports SCs differentiation during tissue regeneration. During the first days following muscle injury FAPs undergo massive expansion, which is followed by their macrophage-mediated clearance and the re-establishment of their steady-state pool. It is during this critical time window that FAPs, together with the other cellular components of the muscle stem cell niche, establish a dynamic network of interactions that culminate in muscle repair. A number of different molecules have been recently identified as important mediators of this cross-talk, and its alteration has been associated with different muscle pathologies. In this review, we will focus on the soluble factors that regulate FAPs activity, highlighting their roles in orchestrating the inter-cellular interactions between FAPs and the other cell populations that participate in muscle regeneration.

Pleiotropic Effects of IL-33 on CD4+ T Cell Differentiation and Effector Functions

IL-33, a member of the IL-1 family of cytokines, was originally described in 2005 as a promoter of type 2 immune responses. However, recent evidence reveals a more complex picture. This cytokine is released locally as an alarmin upon cellular damage where innate cell types respond to IL-33 by modulating their differentiation and influencing the polarizing signals they provide to T cells at the time of antigen presentation. Moreover, the prominent expression of the IL-33 receptor, ST2, on GATA3+ T helper 2 cells (TH2) demonstrated that IL-33 could have a direct impact on T cells. Recent observations reveal that T-bet+ TH1 cells and Foxp3+ regulatory T (TREG) cells can also express the ST2 receptor, either transiently or permanently. As such, IL-33 can have a direct effect on the dynamics of T cell populations. As IL-33 release was shown to play both an inflammatory and a suppressive role, understanding the complex effect of this cytokine on T cell homeostasis is paramount. In this review, we will focus on the factors that modulate ST2 expression on T cells, the effect of IL-33 on helper T cell responses and the role of IL-33 on TREG cell function.