IL-33-mediated IL-13 secretion by ST2+ Tregs controls inflammation after lung injury

Control of Asthma and Allergy by Regulatory T Cells

BACKGROUND

Epithelial barriers, such as the lungs and skin, face the challenge of providing the tissues' physiological function and maintaining tolerance to the commensal microbiome and innocuous environmental factors while defending the host against infectious microbes. Asthma and allergic diseases can result from maladaptive immune responses, resulting in exaggerated and persistent type 2 immunity and tissue inflammation.

SUMMARY

Among the diverse populations of tissue immune cells, CD4+ regulatory T cells (Treg cells) are central to controlling immune responses and inflammation and restoring tissue homeostasis. Humans and mice that are deficient in Treg cells experience extensive inflammation in their mucosal organs and skin. During past decades, major progress has been made toward understanding the immunobiology of Treg cells and the molecular and cellular mechanisms that control their differentiation and function. It is now clear that Treg cells are not a single cell type and that they demonstrate diversity and plasticity depending on their differentiation stages and tissue environment. They could also take on a proinflammatory phenotype in certain conditions.

KEY MESSAGES

Treg cells perform distinct functions, including the induction of immune tolerance, suppression of inflammation, and promotion of tissue repair. Subsets of Treg cells in mucosal tissues are regulated by their differentiation stage and tissue inflammatory milieu. Treg cell dysfunction likely plays roles in persistent immune responses and tissue inflammation in asthma and allergic diseases.

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.

Matrix-bound nanovesicle-associated IL-33 supports functional recovery after skeletal muscle injury by initiating a pro-regenerative macrophage phenotypic transition

Injuries to skeletal muscle are among the most common injuries in civilian and military populations, accounting for nearly 60% of extremity injuries. The standard of care for severe extremity injury has been focused upon limb salvage procedures and the utilization of tissue grafts or orthotics in conjunction with rehabilitation to avoid amputation. Nonetheless, many patients have persistent strength and functional deficits that permanently impact their quality of life. Preclinical and clinical studies have shown that partial restoration of functional skeletal muscle tissue following injury can be achieved by the implantation of a biologic scaffold composed of extracellular matrix (ECM). These favorable outcomes are mediated, at least in part, through local immunomodulation. The mechanisms underlying this immunomodulatory effect, however, are poorly understood. The present study investigates a potential mechanistic driver of the immunomodulatory effects; specifically, the effect of selected ECM components upon inflammation resolution and repair. Results show that the host response to skeletal muscle injury is profoundly altered and functional recovery decreased in il33-/- mice compared to age- and sex-matched wildtype counterparts by 14 days post-injury. Results also show that IL-33, contained within matrix-bound nanovesicles (MBV), supports skeletal muscle regeneration by regulating local macrophage activation toward a pro-remodeling phenotype via canonical and non-canonical pathways to improve functional recovery from injury compared to untreated il33-/- counterparts. Taken together, these data suggest that MBV and their associated IL-33 cargo represent a novel homeostatic signaling mechanism that contributes to skeletal muscle repair.

Tregs in transplantation tolerance: role and therapeutic potential

CD4+ Foxp3+ regulatory T cells (Tregs) are indispensable for preventing autoimmunity, and they play a role in cancer and transplantation settings by restraining immune responses. In this review, we describe evidence for the importance of Tregs in the induction versus maintenance of transplantation tolerance, discussing insights into mechanisms of Treg control of the alloimmune response. Further, we address the therapeutic potential of Tregs as a clinical intervention after transplantation, highlighting engineered CAR-Tregs as well as expansion of donor and host Tregs.

TNF+ regulatory T cells regulate the stemness of gastric cancer cells through the IL13/STAT3 pathway

Regulatory T cells (Tregs) are an important component of the tumor microenvironment; however, the interaction between Tregs and gastric cancer cells is not completely understood. Recent studies have shown that Tregs participate in cancer cell stemness maintenance. In this study, we performed single-cell RNA sequencing of gastric cancer and adjacent tissues and found that Tregs with high TNF expression were recruited to gastric cancer tissues and were significantly correlated with patient survival. TNF+ Tregs significantly contribute to tumor growth and progression. Our studies have further demonstrated that TNF+ Tregs promote the stemness of gastric cancer cells through the IL13/STAT3 pathway. Therefore, blocking the interaction between TNF+ Tregs and gastric cancer cells may be a new approach in the treatment of gastric cancer.

T helper 2 cells in asthma

Allergic asthma is among the most common immune-mediated diseases across the world, and type 2 immune responses are thought to be central to pathogenesis. The importance of T helper 2 (Th2) cells as central regulators of type 2 responses in asthma has, however, become less clear with the discovery of other potent innate sources of type 2 cytokines and innate mediators of inflammation such as the alarmins. This review provides an update of our current understanding of Th2 cells in human asthma, highlighting their many guises and functions in asthma, both pathogenic and regulatory, and how these are influenced by the tissue location and disease stage and severity. It also explores how biologics targeting type 2 immune pathways are impacting asthma, and how these have the potential to reveal hitherto underappreciated roles for Th2 cell in lung inflammation.

Regulatory T cells in peripheral tissue tolerance and diseases

Maintenance of peripheral tolerance by CD4+Foxp3+ regulatory T cells (Tregs) is essential for regulating autoreactive T cells. The loss of function of Foxp3 leads to autoimmune disease in both animals and humans. An example is the rare, X-linked recessive disorder known as IPEX (Immune Dysregulation, Polyendocrinopathy, Enteropathy X-linked) syndrome. In more common human autoimmune diseases, defects in Treg function are accompanied with aberrant effector cytokines such as IFNγ. It has recently become appreciated that Tregs plays an important role in not only maintaining immune homeostasis but also in establishing the tissue microenvironment and homeostasis of non-lymphoid tissues. Tissue resident Tregs show profiles that are unique to their local environments which are composed of both immune and non-immune cells. Core tissue-residence gene signatures are shared across different tissue Tregs and are crucial to homeostatic regulation and maintaining the tissue Treg pool in a steady state. Through interaction with immunocytes and non-immunocytes, tissue Tregs exert a suppressive function via conventional ways involving contact dependent and independent processes. In addition, tissue resident Tregs communicate with other tissue resident cells which allows Tregs to adopt to their local microenvironment. These bidirectional interactions are dependent on the specific tissue environment. Here, we summarize the recent advancements of tissue Treg studies in both human and mice, and discuss the molecular mechanisms that maintain tissue homeostasis and prevent pathogenesis.

CC16 augmentation reduces exaggerated COPD-like disease in Cc16-deficient mice

Low Club Cell 16 kDa protein (CC16) plasma levels are linked to accelerated lung function decline in patients with chronic obstructive pulmonary disease (COPD). Cigarette smoke-exposed (CS-exposed) Cc16-/- mice have exaggerated COPD-like disease associated with increased NF-κB activation in their lungs. It is unclear whether CC16 augmentation can reverse exaggerated COPD in CS-exposed Cc16-/- mice and whether increased NF-κB activation contributes to the exaggerated COPD in CS-exposed Cc16-/- lungs. CS-exposed WT and Cc16-/- mice were treated with recombinant human CC16 (rhCC16) or an NF-κB inhibitor versus vehicle beginning at the midpoint of the exposures. COPD-like disease and NF-κB activation were measured in the lungs. RhCC16 limited the progression of emphysema, small airway fibrosis, and chronic bronchitis-like disease in WT and Cc16-/- mice partly by reducing pulmonary inflammation (reducing myeloid leukocytes and/or increasing regulatory T and/or B cells) and alveolar septal cell apoptosis, reducing NF-κB activation in CS-exposed Cc16-/- lungs, and rescuing the reduced Foxj1 expression in CS-exposed Cc16-/- lungs. IMD0354 treatment reduced exaggerated lung inflammation and rescued the reduced Foxj1 expression in CS-exposed Cc16-/- mice. RhCC16 treatment reduced NF-κB activation in luciferase reporter A549 cells. Thus, rhCC16 treatment limits COPD progression in CS-exposed Cc16-/- mice partly by inhibiting NF-κB activation and represents a potentially novel therapeutic approach for COPD.

Obesity control by SHIP inhibition requires pan-paralog inhibition and an intact eosinophil compartment

Here we extend the understanding of how chemical inhibition of SHIP paralogs controls obesity. We compare different classes of SHIP inhibitors and find that selective inhibitors of SHIP1 or SHIP2 are unable to prevent weight gain and body fat accumulation during increased caloric intake. Surprisingly, only pan-SHIP1/2 inhibitors (pan-SHIPi) prevent diet-induced obesity. We confirm that pan-SHIPi is essential by showing that dual treatment with SHIP1 and SHIP2 selective inhibitors reduced adiposity during excess caloric intake. Consistent with this, genetic inactivation of both SHIP paralogs in eosinophils or myeloid cells also reduces obesity and adiposity. In fact, pan-SHIPi requires an eosinophil compartment to prevent diet-induced adiposity, demonstrating that pan-SHIPi acts via an immune mechanism. We also find that pan-SHIPi increases ILC2 cell function in aged, obese mice to reduce their obesity. Finally, we show that pan-SHIPi also reduces hyperglycemia, but not via eosinophils, indicating a separate mechanism for glucose control.

Regulatory T cell and macrophage crosstalk in acute lung injury: future perspectives

Acute lung injury (ALI) describes the injury to endothelial cells in the lungs and associated vessels due to various factors. Furthermore, ALI accompanied by inflammation and thrombosis has been reported as a common complication of SARS-COV-2 infection. It is widely accepted that inflammation and the cytokine storm are main causes of ALI. Two classical anti-inflammatory cell types, regulatory T cells (Tregs) and M2 macrophages, are theoretically capable of resisting uncontrolled inflammation. Recent studies have indicated possible crosstalk between Tregs and macrophages involving their mutual activation. In this review, we discuss the current findings related to ALI pathogenesis and the role of Tregs and macrophages. In particular, we review the molecular mechanisms underlying the crosstalk between Tregs and macrophages in ALI pathogenesis. Understanding the role of Tregs and macrophages will provide the potential targets for treating ALI.

Stepwise acquisition of unique epigenetic signatures during differentiation of tissue Treg cells

Regulatory T cells in non-lymphoid tissues are not only critical for maintaining self-tolerance, but are also important for promoting organ homeostasis and tissue repair. It is proposed that the generation of tissue Treg cells is a stepwise, multi-site process, accompanied by extensive epigenome remodeling, finally leading to the acquisition of unique tissue-specific epigenetic signatures. This process is initiated in the thymus, where Treg cells acquire core phenotypic and functional properties, followed by a priming step in secondary lymphoid organs that permits Treg cells to exit the lymphoid organs and seed into non-lymphoid tissues. There, a final specialization process takes place in response to unique microenvironmental cues in the respective tissue. In this review, we will summarize recent findings on this multi-site tissue Treg cell differentiation and highlight the importance of epigenetic remodeling during these stepwise events.

Cilia-Mediated Insulin/Akt and ST2/JNK Signaling Pathways Regulate the Recovery of Muscle Injury

Following injury, skeletal muscle regenerates but fatty tissue accumulation is seen in aged muscle or muscular dystrophies. Fibro/adipogenic progenitors (FAPs) are key players in these events; however, the effect of primary cilia on FAPs remains unclear. Here, it is reported that genetic ablation of trichoplein (TCHP), a ciliary regulator, induces ciliary elongation on FAPs after injury, which promotes muscle regeneration while inhibiting adipogenesis. The defective adipogenic differentiation of FAPs is attributed to dysfunction of cilia-dependent lipid raft dynamics, which is critical for insulin/Akt signaling. It is also found that interleukin (IL) 13 is substantially produced by intramuscular FAPs, which are upregulated by ciliary elongation and contribute to regeneration. Mechanistically, upon injury, long cilia excessively activate the IL33/ST2/JNK axis to enhance IL13 production, facilitating myoblast proliferation and M2 macrophage polarization. The results indicate that FAPs organize the regenerative responses to skeletal muscle injury via cilia-mediated insulin/Akt and ST2/JNK signaling pathways.

Interleukin-33 Derived from Endometriotic Lesions Promotes Fibrogenesis through Inducing the Production of Profibrotic Cytokines by Regulatory T Cells

In endometriosis, it has been widely believed that the local immunological milieu is Th2-skewed. Regulatory T cells (Tregs) promote fibrogenesis of endometriosis through the transforming growth factor β1 (TGF-β1) and platelet-derived growth factor (PDGF) signaling pathways. We aimed to explore whether Tregs in endometriotic lesions acquire increased production of effector cytokines under the influence of lesion-derived interleukin (IL)-33. We extracted lymphocytes from normal endometrium and ovarian endometrioma to evaluate the expression of IL-4, IL-13, interferon-γ (IFN-γ), TGF-β1, and the IL-33 receptor (ST2) by Tregs from these tissues. Colocalization of IL-33 and FOXP3 in normal endometrium and ovarian endometrioma was evaluated by immunofluorescence. Tregs and endometriotic stromal cells were co-cultured and treated with anti-IL-33 antibody, and the cytokines produced by Tregs were analyzed by flow cytometry and enzyme-linked immunosorbent assay (ELISA). Tregs in ovarian endometrioma produced significant amounts of IL-4, IL-13, TGF-β1, and ST2. Colocalization of IL-33 and FOXP3 was detected in ovarian endometrioma. IL-33 from endometriotic stromal cells caused the differentiation of lesional Tregs into type 2 T helper (Th2)-like cells, along with increased production of TGF-β1 by Tregs. Thus, Tregs and endometriotic lesions engage active crosstalk through IL-33 to promote fibrogenesis in endometriosis, and, as such, this finding opens up new avenues to identify novel therapeutic targets for endometriosis.

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.

Selective activation and expansion of regulatory T cells using lipid encapsulated mRNA encoding a long-acting IL-2 mutein

Interleukin-2 (IL-2) is critical for regulatory T cell (Treg) function and homeostasis. At low doses, IL-2 can suppress immune pathologies by expanding Tregs that constitutively express the high affinity IL-2Rα subunit. However, even low dose IL-2, signaling through the IL2-Rβ/γ complex, may lead to the activation of proinflammatory, non-Treg T cells, so improving specificity toward Tregs may be desirable. Here we use messenger RNAs (mRNA) to encode a half-life-extended human IL-2 mutein (HSA-IL2m) with mutations promoting reliance on IL-2Rα. Our data show that IL-2 mutein subcutaneous delivery as lipid-encapsulated mRNA nanoparticles selectively activates and expands Tregs in mice and non-human primates, and also reduces disease severity in mouse models of acute graft versus host disease and experimental autoimmune encephalomyelitis. Single cell RNA-sequencing of mouse splenic CD4+ T cells identifies multiple Treg states with distinct response dynamics following IL-2 mutein treatment. Our results thus demonstrate the potential of mRNA-encoded HSA-IL2m immunotherapy to treat autoimmune diseases.

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.

Adenosinergic Pathway and Linked Suppression: Two Critical Suppressive Mechanisms of Human Donor Antigen Specific Regulatory T Cell Lines Expanded Post Transplant

Regulatory T cells are an important component of an immune response shaping the overall behavior to potential antigens including alloantigens. Multiple mechanisms have been shown to contribute towards developing and sustaining a immunological regulatory response. One of the described contact dependent suppressive mechanisms regulatory cells have been shown to utilize is through the production of adenosine from extracellular ATP mediated by CD39 and CD73. In this study we demonstrate that the adenosinergic pathway plays a major role in the suppressive/regulatory effects antigen specific regulatory T cell enriched lines (ASTRLs) that have been of expanded ex vivo from stable kidney transplant patients. We have previously shown that these ASTRL cells are capable of suppressing alloimmune responses in vitro and significantly prolonging allograft survival in an animal model of kidney transplantation. For this study nineteen ASTRLs were expanded from 17 kidney transplant patients by repeated stimulation of recipient peripheral blood mononuclear cells with donor specific HLA-DR peptides. All 19 ASTRLs showed upregulation of numerous markers associated with regulatory cells and were able to inhibit donor antigen specific T cell proliferation in a dose dependent fashion. ASTRLs suppressed indirect and direct alloimmune responses compatible with our previous animal study findings. Upregulation of both CD39 and CD73 was observed post expansion and ASTRLs demonstrated extracellular hydrolysis of ATP, indicating functionality of the upregulated proteins. We also showed that inhibition of the adenosinergic pathway using inhibitors of CD39 resulted in abrogation of suppression and increased antigen specific T cell proliferation. This demonstrates that the main mechanism of action of the suppressive activity donor peptide driven ASTRLs generated from kidney transplant patients is the adenosinergic pathway. Furthermore this suggests the possibility that combining infusion of Tregs with other treatments, such as adenosine receptor agonists or increasing CD39 expression in the grafts may further enhance a regulatory response to the allograft and possibly achieve transplantation tolerance.

Tissue Resident Foxp3+ Regulatory T Cells: Sentinels and Saboteurs in Health and Disease

Foxp3⁺ regulatory T (Treg) cells are a CD4 T cell subset with unique immune regulatory function that are indispensable in immunity and tolerance. Their indisputable importance has been investigated in numerous disease settings and experimental models. Despite the extensive efforts in determining the cellular and molecular mechanisms operating their functions, our understanding their biology especially in vivo remains limited. There is emerging evidence that Treg cells resident in the non-lymphoid tissues play a central role in regulating tissue homeostasis, inflammation, and repair. Furthermore, tissue-specific properties of those Treg cells that allow them to express tissue specific functions have been explored. In this review, we will discuss the potential mechanisms and key cellular/molecular factors responsible for the homeostasis and functions of tissue resident Treg cells under steady-state and inflammatory conditions.

A Comprehensive Review on the Surgical Aspect of Lung Transplant Models in Mice and Rats

Lung transplantation improves the outcome and quality of life of patients with end-stage pulmonary disease. However, the procedure is still hampered by the lack of suitable donors, the complexity of the surgery, and the risk of developing chronic lung allograft dysfunction. Over the past decades, translational experiments in animal models have led to a better understanding of physiology and immunopathology following the lung transplant procedure. Small animal models (e.g., rats and mice) are mostly used in experiments regarding immunology and pathobiology and are preferred over large animal models due to the ethical aspects, the cost-benefit balance, and the high throughput possibility. In this comprehensive review, we summarize the reported surgical techniques for lung transplantation in rodent models and the management of perioperative complications. Furthermore, we propose a guide to help identify the appropriate species for a given experiment and discuss recent experimental findings in small animal lung transplant models.

Mucosal tissue regulatory T cells are integral in balancing immunity and tolerance at portals of antigen entry

Foxp3+ regulatory T cells (Tregs) are a subset of CD4+ T cells that exert suppressive control over other immune cells. Tregs are critical for preventing systemic autoimmunity and maintaining peripheral tolerance, and yet they also assist in orchestration of immunity to pathogenic insult, wherein they limit collateral immunopathology and assist in facilitating a fine balance between immune tolerance and effector activity. Tregs have been extensively studied in lymphoid tissues, and a growing body of work has characterized phenotypically distinct Tregs localized in various nonlymphoid tissue compartments. These tissue Tregs can perform location-specific, alternative functions, highlighting their dynamic, context-dependent roles. Tregs have also been identified in mucosal tissues where specialized physiological functions are paramount, including helping the host to respond appropriately to pathogenic versus innocuous antigens that are abundant at mucosal portals of antigen entry. As in other tissue Treg compartments, mucosal Tregs in the respiratory, gastrointestinal, and genitourinary tracts are distinct from circulating counterparts and can carry out mucosa-specific functions as well as classic suppressive functions that are the hallmark of Tregs. In this review, we summarize current knowledge regarding mucosal Tregs in both health and disease.

IL-2 availability regulates the tissue specific phenotype of murine intra-hepatic Tregs

CD4+CD25+Foxp3+ Tregs are known to acquire tissue-specific features and exert cytoprotective and regenerative functions. The extent to which this applies to liver-resident Tregs is unknown. In this study, we aimed to explore the phenotypic and functional characteristics of adult murine liver resident Tregs during homeostasis. Additionally, we investigated their role in ameliorating liver inflammation and tissue damage. Quantification of Foxp3+CD4+CD25+ cells comparing different tissues showed that the liver contained significantly fewer resident Tregs. A combination of flow cytometry phenotyping and microarray analysis of intra-hepatic and splenic Tregs under homeostatic conditions revealed that, although intra-hepatic Tregs exhibited the core transcriptional Treg signature, they expressed a distinct transcriptional profile. This was characterized by reduced CD25 expression and increased levels of pro-inflammatory Th1 transcripts Il1b and Ifng. In vivo ablation of Tregs in the Foxp3-DTR mouse model showed that Tregs had a role in reducing the magnitude of systemic and intra-hepatic inflammatory responses following acute carbon tetrachloride (CCl₄) injury, but their absence did not impact the development of hepatocyte necrosis. Conversely, the specific expansion of Tregs by administration of IL-2 complexes increased the number of intra-hepatic Tregs and significantly ameliorated tissue damage following CCl₄ administration in C57BL/6 mice. The cytoprotective effect observed in response to IL-2c was associated with the increased expression of markers known to regulate Treg suppressive function. Our results offer insight into the transcriptome and complex immune network of intra-hepatic Tregs and suggest that strategies capable of selectively increasing the pool of intra-hepatic Tregs could constitute effective therapies in inflammatory liver diseases.

Endothelial dysfunction contributes to severe COVID-19 in combination with dysregulated lymphocyte responses and cytokine networks

The systemic processes involved in the manifestation of life-threatening COVID-19 and in disease recovery are still incompletely understood, despite investigations focusing on the dysregulation of immune responses after SARS-CoV-2 infection. To define hallmarks of severe COVID-19 in acute disease (n = 58) and in disease recovery in convalescent patients (n = 28) from Hannover Medical School, we used flow cytometry and proteomics data with unsupervised clustering analyses. In our observational study, we combined analyses of immune cells and cytokine/chemokine networks with endothelial activation and injury. ICU patients displayed an altered immune signature with prolonged lymphopenia but the expansion of granulocytes and plasmablasts along with activated and terminally differentiated T and NK cells and high levels of SARS-CoV-2-specific antibodies. The core signature of seven plasma proteins revealed a highly inflammatory microenvironment in addition to endothelial injury in severe COVID-19. Changes within this signature were associated with either disease progression or recovery. In summary, our data suggest that besides a strong inflammatory response, severe COVID-19 is driven by endothelial activation and barrier disruption, whereby recovery depends on the regeneration of the endothelial integrity.

Toward a Paradigm to Distinguish Distinct Functions of FOXP3+ Regulatory T Cells

FOXP3⁺ regulatory T (Treg) cells are a unique subset of CD4⁺ T cells that classically function as master regulators of immune homeostasis. Besides this canonical suppressive role, which is required to maintain self-tolerance, a growing body of literature has identified Treg cells as critical orchestrators of tissue protection during acute stress and as effector cells that drive repair following tissue injury. Despite substantial interest in these distinct roles, the field has struggled to disentangle Treg cell suppressive functions from those that promote tissue defense and repair. In this article, we will examine the literature in the context of specific physiologic settings, contrasting the suppressive function of Treg cells with their emerging roles in promoting tissue homeostasis and tissue repair. Further, we will discuss a new paradigm differentiating tissue defense from tissue repair-a paradigm needed to translate Treg cell-based therapies to the clinic.

Exacerbation of Mycobacterium avium pulmonary infection by comorbid allergic asthma is associated with diminished mycobacterium-specific Th17 responses

Accumulating evidence suggests that two chronic respiratory diseases, nontuberculous mycobacterium (NTM)-pulmonary disease (PD) and allergic asthma, are frequently present together and that they likely influence the disease development and progression of each other. However, their precise interactions regarding the pathogenesis of comorbid diseases versus that of individual diseases are not well understood. In this study, comorbid diseases (i.e., Mycobacteria avium (Mav) pulmonary infection (PI) (Mav-PI) and ovalbumin-induced allergic asthma) were established in mice in different orders and at different time periods. Individual disease-specific characteristics, including alterations in immune cell populations and antigen-specific immune responses, were analyzed and compared. To assess Mav-PI pathogenesis, lung inflammation and bacterial burden levels were also determined. Allergic asthma induction in the presence of Mav-PI markedly aggravated Mav-PI pathogenesis by increasing the bacterial burden and the severity of lung inflammation. Interestingly, the general outcome of allergic asthma with goblet cell hyperplasia was alleviated at a chronic stage in the comorbid mouse model. Overall, the increase in the number of Mav CFUs was inversely correlated with the Mav-specific Th17 response, as confirmed by comparing BALB/c and C57BL/6J mice. Overall, the pathogenesis of existing Mav-PI is more severely affected by allergen exposure than vice versa. This Mav-PI exacerbation is associated with disruption of Mav-specific Th17 responses. This study provides the first evidence that the Mav-specific Th17 response plays an important role in the control of Mav pathogenesis in the presence of allergic asthma, indicating that targeting the Th17 response has therapeutic potential for NTM-PD accompanied by allergic asthma.

T reg cell-intrinsic requirements for ST2 signaling in health and neuroinflammation

ST2, the receptor for the alarmin IL-33, is expressed by a subset of regulatory T (T reg) cells residing in nonlymphoid tissues, and these cells can potently expand upon provision of exogenous IL-33. Whether the accumulation and residence of T reg cells in tissues requires their cell-intrinsic expression of and signaling by ST2, or whether indirect IL-33 signaling acting on other cells suffices, has been a matter of contention. Here, we report that ST2 expression on T reg cells is largely dispensable for their accumulation and residence in nonlymphoid organs, including the visceral adipose tissue (VAT), even though cell-intrinsic sensing of IL-33 promotes type 2 cytokine production by VAT-residing T reg cells. In addition, we uncovered a novel ST2-dependent role for T reg cells in limiting the size of IL-17A–producing γδT cells in the CNS in a mouse model of neuroinflammation, experimental autoimmune encephalomyelitis (EAE). Finally, ST2 deficiency limited to T reg cells led to disease exacerbation in EAE.

IL-33-mediated Eosinophilia Protects against Acute Lung Injury

Pneumonia-induced lung injury and acute respiratory distress syndrome can develop because of an inappropriate inflammatory response to acute infections, leading to a compromised alveolar barrier. Recent work suggests that hospitalized patients with allergies/asthma are less likely to die of pulmonary infections and that there is a correlation between survival from acute respiratory distress syndrome and higher eosinophil counts; thus, we hypothesized that eosinophils associated with a type 2 immune response may protect against pneumonia-induced acute lung injury. To test this hypothesis, mice were treated with the type 2–initiating cytokine IL-33 intratracheally 3 days before induction of pneumonia with airway administration of a lethal dose of Staphylococcus aureus. Interestingly, IL-33 pretreatment promoted survival by inhibiting acute lung injury: amount of BAL fluid proinflammatory cytokines and pulmonary edema were both reduced, with an associated increase in oxygen saturation. Pulmonary neutrophilia was also reduced, whereas eosinophilia was strongly increased. This eosinophilia was key to protection; eosinophil reduction eliminated both IL-33–mediated protection against mortality and inhibition of neutrophilia and pulmonary edema. Together, these data reveal a novel role for eosinophils in protection against lung injury and suggest that modulation of pulmonary type 2 immunity may represent a novel therapeutic strategy.

Reparative and Maladaptive Inflammation in Tendon Healing

Tendon injuries are common and debilitating, with non-regenerative healing often resulting in chronic disease. While there has been considerable progress in identifying the cellular and molecular regulators of tendon healing, the role of inflammation in tendon healing is less well understood. While inflammation underlies chronic tendinopathy, it also aids debris clearance and signals tissue repair. Here, we highlight recent findings in this area, focusing on the cells and cytokines involved in reparative inflammation. We also discuss findings from other model systems when research in tendon is minimal, and explore recent studies in the treatment of human tendinopathy to glean further insights into the immunobiology of tendon healing.

Role of Interleukin-1 Receptor-Like 1 (ST2) in Cerebrovascular Disease

Following both ischemic and hemorrhagic stroke, innate immune cells initiate a proinflammatory response that further exacerbate tissue injury in the acute phase, but these cells also play an important reparative role thereafter. Numerous cytokines and signaling pathways have been implicated in driving the deleterious proinflammatory response, but less is known about the mediators that connect the initial vascular injury to the systemic immune response and the relationship between proinflammatory and reparative immune responses. The Interleukin-33 (IL-33) and serum stimulation-2 (ST2) axis is an interleukin signaling pathway that is a prime candidate to fulfill this role. In this review, we describe the biology of the IL-33/ST2 system, present evidence that its soluble decoy receptor, soluble ST2 (sST2), plays a key role in secondary neurologic injury after stroke, and discuss this in the context of the known role of IL-33/ST2 in other disease.

The Mechanism of CD8+ T Cells for Reducing Myofibroblasts Accumulation during Renal Fibrosis

Renal fibrosis is a hallmark of chronic kidney disease (CKD) and a common manifestation of end-stage renal disease that is associated with multiple types of renal insults and functional loss of the kidney. Unresolved renal inflammation triggers fibrotic processes by promoting the activation and expansion of extracellular matrix-producing fibroblasts and myofibroblasts. Growing evidence now indicates that diverse T cells and macrophage subpopulations play central roles in the inflammatory microenvironment and fibrotic process. The present review aims to elucidate the role of CD8⁺ T cells in renal fibrosis, and identify its possible mechanisms in the inflammatory microenvironment.

Untangling Local Pro-Inflammatory, Reparative, and Regulatory Damage-Associated Molecular-Patterns (DAMPs) Pathways to Improve Transplant Outcomes

Detrimental inflammatory responses after solid organ transplantation are initiated when immune cells sense pathogen-associated molecular patterns (PAMPs) and certain damage-associated molecular patterns (DAMPs) released or exposed during transplant-associated processes, such as ischemia/reperfusion injury (IRI), surgical trauma, and recipient conditioning. These inflammatory responses initiate and propagate anti-alloantigen (AlloAg) responses and targeting DAMPs and PAMPs, or the signaling cascades they activate, reduce alloimmunity, and contribute to improved outcomes after allogeneic solid organ transplantation in experimental studies. However, DAMPs have also been implicated in initiating essential anti-inflammatory and reparative functions of specific immune cells, particularly Treg and macrophages. Interestingly, DAMP signaling is also involved in local and systemic homeostasis. Herein, we describe the emerging literature defining how poor outcomes after transplantation may result, not from just an over-abundance of DAMP-driven inflammation, but instead an inadequate presence of a subset of DAMPs or related molecules needed to repair tissue successfully or re-establish tissue homeostasis. Adverse outcomes may also arise when these homeostatic or reparative signals become dysregulated or hijacked by alloreactive immune cells in transplant niches. A complete understanding of the critical pathways controlling tissue repair and homeostasis, and how alloimmune responses or transplant-related processes disrupt these will lead to new immunotherapeutics that can prevent or reverse the tissue pathology leading to lost grafts due to chronic rejection.

IL-4Rα signaling in CD4+CD25+FoxP3+ T regulatory cells restrains airway inflammation via limiting local tissue IL-33

Impaired tolerance to innocuous particles during allergic asthma has been linked to increased plasticity of FoxP3+ regulatory T cells (Tregs) reprogramming into pathogenic effector cells, thus exacerbating airway disease. However, failure of tolerance mechanisms is driven by Th2 inflammatory signals. Therefore, the in vivo role of canonical IL-4 receptor α (IL-4Rα) signaling, an essential driver of Th2-type airway responses to allergens, on the regulatory function of FoxP3+ Tregs in allergic asthma was explored. Here, we used transgenic Foxp3cre IL-4Rα-/lox and littermate control mice to investigate the role of IL-4 and IL-13 signaling via Tregs in house dust mite-induced (HDM-induced) allergic airway disease. We sensitized mice intratracheally on day 0, challenged them on days 6-10, and analyzed airway hyperresponsiveness (AHR), airway inflammation, mucus production, and cellular profile on day 14. In the absence of IL-4Rα responsiveness on FoxP3+ Tregs, exacerbated AHR and airway inflammation were shown in HDM-sensitized mice. Interestingly, reduced induction of FoxP3+ Tregs accompanied increased IL-33 alarmin production and type 2 innate lymphoid cell activation in the lung, exacerbating airway hyperreactivity and lung eosinophilia. Taken together, our findings indicate that IL-4Rα-unresponsive FoxP3+ Tregs result in exaggerated innate Th2-type, IL-33-dependent airway inflammation and a break in tolerance during allergic asthma.

Neuroprotective Activities of Long-Acting Granulocyte-Macrophage Colony-Stimulating Factor (mPDM608) in 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine-Intoxicated Mice

Loss of dopaminergic neurons along the nigrostriatal axis, neuroinflammation, and peripheral immune dysfunction are the pathobiological hallmarks of Parkinson's disease (PD). Granulocyte-macrophage colony-stimulating factor (GM-CSF) has been successfully tested for PD treatment. GM-CSF is a known immune modulator that induces regulatory T cells (Tregs) and serves as a neuronal protectant in a broad range of neurodegenerative diseases. Due to its short half-life, limited biodistribution, and potential adverse effects, alternative long-acting treatment schemes are of immediate need. A long-acting mouse GM-CSF (mPDM608) was developed through Calibr, a Division of Scripps Research. Following mPDM608 treatment, complete hematologic and chemistry profiles and T-cell phenotypes and functions were determined. Neuroprotective and anti-inflammatory capacities of mPDM608 were assessed in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-intoxicated mice that included transcriptomic immune profiles. Treatment with a single dose of mPDM608 resulted in dose-dependent spleen and white blood cell increases with parallel enhancements in Treg numbers and immunosuppressive function. A shift in CD4+ T-cell gene expression towards an anti-inflammatory phenotype corresponded with decreased microgliosis and increased dopaminergic neuronal cell survival. mPDM608 elicited a neuroprotective peripheral immune transformation. The observed phenotypic shift and neuroprotective response was greater than observed with recombinant GM-CSF (rGM-CSF) suggesting human PDM608 as a candidate for PD treatment.

Graft IL-33 regulates infiltrating macrophages to protect against chronic rejection

Alarmins, sequestered self-molecules containing damage-associated molecular patterns, are released during tissue injury to drive innate immune cell proinflammatory responses. Whether endogenous negative regulators controlling early immune responses are also released at the site of injury is poorly understood. Herein, we establish that the stromal cell-derived alarmin interleukin 33 (IL-33) is a local factor that directly restricts the proinflammatory capacity of graft-infiltrating macrophages early after transplantation. By assessing heart transplant recipient samples and using a mouse heart transplant model, we establish that IL-33 is upregulated in allografts to limit chronic rejection. Mouse cardiac transplants lacking IL-33 displayed dramatically accelerated vascular occlusion and subsequent fibrosis, which was not due to altered systemic immune responses. Instead, a lack of graft IL-33 caused local augmentation of proinflammatory iNOS+ macrophages that accelerated graft loss. IL-33 facilitated a metabolic program in macrophages associated with reparative and regulatory functions, and local delivery of IL-33 prevented the chronic rejection of IL-33-deficient cardiac transplants. Therefore, IL-33 represents what we believe is a novel regulatory alarmin in transplantation that limits chronic rejection by restraining the local activation of proinflammatory macrophages. The local delivery of IL-33 in extracellular matrix-based materials may be a promising biologic for chronic rejection prophylaxis.

What Makes the Lung Unique – Tissue-Specific Immunity in the Respiratory Tract

The immune system constitutes a critical mechanism of the human body to preserve health and mitigate disease. In the lung, immunity is seen as a critical driver in many respiratory diseases, in particular in those characterised by aberrant inflammation, such as chronic obstructive pulmonary disease, fibrosis, and asthma. In this review, the specialised set of immune cells and lung tissue-specific regulators, including key cytokines such as granulocyte-macrophage colony-stimulating factor and transforming growth factor β, that control immune responses in the respiratory tract will be discussed. Furthermore, the current understanding of the impact of key environmental components such as the role of oxygen and lung microbiota on lung immunity will be highlighted. The goal is to identify the unique aspects of lung immune biology to facilitate insights into the aetiology of common lung inflammatory diseases and to provide the basis for a deeper mechanistic understanding of the underlying immune processes. Finally, key future avenues of research such as using more comprehensive quantitative approaches for elucidating molecular disease mechanisms as well as the potential to exploit tissue-specific regulators of immunity for therapy of lung inflammatory disorders will be discussed.

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.

Tissue regulatory T cells

Foxp3+  CD4+ regulatory T cells (Tregs) are an immune cell lineage endowed with immunosuppressive functionality in a wide array of contexts, including both anti-pathogenic and anti-self responses. In the past decades, our understanding of the functional diversity of circulating or lymphoid Tregs has grown exponentially. Only recently, the importance of Tregs residing within non-lymphoid tissues, such as visceral adipose tissue, muscle, skin and intestine, has been recognized. Not only are Tregs critical for influencing the kinetics and strength of immune responses, but the regulation of non-immune or parenchymal cells, also fall within the purview of tissue-resident or infiltrating Tregs. This review focuses on providing a systematic and comprehensive comparison of the molecular maintenance, local adaptation and functional specializations of Treg populations operating within different tissues.

The Functional Roles of IL-33/ST2 Axis in Ocular Diseases

Interleukin-33 (IL-33), an important member of the IL-1 family, plays a pivotal role in regulating immune responses via combining with its receptor suppression of tumorigenicity 2 (ST2). We have already known IL-33/ST2 axis participates in the pathogenesis of various diseases, including liver diseases, renal diseases, and neurological diseases. Recently, emerging studies are indicating that IL-33/ST2 is also involved in a wide range of ocular diseases, such as allergic eye disease, keratitis and corneal regeneration, dry eye disease, uveitis, vitreoretinal diseases, and neuromyelitis optica spectrum disorder. In this review, we will summarize and discuss the current understanding about the functional roles of IL-33/ST2 in eyes, with an attempt to explore the possible study perspectives and therapeutic alternatives in the future.

Regulatory T Cells: An Emerging Player in Radiation-Induced Lung Injury

Regulatory T cells (Tregs), which have long been recognized as essential regulators of both inflammation and autoimmunity, also impede effective antitumor immune response due to their immunosuppressive properties. Combined radiotherapy and immunotherapeutic interventions focusing on the removal of Tregs have recently garnered interest as a promising strategy to reverse immunosuppression. Meanwhile, Tregs are emerging as a key player in the pathogenesis of radiation-induced lung injury (RILI), a frequent and potentially life-threatening complication of thoracic radiotherapy. Recognition of the critical role of Tregs in RILI raises the important question of whether radiotherapy combined with Treg-targeting immunotherapy offers any beneficial effects in the protection of normal lung tissue. This present review focuses on the contributions of Tregs to RILI, with particular emphasis on the suspected differential role of Tregs in the pneumonitic phase and fibrotic phase of RILI. We also introduce recent progress on the potential mechanisms by which Tregs modulate RILI and the crosstalk among Tregs, other infiltrating T cells, fibrocytes, and resident epithelial cells driving disease pathogenesis. Finally, we discuss whether Tregs also hold promise as a potential target for immunotherapeutic interventions for RILI.

Damage-associated molecular patterns in trauma

In 1994, the "danger model" argued that adaptive immune responses are driven rather by molecules released upon tissue damage than by the recognition of "strange" molecules. Thus, an alternative to the "self versus non-self recognition model" has been provided. The model, which suggests that the immune system discriminates dangerous from safe molecules, has established the basis for the future designation of damage-associated molecular patterns (DAMPs), a term that was coined by Walter G. Land, Seong, and Matzinger. The pathological importance of DAMPs is barely somewhere else evident as in the posttraumatic or post-surgical inflammation and regeneration. Since DAMPs have been identified to trigger specific immune responses and inflammation, which is not necessarily detrimental but also regenerative, it still remains difficult to describe their "friend or foe" role in the posttraumatic immunogenicity and healing process. DAMPs can be used as biomarkers to indicate and/or to monitor a disease or injury severity, but they also may serve as clinically applicable parameters for optimized indication of the timing for, i.e., secondary surgeries. While experimental studies allow the detection of these biomarkers on different levels including cellular, tissue, and circulatory milieu, this is not always easily transferable to the human situation. Thus, in this review, we focus on the recent literature dealing with the pathophysiological importance of DAMPs after traumatic injury. Since dysregulated inflammation in traumatized patients always implies disturbed resolution of inflammation, so-called model of suppressing/inhibiting inducible DAMPs (SAMPs) will be very briefly introduced. Thus, an update on this topic in the field of trauma will be provided.

Bcl6 and Blimp1 reciprocally regulate ST2+ Treg-cell development in the context of allergic airway inflammation

BACKGROUND

Bcl6 is required for the development of T follicular helper cells and T follicular regulatory (Tfr) cells that regulate germinal center responses. Bcl6 also affects the function of regulatory T (Treg) cells.

OBJECTIVE

The goal of this study was to define the functions of Bcl6 in Treg cells, including Tfr cells, in the context of allergic airway inflammation.

METHODS

We used a model of house dust mite sensitization to challenge wild-type, Bcl6^fl/fl Foxp3-Cre, and Prdm1 (Blimp1)^fl/fl Foxp3-Cre mice to study the reciprocal roles of Bcl6 and Blimp1 in allergic airway inflammation.

RESULTS

In the house dust mite model, Tfr cells repress the production of IgE and Bcl6⁺ Treg cells suppress the generation of type 2 cytokine-producing cells in the lungs. In mice with Bcl6-deficient Treg cells, twice as many ST2⁺ (IL-33R⁺) Treg cells develop as are observed in wild-type mice. ST2⁺ Treg cells in the context of allergic airway inflammation are Blimp1 dependent, express type 2 cytokines, and share features of visceral adipose tissue Treg cells. Bcl6-deficient Treg cells are more susceptible, and Blimp1-deficient Treg cells are resistant, to acquiring the ST2⁺ Treg-cell phenotype in vitro and in vivo in response to IL-33. Bcl6-deficient ST2⁺ Treg cells, but not Bcl6-deficient ST2⁺ conventional T cells, strongly promote allergic airway inflammation when transferred into recipient mice. Lastly, ST2 is required for the exacerbated allergic airway inflammation in Bcl6^fl/fl Foxp3-Cre mice.

CONCLUSIONS

During allergic airway inflammation, Bcl6 and Blimp1 play dual roles in regulating Tfr-cell activity in the germinal center and in the development of ST2⁺ Treg cells that promote type 2 cytokine responses.

BCG vaccination reduces the mortality of Mycobacterium tuberculosis-infected type 2 diabetes mellitus mice

Diabetes is a significant risk factor for the development of active tuberculosis. In this study, we used a mouse model of type 2 diabetes mellitus (T2DM) to determine the effect of prior Bacillus Calmette-Guérin (BCG) vaccination on immune responses to Mycobacterium tuberculosis (Mtb) infection. We found that, at 6-7 months after Mtb infection, 90% of the Mtb-infected T2DM mice died, whereas only 50% of BCG-vaccinated T2DM-Mtb-infected mice died. Moreover, 40% of the PBS-treated uninfected T2DM mice and 30% of the uninfected BCG-vaccinated T2DM mice died, whereas all uninfected and infected nondiabetic mice survived. BCG vaccination was less effective in reducing the lung bacterial burden of Mtb-infected T2DM mice compared with Mtb-infected nondiabetic mice. BCG vaccination significantly reduced lung inflammation in Mtb-infected T2DM mice compared with that of unvaccinated T2DM mice infected with Mtb. Furthermore, reduced mortality of BCG-vaccinated Mtb-infected T2DM mice is associated with expansion of IL-13-producing CXCR3+ Tregs in the lungs of Mtb-infected T2DM mice. Recombinant IL-13 and Tregs from BCG-vaccinated Mtb-infected T2DM mice converted proinflammatory M1 macrophages to antiinflammatory M2 macrophages. Our findings suggest a potentially novel role for BCG in preventing excess inflammation and mortality in T2DM mice infected with Mtb.

Immune cell landscaping reveals a protective role for regulatory T cells during kidney injury and fibrosis

Acute kidney injury (AKI) and chronic kidney diseases are associated with high mortality and morbidity. Although the underlying mechanisms determining the transition from acute to chronic injury are not completely understood, immune-mediated processes are critical in renal injury. We have performed a comparison of 2 mouse models leading to either kidney regeneration or fibrosis. Using global gene expression profiling we could identify immune-related pathways accounting for the majority of the observed transcriptional changes during fibrosis. Unbiased examination of the immune cell composition, using single-cell RNA sequencing, revealed major changes in tissue-resident macrophages and T cells. Following injury, there was a marked increase in tissue-resident IL-33R+ and IL-2Ra+ regulatory T cells (Tregs). Expansion of this population before injury protected the kidney from injury and fibrosis. Transcriptional profiling of Tregs showed a differential upregulation of regenerative and proangiogenic pathways during regeneration, whereas in the fibrotic environment they expressed markers of hyperactivation and fibrosis. Our data point to a hitherto underappreciated plasticity in Treg function within the same tissue, dictated by environmental cues. Overall, we provide a detailed cellular and molecular characterization of the immunological changes during kidney injury, regeneration, and fibrosis.

Interleukin-33 (IL-33) as a Diagnostic and Prognostic Factor in Traumatic Brain Injury

Interleukin-33 (IL-33) is a cytokine involved in interleukin-1 family. Role of IL-33 in immune system activation is well described in the literature. IL-33 has been identified as an endogenous alarm signal (alarmin) to alert various types of immune cells to trauma. In this narrative review, we aimed to underline the diagnostic and prognostic importance of IL-33 in trauma, particularly in brain trauma.

Reparative T lymphocytes in organ injury

Acute organ injuries such as acute cerebrovascular accidents, myocardial infarction, acute kidney injury, acute lung injury, and others are among the leading causes of death worldwide. Dysregulated or insufficient organ repair mechanisms limit restoration of homeostasis and contribute to chronic organ failure. Studies reveal that both humans and mice harness potent non-stem cells that are capable of directly or indirectly promoting tissue repair. Specific populations of T lymphocytes have emerged as important reparative cells with context-specific actions. These T cells can resolve inflammation and secrete reparative cytokines and growth factors as well as interact with other immune and stromal cells to promote the complex and active process of tissue repair. This Review focuses on the major populations of T lymphocytes known to mediate tissue repair, their reparative mechanisms, and the diseases in which they have been implicated. Elucidating and harnessing the mechanisms that promote the reparative functions of these T cells could greatly improve organ dysfunction after acute injury.