γδ T cells attenuate bleomycin-induced fibrosis through the production of CXCL10

The modulation of immune cell death in connection to microRNAs and natural products

Immunogenic cell death (ICD) spatiotemporally regulates damage-associated molecular patterns (DAMPs) derived from dying cancer cells to signal the immune response. Intriguingly, these DAMPs and cytokines also induce cellular responses in non-immune cells, particularly cancer cells. Several ICD-modulating natural products and miRNAs have been reported to regulate the DAMP, cytokine, and cell death responses, but they lack systemic organization and connection. This review summarizes the impacts of natural products and miRNAs on the DAMP and cytokine responses and cancer cell death responses (apoptosis, autophagy, ferroptosis, necroptosis, and pyroptosis). We establish the rationale that ICD inducers of natural products have modulating effects on miRNAs, targeting DAMPs and cytokines for immune and cancer cell death responses. In conclusion, DAMP, cytokine, and cell death responses are intricately linked in cancer cells, and they are influenced by ICD-modulating natural products and miRNAs.

Toxicogenomic assessment of in vitro macrophages exposed to profibrotic challenge reveals a sustained transcriptomic immune signature

Immune signalling is a crucial component in the progression of fibrosis. However, approaches for the safety assessment of potentially profibrotic substances, that provide information on mechanistic immune responses, are underdeveloped. This study aimed to develop a novel framework for assessing the immunotoxicity of fibrotic compounds. We exposed macrophages in vitro to multiple sublethal concentrations of the profibrotic agent bleomycin, over multiple timepoints, and generated RNA sequencing data. Using a toxicogenomic approach, we performed dose-dependent analysis to discover genes dysregulated by bleomycin exposure in a dose-responsive manner. A subset of immune genes displayed a sustained dose-dependent and differential expression response to profibrotic challenge. An immunoassay revealed cytokines and proteinases responding to bleomycin exposure that closely correlated to transcriptomic alterations, underscoring the integration between transcriptional immune response and external immune signalling activity. This study not only increases our understanding of the immunological mechanisms of fibrosis, but also offers an innovative framework for the toxicological evaluation of substances with potential fibrogenic effects on macrophage signalling. Our work brings a new immunotoxicogenomic direction for hazard assessment of fibrotic compounds, through the implementation of a time and resource efficient in vitro methodology.

Interplay between pulmonary epithelial stem cells and innate immune cells contribute to the repair and regeneration of ALI/ARDS

Mammalian lung is the important organ for ventilation and exchange of air and blood. Fresh air and venous blood are constantly delivered through the airway and vascular tree to the alveolus. Based on this, the airways and alveolis are persistently exposed to the external environment and are easily suffered from toxins, irritants and pathogens. For example, acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a common cause of respiratory failure in critical patients, whose typical pathological characters are diffuse epithelial and endothelial damage resulting in excessive accumulation of inflammatory fluid in the alveolar cavity. The supportive treatment is the main current treatment for ALI/ARDS with the lack of targeted effective treatment strategies. However, ALI/ARDS needs more targeted treatment measures. Therefore, it is extremely urgent to understand the cellular and molecular mechanisms that maintain alveolar epithelial barrier and airway integrity. Previous researches have shown that the lung epithelial cells with tissue stem cell function have the ability to repair and regenerate after injury. Also, it is able to regulate the phenotype and function of innate immune cells involving in regeneration of tissue repair. Meanwhile, we emphasize that interaction between the lung epithelial cells and innate immune cells is more supportive to repair and regenerate in the lung epithelium following acute lung injury. We reviewed the recent advances in injury and repair of lung epithelial stem cells and innate immune cells in ALI/ARDS, concentrating on alveolar type 2 cells and alveolar macrophages and their contribution to post-injury repair behavior of ALI/ARDS through the latest potential molecular communication mechanisms. This will help to develop new research strategies and therapeutic targets for ALI/ARDS.

Correlation between the dynamic changes of γδT cells, Th17 cells, CD4+CD25+ regulatory T cells in peripheral blood and pharmacological interventions against bleomycin-induced pulmonary fibrosis progression in mice

The involvement of γδT cells, Th17 cells, and CD4+CD25+ regulatory T cells (Tregs) is crucial in the progression of pulmonary fibrosis (PF), particularly in maintaining immune tolerance and homeostasis. However, the dynamics of these cells in relation to PF progression, especially under pharmacological interventions, remains poorly understood. This study aims to unravel the interplay between the dynamic changes of these cells and the effect of pharmacological agents in a mouse model of PF induced by intratracheal instillation of bleomycin. We analyzed changes in lung histology, lung index, hydroxyproline levels, and the proportions of γδT cells, Th17 cells, and Tregs on the 3rd, 14th, and 28th days following treatment with Neferine, Isoliensinine, Pirfenidone, and Prednisolone. Our results demonstrate that these drugs can partially or dynamically reverse weight loss, decrease lung index and hydroxyproline levels, and ameliorate lung histopathological damage. Additionally, they significantly modulated the abnormal changes in γδT, Th17, and Treg cell proportions. Notably, on day 3, the proportion of γδT cells increased in the Neferine and Prednisolone groups but decreased in the Isoliensinine and Pirfenidone groups, while the proportion of Th17 cells decreased across all treated groups. On day 14, the Neferine group showed an increase in all three cell types, whereas the Pirfenidone group exhibited a decrease. In the Isoliensinine group, γδT and Th17 cells increased, and in the Prednisolone group, only Tregs increased. By day 28, an increase in Th17 cell proportion was observed in all treatment groups, with a decrease in γδT cells noted in the Neferine group. These shifts in cell proportions are consistent with the pathogenesis changes induced by these anti-PF drugs, suggesting a correlation between cellular dynamics and pharmacological interventions in PF progression. Our findings imply potential strategies for assessing the efficacy and timing of anti-PF treatments based on these cellular changes.

CD5L as a promising biological therapeutic for treating sepsis

Sepsis results from systemic, dysregulated inflammatory responses to infection, culminating in multiple organ failure. Here, we demonstrate the utility of CD5L for treating experimental sepsis caused by cecal ligation and puncture (CLP). We show that CD5L's important features include its ability to enhance neutrophil recruitment and activation by increasing circulating levels of CXCL1, and to promote neutrophil phagocytosis. CD5L-deficient mice exhibit impaired neutrophil recruitment and compromised bacterial control, rendering them susceptible to attenuated CLP. CD5L-/- peritoneal cells from mice subjected to medium-grade CLP exhibit a heightened pro-inflammatory transcriptional profile, reflecting a loss of control of the immune response to the infection. Intravenous administration of recombinant CD5L (rCD5L) in immunocompetent C57BL/6 wild-type (WT) mice significantly ameliorates measures of disease in the setting of high-grade CLP-induced sepsis. Furthermore, rCD5L lowers endotoxin and damage-associated molecular pattern (DAMP) levels, and protects WT mice from LPS-induced endotoxic shock. These findings warrant the investigation of rCD5L as a possible treatment for sepsis in humans.

IL-22 Binding Protein Controls IL-22-Driven Bleomycin-Induced Lung Injury

The high mortality rates of acute lung injury and acute respiratory distress syndrome challenge the field to identify biomarkers and factors that can be exploited for therapeutic approaches. IL-22 is a cytokine that has antibacterial and reparative properties in the lung. However, it also can exacerbate inflammation and requires tight control by the extracellular inhibitory protein known as IL-22 binding protein (IL-22BP) (Il22ra2). This study showed the necessity of IL-22BP in controlling and preventing acute lung injury using IL-22BP knockout mice (Il22ra2-/-) in the bleomycin model of acute lung injury/acute respiratory distress syndrome. Il22ra2-/- mice had greater sensitivity (weight loss and death) and pulmonary inflammation in the acute phase (first 7 days) of the injury compared with wild-type C57Bl/6 controls. The inflammation was driven by excess IL-22 production, inducing the influx of pathogenic IL-17A+ γδ T cells to the lung. Interestingly, this inflammation was initiated in part by the noncanonical IL-22 signaling to macrophages, which express the IL-22 receptor (Il22ra1) in vivo after bleomycin challenge. This study further showed that IL-22 receptor alpha-1+ macrophages can be stimulated by IL-22 to produce a number of IL-17-inducing cytokines such as IL-1β, IL-6, and transforming growth factor-β1. Together, the results suggest that IL-22BP prevents IL-22 signaling to macrophages and reduces bleomycin-mediated lung injury.

Periodontitis aggravates COPD through the activation of γδ T cell and M2 macrophage

Chronic obstructive pulmonary disease (COPD) is a chronic systemic inflammatory disease with high morbidity and mortality. Periodontitis exacerbates COPD progression; however, the immune mechanisms by which periodontitis affects COPD remain unclear. Here, by constructing periodontitis and COPD mouse models, we demonstrated that periodontitis and COPD could mutually aggravate disease progression. For the first time, we found that the progression was associated with the activation of γδ T cells and M2 macrophages, and M2 polarization of macrophages was affected by γδ T cells activation. In the lung tissues of COPD with periodontitis, the activation of γδ T cells finally led to the increase of IL 17 and IFN γ expression and M2 macrophage polarization. Furthermore, we found that the periodontitis-associated bacteria Porphyromonas gingivalis (P. gingivalis) promoted the activation of γδ T cells and M2 macrophages ex vivo. The data from clinical bronchoalveolar lavage fluid (BALF) samples were consistent with the in vivo and ex vivo experiments. For the first time, our results identified the crucial role of γδ T-M2 immune mechanism in mediating periodontitis-promoted COPD progression. Therefore, targeting at periodontitis treatment and the γδ T-M2 immune mechanism might provide a new practical strategy for COPD prevention or control.IMPORTANCEPeriodontitis exacerbates chronic obstructive pulmonary disease (COPD) progression. For the first time, the current study identified that the impact of periodontitis on COPD progression was associated with the activation of γδ T cells and M2 macrophages and that M2 polarization of macrophages was affected by γδ T cells activation. The results indicated that targeting at periodontitis treatment and the γδ T-M2 immune mechanism might provide a new practical strategy for COPD prevention or control.

Unveiling the landscape of cytokine research in glioma immunotherapy: a scientometrics analysis

Background: Cytokines modulate the glioma tumor microenvironment, influencing occurrence, progression, and treatment response. Strategic cytokine application may improve glioma immunotherapy outcomes. Gliomas remain refractory to standard therapeutic modalities, but immunotherapy shows promise given the integral immunomodulatory roles of cytokines. However, systematic evaluation of cytokine glioma immunotherapy research is absent. Bibliometric mapping of the research landscape, recognition of impactful contributions, and elucidation of evolutive trajectories and hot topics has yet to occur, potentially guiding future efforts. Here, we analyzed the structure, evolution, trends, and hotspots of the cytokine glioma immunotherapy research field, subsequently focusing on avenues for future investigation. Methods: This investigation conducted comprehensive bibliometric analyses on a corpus of 1529 English-language publications, from 1 January 2000, to 4 October 2023, extracted from the Web of Science database. The study employed tools including Microsoft Excel, Origin, VOSviewer, CiteSpace, and the Bibliometrix R package, to systematically assess trends in publication, contributions from various countries, institutions, authors, and journals, as well as to examine literature co-citation and keyword distributions within the domain of cytokines for glioma immunotherapy. The application of these methodologies facilitated a detailed exploration of the hotspots, the underlying knowledge structure, and the developments in the field of cytokines for glioma immunotherapy. Results: This bibliometric analysis revealed an exponential growth in annual publications, with the United States, China, and Germany as top contributors. Reviews constituted 17% and research articles 83% of total publications. Analysis of keywords like "interleukin-13," "TGF-beta," and "dendritic cells" indicated progression from foundational cytokine therapies to sophisticated understanding of the tumor microenvironment and immune dynamics. Key research avenues encompassed the tumor microenvironment, epidermal growth factor receptor, clinical trials, and interleukin pathways. This comprehensive quantitative mapping of the glioma immunotherapy cytokine literature provides valuable insights to advance future research and therapeutic development. Conclusion: This study has identified remaining knowledge gaps regarding the role of cytokines in glioma immunotherapy. Future research will likely focus on the tumor microenvironment, cancer vaccines, epidermal growth factor receptor, and interleukin-13 receptor alpha 2. Glioma immunotherapy development will continue through investigations into resistance mechanisms, microglia and macrophage biology, and interactions within the complex tumor microenvironment.

The Role of Immune Cells in the Pathogenesis of Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a devastating disease of unknown etiology with limited treatment options. The role of the immune system in IPF has received increasing attention. Uncontrolled immune responses drive the onset and progression of IPF. This article provides an overview of the role of innate immune cells (including macrophages, neutrophils, mast cells, eosinophils, dendritic cells, nature killer cells, nature kill cells and γδ T cells) and adaptive immune cells (including Th1 cells, Th2 cells, Th9 cells, Th17 cells, Th22 cells, cytotoxic T cells, B lymphocytes and Treg cells) in IPF. In addition, we review the current status of pharmacological treatments for IPF and new developments in immunotherapy. A deeper comprehension of the immune system's function in IPF may contribute to the development of targeted immunomodulatory therapies that can alter the course of the disease.

The Regenerative Power of Stem Cells: Treating Bleomycin-Induced Lung Fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive lung disease with no known cure, characterized by the formation of scar tissue in the lungs, leading to respiratory failure. Although the exact cause of IPF remains unclear, the condition is thought to result from a combination of genetic and environmental factors. One of the most widely used animal models to study IPF is the bleomycin-induced lung injury model in mice. In this model, the administration of the chemotherapeutic agent bleomycin causes pulmonary inflammation and fibrosis, which closely mimics the pathological features of human IPF. Numerous recent investigations have explored the functions of various categories of stem cells in the healing process of lung injury induced by bleomycin in mice, documenting the beneficial effects and challenges of this approach. Differentiation of stem cells into various cell types and their ability to modulate tissue microenvironment is an emerging aspect of the regenerative therapies. This review article aims to provide a comprehensive overview of the role of stem cells in repairing bleomycin-induced lung injury. It delves into the mechanisms through which various types of stem cells, including mesenchymal stem cells, embryonic stem cells, induced pluripotent stem cells, and lung resident stem cells, exert their therapeutic effects in this specific model. We have also discussed the unique set of intermediate markers and signaling factors that can influence the proliferation and differentiation of alveolar epithelial cells both during lung repair and homeostasis. Finally, we highlight the challenges and opportunities associated with translating stem cell therapy to the clinic for IPF patients. The novelty and implications of this review extend beyond the understanding of the potential of stem cells in treating IPF to the broader field of regenerative medicine. We believe that the review paves the way for further advancements in stem cell therapies, offering hope for patients suffering from this debilitating and currently incurable disease.

Allies or enemies? The effect of regulatory T cells and related T lymphocytes on the profibrotic environment in bleomycin-injured lung mouse models

Idiopathic pulmonary fibrosis (IPF) is characterized by permanent scarring of lung tissue and declining lung function, and is an incurable disease with increase in prevalence over the past decade. The current consensus is that aberrant wound healing following repeated injuries to the pulmonary epithelium is the most probable cause of IPF, with various immune inflammatory pathways having been reported to impact disease pathogenesis. While the role of immune cells, specifically T lymphocytes and regulatory T cells (Treg), in IPF pathogenesis has been reported and discussed recently, the pathogenic or beneficial roles of these cells in inducing or preventing lung fibrosis is still debated. This lack of understanding could be due in part to the difficulty in obtaining diseased human lung tissue for research purposes. For this reason, many animal models have been developed over the years to attempt to mimic the main clinical hallmarks of IPF: among these, inducing lung injury in rodents with the anti-cancer agent bleomycin has now become the most commonly studied animal model of IPF. Pulmonary fibrosis is the major side effect when bleomycin is administered for cancer treatment in human patients, and a similar effect can be observed after intra-tracheal administration of bleomycin to rodents. Despite many pathophysiological pathways of lung fibrosis having been investigated in bleomycin-injured animal models, one central facet still remains controversial, namely the involvement of specific T lymphocyte subsets, and in particular Treg, in disease pathogenesis. This review aims to summarize the major findings and conclusions regarding the involvement of immune cells and their receptors in the pathogenesis of IPF, and to elaborate on important parallels between animal models and the human disease. A more detailed understanding of the role of Treg and other immune cell subsets in lung injury and fibrosis derived from animal models is a critical basis for translating this knowledge to the development of new immune-based therapies for the treatment of human IPF.

Two Distinct Mechanisms Underlying γδ T Cell-Mediated Regulation of Collagen Type I in Lung Fibroblasts

Idiopathic pulmonary fibrosis is a chronic intractable lung disease, leading to respiratory failure and death. Although anti-fibrotic agents delay disease progression, they are not considered curative treatments, and alternative modalities have attracted attention. We examined the effect of human γδ T cells on collagen type I in lung fibroblasts. Collagen type I was markedly reduced in a γδ T cell number-dependent manner following treatment with γδ T cells expanded with tetrakis-pivaloxymethyl 2-(thiazole-2-ylamino) ethylidene-1,1-bisphosphonate (PTA) and interleukin-2. Collagen type I levels remained unchanged on addition of γδ T cells to the culture system through a trans-well culture membrane, suggesting that cell–cell contact is essential for reducing its levels in lung fibroblasts. Re-stimulating γδ T cells with (E)-4-hydroxy-3-methylbut-2-enyl diphosphate (HMBPP) reduced collagen type I levels without cell–cell contact, indicating the existence of HMBPP-induced soluble anti-fibrotic factors in γδ T cells. Adding anti-interferon-γ (IFN-γ)-neutralizing mAb restored collagen type I levels, demonstrating that human γδ T cell-derived IFN-γ reduces collagen type I levels. Conversely, interleukin-18 augmented γδ T cell-induced suppression of collagen type I. Therefore, human γδ T cells reduce collagen levels in lung fibroblasts via two distinct mechanisms; adoptive γδ T cell transfer is potentially a new therapeutic candidate.

The role of immune response in the pathogenesis of idiopathic pulmonary fibrosis: far beyond the Th1/Th2 imbalance

INTRODUCTION

. Idiopathic pulmonary fibrosis (IPF) is a chronic disease of unknown origin characterized by progressive scarring of the lung leading to irreversible loss of function. Despite the availability of two drugs that are able to slow down disease progression, IPF remains a deadly disease. The pathogenesis of IPF is poorly understood, but a dysregulated wound healing response following recurrent alveolar epithelial injury is thought to be crucial. Areas covered. In the last few years, the role of the immune system in IPF pathobiology has been reconsidered; indeed, recent data suggest that a dysfunctional immune system may promote and unfavorable interplay with pro-fibrotic pathways thus acting as a cofactor in disease development and progression. In this article, we review and critically discuss the role of T cells in the pathogenesis and progression of IPF in the attempt to highlight ways in which further research in this area may enable the development of targeted immunomodulatory therapies for this dreadful disease.

EXPERT OPINION

A better understanding of T cells interactions has the potential to facilitate the development of immune modulators targeting multiple T cell-mediated pathways thus halting disease initiation and progression.

Immune determinants of chronic sequelae after respiratory viral infection

The acute effects of various respiratory viral infections have been well studied, with extensive characterization of the clinical presentation as well as viral pathogenesis and host responses. However, over the course of the recent COVID-19 pandemic, the incidence and prevalence of chronic sequelae after acute viral infections have become increasingly appreciated as a serious health concern. Post-acute sequelae of COVID-19, alternatively described as “long COVID-19,” are characterized by symptoms that persist for longer than 28 days after recovery from acute illness. Although there exists substantial heterogeneity in the nature of the observed sequelae, this phenomenon has also been observed in the context of other respiratory viral infections including influenza virus, respiratory syncytial virus, rhinovirus, severe acute respiratory syndrome coronavirus, and Middle Eastern respiratory syndrome coronavirus. In this Review, we discuss the various sequelae observed following important human respiratory viral pathogens and our current understanding of the immunological mechanisms underlying the failure of restoration of homeostasis in the lung.

Contributions of Immune Cells and Stromal Cells to the Pathogenesis of Systemic Sclerosis: Recent Insights

Systemic sclerosis (SSc) is a multisystem rheumatic disease characterized by vascular dysfunction, autoimmune abnormalities, and progressive organ fibrosis. A series of studies in SSc patients and fibrotic models suggest that immune cells, fibroblasts, and endothelial cells participate in inflammation and aberrant tissue repair. Furthermore, the growing number of studies on single-cell RNA sequencing (scRNA-seq) technology in SSc elaborate on the transcriptomics and heterogeneities of these cell subsets significantly. In this review, we summarize the current knowledge regarding immune cells and stromal cells in SSc patients and discuss their potential roles in SSc pathogenesis, focusing on recent advances in the new subtypes by scRNA-seq.

Targeting PI3K/AKT signaling for treatment of idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic progressive fibrotic interstitial pneumonia with unknown causes. The incidence rate increases year by year and the prognosis is poor without cure. Recently, phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB/AKT) signaling pathway can be considered as a master regulator for IPF. The contribution of the PI3K/AKT in fibrotic processes is increasingly prominent, with PI3K/AKT inhibitors currently under clinical evaluation in IPF. Therefore, PI3K/AKT represents a critical signaling node during fibrogenesis with potential implications for the development of novel anti-fibrotic strategies. This review epitomizes the progress that is being made in understanding the complex interpretation of the cause of IPF, and demonstrates that PI3K/AKT can directly participate to the greatest extent in the formation of IPF or cooperate with other pathways to promote the development of fibrosis. We further summarize promising PI3K/AKT inhibitors with IPF treatment benefits, including inhibitors in clinical trials and pre-clinical studies and natural products, and discuss how these inhibitors mitigate fibrotic progression to explore possible potential agents, which will help to develop effective treatment strategies for IPF in the near future.

Effect of PM10 on pulmonary immune response and fetus development

Despite numerous reports that ambient particulate matter is a key determinant for human health, toxicity data produced based on physicochemical properties of particulate matters is very lack, suggesting lack of scientific evidence for regulation. In this study, we sampled inhalable particulate matters (PM10) in northern Seoul, Korea. PM10 showed atypical- and fiber-type particles with the average size and the surface charge of 1,598.1 ± 128.7 nm and -27.5 ± 2.8, respectively, and various toxic elements were detected in the water extract. On day 90 after the first pulmonary exposure, total cell number dose-dependently increased in the lungs of both sexes of mice. PM10 induced Th1-dominant immune response with pathological changes in both sexes of mice. Meanwhile, composition of total cells and expression of proteins which functions in cell-to-cell communication showed different trends between sexes. Following, male and female mice were mated to identify effects of PM10 to the next generation. PM10 remained in the lung of dams until day 21 after birth, and the levels of IgA and IgE increased in the blood of dams exposed to the maximum dose compared to control. In addition, the interval between births of fetuses, the number of offspring, the neonatal survival rate (day 4 after birth) and the sex ratio seemed to be affected at the maximum dose, and particularly, all offspring from one dam were stillborn. In addition, expression of HIF-1α protein increased in the lung tissue of dams exposed to PM10, and level of hypoxia-related proteins was notably enhanced in PM10-exposed bronchial epithelial cells compared to control. Taken together, we suggest that inhaled PM10 may induce Th1-shifting immune response in the lung, and that it may affect reproduction (fetus development) by causing lung hypoxia. Additionally, we propose that further study is needed to identify particle-size-dependent effects on development of the next generation.

Cellular uptake of collagens and implications for immune cell regulation in disease

As the dominant constituent of the extracellular matrix (ECM), collagens of different types are critical for the structural properties of tissues and make up scaffolds for cellular adhesion and migration. Importantly, collagens also directly modulate the phenotypic state of cells by transmitting signals that influence proliferation, differentiation, polarization, survival, and more, to cells of mesenchymal, epithelial, or endothelial origin. Recently, the potential of collagens to provide immune regulatory signals has also been demonstrated, and it is believed that pathological changes in the ECM shape immune cell phenotype. Collagens are themselves heavily regulated by a multitude of structural modulations or by catabolic pathways. One of these pathways involves a cellular uptake of collagens or soluble collagen-like defense collagens of the innate immune system mediated by endocytic collagen receptors. This cellular uptake is followed by the degradation of collagens in lysosomes. The potential of this pathway to regulate collagens in pathological conditions is evident from the increased extracellular accumulation of both collagens and collagen-like defense collagens following endocytic collagen receptor ablation. Here, we review how endocytic collagen receptors regulate collagen turnover during physiological conditions and in pathological conditions, such as fibrosis and cancer. Furthermore, we highlight the potential of collagens to regulate immune cells and discuss how endocytic collagen receptors can directly regulate immune cell activity in pathological conditions or do it indirectly by altering the extracellular milieu. Finally, we discuss the potential collagen receptors utilized by immune cells to directly detect ECM-related changes in the tissues which they encounter.

Bi-directional communication: Conversations between fibroblasts and immune cells in systemic sclerosis

Systemic Sclerosis (SSc) is an autoimmune idiopathic connective tissue disease, characterized by aberrant fibro-proliferative and inflammatory responses, causing fibrosis of multiple organs. In recent years the interactions between innate and adaptive immune cells with resident fibroblasts have been uncovered. Cross-talk between immune and stromal cells mediates activation of stromal cells to myofibroblasts; key cells in the pathophysiology of fibrosis. These cells and their cytokines appear to mediate their effects in both a paracrine and autocrine fashion. This review examines the role of innate and adaptive immune cells in SSc, focusing on recent advances that have illuminated our understanding of ongoing bi-directional communication between immune and stromal cells. Finally, we appraise current and future therapies and how these may be useful in a disease that currently has no specific disease modifying treatment.

T Cells in Fibrosis and Fibrotic Diseases

Fibrosis is the extensive deposition of fibrous connective tissue, and it is characterized by the accumulation of collagen and other extracellular matrix (ECM) components. Fibrosis is essential for wound healing and tissue repair in response to a variety of triggers, which include infection, inflammation, autoimmune disorder, degenerative disease, tumor, and injury. Fibrotic remodeling in various diseases, such as liver cirrhosis, pulmonary fibrosis, renal interstitial fibrosis, myocardial infarction, systemic sclerosis (SSc), and graft-versus-host disease (GVHD), can impair organ function, causing high morbidity and mortality. Both innate and adaptive immunity are involved in fibrogenesis. Although the roles of macrophages in fibrogenesis have been studied for many years, the underlying mechanisms concerning the manner in which T cells regulate fibrosis are not completely understood. The T cell receptor (TCR) engages the antigen and shapes the repertoire of antigen-specific T cells. Based on the divergent expression of surface molecules and cell functions, T cells are subdivided into natural killer T (NKT) cells, γδ T cells, CD8⁺ cytotoxic T lymphocytes (CTL), regulatory T (Treg) cells, T follicular regulatory (Tfr) cells, and T helper cells, including Th1, Th2, Th9, Th17, Th22, and T follicular helper (Tfh) cells. In this review, we summarize the pro-fibrotic or anti-fibrotic roles and distinct mechanisms of different T cell subsets. On reviewing the literature, we conclude that the T cell regulations are commonly disease-specific and tissue-specific. Finally, we provide perspectives on microbiota, viral infection, and metabolism, and discuss the current advancements of technologies for identifying novel targets and developing immunotherapies for intervention in fibrosis and fibrotic diseases.

Deficiency of CRTH2, a Prostaglandin D2 Receptor, Aggravates Bleomycin-induced Pulmonary Inflammation and Fibrosis

Chemoattractant receptor homologous with T-helper cell type 2 cells (CRTH2), a receptor for prostaglandin D₂, is preferentially expressed on T-helper cell type 2 lymphocytes, group 2 innate lymphoid cells, eosinophils, and basophils, and elicits the production of type 2 cytokines, including profibrotic IL-13. We hypothesized that lack of CRTH2 might protect against fibrotic lung disease, and we tested this hypothesis using a bleomycin-induced lung inflammation and fibrosis model in CRTH2-deficient (CRTH2^-/-) or wild-type BALB/c mice. Compared with wild-type mice, CRTH2^-/- mice treated with bleomycin exhibited significantly higher mortality, enhanced accumulation of inflammatory cells 14-21 days after bleomycin injection, reduced pulmonary compliance, and increased levels of collagen and total protein in the lungs. These phenotypes were associated with decreased levels of IFN-γ, IL-6, IL-10, and IL-17A in BAL fluid. Adoptive transfer of splenocytes from wild-type, but not CRTH2^-/-, mice 2 days before injection of bleomycin resolved the sustained inflammation as well as the increased collagen and protein accumulation in the lungs of CRTH2^-/- mice. We consider that the disease model is driven by γδT cells that express CRTH2; thus, the adoptive transfer of γδT cells could ameliorate bleomycin-induced alveolar inflammation and fibrosis.

Combination of L-Arginine and L-Norvaline protects against pulmonary fibrosis progression induced by bleomycin in mice

Pulmonary fibrosis (PF) progression may be involved with arginine (Arg) metabolism and immune balance. The present study aimed to explore the effects of L-Arginine (L-Arg) and L-Norvaline (L-Nor) on bleomycin (BLM)-induced PF in mice, meanwhile, and observe dynamic changes of Arg metabolism, immune balance and crosstalk between them in PF progression. Followed intratracheal instillation of BLM or saline, Kunming mice were treated orally with saline, L-Arg, L-Nor and L-Arg + L-Nor three times a day. And the mice were sacrificed on Day 3, 14 and 28 after treatment. Changes of body weight, lung index, lung hydroxyproline and histopathology were analyzed to evaluate the PF degree. Peripheral blood Arg, Citrulline (Cit), Ornithine (Orn) and Proline (Pro), lung NO, NOS and arginase were analyzed to evaluate the Arg metabolism. Peripheral blood Tregs, Th17 and γδT cells were analyzed to evaluate the immune balance. Our data showed that combination of L-Arg and L-Nor dynamically reversed the weight loss, decreased lung index and hydroxyproline, and improved lung histopathological damages induced by BLM. The combination dynamically and significantly rectified Tregs, Th17, γδT and Tregs/Th17 abnormal changes. Meanwhile, these disorders of peripheral blood Arg, Cit, Orn, Pro, Orn/Cit and Pro/Orn, and lung NO, iNOS and TNOS were also improved accordingly. These results demonstrated that combination of L-Arg and L-Nor had inhibitory effects on BLM-induced PF progression, possibly due to their corrective action on immune imbalance, Arg metabolism disorder and crosstalk abnormality in the progression of PF.

The diversity of myeloid immune cells shaping wound repair and fibrosis in the lung

In healthy circumstances the immune system coordinates tissue repair responses in a tight balance that entails efficient inflammation for removal of potential threats, proper wound closure, and regeneration to regain tissue function. Pathological conditions, continuous exposure to noxious agents, and even ageing can dysregulate immune responses after injury. This dysregulation can lead to a chronic repair mechanism known as fibrosis. Alterations in wound healing can occur in many organs, but our focus lies with the lung as it requires highly regulated immune and repair responses with its continuous exposure to airborne threats. Dysregulated repair responses can lead to pulmonary fibrosis but the exact reason for its development is often not known. Here, we review the diversity of innate immune cells of myeloid origin that are involved in tissue repair and we illustrate how these cell types can contribute to the development of pulmonary fibrosis. Moreover, we briefly discuss the effect of age on innate immune responses and therefore on wound healing and we conclude with the implications of current knowledge on the avenues for future research.

The atypical chemokine receptor ACKR2 drives pulmonary fibrosis by tuning influx of CCR2+ and CCR5+ IFNγ-producing γδT cells in mice

Chemokines coordinate lung inflammation and fibrosis by acting on chemokine receptors expressed on leukocytes and other cell types. Atypical chemokine receptors (ACKRs) bind, internalize, and degrade chemokines, tuning homeostasis and immune responses. ACKR2 recognizes and decreases the levels of inflammatory CC chemokines. The role of ACKR2 in fibrogenesis is unknown. The purpose of the study was to investigate the role of ACKR2 in the context of pulmonary fibrosis. The effects of ACKR2 expression and deficiency during inflammation and fibrosis were analyzed using a bleomycin-model of fibrosis, ACKR2-deficient mice, bone marrow chimeras, and antibody-mediated leukocyte depletion. ACKR2 was upregulated acutely in response to bleomycin and normalized over time. ACKR2^-/- mice showed reduced lethality and lung fibrosis. Bone marrow chimeras showed that lethality and fibrosis depended on ACKR2 expression in pulmonary resident (nonhematopoietic) cells but not on leukocytes. ACKR2^-/- mice exhibited decreased expression of tissue-remodeling genes, reduced leukocyte influx, pulmonary injury, and dysfunction. ACKR2^-/- mice had early increased levels of CCL5, CCL12, CCL17, and IFNγ and an increased number of CCR2⁺ and CCR5⁺ IFNγ-producing γδT cells in the airways counterbalanced by low Th17-lymphocyte influx. There was reduced accumulation of IFNγ-producing γδT cells in CCR2^-/- and CCR5^-/- mice. Moreover, depletion of γδT cells worsened the clinical symptoms induced by bleomycin and reversed the phenotype of ACKR2^-/- mice exposed to bleomycin. ACKR2 controls the CC chemokine expression that drives the influx of CCR2⁺ and CCR5⁺ IFNγ-producing γδT cells, tuning the Th17 response that mediated pulmonary fibrosis triggered by bleomycin instillation.

Fli1-haploinsufficient dermal fibroblasts promote skin-localized transdifferentiation of Th2-like regulatory T cells

Background

Friend leukemia virus integration 1 (Fli1) deficiency, a predisposing factor of systemic sclerosis (SSc), induces SSc-like phenotypes in various cell types. A recent study demonstrated the transdifferentiation of T helper type 2 cell (Th2)-like regulatory T cells (Tregs) in SSc lesional skin through interleukin (IL)-33 produced by fibroblasts. Therefore, we investigated the role of Fli1 deficiency in dermal fibroblast-mediated transdifferentiation of Tregs.

Methods

Cytokine expression was assessed in Tregs by flow cytometry and in skin samples and cultivated cells by immunostaining, immunoblotting, and/or qRT-PCR. Fli1 binding to the target gene promoters was examined by chromatin immunoprecipitation. Murine dermal fibroblasts and Tregs were cocultured with or without blocking antibodies against target cytokines.

Results

Th2- and Th17-like cell proportions in skin-homing Tregs were increased in bleomycin-treated Fli1^+/− mice compared with bleomycin-treated wild-type mice, whereas Th1-, Th2-, and Th17-like cell proportions in splenic Tregs were comparable. Fli1^+/− fibroblasts overproduced IL-33 and IL-6, in particular IL-33, and Fli1 occupied the IL33 and IL6 promoters in dermal fibroblasts. Importantly, the IL-4-producing cell proportion was significantly higher in wild-type Tregs cocultured with Fli1^+/− fibroblasts than in those cocultured with wild-type fibroblasts, which were canceled by neutralizing anti-IL-33 antibody. Under the same coculture condition, an increased tendency of IL-17A-producing cell proportion, which was possibly mediated by IL-6, was evident.

Conclusions

Fli1 haploinsufficiency increases the proportions of Th2- and Th17-like Tregs in bleomycin-induced profibrotic skin conditions, in which IL-33-producing dermal fibroblasts contribute to Th2-like Treg transdifferentiation, suggesting a critical role of Fli1 deficiency in the interaction of dermal fibroblasts with immune cells in pathological skin fibrosis.

Electronic supplementary material

The online version of this article (10.1186/s13075-018-1521-3) contains supplementary material, which is available to authorized users.

Lung-resident γδ T cells and their roles in lung diseases

γδ T cells are greatly enriched in mucosal and epithelial sites, such as the skin, respiratory, digestive and reproductive tracts, and they are defined as tissue-resident immune cells. In these tissues, the characteristics and biological roles of γδ T cells are distinguished from each other. The lungs represent the most challenging immunological dilemma for the host, and they have their own effective immune system. The abundance of γδ T cells, an estimated 8-20% of resident pulmonary lymphocytes in the lung, maintains lung tissue homeostasis. In this review, we summarize the recent research progress regarding lung-resident γδ T cells, including their development, residency and immune characteristics, and discuss the involvement of γδ T cells in infectious diseases of the lung, including bacterial, viral and fungal infections; lung allergic disease; lung inflammation and fibrosis; and lung cancer.

Ocular surface cytokine profile in chronic Stevens-Johnson syndrome and its response to mucous membrane grafting for lid margin keratinisation

BACKGROUND

To study the tear cytokine and the conjunctival and oral mucosal marker profile in chronic ocular Stevens-Johnson syndrome (SJS) and their alteration following mucous membrane grafting (MMG) for lid margin keratinisation (LMK).

METHODS

In a 1-year prospective study, SJS cases (n=25) and age-matched/sex-matched healthy controls (n=25) were recruited. Tear specimen (Schirmer's strip), conjunctival and oral mucosal imprints were collected from controls and SJS cases pre-MMG and post-MMG (at first follow-up, n=17). Tear cytokines were profiled using 27-bioplex array. Transforming growth factor-beta (TGF-β)-mediated extracellular matrix changes in conjunctival and oral mucosal cells were analysed by gene expression studies. 30 RESULTS: Tear cytokine profiling of chronic SJS cases at pre-MMG stage revealed significant upregulation of cytokines granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-8, IL-1β, monocyte chemoattractant protein-1, IL-15, IL-2, IL-17A and basic fibroblast growth factor (bFGF) with downregulation of IP-10 (interferon gamma-induced protein 10), tumour necrosis factor-α, interferon-γ, IL-10, vascular endothelial growth factor, regulated upon activation normal T-cell expressed and secreted (RANTES), IL-7, IL-12p70 and IL-13, with maximal increase in GM-CSF and maximal downregulation of IP-10, respectively. Of these, IL-2, IL-15, bFGF and IL-17A showed significant correlation with disease severity, pre-MMG. Conjunctival cells pre-MMG showed increase in TGF-β1, TGF-βRII, connective tissue growth factor and collagen-III gene expression by 10, 67, 173 and 184 folds, respectively, which dropped to 1.3, 11, 13.5 and 19 folds correspondingly, post-MMG. However, their expressions in oral mucosa were negligible.

CONCLUSION

A proinflammatory, profibrotic, antiapoptotic ocular surface milieu characterises chronic ocular SJS. IP-10, an antifibrotic cytokine was noted to be maximally downregulated, unlike in other forms of chronic dry eye disease. The alterations in the ocular surface are seen to reverse largely with MMG for LMK.

Neutrophils regulate the lung inflammatory response via γδ T cell infiltration in an experimental mouse model of human metapneumovirus infection

Neutrophils are the most abundant leukocytes in human circulation. They are the first immune cell population recruited to the sites of infection. However, the role of neutrophils to regulate host immune responses during respiratory viral infections is largely unknown. To elucidate the role of neutrophils in respiratory antiviral defense, we used an experimental mouse model of human metapneumovirus (HMPV) infection. HMPV, a member of the Paramyxoviridae family, is a leading respiratory pathogen causing severe symptoms, such as bronchiolitis and pneumonia, in young, elderly, and immunocompromised patients. We demonstrate that neutrophils are the predominant population of immune cells recruited into the lungs after HMPV infection. This led us to hypothesize that neutrophils represent a key player of the immune response during HMPV infection, thereby regulating HMPV-induced lung pathogenesis. Specific depletion of neutrophils in vivo using a mAb and simultaneous infection with HMPV exhibited higher levels of inflammatory cytokines, pulmonary inflammation, and severe clinical disease compared with HMPV-infected, competent mice. Interestingly, the lack of neutrophils altered γδ T cell accumulation in the lung. The absence of γδ T cells during HMPV infection led to reduced pulmonary inflammation. These novel findings demonstrate that neutrophils play a critical role in controlling HMPV-induced inflammatory responses by regulating γδ T cell infiltration to the site of infection.

The Role of γδ T Cells in Fibrotic Diseases

Inflammation induced by toxins, micro-organisms, or autoimmunity may result in pathogenic fibrosis, leading to long-term tissue dysfunction, morbidity, and mortality. Immune cells play a role in both induction and resolution of fibrosis. γδ T cells are an important group of unconventional T cells characterized by their expression of non-major histocompatibility complex restricted clonotypic T cell receptors for non-peptide antigens. Accumulating evidence suggests that subsets of γδ T cells in experimentally induced fibrosis following bleomycin treatment, or infection with Bacillus subtilis, play pro-inflammatory roles that instigate fibrosis, whereas the same cells may also play a role in resolving fibrosis. These processes appear to be linked at least in part to the cytokines produced by the cells at various stages, with interleukin (IL)-17 playing a central role in the inflammatory phase driving fibrosis, but later secretion of IL-22, interferon γ, and CXCL10 preventing pathologic fibrosis. Moreover, γδ T cells appear to be involved, in an antigen-driven manner, in the prototypic human fibrotic disease, systemic sclerosis (SSc). In this paper we review in brief the scientific publications that have implicated γδ T cells in fibrotic diseases and their pro- and anti-fibrotic effects.

Prospects for chimeric antigen receptor (CAR) γδ T cells: A potential game changer for adoptive T cell cancer immunotherapy

Excitement is growing for therapies that harness the power of patients' immune systems to combat their diseases. One approach to immunotherapy involves engineering patients' own T cells to express a chimeric antigen receptor (CAR) to treat advanced cancers, particularly those refractory to conventional therapeutic agents. Although these engineered immune cells have made remarkable strides in the treatment of patients with certain hematologic malignancies, success with solid tumors has been limited, probably due to immunosuppressive mechanisms in the tumor niche. In nearly all studies to date, T cells bearing αβ receptors have been used to generate CAR T cells. In this review, we highlight biological characteristics of γδ T cells that are distinct from those of αβ T cells, including homing to epithelial and mucosal tissues and unique functions such as direct antigen recognition, lack of alloreactivity, and ability to present antigens. We offer our perspective that these features make γδ T cells promising for use in cellular therapy against several types of solid tumors, including melanoma and gastrointestinal cancers. Engineered γδ T cells should be considered as a new platform for adoptive T cell cancer therapy for mucosal tumors.

Deletion of mTORC1 Activity in CD4+ T Cells Is Associated with Lung Fibrosis and Increased γδ T Cells

Pulmonary fibrosis is a devastating, incurable disease in which chronic inflammation and dysregulated, excessive wound healing lead to progressive fibrosis, lung dysfunction, and ultimately death. Prior studies have implicated the cytokine IL-17A and Th17 cells in promoting the development of fibrosis. We hypothesized that loss of Th17 cells via CD4-specific deletion of mTORC1 activity would abrogate the development of bleomycin-induced pulmonary fibrosis. However, in actuality loss of Th17 cells led to increased mortality and fibrosis in response to bleomycin. We found that in the absence of Th17 cells, there was continued production of IL-17A by γδ T cells. These IL-17A+ γδ T cells were associated with increased lung neutrophils and M2 macrophages, accelerated development of fibrosis, and increased mortality. These data elucidate the critical role of IL-17A+ γδ T cells in promoting chronic inflammation and fibrosis, and reveal a novel therapeutic target for treatment of pulmonary fibrosis.

The regulatory role of interferon-γ producing gamma delta T cells via the suppression of T helper 17 cell activity in bleomycin-induced pulmonary fibrosis

Interstitial pneumonia (IP) is a chronic progressive interstitial lung disease associated with poor prognosis and high mortality. However, the pathogenesis of IP remains to be elucidated. The aim of this study was to clarify the role of pulmonary γδT cells in IP. In wild-type (WT) mice exposed to bleomycin, pulmonary γδT cells were expanded and produced large amounts of interferon (IFN)-γ and interleukin (IL)-17A. Histological and biochemical analyses showed that bleomycin-induced IP was more severe in T cell receptor (TCR-δ-deficient (TCRδ(-/-) ) mice than WT mice. In TCRδ(-/-) mice, pulmonary IL-17A(+) CD4(+) Τ cells expanded at days 7 and 14 after bleomycin exposure. In TCRδ(-/-) mice infused with γδT cells from WT mice, the number of pulmonary IL-17A(+) CD4(+) T cells was lower than in TCRδ(-/-) mice. The examination of IL-17A(-/-) TCRδ(-/-) mice indicated that γδT cells suppressed pulmonary fibrosis through the suppression of IL-17A(+) CD4(+) T cells. The differentiation of T helper (Th)17 cells was determined in vitro, and CD4(+) cells isolated from TCRδ(-/-) mice showed normal differentiation of Th17 cells compared with WT mice. Th17 cell differentiation was suppressed in the presence of IFN-γ producing γδT cells in vitro. Pulmonary fibrosis was attenuated by IFN-γ-producing γδT cells through the suppression of pulmonary IL-17A(+) CD4(+) T cells. These results suggested that pulmonary γδT cells seem to play a regulatory role in the development of bleomycin-induced IP mouse model via the suppression of IL-17A production.

Genetic and epigenetic regulation of intestinal fibrosis

Crohn's disease affects those individuals with polygenic risk factors. The identified risk loci indicate that the genetic architecture of Crohn's disease involves both innate and adaptive immunity and the response to the intestinal environment including the microbiome. Genetic risk alone, however, predicts only 25% of disease, indicating that other factors, including the intestinal environment, can shape the epigenome and also confer heritable risk to patients. Patients with Crohn's disease can have purely inflammatory disease, penetrating disease or fibrostenosis. Analysis of the genetic risk combined with epigenetic marks of Crohn's disease and other disease associated with organ fibrosis reveals common events are affecting the genes and pathways key to development of fibrosis. This review will focus on what is known about the mechanisms by which genetic and epigenetic risk factors determine development of fibrosis in Crohn's disease and contrast that with other fibrotic conditions.

The Role of γδ T Cells in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease that is characterized by the overproduction of autoantibodies against an array of nuclear and cytoplasmic antigens and affects multiple organs, such as the skin, joints, kidneys, and neuronal tissues. T cells have been recognized as important players in the development of SLE due to their functions in cytokine secretion, antigen presentation, and supporting B cells for antibody production. γδ T cells are a minor population of T cells that play important roles in infection and tumor-associated disease. In recent years, the role of γδ T cells in autoimmune diseases has been investigated. In this review, we discussed the role of γδ T cells in the pathogenesis of SLE.

PPARγ activation following apoptotic cell instillation promotes resolution of lung inflammation and fibrosis via regulation of efferocytosis and proresolving cytokines

Changes in macrophage phenotype have been implicated in apoptotic cell-mediated immune modulation via induction of peroxisome proliferator-activated receptor-γ (PPARγ). In this study, we characterized PPARγ induction by apoptotic cell instillation over the course of bleomycin-induced lung injury in C57BL/6 mice. Next, the role of PPARγ activation in resolving lung inflammation and fibrosis was investigated. Our data demonstrate that apoptotic cell instillation after bleomycin results in immediate and prolonged enhancement of PPARγ mRNA and protein in alveolar macrophages and lung. Moreover, PPARγ activity and expression of its target molecules, including CD36, macrophage mannose receptor, and arginase 1, were persistently enhanced following apoptotic cell instillation. Coadministration of the PPARγ antagonist, GW9662, reversed the enhanced efferocytosis, and the reduced proinflammatory cytokine expression, neutrophil recruitment, myeloperoxidase activity, hydroxyproline contents, and fibrosis markers, including type 1 collagen α2, fibronectin and α-smooth muscle actin (α-SMA), in the lung by apoptotic cell instillation. In addition, inhibition of PPARγ activity reversed the expression of transforming growth factor-β (TGF-β), interleukin (IL)-10, and hepatocyte growth factor (HGF). These findings indicate that one-time apoptotic cell instillation contributes to anti-inflammatory and antifibrotic responses via upregulation of PPARγ expression and subsequent activation, leading to regulation of efferocytosis and production of proresolving cytokines.

Hydrogen Sulfide as a Potential Therapeutic Target in Fibrosis

Hydrogen sulfide (H2S), produced endogenously by the activation of two major H2S-generating enzymes (cystathionine β-synthase and cystathionine γ-lyase), plays important regulatory roles in different physiologic and pathologic conditions. The abnormal metabolism of H2S is associated with fibrosis pathogenesis, causing damage in structure and function of different organs. A number of in vivo and in vitro studies have shown that both endogenous H2S level and the expressions of H2S-generating enzymes in plasma and tissues are significantly downregulated during fibrosis. Supplement with exogenous H2S mitigates the severity of fibrosis in various experimental animal models. The protective role of H2S in the development of fibrosis is primarily attributed to its antioxidation, antiapoptosis, anti-inflammation, proangiogenesis, and inhibition of fibroblasts activities. Future studies might focus on the potential to intervene fibrosis by targeting the pathway of endogenous H2S-producing enzymes and H2S itself.

All hands on DE(T)C: Epithelial-resident γδ T cells respond to tissue injury

Immunology has traditionally focused on the lymphocytes circulating among primary lymphoid organs while the large reservoir of tissue-resident T cells have received relatively less attention. In epithelia, these populations are comprised of significant, and sometimes exclusive, subsets of γδ T cells that are highly specialized in promoting tissue homeostasis. As the epithelial layers of the skin and gut are permanently exposed to the environment, they are continually subject to injury and therefore require highly efficient repair processes to maintain barrier functions. Here, we review the role of γδ T cells in promoting wound healing, a critical and complex process occurring in the skin and other barrier sites.

γδ T Cell-Mediated Immune Responses in Disease and Therapy

The role of γδ T cells in immunotherapy has gained specific importance in the recent years because of their prominent function involving directly or indirectly in the rehabilitation of the diseases. γδ T cells represent a minor population of T cells that express a distinct T cell receptor (TCR) composed of γδ chains instead of αβ chains. Unlike αβ T cells, γδ T cells display a restricted TCR repertoire and recognize mostly unknown non-peptide antigens. γδ T cells act as a link between innate and adaptive immunity, because they lack precise major histocompatibility complex (MHC) restriction and seize the ability to recognize ligands that are generated during affliction. Skin epidermal γδ T cells recognize antigen expressed by damaged or stressed keratinocytes and play an indispensable role in tissue homeostasis and repair through secretion of distinct growth factors. γδ T cell based immunotherapy strategies possess great prominence in the treatment because of the property of their MHC-independent cytotoxicity, copious amount of cytokine release, and a immediate response in infections. Understanding the role of γδ T cells in pathogenic infections, wound healing, autoimmune diseases, and cancer might provide knowledge for the successful treatment of these diseases using γδ T cell based immunotherapy. Enhancing the human Vγ9Vδ2 T cells functions by administration of aminobisphosphonates like zoledronate, pamidronate, and bromohydrin pyrophosphate along with cytokines and monoclonal antibodies shows a hopeful approach for treatment of tumors and infections. The current review summarizes the role of γδ T cells in various human diseases and immunotherapeutic approaches using γδ T cells.

γδ T cells are required for pulmonary IL-17A expression after ozone exposure in mice: role of TNFα

Ozone is an air pollutant that causes pulmonary symptoms. In mice, ozone exposure causes pulmonary injury and increases bronchoalveolar lavage macrophages and neutrophils. We have shown that IL-17A is important in the recruitment of neutrophils after subacute ozone exposure (0.3 ppm for 24–72 h). We hypothesized that γδ T cells are the main producers of IL-17A after subacute ozone. To explore this hypothesis we exposed wildtype mice and mice deficient in γδ T cells (TCRδ^−/−) to ozone or room air. Ozone-induced increases in BAL macrophages and neutrophils were attenuated in TCRδ^−/− mice. Ozone increased the number of γδ T cells in the lungs and increased pulmonary Il17a mRNA expression and the number of IL-17A⁺ CD45⁺ cells in the lungs and these effects were abolished in TCRδ^−/− mice. Ozone-induced increases in factors downstream of IL-17A signaling, including G-CSF, IL-6, IP-10 and KC were also decreased in TCRδ^−/− versus wildtype mice. Neutralization of IL-17A during ozone exposure in wildtype mice mimicked the effects of γδ T cell deficiency. TNFR2 deficiency and etanercept, a TNFα antagonist, also reduced ozone-induced increases in Il17a mRNA, IL-17A⁺ CD45⁺ cells and BAL G-CSF as well as BAL neutrophils. TNFR2 deficient mice also had decreased ozone-induced increases in Ccl20, a chemoattractant for IL-17A⁺ γδ T cells. Il17a mRNA and IL-17A⁺ γδ T cells were also lower in obese Cpe^fat versus lean WT mice exposed to subacute ozone, consistent with the reduced neutrophil recruitment observed in the obese mice. Taken together, our data indicate that pulmonary inflammation induced by subacute ozone requires γδ T cells and TNFα-dependent recruitment of IL-17A⁺ γδ T cells to the lung.

Lung inflammation and thymic atrophy after bleomycin are controlled by the prostaglandin D2 receptor DP1

Acute lung injury (ALI) can be accompanied by secondary systemic manifestations. In a model of ALI induced by bleomycin (bleo), we examined the response of D prostanoid receptor 1 (DP1)-deficient mice (DP1(-/-)) to better understand these processes. DP1 deficiency aggravated the toxicity of bleo as indicated by enhanced body weight loss, mortality, and lung inflammation including bronchoalveolar permeability and neutrophilia. Thymic atrophy was also observed after bleo and was strongly exacerbated in DP1(-/-) mice. This resulted from the enhanced depletion of immature T lymphocytes in the thymus of DP1(-/-) mice, a phenomenon usually related to increased glucocorticoid release in blood. Serum corticosterone was more elevated in DP1(-/-) mice after bleo than in wild-type (wt) mice. Thymocytes of DP1(-/-) mice were not more sensitive to dexamethasone in vitro, and systemic delivery of dexamethasone or peritoneal inflammation after LPS induced a similar thymic atrophy in wt and DP1(-/-) mice, indicating that pulmonary DP1 was critical to the control of thymic atrophy after bleo. DP1(-/-) mice showed increased lung and/or blood mediators involved in neutrophil recruitment and/or glucocorticoid production/thymic atrophy (osteopontin, leukemia inhibitory factor, and keratinocyte-derived chemokine) after bleo. Finally, local pulmonary DP1 activation or inhibition in wt mice abrogated or amplified thymic atrophy after bleo, respectively. Altogether, our data reveal that ALI can perturb the systemic T-cell pool by inducing thymic atrophy and that both pathological processes are controlled by the pulmonary DP1 receptor. This new pathway represents a potential therapeutic target in ALI.

Egr3 induces a Th17 response by promoting the development of γδ T cells

The transcription factor Early Growth Response 3 (Egr3) has been shown to play an important role in negatively regulating T cell activation and promoting T cell anergy in Th1 cells. However, its role in regulating other T helper subsets has yet to be described. We sought to determine the role of Egr3 in a Th17 response using transgenic mice that overexpress Egr3 in T cells (Egr3 TG). Splenocytes from Egr3 TG mice demonstrated more robust generation of Th17 cells even under non-Th17 skewing conditions. We found that while Egr3 TG T cells were not intrinsically more likely to become Th17 cells, the environment encountered by these cells was more conducive to Th17 development. Further analysis revealed a considerable increase in the number of γδ T cells in both the peripheral lymphoid organs and mucosal tissues of Egr3 TG mice, a cell type which normally accounts for only a small fraction of peripheral lymphocytes. Consistent with this marked increase in peripheral γδ T cells, thymocytes from Egr3 TG mice also appear biased toward γδ T cell development. Coculture of these Egr3-induced γδ T cells with wildtype CD4+ T cells increases Th17 differentiation, and Egr3 TG mice are more susceptible to bleomycin-induced lung inflammation. Overall our findings strengthen the role for Egr3 in promoting γδ T cell development and show that Egr3-induced γδ T cells are both functional and capable of altering the adaptive immune response in a Th17-biased manner. Our data also demonstrates that the role played by Egr3 in T cell activation and differentiation is more complex than previously thought.

Phenotypic and functional plasticity of gamma-delta (γδ) T cells in inflammation and tolerance

Gamma-delta T cells (γδ T cells) are an unique group of lymphocytes and play an important role in bridging the gap between innate and adaptive immune systems under homeostatic condition as well as during infection and inflammation. They are predominantly localized into the mucosal and epithelial sites, but also exist in other peripheral tissues and secondary lymphoid organs. γδ T cells can produce cytokines and chemokines to regulate the migration of other immune cells, can bring about lysis of infected or stressed cells by secreting granzymes, provide help to B cells and induce IgE production, can present antigen to conventional T cells, activate antigen presenting cells (APC) maturation, and are also known to produce growth factors that regulate the stromal cell function. γδ T cells spontaneously produce IFN-γ and IL-17 cytokines compared to delayed differentiation of Th1 and Th17 cells. In this review, we discussed the current knowledge about the mechanism of γδ T cell function including its mode of antigen recognition, and differentiation into various subsets of γδ T cells. We also explored how γδ T cells interact with different types of innate and adaptive immune cells, and how these interactions shape the immune response highlighting the plasticity and role of these cells-protective or pathogenic under inflammatory and tolerogenic conditions.

Hydrogen sulfide protects against bleomycin-induced pulmonary fibrosis in rats by inhibiting NF-κB expression and regulating Th1/Th2 balance

Hydrogen sulfide (H2S) displays vasodilative, anti-oxidative, anti-inflammatory and cytoprotective activities. The objective of this study was to evaluate the inhibitory effect of H2S on bleomycin (BLM)-induced pulmonary fibrosis in rats and its possible mechanisms. Fifty-four pathogen-free Male Wistar rats were randomly divided into three groups: control, BLM and H2S treated groups with 18 rats in each group. Each group was then divided into three subgroups based on time of study (7, 14 and 28 day). Pulmonary fibrosis model was established by a single intratracheal instillation of BLM A5 (5 mg/kg). While control rats received saline, rats of the treated group simultaneously were administered intraperitoneal injections of NaHS (the H2S donor, 28 μmol/kg) once daily. BLM induced pulmonary inflammation and fibrosis, increased lung hydroxyproline levels, lung index, total cell counts, neutrophils and eosinophils counts and expression of NF-κB p65 in lung tissue, decreased lymphocytes and macrophages counts. In addition, Th1 response is suppressed as shown by diminished IFN-γ in bronchoalveolar lavage fluid (BALF) after BLM exposure, and enhancement of Th2 response is marked by increased IL-4 in BALF. H2S administration significantly attenuated these effects. The findings reveal the therapeutic potential of H2S for BLM-induced pulmonary fibrosis in male rats, which were at least partly due to inhibition NF-κB p65 expression and regulation of Th1/Th2 balance.

Altered Th1/Th2 commitment contributes to lung senescence in CXCR3-deficient mice

Aging is an inevitable process associated with immune imbalance, which is characterized by a progressive functional decline in major organs, including lung. However, effects of altered Th1/Th2 commitment on lung senescence are largely unknown. To examine effects of altered Th1/Th2 balance on lung aging, we measured proportions of Th1 and Th2 cells and expression of cytokines, chemokines, collagen deposition and other relevant physiological and pathological parameters in 2- and 20-months-old (mo) CXCR3-deficient (CXCR3(-/-)) C57BL/6J mice compared with wild-type (WT) mice. There was a significant weight-loss observed in 20-mo CXCR3(-/-) mice compared with the same aged WT group. Although lung function and structure changed with age in both groups, central airway resistance (Rn), tissue elastance (H) and damping (G) were significantly lower in 20-mo CXCR3(-/-) mice than those of WT mice. In contrast, the whole lung volume (V(L)), the mean linear intercept length of alveolar (L(m)), and the total lung collagen content were significantly elevated in 20-mo CXCR3(-/-) mice. With aging, the lungs of WT mice had typical Th1-type status (increased population of Th1 cells and concentrations of cytokine IFN-γ and CXCR3 ligands) while CXCR3(-/-) mice showed Th2-type polarization (decreased proportion of Th1 cells and concentrations of CXCR3 ligands but increased level of IL-4). Our data suggest that Immunosenescence is associated with lung aging, and that altered Th1/Th2 imbalance favors Th2 predominance in CXCR3(-/-) mice, which contributes to the process of accelerated lung aging in this model.

IL-22 is essential for lung epithelial repair following influenza infection

Influenza infection is widespread in the United States and the world. Despite low mortality rates due to infection, morbidity is common and little is known about the molecular events involved in recovery. Influenza infection results in persistent distal lung remodeling, and the mechanism(s) involved are poorly understood. Recently IL-22 has been found to mediate epithelial repair. We propose that IL-22 is critical for recovery of normal lung function and architecture after influenza infection. Wild-type and IL-22(-/-) mice were infected with influenza A PR8/34 H1N1 and were followed up for up to 21 days post infection. IL-22 receptor was localized to the airway epithelium in naive mice but was expressed at the sites of parenchymal lung remodeling induced by influenza infection. IL-22(-/-) mice displayed exacerbated lung injury compared with wild-type mice, which correlated with decreased lung function 21 days post infection. Epithelial metaplasia was observed in wild-type mice but was not evident in IL-22(-/-) animals that were characterized with an increased fibrotic phenotype. Gene expression analysis revealed aberrant expression of epithelial genes involved in repair processes, among changes in several other biological processes. These data indicate that IL-22 is required for normal lung repair after influenza infection. IL-22 represents a novel pathway involved in interstitial lung disease.

Profibrotic activities for matrix metalloproteinase-8 during bleomycin-mediated lung injury

Matrix metalloproteinase-8 (MMP-8) is a potent interstitial collagenase thought to be expressed mainly by polymorphonuclear neutrophils. To determine whether MMP-8 regulates lung inflammatory or fibrotic responses to bleomycin, we delivered bleomycin by the intratracheal route to wild-type (WT) versus Mmp-8(-/-) mice and quantified MMP-8 expression, and inflammation and fibrosis in the lung samples. Mmp-8 steady state mRNA and protein levels increase in whole lung and bronchoalveolar lavage samples when WT mice are treated with bleomycin. Activated murine lung fibroblasts express Mmp-8 in vitro. MMP-8 expression is increased in leukocytes in the lungs of patients with idiopathic pulmonary fibrosis compared with control lung samples. Compared with bleomycin-treated WT mice, bleomycin-treated Mmp-8(-/-) mice have greater lung inflammation, but reduced lung fibrosis. Whereas bleomycin-treated Mmp-8(-/-) and WT mice have similar lung levels of several pro- and antifibrotic mediators (TGF-β, IL-13, JE, and IFN-γ), Mmp-8(-/-) mice have higher lung levels of IFN-γ-inducible protein-10 (IP-10) and MIP-1α. Genetically deleting either Ip-10 or Mip-1α in Mmp-8(-/-) mice abrogates their lung inflammatory response to bleomycin, but reconstitutes their lung fibrotic response to bleomycin. Studies of bleomycin-treated Mmp-8 bone marrow chimeric mice show that both leukocytes and lung parenchymal cells are sources of profibrotic MMP-8 during bleomycin-mediated lung fibrosis. Thus, during bleomycin-mediated lung injury, MMP-8 dampens the lung acute inflammatory response, but promotes lung fibrosis by reducing lung levels of IP-10 and MIP-1α. These data indicate therapeutic strategies to reduce lung levels of MMP-8 may limit fibroproliferative responses to injury in the human lung.