A TNFRSF14-FcɛRI-mast cell pathway contributes to development of multiple features of asthma pathology in mice

Endoplasmic reticulum stress drives macrophages to produce IL-33 to favor Th2 polarization in the airways

Interleukin (IL)-33 is a key driver of T helper 2 (Th2) cell polarization. Endoplasmic reticulum (ER) stress plays a role in the skewed T cell activation. The objective of this project is to elucidate the role of IL-33 derived from macrophages in inducing Th2 polarization in the airways. In this study, bronchoalveolar lavage fluids (BALF) were collected from patients with asthma and healthy control subjects. Macrophages were isolated from the BALF by flow cytometry cell sorting. An asthmatic mouse model was established using the ovalbumin/alum protocol. The results showed that increased IL33 gene activity and ER stress-related molecules in BALF-derived M2a macrophages was observed in asthmatic patients. Levels of IL33 gene activity in M2a cells were positively correlated with levels of asthma response in asthma patients. Sensitization exacerbated the ER stress in the airway macrophages, which increased the expression of IL-33 in macrophages of airway in sensitized mice. Conditional ablation of Il33 or Perk or Atf4 genes in macrophages prevented induction of airway allergy in mice. In conclusion, asthma airway macrophages express high levels of IL-33 and at high ER stress status. Inhibition of IL-33 or ER stress in macrophages can effectively alleviate experimental asthma.

TMEM59 ablation leads to loss of olfactory sensory neurons and impairs olfactory functions via interaction with inflammation

The olfactory epithelium undergoes constant neurogenesis throughout life in mammals. Several factors including key signaling pathways and inflammatory microenvironment regulate the maintenance and regeneration of the olfactory epithelium. In this study, we identify TMEM59 (also known as DCF1) as a critical regulator to the epithelial maintenance and regeneration. Single-cell RNA-Seq data show downregulation of TMEM59 in multiple epithelial cell lineages with aging. Ablation of TMEM59 leads to apparent alteration at the transcriptional level, including genes associated with olfactory transduction and inflammatory/immune response. These differentially expressed genes are key components belonging to several signaling pathways, such as NF-κB, chemokine, etc. TMEM59 deletion impairs olfactory functions, attenuates proliferation, causes loss of both mature and immature olfactory sensory neurons, and promotes infiltration of inflammatory cells, macrophages, microglia cells and neutrophils into the olfactory epithelium and lamina propria. TMEM59 deletion deteriorates regeneration of the olfactory epithelium after injury, with significant reduction in the number of proliferative cells, immature and mature sensory neurons, accompanied by the increasing number of inflammatory cells and macrophages. Anti-inflammation by dexamethasone recovers neuronal generation and olfactory functions in the TMEM59-KO animals, suggesting the correlation between TMEM59 and inflammation in regulating the epithelial maintenance. Collectively, TMEM59 regulates olfactory functions, as well as neuronal generation in the olfactory epithelium via interaction with inflammation, suggesting a potential role in therapy against olfactory dysfunction associated with inflamm-aging.

A Deficiency in the Cytokine TNFSF14/LIGHT Limits Inflammation and Remodeling in Murine Eosinophilic Esophagitis

Eosinophilic esophagitis (EoE) is a chronic type 2 allergic disease, with esophageal tissue remodeling as the mechanism behind clinical dysphagia and strictures. IL-13 is thought to be a central driver of disease, but other inflammatory factors, such as IFNs and TNF superfamily members, have been hypothesized to play a role in disease pathogenesis. We recently found that the cytokine TNFSF14/LIGHT is upregulated in the esophagus of patients with EoE and that LIGHT promotes inflammatory activity in esophageal fibroblasts. However, the global effects of LIGHT on EoE pathogenesis in vivo remain unknown. We investigated the impact of a LIGHT deficiency in a murine model of EoE driven by house dust mite allergen. Chronic intranasal challenge with house dust mite promoted esophageal eosinophilia and increased CD4+ T cell numbers and IL-13 and CCL11 production in wild-type mice. Esophageal remodeling was reflected by submucosal collagen accumulation, increased muscle density, and greater numbers of fibroblasts. LIGHT-/- mice displayed normal esophageal eosinophilia, but exhibited reduced frequencies of CD4 T cells, IL-13 expression, submucosal collagen, and muscle density and a decrease in esophageal accumulation of fibroblasts. In vitro, LIGHT increased division of human esophageal fibroblasts and selectively enhanced IL-13-mediated expression of a subset of inflammatory and fibrotic genes. These results show that LIGHT contributes to various features of murine EoE, impacting the accumulation of CD4 T cells, IL-13 production, fibroblast proliferation, and esophagus remodeling. These findings suggest that LIGHT may be, to our knowledge, a novel therapeutic target for the treatment of EoE.

Association between genetic variants and the risk of nivolumab-induced immune-related adverse events

Aim: We sought to identify the variants that could predict the risk of nivolumab-induced immune-related adverse events (irAEs) in patients with cancer. Patients & methods: We enrolled 622 Japanese patients and carried out a genome-wide association study. The associations for 507 single nucleotide polymorphisms (SNPs) showing p < 0.001 were further investigated using an independent cohort. Results: In the combined analysis, possible associations were found for a total of 90 SNPs. Although no SNPs were identified to be significantly associated with nivolumab-induced irAEs, the SNP most strongly associated with nivolumab-induced irAEs was rs469490. Conclusion: This study is an important hypothesis-generating study to guide future studies in larger and/or other ethnic cohorts.

Realigning the LIGHT signaling network to control dysregulated inflammation

Advances in understanding the physiologic functions of the tumor necrosis factor superfamily (TNFSF) of ligands, receptors, and signaling networks are providing deeper insight into pathogenesis of infectious and autoimmune diseases and cancer. LIGHT (TNFSF14) has emerged as an important modulator of critical innate and adaptive immune responses. LIGHT and its signaling receptors, herpesvirus entry mediator (TNFRSF14), and lymphotoxin β receptor, form an immune regulatory network with two co-receptors of herpesvirus entry mediator, checkpoint inhibitor B and T lymphocyte attenuator, and CD160. Deciphering the fundamental features of this network reveals new understanding to guide therapeutic development. Accumulating evidence from infectious diseases points to the dysregulation of the LIGHT network as a disease-driving mechanism in autoimmune and inflammatory reactions in barrier organs, including coronavirus disease 2019 pneumonia and inflammatory bowel diseases. Recent clinical results warrant further investigation of the LIGHT regulatory network and application of target-modifying therapeutics for disease intervention.

LIGHT controls distinct homeostatic and inflammatory gene expression profiles in esophageal fibroblasts via differential HVEM and LTβR-mediated mechanisms

Fibroblasts mediate tissue remodeling in eosinophilic esophagitis (EoE), a chronic allergen-driven inflammatory pathology. Diverse fibroblast subtypes with homeostasis-regulating or inflammatory profiles have been recognized in various tissues, but which mediators induce these alternate differentiation states remain largely unknown. We recently identified that TNFSF14/LIGHT promotes an inflammatory esophageal fibroblast in vitro. Herein we used esophageal biopsies and primary fibroblasts to investigate the role of the LIGHT receptors, herpes virus entry mediator (HVEM) and lymphotoxin-beta receptor (LTβR), and their downstream activated pathways, in EoE. In addition to promoting inflammatory gene expression, LIGHT down-regulated homeostatic factors including WNTs, BMPs and type 3 semaphorins. In vivo, WNT2B⁺ fibroblasts were decreased while ICAM-1⁺ and IL-34⁺ fibroblasts were expanded in EoE, suggesting that a LIGHT-driven gene signature was imprinted in EoE versus normal esophageal fibroblasts. HVEM and LTβR overexpression and deficiency experiments demonstrated that HVEM regulates a limited subset of LIGHT targets, whereas LTβR controls all transcriptional effects. Pharmacologic blockade of the non-canonical NIK/p100/p52-mediated NF-κB pathway potently silenced LIGHT's transcriptional effects, with a lesser role found for p65 canonical NF-κB. Collectively, our results show that LIGHT promotes differentiation of esophageal fibroblasts toward an inflammatory phenotype and represses homeostatic gene expression via a LTβR-NIK-p52 NF-κB dominant pathway.

HES5-mediated repression of LIGHT transcription may contribute to apoptosis in hepatocytes

Non-alcoholic fatty liver disease (NAFLD) is prototypical form of metabolic syndrome and has become a global pandemic. Hepatocytes undergo apoptosis in the pathogenesis of NAFLD. We report that the lymphokine LIGHT/TNFSF14 was upregulated in the murine NAFLD livers and in hepatocytes treated with free fatty acids (palmitate, PA). LIGHT knockdown or neutralization attenuated PA-induced apoptosis of hepatocytes. Similarly, knockdown or blockade of LTβR, the receptor for LIGHT, ameliorated apoptosis in hepatocytes exposed to PA. Ingenuity pathway analysis (IPA) revealed several Notch-related transcription factors as upstream regulators of LIGHT, of which HES5 expression was downregulated paralleling LIGHT induction in the pathogenesis of NAFLD. HES5 knockdown enhanced whereas HES5 over-expression weakened LIGHT induction in hepatocytes. HES5 was found to directly bind to the LIGHT promoter and repress LIGHT transcription. Mechanistically, HES5 interacted with SIRT1 to deacetylate histone H3/H4 on the LIGHT promoter to repress LIGHT transcription. SIRT1 knockdown or inhibition offset the effect of HES5 over-expression on LIGHT transcription and hepatocyte apoptosis. In conclusion, our data unveil a novel mechanism that might contribute to excessive apoptosis in hepatocyte exposed to free fatty acids.

Dissecting Abdominal Aortic Aneurysm Is Aggravated by Genetic Inactivation of LIGHT (TNFSF14)

Abdominal aortic aneurysm (AAA), is a complex disorder characterized by vascular vessel wall remodeling. LIGHT (TNFSF14) is a proinflammatory cytokine associated with vascular disease. In the present study, the impact of genetic inactivation of Light was investigated in dissecting AAA induced by angiotensin II (AngII) in the Apolipoprotein E-deficient (Apoe^−/−) mice. Studies in aortic human (ah) vascular smooth muscle cells (VSMC) to study potential translation to human pathology were also performed. AngII-treated Apoe^−/−Light^−/− mice displayed increased abdominal aorta maximum diameter and AAA severity compared with Apoe^−/− mice. Notably, reduced smooth muscle α-actin+ area and Acta2 and Col1a1 gene expression were observed in AAA from Apoe^−/−Light^−/− mice, suggesting a loss of VSMC contractile phenotype compared with controls. Decreased Opn and augmented Sox9 expression, which are associated with detrimental and non-contractile osteochondrogenic VSMC phenotypes, were also seen in AngII-treated Apoe^−/−Light^−/− mouse AAA. Consistent with a role of LIGHT preserving VSMC contractile characteristics, LIGHT-treatment of ahVSMCs diminished the expression of SOX9 and of the pluripotency marker CKIT. These effects were partly mediated through lymphotoxin β receptor (LTβR) as the silencing of its gene ablated LIGHT effects on ahVSMCs. These studies suggest a protective role of LIGHT through mechanisms that prevent VSMC trans-differentiation in an LTβR-dependent manner.

Mast Cells in Inflammation and Disease: Recent Progress and Ongoing Concerns

Mast cells have existed long before the development of adaptive immunity, although they have been given different names. Thus, in the marine urochordate Styela plicata, they have been designated as test cells. However, based on their morphological characteristics (including prominent cytoplasmic granules) and mediator content (including heparin, histamine, and neutral proteases), test cells are thought to represent members of the lineage known in vertebrates as mast cells. So this lineage presumably had important functions that preceded the development of antibodies, including IgE. Yet mast cells are best known, in humans, as key sources of mediators responsible for acute allergic reactions, notably including anaphylaxis, a severe and potentially fatal IgE-dependent immediate hypersensitivity reaction to apparently harmless antigens, including many found in foods and medicines. In this review, we briefly describe the origins of tissue mast cells and outline evidence that these cells can have beneficial as well as detrimental functions, both innately and as participants in adaptive immune responses. We also discuss aspects of mast cell heterogeneity and comment on how the plasticity of this lineage may provide insight into its roles in health and disease. Finally, we consider some currently open questions that are yet unresolved.

Dual vaccination against IL-4 and IL-13 protects against chronic allergic asthma in mice

Allergic asthma is characterized by elevated levels of IgE antibodies, type 2 cytokines such as interleukin-4 (IL-4) and IL-13, airway hyperresponsiveness (AHR), mucus hypersecretion and eosinophilia. Approved therapeutic monoclonal antibodies targeting IgE or IL-4/IL-13 reduce asthma symptoms but require costly lifelong administrations. Here, we develop conjugate vaccines against mouse IL-4 and IL-13, and demonstrate their prophylactic and therapeutic efficacy in reducing IgE levels, AHR, eosinophilia and mucus production in mouse models of asthma analyzed up to 15 weeks after initial vaccination. More importantly, we also test similar vaccines specific for human IL-4/IL-13 in mice expressing human IL-4/IL-13 and the related receptor, IL-4Rα, to find efficient neutralization of both cytokines and reduced IgE levels for at least 11 weeks post-vaccination. Our results imply that dual IL-4/IL-13 vaccination may represent a cost-effective, long-term therapeutic strategy for the treatment of allergic asthma as demonstrated in mouse models, although additional studies are warranted to assess its safety and feasibility.

Asthma is caused by hyperreactivity to benign antigens, with humoral immunity orchestrated by interleukin-4 (IL-4) and IL-13 being the key etiological factor. Here the authors show, in humanized mouse models, that dual vaccination against IL-4 and IL-13 induces their durable suppression ameliorate experimental asthma, and to hint clinical translation.

Accelerator or Brake: Immune Regulators in Malaria

Malaria is a life-threatening infectious disease, affecting over 250 million individuals worldwide each year, eradicating malaria has been one of the greatest challenges to public health for a century. Growing resistance to anti-parasitic therapies and lack of effective vaccines are major contributing factors in controlling this disease. However, the incomplete understanding of parasite interactions with host anti-malaria immunity hinders vaccine development efforts to date. Recent studies have been unveiling the complexity of immune responses and regulators against Plasmodium infection. Here, we summarize our current understanding of host immune responses against Plasmodium-derived components infection and mainly focus on the various regulatory mechanisms mediated by recent identified immune regulators orchestrating anti-malaria immunity.

Increased Production of LIGHT by T Cells in Eosinophilic Esophagitis Promotes Differentiation of Esophageal Fibroblasts Toward an Inflammatory Phenotype

BACKGROUND & AIMS

Eosinophilic esophagitis (EoE) is an antigen-mediated eosinophilic disease of the esophagus that involves fibroblast activation and progression to fibrostenosis. Cytokines produced by T-helper type 2 cells and transforming growth factor beta 1 (TGFβ1) contribute to the development of EoE, but other cytokines involved in pathogenesis are unknown. We investigate the effects of tumor necrosis factor superfamily member 14 (TNFSF14, also called LIGHT) on fibroblasts in EoE.

METHODS

We analyzed publicly available esophageal CD3+ T-cell single-cell sequencing data for expression of LIGHT. Esophageal tissues were obtained from pediatric patients with EoE or control individuals and analyzed by immunostaining. Human primary esophageal fibroblasts were isolated from esophageal biopsy samples of healthy donors or patients with active EoE. Fibroblasts were cultured; incubated with TGFβ1 and/or LIGHT; and analyzed by RNA sequencing, flow cytometry, immunoblots, immunofluorescence, or reverse transcription polymerase chain reaction. Eosinophils were purified from peripheral blood of healthy donors, incubated with interleukin 5, cocultured with fibroblasts, and analyzed by immunohistochemistry.

RESULTS

LIGHT was up-regulated in the esophageal tissues from patients with EoE, compared with control individuals, and expressed by several T-cell populations, including T-helper type 2 cells. TNF receptor superfamily member 14 (TNFRSF14, also called HVEM) and lymphotoxin beta receptor are receptors for LIGHT that were expressed by fibroblasts from healthy donors or patients with active EoE. Stimulation of esophageal fibroblasts with LIGHT induced inflammatory gene transcription, whereas stimulation with TGFβ1 induced transcription of genes associated with a myofibroblast phenotype. Stimulation of fibroblasts with TGFβ1 increased expression of HVEM; subsequent stimulation with LIGHT resulted in their differentiation into cells that express markers of myofibroblasts and inflammatory chemokines and cytokines. Eosinophils tethered to esophageal fibroblasts after LIGHT stimulation via intercellular adhesion molecule-1.

CONCLUSIONS

T cells in esophageal tissues from patients with EoE express increased levels of LIGHT compared with control individuals, which induces differentiation of fibroblasts into cells with inflammatory characteristics. TGFβ1 increases fibroblast expression of HVEM, a receptor for LIGHT. LIGHT mediates interactions between esophageal fibroblasts and eosinophils via ICAM1. This pathway might be targeted for the treatment of EoE.

Lymph node fibroblastic reticular cells deposit fibrosis-associated collagen following organ transplantation

Although the immune response within draining lymph nodes (DLNs) has been studied for decades, how their stromal compartment contributes to this process remains to be fully explored. Here, we show that donor mast cells were prominent activators of collagen I deposition by fibroblastic reticular cells (FRCs) in DLNs shortly following transplantation. Serial analysis of the DLN indicated that the LN stroma did not return to its baseline microarchitecture following organ rejection and that the DLN contained significant fibrosis following repetitive organ transplants. Using several FRC conditional-knockout mice, we show that induction of senescence in the FRCs of the DLN resulted in massive production of collagen I and a proinflammatory milieu within the DLN. Stimulation of herpes virus entry mediator (HVEM) on FRCs by its ligand LIGHT contributed chiefly to the induction of senescence in FRCs and overproduction of collagen I. Systemic administration of ex vivo-expanded FRCs to mice decreased DLN fibrosis and strengthened the effect of anti-CD40L in prolonging heart allograft survival. These data demonstrate that the transformation of FRCs into proinflammatory myofibroblasts is critically important for the maintenance of a proinflammatory milieu within a fibrotic DLN.

Airborne particulate matter from goat farm increases acute allergic airway responses in mice

Background: Inhalation exposure to biological particulate matter (BioPM) from livestock farms may provoke exacerbations in subjects suffering from allergy and asthma. The aim of this study was to use a murine model of allergic asthma to determine the effect of BioPM derived from goat farm on airway allergic responses.Methods: Fine (<2.5 μm) BioPM was collected from an indoor goat stable. Female BALB/c mice were ovalbumin (OVA) sensitized and challenged with OVA or saline as control. The OVA and saline groups were divided in sub-groups and exposed intranasally to different concentrations (0, 0.9, 3, or 9 μg) of goat farm BioPM. Bronchoalveolar lavage fluid (BALF), blood and lung tissues were collected.Results: In saline-challenged mice, goat farm BioPM induced 1) a dose-dependent increase in neutrophils in BALF and 2) production of macrophage inflammatory protein-3a. In OVA-challenged mice, BioPM induced 1) inflammatory cells in BALF, 2) OVA-specific Immunoglobulin (Ig)G1, 3) airway mucus secretion-specific gene expression. RNAseq analysis of lungs indicates that neutrophil chemotaxis and oxidation-reduction processes were the representative genomic pathways in saline and OVA-challenged mice, respectively.Conclusions: A single exposure to goat farm BioPM enhanced airway inflammation in both saline and OVA-challenged allergic mice, with neutrophilic response as Th17 disorder and eosinophilic response as Th2 disorder indicative of the severity of allergic responses. Identification of the mode of action by which farm PM interacts with airway allergic pathways will be useful to design potential therapeutic approaches.

PDE3 Inhibition Reduces Epithelial Mast Cell Numbers in Allergic Airway Inflammation and Attenuates Degranulation of Basophils and Mast Cells

Epithelial mast cells are generally present in the airways of patients with allergic asthma that are inadequately controlled. Airway mast cells (MCs) are critically involved in allergic airway inflammation and contribute directly to the main symptoms of allergic patients. Phosphodiesterase 3 (PDE3) tailors signaling of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), which are critical intracellular second messenger molecules in various signaling pathways. This paper investigates the pathophysiological role and disease-modifying effects of PDE3 in mouse bone marrow-derived MCs (bmMCs), human LAD2- and HMC1 mast cell lines, human blood basophils, and peripheral blood-derived primary human MCs (HuMCs). In a chronic house dust mite (HDM)-driven allergic airway inflammation mouse model, we observed that PDE3 deficiency or PDE3 inhibition (PDE3i) therapy reduced the numbers of epithelial MCs, when compared to control mice. Mouse bone marrow-derived MCs (bmMCs) and the human HMC1 and LAD2 cell lines predominantly expressed PDE3B and PDE4A. BmMCs from Pde3^−/− mice showed reduced loss of the degranulation marker CD107b compared with wild-type BmMCs, when stimulated in an immunoglobulin E (IgE)-dependent manner. Following both IgE-mediated and substance P-mediated activation, PDE3i-pretreated basophils, LAD2 cells, and HuMCs, showed less degranulation than diluent controls, as measured by surface CD63 expression. MCs lacking PDE3 or treated with the PDE3i enoximone exhibited a lower calcium flux upon stimulation with ionomycine. In conclusion PDE3 plays a critical role in basophil and mast cell degranulation and therefore its inhibition may be a treatment option in allergic disease.

Development of multiple features of antigen-induced asthma pathology in a new strain of mast cell deficient BALB/c-KitW-sh/W-sh mice

Mast cell-deficient mice are widely used to identify and quantify contributions of mast cells to diverse biological responses in vivo, including allergic inflammation. However, despite the fact that scores of genes have been identified as modifiers of allergic inflammation, most mast cell-deficient models have been available only on a single genetic background. We transferred the KitW-sh allele onto the BALB/c background to generate BALB/c mast cell-deficient mice (BALB/c-KitW-sh/W-sh). BALB/c-KitW-sh/W-sh mice have dramatically reduced mast cell numbers (0-2% of wild type) in all tissues examined, as well as subtle hematologic differences from the corresponding wild type mice, including splenomegaly with evidence of increased splenic hematopoiesis. We examined in BALB/c-KitW-sh/W-sh mice models of allergic inflammation that are substantially diminished in C57BL/6-KitW-sh/W-sh mast cell-deficient mice. In a model of acute allergic inflammation, i.e., IgE-dependent passive cutaneous anaphylaxis, both ear swelling and leukocyte infiltration were largely or entirely absent in BALB/c-KitW-sh/W-sh mice. In contrast, in two different models of allergic airway inflammation, airway hyperresponsiveness, lung inflammation, and airway remodeling developed robustly in mast cell-deficient BALB/c-KitW-sh/W-sh mice. These results support the conclusion that the importance of mast cell contributions in various models of allergic inflammation may be at least partially determined by genetic background.

Expression of herpesvirus entry mediator gene as a potential biomarker for disease severity in patients with persistent asthma

Objectives: Herpes virus entry mediator (HVEM) is a costimulatory molecule, and has been proved to play an important role in airway inflammatory and remodeling processes of asthma. We aimed to investigate the expression of HVEM gene in patients with asthma as a means of assessing disease severity.Methods: This study was carried out on 59 subjects, 16 patients with mild persistent asthma, 11 patients with moderate persistent asthma, 13 patients with severe persistent asthma, and 19 age and gender matched healthy controls. The HVEM mRNA expressions of all subjects were determined by real time PCR. Correlations between HVEM mRNA expression and fractional exhaled nitric oxide (FeNO), pulmonary function test values, total blood white cell count and differential, total immunoglobulin E (IgE) level, and Asthma Control Test (ACT) score were analyzed, respectively. The discrimination abilities of HVEM mRNA between different groups were tested using receiver operating characteristics (ROC) curve analyses.Results: This study showed the expressions of HVEM mRNA were significantly higher in the patients with severe and moderate persistent asthma than in patients with mild persistent asthma and healthy subjects (2.97 ± 1.23 vs. 1.17 ± 0.42 vs. 0.62 ± 0.38 vs. 0.46 ± 0.18/NAPDH, p < 0.001), but there was no significant difference between patients with mild persistent asthma and health controls (0.62 ± 0.38 vs. 0.46 ± 0.18/NAPDH, p = 0.557). HVEM mRNA expression at cut off point [1.01/NAPDH, area under the ROC curve (AUC) = 0.99] is sufficient to discriminate severe patients from mild-to-moderate patients, and at cut off point (0.93/NAPDH, AUC = 0.91) for discrimination of moderate-to-severe patients from mild ones, while at cut off point (0.76/NAPDH, AUC = 0.75) for discrimination of asthmatic patients from controls. Furthermore, HVEM mRNA expression was positively correlated with FeNO level (r = 0.524, p = 0.015), and total lymphocyte count (r = 0.426, p = 0.017) in patients with persistent asthma.Conclusions: HVEM gene expressions can be used as a potential biomarker for evaluating the severity of patients with persistent asthma.

A Transcriptomic Insight into the Impact of Colon Cancer Cells on Mast Cells

Mast cells (MCs) are one of the first immune cells recruited to a tumor. It is well recognized that MCs accumulate in colon cancer lesion and their density is associated with the clinical outcomes. However, the molecular mechanism of how colon cancer cells may modify MC function is still unclear. In this study, primary human MCs were generated from CD34⁺ progenitor cells and a 3D coculture model was developed to study the interplay between colon cancer cells and MCs. By comparing the transcriptomic profile of colon cancer-cocultured MCs versus control MCs, we identified a number of deregulated genes, such as MMP-2, VEGF-A, PDGF-A, COX2, NOTCH1 and ISG15, which contribute to the enrichment of cancer-related pathways. Intriguingly, pre-stimulation with a TLR2 agonist prior to colon cancer coculture induced upregulation of multiple interferon-inducible genes as well as MHC molecules in MCs. Our study provides an alternative approach to study the influence of colon cancer on MCs. The transcriptome signature of colon cancer-cocultured MCs may potentially reflect the mechanism of how colon cancer cells educate MCs to become pro-tumorigenic in the initial phase and how a subsequent inflammatory signal—e.g., TLR2 ligands—may modify their responses in the cancer milieu.

Mast cells within cellular networks

Mast cells are highly versatile in terms of their mode of activation by a host of stimuli and their ability to flexibly release a plethora of biologically highly active mediators. Within the immune system, mast cells can best be designated as an active nexus interlinking innate and adaptive immunity. Here we try to draw an arc from initiation of acute inflammatory reactions to microbial pathogens to development of adaptive immunity and allergies. This multifaceted nature of mast cells is made possible by interaction with multiple cell types of immunologic and nonimmunologic origin. Examples for the former include neutrophils, eosinophils, T cells, and professional antigen-presenting cells. These interactions allow mast cells to orchestrate inflammatory innate reactions and complex adaptive immunity, including the pathogenesis of allergies. Important partners of nonimmunologic origin include cells of the sensory neuronal system. The intimate association between mast cells and sensory nerve fibers allows bidirectional communication, leading to neurogenic inflammation. Evidence is accumulating that this mast cell/nerve crosstalk is of pathophysiologic relevance in patients with allergic diseases, such as asthma.

Is it time for a new classification of mast cells? What do we know about mast cell heterogeneity?

Mast cells (MCs) are derived from committed precursors that leave the hematopoietic tissue, migrate in the blood, and colonize peripheral tissues where they terminally differentiate under microenvironment stimuli. They are distributed in almost all vascularized tissues where they act both as immune effectors and housekeeping cells, contributing to tissue homeostasis. Historically, MCs were classified into 2 subtypes, according to tryptic enzymes expression. However, MCs display a striking heterogeneity that reflects a complex interplay between different microenvironmental signals delivered by various tissues, and a differentiation program that decides their identity. Moreover, tissue-specific MCs show a trained memory, which contributes to shape their function in a specific microenvironment. In this review, we summarize the current state of our understanding of MC heterogeneity that reflects their different tissue experiences. We describe the discovery of unique cell molecules that can be used to distinguish specific MC subsets in vivo, and discuss how the improved ability to recognize these subsets provided new insights into the biology of MCs. These recent advances will be helpful for the understanding of the specific role of individual MC subsets in the control of tissue homeostasis, and in the regulation of pathological conditions such as infection, autoimmunity, and cancer.

Human mast cells and basophils-How are they similar how are they different?

Mast cells and basophils are key contributors to allergies and other inflammatory diseases since they are the most prominent source of histamine as well as numerous additional inflammatory mediators which drive inflammatory responses. However, a closer understanding of their precise roles in allergies and other pathological conditions has been marred by the considerable heterogeneity that these cells display, not only between mast cells and basophils themselves but also across different tissue locations and species. While both cell types share the ability to rapidly degranulate and release histamine following high-affinity IgE receptor cross-linking, they differ markedly in their ability to either react to other stimuli, generate inflammatory eicosanoids or release immunomodulating cytokines and chemokines. Furthermore, these cells display considerable pharmacological heterogeneity which has stifled attempts to develop more effective anti-allergic therapies. Mast cell- and basophil-specific transcriptional profiling, at rest and after activation by innate and adaptive stimuli, may help to unravel the degree to which these cells differ and facilitate a clearer understanding of their biological functions and how these could be targeted by new therapies.

HVEM and CD160: Regulators of Immunopathology During Malaria Blood-Stage

CD8⁺ T cells are key players during infection with the malaria parasite Plasmodium berghei ANKA (PbA). While they cannot provide protection against blood-stage parasites, they can cause immunopathology, thus leading to the severe manifestation of cerebral malaria. Hence, the tight control of CD8⁺ T cell function is key in order to prevent fatal outcomes. One major mechanism to control CD8⁺ T cell activation, proliferation and effector function is the integration of co-inhibitory and co-stimulatory signals. In this study, we show that one such pathway, the HVEM-CD160 axis, significantly impacts CD8⁺ T cell regulation and thereby the incidence of cerebral malaria. Here, we show that the co-stimulatory molecule HVEM is indeed required to maintain CD8⁺ T effector populations during infection. Additionally, by generating a CD160^-/- mouse line, we observe that the HVEM ligand CD160 counterbalances stimulatory signals in highly activated and cytotoxic CD8⁺ T effector cells, thereby restricting immunopathology. Importantly, CD160 is also induced on cytotoxic CD8⁺ T cells during acute Plasmodium falciparum malaria in humans. In conclusion, CD160 is specifically expressed on highly activated CD8⁺ T effector cells that are harmful during the blood-stage of malaria.

TH17-Induced Neutrophils Enhance the Pulmonary Allergic Response Following BALB/c Exposure to House Dust Mite Allergen and Fine Particulate Matter From California and China

Asthma is a global and increasingly prevalent disease. According to the World Health Organization, approximately 235 million people suffer from asthma. Studies suggest that fine particulate matter (PM2.5) can induce innate immune responses, promote allergic sensitization, and exacerbate asthmatic symptoms and airway hyper-responsiveness. Recently, severe asthma and allergic sensitization have been associated with T-helper cell type 17 (TH17) activation. Few studies have investigated the links between PM2.5 exposure, allergic sensitization, asthma, and TH17 activation. This study aimed to determine whether (1) low-dose extracts of PM2.5 from California (PMCA) or China (PMCH) enhance allergic sensitization in mice following exposure to house dust mite (HDM) allergen; (2) eosinophilic or neutrophilic inflammatory responses result from PM and HDM exposure; and (3) TH17-associated cytokines are increased in the lung following exposure to PM and/or HDM. Ten-week-old male BALB/c mice (n = 6-10/group) were intranasally instilled with phosphate-buffered saline (PBS), PM+PBS, HDM, or PM+HDM, on days 1, 3, and 5 (sensitization experiments), and PBS or HDM on days 12-14 (challenge experiments). Pulmonary function, bronchoalveolar lavage cell differentials, plasma immunoglobulin (Ig) protein levels, and lung tissue pathology, cyto-/chemo-kine proteins, and gene expression were assessed on day 15. Results indicated low-dose PM2.5 extracts can enhance allergic sensitization and TH17-associated responses. Although PMCA+HDM significantly decreased pulmonary function, and significantly increased neutrophils, Igs, and TH17-related protein and gene levels compared with HDM, there were no significant differences between HDM and PMCH+HDM treatments. This may result from greater copper and oxidized organic content in PMCA versus PMCH.

Hematopoietic cell-derived RELMα regulates hookworm immunity through effects on macrophages

Resistin-like molecule α (RELMα) is a highly secreted protein in type 2 (Th2) cytokine-induced inflammation including helminth infection and allergy. In infection with Nippostrongylus brasiliensis (Nb), RELMα dampens Th2 inflammatory responses. RELMα is expressed by immune cells, and by epithelial cells (EC); however, the functional impact of immune versus EC-derived RELMα is unknown. We generated bone marrow (BM) chimeras that were RELMα deficient (RELMα^{-/ -} ) in BM or non BM cells and infected them with Nb. Non BM RELMα^-/- chimeras had comparable inflammatory responses and parasite burdens to RELMα^+/+ mice. In contrast, both RELMα^-/- and BM RELMα^-/- mice exhibited increased Nb-induced lung and intestinal inflammation, correlated with elevated Th2 cytokines and Nb killing. CD11c⁺ lung macrophages were the dominant BM-derived source of RELMα and can mediate Nb killing. Therefore, we employed a macrophage-worm co-culture system to investigate whether RELMα regulates macrophage-mediated Nb killing. Compared to RELMα^{+ /+} macrophages, RELMα^-/- macrophages exhibited increased binding to Nb and functionally impaired Nb development. Supplementation with recombinant RELMα partially reversed this phenotype. Gene expression analysis revealed that RELMα decreased cell adhesion and Fc receptor signaling pathways, which are associated with macrophage-mediated helminth killing. Collectively, these studies demonstrate that BM-derived RELMα is necessary and sufficient to dampen Nb immune responses, and identify that one mechanism of action of RELMα is through inhibiting macrophage recruitment and interaction with Nb. Our findings suggest that RELMα acts as an immune brake that provides mutually beneficial effects for the host and parasite by limiting tissue damage and delaying parasite expulsion.

The transcriptional program, functional heterogeneity, and clinical targeting of mast cells

Cildir et al. discuss the recent findings in transcriptional regulation of mast cell development and activation and provide insights into the plasticity and clinical targeting of mast cell functions.

Mast cells are unique tissue-resident immune cells that express an array of receptors that can be activated by several extracellular cues, including antigen–immunoglobulin E (IgE) complexes, bacteria, viruses, cytokines, hormones, peptides, and drugs. Mast cells constitute a small population in tissues, but their extraordinary ability to respond rapidly by releasing granule-stored and newly made mediators underpins their importance in health and disease. In this review, we document the biology of mast cells and introduce new concepts and opinions regarding their role in human diseases beyond IgE-mediated allergic responses and antiparasitic functions. We bring to light recent discoveries and developments in mast cell research, including regulation of mast cell functions, differentiation, survival, and novel mouse models. Finally, we highlight the current and future opportunities for therapeutic intervention of mast cell functions in inflammatory diseases.