IL-13-producing BLT1-positive CD8 cells are increased in asthma and are associated with airway obstruction

Type-2 CD8+ T-cell formation relies on interleukin-33 and is linked to asthma exacerbations

CD4+ T helper 2 (Th2) cells and group 2 innate lymphoid cells are considered the main producers of type-2 cytokines that fuel chronic airway inflammation in allergic asthma. However, CD8+ cytotoxic T (Tc) cells - critical for anti-viral defense - can also produce type-2 cytokines (referred to as 'Tc2' cells). The role of Tc cells in asthma and virus-induced disease exacerbations remains poorly understood, including which micro-environmental signals and cell types promote Tc2 cell formation. Here we show increased circulating Tc2 cell abundance in severe asthma patients, reaching peak levels during exacerbations and likely emerging from canonical IFNγ+ Tc cells through plasticity. Tc2 cell abundance is associated with increased disease burden, higher exacerbations rates and steroid insensitivity. Mouse models of asthma recapitulate the human disease by showing extensive type-2 skewing of lung Tc cells, which is controlled by conventional type-1 dendritic cells and IFNγ. Importantly, we demonstrate that the alarmin interleukin-33 (IL-33) critically promotes type-2 cytokine production by lung Tc cells in experimental allergic airway inflammation. Our data identify Tc cells as major producers of type-2 cytokines in severe asthma and during exacerbations that are remarkably sensitive to alterations in their inflammatory tissue micro-environment, with IL-33 emerging as an important regulator of Tc2 formation.

Role for the metalloproteinase ADAM28 in the control of airway inflammation, remodelling and responsiveness in asthma

Background

Asthma is characterized by morphological modifications of the airways (inflammation and remodelling) and bronchial hyperresponsiveness. Mechanisms linking these two key features of asthma are still poorly understood. ADAM28 (a disintegrin and metalloproteinase 28) might play a role in asthma pathophysiology. ADAM28 exists as membrane-bound and soluble forms and is mainly expressed by lymphocytes and epithelial cells.

Methods

ADAM28^-/- mice and ADAM28^+/+ counterparts were sensitized and exposed to ovalbumin (OVA). Airway responsiveness was measured using the flexiVent^® system. After sacrifice, bronchoalveolar lavage (BAL) was performed and lungs were collected for analysis of airway inflammation and remodelling.

Results

The expression of the soluble form of ADAM28 was lower in the lungs of OVA-exposed mice (as compared to PBS-exposed mice) and progressively increased in correlation with the duration of allergen exposure. In lungs of ADAM28^-/- mice exposed to allergens, the proportion of Th2 cells among CD 4 + cells and the number of B cells were decreased. Bronchial responsiveness was lower in ADAM28^-/- mice exposed to allergens and similar to the responsiveness of sham-challenged mice. Similarly, features of airway remodelling (collagen deposition, smooth muscle hyperplasia, mucous hyperplasia) were significantly less developed in OVA-exposed ADAM28^-/- animals in sharp contrasts to ADAM28^+/+. In addition, we report the first evidence of ADAM28 RNA expression by lung fibroblasts and we unveil a decreased capacity of lung fibroblasts extracted from OVA-exposed ADAM28^-/- mice to proliferate as compared to those extracted from OVA-exposed ADAM28^+/+ suggesting a direct contribution of this enzyme to the modulation of airway remodelling.

Conclusion

These results suggest that ADAM28 might be a key contributor to the pathophysiology of asthma.

Large-scale provocation studies identify maladaptive responses to ubiquitous aeroallergens as a correlate of severe allergic rhinoconjunctivitis and asthma

BACKGROUND

Allergic asthma (AA) and allergic rhinoconjunctivitis (ARC) are common comorbid environmentally triggered diseases. We hypothesized that severe AA/ARC reflects a maladaptive or unrestrained response to ubiquitous aeroallergens.

METHODS

We performed provocation studies wherein six separate cohorts of persons (total n = 217) with ARC, with or without AA, were challenged once or more with fixed concentrations of seasonal or perennial aeroallergens in an aeroallergen challenge chamber (ACC).

RESULTS

Aeroallergen challenges elicited fully or partially restrained vs. unrestrained evoked symptom responsiveness, corresponding to the resilient and adaptive vs. maladaptive AA/ARC phenotypes, respectively. The maladaptive phenotype was evoked more commonly during challenge with a non-endemic versus endemic seasonal aeroallergen. In an AA cohort, symptom responses evoked after house dust mite (HDM) challenges vs. recorded in the natural environment were more accurate and precise predictors of asthma severity and control, lung function (FEV1), and mechanistic correlates of maladaptation. Correlates included elevated levels of peripheral blood CD4+ and CD8+ T-cells, eosinophils, and T-cell activation, as well as gene expression proxies for ineffectual epithelial injury/repair responses. Evoked symptom severity after HDM challenge appeared to be more closely related to levels of CD4+ and CD8+ T-cells than eosinophils, neutrophils, or HDM-specific IgE.

CONCLUSIONS

Provocation studies support the concept that resilience, adaptation, and maladaptation to environmental disease triggers calibrate AA/ARC severity. Despite the ubiquity of aeroallergens, in response to these disease triggers in controlled settings (ie, ACC), most atopic persons manifest the resilient or adaptive phenotype. Thus, ARC/AA disease progression may reflect the failure to preserve the resilient or adaptive phenotype. The triangulation of CD8+ T-cell activation, airway epithelial injury/repair processes and maladaptation in mediating AA disease severity needs more investigation.

CD8+ T cell-derived IL-13 increases macrophage IL-10 to resolve neuropathic pain

Understanding the endogenous mechanisms regulating resolution of pain may identify novel targets for treatment of chronic pain. Resolution of chemotherapy-induced peripheral neuropathy (CIPN) after treatment completion depends on CD8⁺ T cells and on IL-10 produced by other cells. Using Rag2^–/– mice lacking T and B cells and adoptive transfer of Il13^–/– CD8⁺ T cells, we showed that CD8⁺ T cells producing IL-13 were required for resolution of CIPN. Intrathecal administration of anti–IL-13 delayed resolution of CIPN and reduced IL-10 production by dorsal root ganglion macrophages. Depleting local CD206⁺ macrophages also delayed resolution of CIPN. In vitro, TIM3⁺CD8⁺ T cells cultured with cisplatin, apoptotic cells, or phosphatidylserine liposomes produced IL-13, which induced IL-10 in macrophages. In vivo, resolution of CIPN was delayed by intrathecal administration of anti-TIM3. Resolution was also delayed in Rag2^–/– mice reconstituted with Havcr2 (TIM3)^–/– CD8⁺ T cells. Our data indicated that cell damage induced by cisplatin activated TIM3 on CD8⁺ T cells, leading to increased IL-13 production, which in turn induced macrophage IL-10 production and resolution of CIPN. Development of exogenous activators of the IL-13/IL-10 pain resolution pathway may provide a way to treat the underlying cause of chronic pain.

Specialized pro-resolving mediators as modulators of immune responses

Specialized pro-resolving mediators (SPMs) are endogenous small molecules produced mainly from dietary omega-3 polyunsaturated fatty acids by both structural cells and cells of the active and innate immune systems. Specialized pro-resolving mediators have been shown to both limit acute inflammation and promote resolution and return to homeostasis following infection or injury. There is growing evidence that chronic immune disorders are characterized by deficiencies in resolution and SPMs have significant potential as novel therapeutics to prevent and treat chronic inflammation and immune system disorders. This review focuses on important breakthroughs in understanding how SPMs are produced by, and act on, cells of the adaptive immune system, specifically macrophages, B cells and T cells. We also highlight recent evidence demonstrating the potential of SPMs as novel therapeutic agents in topics including immunization, autoimmune disease and transplantation.

Repetitive aeroallergen challenges elucidate maladaptive epithelial and inflammatory traits that underpin allergic airway diseases

BACKGROUND

Signifying the 2-compartments/1-disease paradigm, allergic rhinoconjunctivitis (ARC) and asthma (AA) are prevalent, comorbid conditions triggered by environmental factors (eg, house dust mites [HDMs]). However, despite the ubiquity of triggers, progression to severe ARC/AA is infrequent, suggesting either resilience or adaptation.

OBJECTIVE

We sought to determine whether ARC/AA severity relates to maladaptive responses to disease triggers.

METHODS

Adults with HDM-associated ARC were challenged repetitively with HDMs in an aeroallergen challenge chamber. Mechanistic traits associated with disease severity were identified.

RESULTS

HDM challenges evoked maladaptive (persistently higher ARC symptoms), adaptive (progressive symptom reduction), and resilient (resistance to symptom induction) phenotypes. Symptom severity in the natural environment was an imprecise correlate of the phenotypes. Nasal airway traits, defined by low inflammation-effectual epithelial integrity, moderate inflammation-effectual epithelial integrity, and higher inflammation-ineffectual epithelial integrity, were hallmarks of the resilient, adaptive, and maladaptive evoked phenotypes, respectively. Highlighting a crosstalk mechanism, peripheral blood inflammatory tone calibrated these traits: ineffectual epithelial integrity associated with CD8⁺ T cells, whereas airway inflammation associated with both CD8⁺ T cells and eosinophils. Hallmark peripheral blood maladaptive traits were increased natural killer and CD8⁺ T cells, lower CD4⁺ mucosal-associated invariant T cells, and deficiencies along the TLR-IRF-IFN antiviral pathway. Maladaptive traits tracking HDM-associated ARC also contributed to AA risk and severity models.

CONCLUSIONS

Repetitive challenges with HDMs revealed that maladaptation to disease triggers may underpin ARC/AA disease severity. A combinatorial therapeutic approach may involve reversal of loss-of-beneficial-function traits (ineffectual epithelial integrity, TLR-IRF-IFN deficiencies), mitigation of gain-of-adverse-function traits (inflammation), and blocking of a detrimental crosstalk between the peripheral blood and airway compartments.

SLAMF7 and IL-6R define distinct cytotoxic versus helper memory CD8+ T cells

The prevailing ‘division of labor’ concept in cellular immunity is that CD8⁺ T cells primarily utilize cytotoxic functions to kill target cells, while CD4⁺ T cells exert helper/inducer functions. Multiple subsets of CD4⁺ memory T cells have been characterized by distinct chemokine receptor expression. Here, we demonstrate that analogous CD8⁺ memory T-cell subsets exist, characterized by identical chemokine receptor expression signatures and controlled by similar generic programs. Among them, Tc2, Tc17 and Tc22 cells, in contrast to Tc1 and Tc17 + 1 cells, express IL-6R but not SLAMF7, completely lack cytotoxicity and instead display helper functions including CD40L expression. CD8⁺ helper T cells exhibit a unique TCR repertoire, express genes related to skin resident memory T cells (T_RM) and are altered in the inflammatory skin disease psoriasis. Our findings reveal that the conventional view of CD4⁺ and CD8⁺ T cell capabilities and functions in human health and disease needs to be revised.

We classically consider the T cell compartment divided into cytotoxic CD8⁺ T cells and multiple, different helper CD4⁺ T cell subsets. Here the authors demonstrate that distinct memory CD8⁺ T cell subsets phenotypically inhabit CD4⁺ T cell like populations including some with helper-like characteristics.

Leukotriene B4 receptors play critical roles in house dust mites-induced neutrophilic airway inflammation and IL-17 production

Increased levels of neutrophils in bronchoalveolar lavage fluid (BALF) were associated with asthma severity. As leukotriene B4 (LTB₄) is a principal chemoattractant molecule for neutrophils, its receptors, BLT1 and BLT2, may contribute to neutrophil-dominant airway inflammation. In the present study, we established a mouse model of steroid-resistant, neutrophil-dominant airway inflammation by house dust mite (HDM)/lipopolysaccharide (LPS) sensitization and HDM challenge, and we investigated whether BLT1/BLT2 signaling was associated with the development of neutrophilic airway inflammation. Blockade of BLT1 or BLT2 significantly suppressed airway inflammation and IL-17 production in this mouse model. The 5-LO and 12-LO enzymes, which catalyze the synthesis of BLT1/BLT2 ligands, were also critically associated with neutrophil-dominant airway inflammation and the synthesis of IL-17. Collectively, our results suggest that the 5-/12-LO-BLT1/BLT2-linked cascade significantly contributes to neutrophil-dominant severe airway inflammation via IL-17 synthesis in HDM-induced neutrophilic asthma.

Cell-by-cell deciphering of T cells in allergic inflammation

Technical advances in single-cell RNA sequencing (scRNA-seq) render it possible to examine the transcriptomes of single cells in patients with allergic inflammation with high resolution in the context of their specific microenvironment, treatment, and disease status. Using a recently published scRNA-seq study of tissue T cells as an example, we introduce the major pipeline steps, illustrate the options of scRNA-seq platforms, summarize new knowledge gained from this study, and provide directions for future research. The presented scRNA-seq study elucidated the T-cell heterogeneity present in an allergic inflammatory tissue focused on eosinophilic esophagitis, a prototypic, chronic, allergic disease, which provided a unique opportunity to probe the pathogenesis of allergic inflammation at the tissue level through readily available endoscopically procured biopsy specimens. scRNA-seq analysis identified 8 populations of CD3⁺ T cells and defined 2 disease-specific populations of CD3⁺CD4⁺ T cells, including a markedly activated type 2 cytokine-producing pathogenic cell population distinguished by expression of the short-chain fatty acid receptor free fatty acid receptor 3 and a population of regulatory T cells. In addition to presenting and interpreting new findings within the prior literature, we postulate about future single-cell next-generation sequencing platforms in this burgeoning field.

The role of the LTB4-BLT1 axis in health and disease

Leukotriene B4 (LTB4) is a major type of lipid mediator that is rapidly generated from arachidonic acid through sequential action of 5-lipoxygenase (5-LO), 5-lipoxygenase-activating protein (FLAP) and LTA4 hydrolase (LTA4H) in response to various stimuli. LTB4 is well known to be a chemoattractant for leukocytes, particularly neutrophils, via interaction with its high-affinity receptor BLT1. Extensive attention has been paid to the role of the LTB4-BLT1 axis in acute and chronic inflammatory diseases, such as infectious diseases, allergy, autoimmune diseases, and metabolic disease via mediating recruitment and/or activation of different types of inflammatory cells depending on different stages or the nature of inflammatory response. Recent studies also demonstrated that LTB4 acts on non-immune cells via BLT1 to initiate and/or amplify pathological inflammation in various tissues. In addition, emerging evidence reveals a complex role of the LTB4-BLT1 axis in cancer, either tumor-inhibitory or tumor-promoting, depending on the different target cells. In this review, we summarize both established understanding and the most recent progress in our knowledge about the LTB4-BLT1 axis in host defense, inflammatory diseases and cancer.

Leukotriene A4 Hydrolase Activation and Leukotriene B4 Production by Eosinophils in Severe Asthma

Asthma is associated with the overproduction of leukotrienes (LTs), including LTB4. Patients with severe asthma can be highly responsive to 5-lipoxygenase (5-LO) inhibition, which blocks production of both the cysteinyl LTs and LTB4. Production of LTB4 has traditionally been ascribed to neutrophils, mononuclear phagocytes, and epithelial cells, and acts as a chemoattractant for inflammatory cells associated with asthma. The source of LTB4 is unclear, especially in eosinophilic asthma. We speculated that the benefit of 5-LO inhibition could be mediated in part by inhibition of eosinophil-derived LTB4. LTB4 concentrations were assayed in BAL fluid from patients with severe asthma characterized by isolated neutrophilic, eosinophilic, and paucigranulocytic inflammation. Expression of LTA4 hydrolase (LTA4H) by airway eosinophils was determined by immunohistochemistry (IHC). Subsequently, peripheral blood eosinophils were activated and secreted LTB4 was quantified by enzyme immunoassay. Blood eosinophil LTA4H expression was determined by flow cytometry, qPCR, and IHC. LTB4 concentrations were elevated in BAL fluid from patients with severe asthma, including those with isolated eosinophilic inflammation, and these eosinophils displayed LTA4H via IHC. LTA4H expression by blood eosinophils was confirmed by flow cytometry, IHC, and qPCR. Robust LTB4 production by blood eosinophils was observed in response to some, but not all, stimuli. We demonstrated that eosinophils express LTA4H transcripts and protein, and can be stimulated to secrete LTB4. We speculate that in many patients with asthma, eosinophil-derived LTB4 is increased, and this may contribute to the efficacy of 5-LO inhibition.

The Intriguing Role of Interleukin 13 in the Pathophysiology of Asthma

Approximately 5–10% of asthmatic patients worldwide suffer from severe asthma. Experimental and clinical studies have demonstrated that IL-13 is an important cytokine in chronic airways inflammation. IL-13 is involved in Th2 inflammation and has been identified as a possible therapeutic target in the treatment of asthma. Two different human monoclonal antibodies (mAbs) anti-IL-13 (tralokinumab and lebrikizumab) block binding and signaling of IL-13 to its receptors, IL-13Rα1 and IL-13Rα2. Several randomized, double-blind, placebo-controlled multicenter studies have evaluated the safety and efficacy of tralokinumab and lebrikizumab in the treatment of adult patients with severe asthma, but all have failed to meet their primary endpoints. No serious adverse events related to the treatment with these anti-IL-13 mAbs have been reported in these studies. These negative clinical results contrast with positive findings from blocking IL-13 signaling in experimental models of asthma, raising doubts about the transferrable value of some models. Interestingly, dupilumab, a mAb which blocks both IL-4 and IL-13 signaling reduces exacerbation rates and improves lung function in severe asthmatics. These results suggest that IL-4 and IL-13 share some, but not all functional activities in airway inflammation. Tralokinumab might show efficacy in a highly selected cohort of asthmatics characterized by overexpression of IL-13.

CD8+ Tc2 cells: underappreciated contributors to severe asthma

The complexity of asthma is underscored by the number of cell types and mediators implicated in the pathogenesis of this heterogeneous syndrome. Type 2 CD4⁺ T-cells (Th2) and more recently, type 2 innate lymphoid cells dominate current descriptions of asthma pathogenesis. However, another important source of these type 2 cytokines, especially interleukin (IL)-5 and IL-13, are CD8⁺ T-cells, which are increasingly proposed to play an important role in asthma pathogenesis, because they are abundant and are comparatively insensitive to corticosteroids. Many common triggers of asthma exacerbations are mediated via corticosteroid-resistant pathways involving neutrophils and CD8⁺ T-cells. Extensive murine data reveal the plasticity of CD8⁺ T-cells and their capacity to enhance airway inflammation and airway dysfunction. In humans, Tc2 cells are predominant in fatal asthma, while in stable state, severe eosinophilic asthma is associated with greater numbers of Tc2 than Th2 cells in blood, bronchoalveolar lavage fluid and bronchial biopsies. Tc2 cells strongly express CRTH2, the receptor for prostaglandin D2, the cysteinyl leukotriene receptor 1 and the leukotriene B4 receptor. When activated, these elicit Tc2 cell chemotaxis and production of chemokines and type 2 and other cytokines, resulting directly or indirectly in eosinophil recruitment and survival. These factors position CD8⁺ Tc2 cells as important and underappreciated effector cells contributing to asthma pathogenesis. Here, we review recent advances and new insights in understanding the pro-asthmatic functions of CD8⁺ T-cells in eosinophilic asthma, especially corticosteroid-resistant asthma, and the molecular mechanisms underlying their pathologic effector function.

Alongside Th2 and ILC2 cells, CD8⁺ T-cells are a cellular source of type 2 cytokines. We review recent findings and insights into the pathologic effector functions of type 2 CD8⁺ T-cells in eosinophilic asthma, especially steroid-resistant disease.http://bit.ly/2KbVGL2

Novel Biological Therapies in Severe Asthma: Targeting the Right Trait

Asthma is a heterogeneous disease characterized by chronic airway inflammation that results in a wide spectrum of clinical manifestations. Patients with severe asthma represent a substantial share of consumption of healthcare resources and hospitalization. Moreover, these patients are at risk of increased morbidity and mortality. Recently, several phenotypes and endotypes of asthma have been identified. The identification of specific subtypes of asthma is fundamental for optimizing the clinical benefit of novel treatments. Although in most patients the disease can be controlled by some combination of pharmacologic agents, in some 5-10% of patients the disease remains uncontrolled. Several monoclonal antibodies (mAbs) targeting pathogenetic molecules (e.g., IgE, IL-5, IL- 5Rα, IL-4, IL-13, TSLP) are currently available or under development for the treatment of different forms of severe type 2 asthma. The identification of diagnostic and predictive biomarkers (e.g., IgE, blood eosinophil count, FeNO, periostin, etc.) has revolutioned the field of targeted therapy in severe asthma. Monoclonal antibodies targeting Th2-driven inflammation are generally safe in adult patients with moderate-to-severe asthma. The long-term safety of these biologics is a relevant issue that should be addressed. Unfortunately, little is known about non-type 2 asthma. Further studies are needed to identify biomarkers to guide targeted therapies of different forms of non-type 2 asthma.

BAL Cell Gene Expression in Severe Asthma Reveals Mechanisms of Severe Disease and Influences of Medications

Rationale: Gene expression of BAL cells, which samples the cellular milieu within the lower respiratory tract, has not been well studied in severe asthma.Objectives: To identify new biomolecular mechanisms underlying severe asthma by an unbiased, detailed interrogation of global gene expression.Methods: BAL cell expression was profiled in 154 asthma and control subjects. Of these participants, 100 had accompanying airway epithelial cell gene expression. BAL cell expression profiles were related to participant (age, sex, race, and medication) and sample traits (cell proportions), and then severity-related gene expression determined by correlating transcripts and coexpression networks to lung function, emergency department visits or hospitalizations in the last year, medication use, and quality-of-life scores.Measurements and Main Results: Age, sex, race, cell proportions, and medications strongly influenced BAL cell gene expression, but leading severity-related genes could be determined by carefully identifying and accounting for these influences. A BAL cell expression network enriched for cAMP signaling components most differentiated subjects with severe asthma from other subjects. Subsequently, an in vitro cellular model showed this phenomenon was likely caused by a robust upregulation in cAMP-related expression in nonsevere and β-agonist-naive subjects given a β-agonist before cell collection. Interestingly, ELISAs performed on BAL lysates showed protein levels may partly disagree with expression changes.Conclusions: Gene expression in BAL cells is influenced by factors seldomly considered. Notably, β-agonist exposure likely had a strong and immediate impact on cellular gene expression, which may not translate to important disease mechanisms or necessarily match protein levels. Leading severity-related genes were discovered in an unbiased, system-wide analysis, revealing new targets that map to asthma susceptibility loci.

T-cell phenotypes are associated with serum IgE levels in Amish and Hutterite children

OBJECTIVES

Amish children raised on traditional farms have lower atopy and asthma risk than Hutterite children raised on modern farms. In our previous study we established that the Amish environment affects the innate immune response to decrease asthma and atopy risk. Here we investigated T-cell phenotypes in the same Amish and Hutterite children as in our earlier study to elucidate how this altered innate immunity affects adaptive T cells.

METHODS

Blood was collected from 30 Amish and 30 Hutterite age- and sex-matched children; cells were cryopreserved until analysis. Flow cytometry was used to analyze cell subsets. Atopy was determined based on allergen-specific and total IgE levels.

RESULTS

Children exposed to Amish farms had increased activated regulatory CD4⁺ T-cell phenotypes, whereas conventional CD4 T cells expressed lower levels of costimulation molecules and other activation markers. The increase in numbers of circulating activated regulatory CD4⁺ T cells was associated with an increase in inhibitory receptors on monocytes in Amish, but not Hutterite, children. Strikingly, the Amish children had a higher proportion of CD28^null CD8 T cells than the Hutterite children (P < .0001, nonparametric t test), a difference that remained even after accounting for the effects of age and sex (conditional log regression exponential β = 1.08, P = .0053). The proportion of these cells correlated with high T-cell IFN-γ production (r_s = 0.573, P = .005) and low serum IgE levels (r_s = -0.417, P = .025). Furthermore, CD28^null CD8 T-cell numbers were increased in Amish children, with high expression of the innate genes TNF and TNF-α-induced protein 3 (TNFAIP3) in peripheral blood leukocytes.

CONCLUSION

Amish children's blood leukocytes are not only altered in their innate immune status but also have distinct T-cell phenotypes that are often associated with increased antigen exposure.

Hypoxia enhances CD8+ TC2 cell-dependent airway hyperresponsiveness and inflammation through hypoxia-inducible factor 1α

BACKGROUND

CD8+ type 2 cytotoxic T (TC2) cells undergo transcriptional reprogramming to IL-13 production in the presence of IL-4 to become potent, steroid-insensitive, pathogenic effector cells in asthmatic patients and in mice in a model of experimental asthma. However, no studies have described the effects of hypoxia exposure on TC2 cell differentiation.

OBJECTIVE

We determined the effects of hypoxia exposure on IL-13-producing CD8+ TC2 cells.

METHODS

CD8+ transgenic OT-1 cells differentiated with IL-2 and IL-4 (TC2 cells) were exposed to normoxia (21% oxygen) or hypoxia (3% oxygen), and IL-13 production in vitro was monitored. After differentiation under these conditions, cells were adoptively transferred into CD8-deficient mice, and lung allergic responses, including airway hyperresponsiveness to inhaled methacholine, were assessed. The effects of pharmacologic inhibitors of hypoxia-inducible factor (HIF) 1α and HIF-2α were determined, as were responses in HIF-1α-deficient OT-1 cells.

RESULTS

Under hypoxic conditioning, CD8+ TC2 cell differentiation was significantly enhanced, with increased numbers of IL-13+ T cells and increased production of IL-13 in vitro. Adoptive transfer of TC2 cells differentiated under hypoxic conditioning restored lung allergic responses in sensitized and challenged CD8-deficient recipients to a greater degree than seen in recipients of TC2 cells differentiated under normoxic conditioning. Pharmacologic inhibition of HIF-1α or genetic manipulation to reduce HIF-1α expression reduced the hypoxia-enhanced differentiation of TC2 cells, IL-13 production, and the capacity of transferred cells to restore lung allergic responses in vivo. IL-4-dependent, hypoxia-mediated increases in HIF-1α and TC2 cell differentiation were shown to be mediated through activation of Janus kinase 1/3 and GATA-3.

CONCLUSIONS

Hypoxia enhances CD8+ TC2 cell-dependent airway hyperresponsiveness and inflammation through HIF-1α activation. These findings coupled with the known insensitivity of CD8+ T cells to corticosteroids suggests that activation of the IL-4-HIF-1α-IL-13 axis might play a role in the development of steroid-refractory asthma.

Expansion of different subpopulations of CD26-/low T cells in allergic and non-allergic asthmatics

CD26 displays variable levels between effector (TH₁₇ ≫ TH₁ > TH₂ > Treg) and naïve/memory (memory > naïve) CD4⁺ T lymphocytes. Besides, IL-6/IL⁻6R is associated with TH₁₇-differentiation and asthma severity. Allergic/atopic asthma (AA) is dominated by TH₂ responses, while TH₁₇ immunity might either modulate the TH₂-dependent inflammation in AA or be an important mechanism boosting non-allergic asthma (NAA). Therefore, in this work we have compared the expression of CD26 and CD126 (IL-6Rα) in lymphocytes from different groups of donors: allergic (AA) and non-allergic (NAA) asthma, rhinitis, and healthy subjects. For this purpose, flow cytometry, haematological/biochemical, and in vitro proliferation assays were performed. Our results show a strong CD26-CD126 correlation and an over-representation of CD26⁻ subsets with a highly-differentiated effector phenotype in AA (CD4⁺CD26^−/low T cells) and NAA (CD4⁻CD26⁻ γδ-T cells). In addition, we found that circulating levels of CD26 (sCD26) were reduced in both AA and NAA, while loss of CD126 expression on different leukocytes correlated with higher disease severity. Finally, selective inhibition of CD26-mRNA translation led to enhanced T cell proliferation in vitro. These findings support that CD26 down-modulation could play a role in facilitating the expansion of highly-differentiated effector T cell subsets in asthma.

Synergistic activation of pro-inflammatory type-2 CD8+ T lymphocytes by lipid mediators in severe eosinophilic asthma

Human type-2 CD8⁺ T cells are a cell population with potentially important roles in allergic disease. We investigated this in the context of severe asthma with persistent airway eosinophilia-a phenotype associated with high exacerbation risk and responsiveness to type-2 cytokine-targeted therapies. In two independent cohorts we show that, in contrast to Th2 cells, type-2 cytokine-secreting CD8⁺CRTH2⁺ (Tc2) cells are enriched in blood and airways in severe eosinophilic asthma. Concentrations of prostaglandin D₂ (PGD₂) and cysteinyl leukotriene E₄ (LTE₄) are also increased in the airways of the same group of patients. In vitro PGD₂ and LTE₄ function synergistically to trigger Tc2 cell recruitment and activation in a TCR-independent manner. These lipids regulate diverse genes in Tc2 cells inducing type-2 cytokines and many other pro-inflammatory cytokines and chemokines, which could contribute to eosinophilia. These findings are consistent with an important innate-like role for human Tc2 cells in severe eosinophilic asthma and suggest a potential target for therapeutic intervention in this and other diseases.

Importance of the leukotriene B4-BLT1 and LTB4-BLT2 pathways in asthma

For several decades, the leukotriene pathways have been implicated as playing a central role in the pathophysiology of asthma. The presence and elevation of numerous metabolites in the blood, sputum, and bronchoalveolar lavage fluid from asthmatics or experimental animals adds support to this notion. However, targeting of the leukotriene pathways has had, in general, limited success. The single exception in asthma therapy has been targeting of the cysteinyl leukotriene receptor 1, which clinically has proven effective but only in certain clinical situations. Interference with 5-lipoxygenase has had limited success, in part due to adverse drug effects. The importance of the LTB4-BLT1 pathway in asthma pathogenesis has extensive experimental support and findings, albeit limited, from clinical samples. The LTB4-BLT1 pathway was shown to be important as a neutrophil chemoattractant. Despite observations made more than two decades ago, the LTB4-BLT1 pathway has only recently been shown to exhibit important activities on subsets of T lymphocytes, both as a chemoattractant and on lymphocyte activation, as well as on dendritic cells, the major antigen presenting cell in the lung. The role of BLT2 in asthma remains unclear. Targeting of components of the LTB4-BLT1 pathway offers innovative therapeutic opportunities especially in patients with asthma that remain uncontrolled despite intensive corticosteroid treatment.

5-/12-Lipoxygenase-linked cascade contributes to the IL-33-induced synthesis of IL-13 in mast cells, thus promoting asthma development

BACKGROUND

As asthma progresses, the levels of IL-33 in serum are markedly increased and contribute to asthmatic development and exacerbation. Mast cells, one of the principal effector cells in the pathogenesis of asthma, express high levels of the IL-33 receptor ST2 and have been shown to be activated by IL-33. Thus, IL-33 stimulates mast cells to produce Th2-type cytokines such as IL-13, thus contributing to asthmatic development. However, the signaling mechanism for IL-33-induced synthesis of Th2 cytokines, particularly IL-13, has not been fully elucidated in mast cells.

METHODS

The role of 5- or 12-LO in the IL-33-induced synthesis of IL-13 was investigated using knockdown or pharmacological inhibitors in bone marrow-derived mast cells (BMMCs) and animal model.

RESULTS

Blockade of 5- or 12-LO significantly suppressed IL-33-induced synthesis of IL-13 in BMMCs. The subsequent action of 5- and 12-LO metabolites through their specific receptor, BLT2, was also critical for IL-33-induced synthesis of IL-13. We also demonstrated that the MyD88-p38 kinase cascade lies upstream of 5-/12-LO and that NF-κB lies downstream of 5-/12-LO to mediate the IL-33-induced synthesis of IL-13 in mast cells. Consistent with these findings, we observed that in an IL-33-administered asthmatic airway inflammation model, IL-13 levels were markedly increased in bronchoalveolar lavage fluid, but its levels were markedly suppressed by treatment with inhibitors of 5-LO, 12-LO or BLT2, further suggesting roles of 5-/12-LO in IL-33-induced IL-13 production.

CONCLUSION

Our results suggest that "MyD88-5-/12-LO-BLT2-NF-κB" cascade significantly contributes to the IL-33-induced synthesis of IL-13 in mast cells, thus potentially contributing to asthmatic development and exacerbation.

Spectrum of T-lymphocyte activities regulating allergic lung inflammation

Despite advances in the treatment of asthma, optimization of symptom control remains an unmet need in many patients. These patients, labeled severe asthma, are responsible for a substantial fraction of the disease burden. In these patients, research is needed to define the cellular and molecular pathways contributing to disease which in large part are refractory to corticosteroid treatment. The causes of steroid-resistant asthma are multifactorial and result from complex interactions of genetics, environmental factors, and innate and adaptive immunity. Adaptive immunity, addressed here, integrates the activities of distinct T-cell subsets and by definition is dynamic and responsive to an ever-changing environment and the influences of epigenetic modifications. These T-cell subsets exhibit different susceptibilities to the actions of corticosteroids and, in some, corticosteroids enhance their functional activation. Moreover, these subsets are not fixed in lineage differentiation but can undergo transcriptional reprogramming in a bidirectional manner between protective and pathogenic effector states. Together, these factors contribute to asthma heterogeneity between patients but also in the same patient at different stages of their disease. Only by carefully defining mechanistic pathways, delineating their sensitivity to corticosteroids, and determining the balance between regulatory and effector pathways will precision medicine become a reality with selective and effective application of targeted therapies.

IL-15-deficient mice develop enhanced allergic responses to airway allergen exposure

BACKGROUND

Interleukin-15 is a pleiotropic cytokine that is critical for the development and survival of multiple haematopoietic lineages. Mice lacking IL-15 have selective defects in populations of several pro-allergic immune cells including natural killer (NK) cells, NKT cells, and memory CD8⁺ T cells. We therefore hypothesized that IL-15^-/- mice will have reduced inflammatory responses during the development of allergic airway disease (AAD).

OBJECTIVE

To determine whether IL-15^-/- mice have attenuated allergic responses in a mouse model of AAD.

METHODS

C57BL/6 wild-type (WT) and IL-15^-/- mice were sensitized and challenged with ovalbumin (OVA), and the development of AAD was ascertained by examining changes in airway inflammatory responses, Th2 responses, and lung histopathology.

RESULTS

Here, we report that IL-15^-/- mice developed enhanced allergic responses in an OVA-induced model of AAD. In the absence of IL-15, OVA-challenged mice exhibited enhanced bronchial eosinophilic inflammation, elevated IL-13 production, and severe lung histopathology in comparison with WT mice. In addition, increased numbers of CD4⁺ T and B cells in the spleens and bronchoalveolar lavage (BAL) were also observed. Examination of OVA-challenged IL-15Rα^-/- animals revealed a similar phenotype resulting in enhanced airway eosinophilia compared to WT mice. Adoptive transfer of splenic CD8⁺ T cells from OVA-sensitized WT mice suppressed the enhancement of eosinophilia in IL-15^-/- animals to levels observed in WT mice, but had no further effects.

CONCLUSION AND CLINICAL RELEVANCE

These data demonstrate that mice with an endogenous IL-15 deficiency are susceptible to the development of severe, enhanced Th2-mediated AAD, which can be regulated by CD8⁺ T cells. Furthermore, the development of disease as well as allergen-specific Th2 responses occurs despite deficiencies in several IL-15-dependent cell types including NK, NKT, and γδ T cells, suggesting that these cells or their subsets are dispensable for the induction of AAD in IL-15-deficient mice.

Human CD8+ T Cells in Asthma: Possible Pathways and Roles for NK-Like Subtypes

Asthma affects approximately 300 million people worldwide and is the most common chronic lung disease, which usually is associated with bronchial inflammation. Most research has focused upon the role of CD4+ T cells, and relatively few studies have addressed the phenotypic and functional roles of CD8+ T cell types and subtypes. Human NK-like CD8+ T cells may involve cells that have been described as CD8+CD28−, CD8+CD28−CD57+, CD8+CD27−, or CD8+ effector memory (TEM) cells, among other. However, most of the data that are available regarding these various cell types were obtained in murine models did not thoroughly characterize these cells with phenotypically or functionally or did not involve asthma-related settings. Nevertheless, one may conceptualize three principal roles for human NK-like CD8+ T cells in asthma: disease-promoting, regulatory, and/or tissue repair. Although evidence for some of these roles is scarce, it is possible to extrapolate some data from overlapping or related CD8+ T cell phenotypes, with caution. Clearly, further research is warranted, namely in terms of thorough functional and phenotypic characterization of human NK-like CD8+ T cells in human asthma of varying severity.

Pediatric Kawasaki Disease and Adult Human Immunodeficiency Virus Kawasaki-Like Syndrome Are Likely the Same Malady

Background.  Pediatric Kawasaki disease (KD) and human immunodeficiency virus (HIV)⁺ adult Kawasaki-like syndrome (KLS) are dramatic vasculitides with similar physical findings. Both syndromes include unusual arterial histopathology with immunoglobulin (Ig)A⁺ plasma cells, and both impressively respond to pooled Ig therapy. Their distinctive presentations, histopathology, and therapeutic response suggest a common etiology. Because blood is in immediate contact with inflamed arteries, we investigated whether KD and KLS share an inflammatory signature in serum. Methods.  A custom multiplex enzyme-linked immunosorbent assay (ELISA) defined the serum cytokine milieu in 2 adults with KLS during acute and convalescent phases, with asymptomatic HIV⁺ subjects not taking antiretroviral therapy serving as controls. We then prospectively collected serum and plasma samples from children hospitalized with KD, unrelated febrile illnesses, and noninfectious conditions, analyzing them with a custom multiplex ELISA based on the KLS data. Results.  Patients with KLS and KD subjects shared an inflammatory signature including acute-phase reactants reflecting tumor necrosis factor (TNF)-α biologic activity (soluble TNF receptor I/II) and endothelial/smooth muscle chemokines Ccl1 (Th2), Ccl2 (vascular inflammation), and Cxcl11 (plasma cell recruitment). Ccl1 was specifically elevated in KD versus febrile controls, suggesting a unique relationship between Ccl1 and KD/KLS pathogenesis. Conclusions.  This study defines a KD/KLS inflammatory signature mirroring a dysfunctional response likely to a common etiologic agent. The KD/KLS inflammatory signature based on elevated acute-phase reactants and specific endothelial/smooth muscle chemokines was able to identify KD subjects versus febrile controls, and it may serve as a practicable diagnostic test for KD.

Strategies targeting the IL-4/IL-13 axes in disease

IL-4 and IL-13 are pleiotropic Th2 cytokines produced by a wide variety of different cell types and responsible for a broad range of biology and functions. Physiologically, Th2 cytokines are known to mediate host defense against parasites but they can also trigger disease if their activities are dysregulated. In this review we discuss the rationale for targeting the IL-4/IL-13 axes in asthma, atopic dermatitis, allergic rhinitis, COPD, cancer, inflammatory bowel disease, autoimmune disease and fibrotic disease as well as evaluating the associated clinical data derived from blocking IL-4, IL-13 or IL-4 and IL-13 together.

Lung function decline in asthma patients with elevated bronchial CD8, CD4 and CD3 cells

Which inflammatory markers in the bronchial mucosa of asthma patients are associated with decline of lung function during 14 years of prospective follow-up?To address this question, 19 mild-to-moderate, atopic asthmatic patients underwent spirometry and bronchoscopy at baseline and after 14 years of follow-up (t=14). Baseline bronchial biopsies were analysed for reticular layer thickness, eosinophil cationic protein (EG2), mast cell tryptase (AA1), CD3, CD4 and CD8. Follow-up biopsies were stained for EG2, AA1, neutrophil elastase, CD3, CD4, CD8, CD20, granzyme B, CD68, DC-SIGN, Ki67 and mucins.Decline in forced expiratory volume in 1 s (FEV1) % predicted was highest in patients with high CD8 (p=0.01, both pre- and post-bronchodilator) or high CD4 counts at baseline (p=0.04 pre-bronchodilator, p=0.03 post-bronchodilator). Patients with high CD8, CD3 or granzyme B counts at t=14 also exhibited faster decline in FEV1 (p=0.00 CD8 pre-bronchodilator, p=0.04 CD8 post-bronchodilator, p=0.01 granzyme B pre-bronchodilator, and p<0.01 CD3 pre-bronchodilator).Long-term lung function decline in asthma is associated with elevation of bronchial CD8 and CD4 at baseline, and CD8, CD3 and granzyme B at follow-up. This suggests that high-risk groups can be identified on the basis of inflammatory phenotypes.

CD4⁺ and CD8⁺ T cells play a central role in a HDM driven model of allergic asthma

Background

The incidence of asthma is increasing at an alarming rate and while the current available therapies are effective in the majority of patients they fail to adequately control symptoms at the more severe end of the disease spectrum. In the search to understand disease pathogenesis and find effective therapies animal models are often employed. As exposure to house dust mite (HDM) has a causative link, it is thought of as the allergen of choice for modelling asthma.

The objective was to develop a HDM driven model of asthmatic sensitisation and characterise the role of key allergic effector cells/mediators.

Methods

Mice were sensitised with low doses of HDM and then subsequently challenged. Cellular inflammation, IgE and airway responsiveness (AHR) was assessed in wild type mice or CD4⁺/CD8⁺ T cells, B cells or IgE knock out mice.

Results

Only those mice sensitised with HDM responded to subsequent low dose topical challenge. Similar to the classical ovalbumin model, there was no requirement for systemic alum sensitisation. Characterisation of the role of effector cells demonstrated that the allergic cellular inflammation and AHR was dependent on CD4⁺ and CD8⁺ T cells but not B cells or IgE. Finally, we show that this model, unlike the classic OVA model, appears to be resistant to developing tolerance.

Conclusions

This CD4⁺/CD8⁺ T cell dependent, HDM driven model of allergic asthma exhibits key features of asthma. Furthermore, we suggest that the ability to repeat challenge with HDM means this model is amenable to studies exploring the effect of therapeutic dosing in chronic, established disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12931-016-0359-y) contains supplementary material, which is available to authorized users.

IL-21 Promotes Pulmonary Fibrosis through the Induction of Profibrotic CD8+ T Cells

Type 2 effector production of IL-13, a demonstrated requirement in models of fibrosis, is routinely ascribed to CD4(+) Th2 cells. We now demonstrate a major role for CD8(+) T cells in a murine model of sterile lung injury. These pulmonary CD8(+) T cells differentiate into IL-13-producing Tc2 cells and play a major role in a bleomycin-induced model of fibrosis. Differentiation of these Tc2 cells in the lung requires IL-21, and bleomycin treated IL-21- and IL-21R-deficient mice develop inflammation but not fibrosis. Moreover, IL-21R-expressing CD8(+) cells are sufficient to reconstitute the fibrotic response in IL-21R-deficient mice. We further show that the combination of IL-4 and IL-21 skews naive CD8(+) T cells to produce IL-21, which, in turn, acts in an autocrine manner to support robust IL-13 production. Our data reveal a novel pathway involved in the onset and regulation of pulmonary fibrosis and identify Tc2 cells as key mediators of fibrogenesis.

Pattern recognition pathways leading to a Th2 cytokine bias in allergic bronchopulmonary aspergillosis patients

BACKGROUND

Allergic bronchopulmonary aspergillosis (ABPA) is characterised by an exaggerated Th2 response to Aspergillus fumigatus, but the immunological pathways responsible for this effect are unknown.

OBJECTIVE

The aim of this study was to decipher the pattern recognition receptors (PRRs) and cytokines involved in the Aspergillus-specific Th2 response and to study Aspergillus-induced responses in healthy controls and ABPA patients.

METHODS

Peripheral blood mononuclear cells (PBMCs) were stimulated with heat-killed Aspergillus conidia, various other pathogens, or PRR ligands. PRRs and cytokine pathways were blocked with PRR-blocking reagents, anti-TNF (Etanercept or Adalimumab), IL-1Ra (Anakinra) or IFNγ (IFN-gamma). ELISA and FACS were used to analyse cytokine responses.

RESULTS

Aspergillus was the only pathogen that stimulated the Th2 cytokines IL-5 and IL-13, while Gram-negative bacteria, Gram-positive bacteria, Candida albicans, chitin, β-glucan or Toll-like receptor (TLR) ligands did not. Depletion of CD4(+) cells abolished IL-13 production. Blocking complement receptor 3 (CR3) significantly reduced IL-5 and IL-13, while blocking TLR2, TLR4 or dectin-1 had no effect. ABPA patients displayed increased Aspergillus-induced IL-5 and IL-13 and decreased IFNγ production compared with healthy controls. All biological agents tested showed the capability to inhibit Th2 responses, but also decreased Aspergillus-induced IFNγ.

CONCLUSIONS AND CLINICAL RELEVANCE

Aspergillus conidia are unique in triggering Th2 responses in human PBMCs, through a CR3-dependent pathway. ABPA patients display a significantly increased Aspergillus-induced Th2/Th1 ratio that can be modulated by biologicals. These data provide a rationale to explore IFNγ therapy in ABPA as a corticosteroid-sparing treatment option, by dampening Th2 responses and supplementing the IFNγ deficiency at the same time.

Human CD8+ T-cells recognizing peptides from Mycobacterium tuberculosis (Mtb) presented by HLA-E have an unorthodox Th2-like, multifunctional, Mtb inhibitory phenotype and represent a novel human T-cell subset

Mycobacterial antigens are not exclusively presented to T-cells by classical HLA-class Ia and HLA-class II molecules, but also through alternative antigen presentation molecules such as CD1a/b/c, MR1 and HLA-E. We recently described mycobacterial peptides that are presented in HLA-E and recognized by CD8+ T-cells. Using T-cell cloning, phenotyping, microbiological, functional and RNA-expression analyses, we report here that these T-cells can exert cytolytic or suppressive functions, inhibit mycobacterial growth, yet express GATA3, produce Th2 cytokines (IL-4,-5,-10,-13) and activate B-cells via IL-4. In TB patients, Mtb specific cells were detectable by peptide-HLA-E tetramers, and IL-4 and IL-13 were produced following peptide stimulation. These results identify a novel human T-cell subset with an unorthodox, multifunctional Th2 like phenotype and cytolytic or regulatory capacities, which is involved in the human immune response to mycobacteria and demonstrable in active TB patients' blood. The results challenge the current dogma that only Th1 cells are able to inhibit Mtb growth and clearly show that Th2 like cells can strongly inhibit outgrowth of Mtb from human macrophages. These insights significantly expand our understanding of the immune response in infectious disease.

IL-6 receptor α defines effector memory CD8+ T cells producing Th2 cytokines and expanding in asthma

RATIONALE

Cytokine receptors can be markers defining different T-cell subsets and considered as therapeutic targets. The association of IL-6 and IL-6 receptor α (IL-6Rα) with asthma was reported, suggesting their involvement in asthma.

OBJECTIVES

To determine whether and how IL-6Rα defines a distinct effector memory (EM) CD8+ T-cell population in health and disease.

METHODS

EM CD8+ T cells expressing IL-6Rα (IL-6Rα(high)) were identified in human peripheral blood and analyzed for function, gene, and transcription factor expression. The relationship of these cells with asthma was determined using blood and sputum.

MEASUREMENTS AND MAIN RESULTS

A unique population of IL-6Rα(high) EM CD8+ T cells was found in peripheral blood. These cells that potently proliferated, survived, and produced high levels of the Th2-type cytokines IL-5 and IL-13 had increased levels of GATA3 and decreased levels of T-bet and Blimp-1 in comparison with other EM CD8+ T cells. In fact, GATA3 was required for IL-6Rα expression. Patients with asthma had an increased frequency of IL-6Rα(high) EM CD8+ T cells in peripheral blood compared with healthy control subjects. Also, IL-6Rα(high) EM CD8+ T cells exclusively produced IL-5 and IL-13 in response to asthma-associated respiratory syncytial virus and bacterial superantigens.

CONCLUSIONS

Human IL-6Rα(high) EM CD8+ T cells is a unique cell subset that may serve as a reservoir for effector CD8+ T cells, particularly the ones producing Th2-type cytokines, and expand in asthma.

Biomarkers Can Identify Pulmonary Tuberculosis in HIV-infected Drug Users Months Prior to Clinical Diagnosis

BACKGROUND

Current diagnostic tests cannot identify which infected individuals are at risk for progression to tuberculosis (TB). Our aim was to identify biomarkers which can predict the development of TB prior to clinical diagnosis.

METHOD

In a retrospective case-control study, RNA of 14 HIV-infected drug users obtained before TB diagnosis (cases) and of 15 who did not develop TB (controls) was analyzed for the expression of 141 genes by dcRT-MLPA followed by Lasso regression analysis.

FINDINGS

A combined analysis of IL13 and AIRE had the highest discriminatory power to identify cases up to 8 months prior to clinical diagnosis. Cases expressing IL13 had a gene expression pattern strongly enriched for type I IFN related signaling genes, suggesting that these genes represent processes that contribute to TB pathogenesis.

INTERPRETATION

We here demonstrated that biomarkers, such as IL13-AIRE, can identify individuals that progress to TB within a high risk population, months prior to clinical diagnosis.

Pathobiology of severe asthma

Severe asthma (SA) afflicts a heterogeneous group of asthma patients who exhibit poor responses to traditional asthma medications. SA patients likely represent 5-10% of all asthma patients; however, they have a higher economic burden when compared with milder asthmatics. Considerable research has been performed on pathological pathways and structural changes associated with SA. Although limitations of the pathological approaches, ranging from sampling, to quantitative assessments, to heterogeneity of disease, have prevented a more definitive understanding of the underlying pathobiology, studies linking pathology to molecular markers to targeted therapies are beginning to solidify the identification of select molecular phenotypes. This review addresses the pathobiology of SA and discusses the current limitations of studies, the inflammatory cells and pathways linked to emerging phenotypes, and the structural and remodeling changes associated with severe disease. In all cases, an effort is made to link pathological findings to specific clinical/molecular phenotypes.

Risk of childhood asthma is associated with CpG-site polymorphisms, regional DNA methylation and mRNA levels at the GSDMB/ORMDL3 locus

Single-nucleotide polymorphisms (SNPs) in GSDMB (Gasdermin B) and ORMDL3 (ORMDL sphingolipid biosynthesis regulator 3) are strongly associated with childhood asthma, but the molecular alterations contributing to disease remain unknown. We investigated the effects of asthma-associated SNPs on DNA methylation and mRNA levels of GSDMB and ORMDL3. Genetic association between GSDMB/ORMDL3 and physician-diagnosed childhood asthma was confirmed in the Swedish birth-cohort BAMSE. CpG-site SNPs (rs7216389 and rs4065275) showed differences in DNA methylation depending on carrier status of the risk alleles, and were significantly associated with methylation levels in two CpG sites in the 5′ UTR (untranslated region) of ORMDL3. In the Swedish Search study, we found significant differences in DNA methylation between asthmatics and controls in five CpG sites; after adjusting for lymphocyte and neutrophil cell counts, three remained significant: one in IKZF3 [IKAROS family zinc finger 3 (Aiolos); cg16293631] and two in the CpG island (CGI) of ORMDL3 (cg02305874 and cg16638648). Also, cg16293631 and cg02305874 correlated with mRNA levels of ORMDL3. The association between methylation and asthma was independent of the genotype in rs7216389, rs4065275 and rs12603332. Both SNPs and CpG sites showed significant associations with ORMDL3 mRNA levels. SNPs influenced expression independently of methylation, and the residual association between methylation and expression was not mediated by these SNPs. We found a differentially methylated region in the CGI shore of ORMDL3 with six CpG sites less methylated in CD8⁺ T-cells. In summary, this study supports that there are differences in DNA methylation at this locus between asthmatics and controls; and both SNPs and CpG sites are independently associated with ORMDL3 expression.

JNK2 regulates the functional plasticity of naturally occurring T regulatory cells and the enhancement of lung allergic responses

Glucocorticoid-induced TNFR family-related protein (GITR)-mediated activation of JNK was shown to regulate the suppressive activity of CD4(+)CD25(+) naturally occurring T regulatory cells (nTregs) in wild-type (WT) hosts. In this study, CD4(+)CD25(+) T cells were shown to be capable of becoming pathogenic effector cells in sensitized and challenged CD8(-/-) recipient mice. Only GITR-expressing CD4(+)CD25(+) T cells, but neither GITR knocked-in CD4(+)CD25(-) T cells nor GITR-silenced CD4(+)CD25(+) T cells, enhanced development of lung allergic responses. Inhibition of JNK in WT nTregs or nTregs from GITR(-/-)and JNK2(-/-) mice failed to enhance lung allergic responses in sensitized and challenged CD8(-/-) recipient mice. The failure to enhance responses was associated with increased bronchoalveolar lavage fluid levels of IL-10 and TGF-β and decreased levels of IL-5, IL-6, and IL-13. In contrast, nTregs from JNK1(-/-) mice, similar to WT nTregs, were fully effective in enhancing responses. Thus, GITR stimulation of nTregs and signaling through JNK2, but not JNK1, triggered the loss of regulatory function while concomitantly gaining pathogenic CD4(+) T effector cell function responsible for exacerbating asthma-like immunopathology.

A turn on and a turn off: BLT1 and BLT2 mechanisms in the lung

Leukotriene B4 (LTB4), a potent lipid mediator of inflammation derived from arachidonic acid through the action of 5-lipoxygenase, has been implicated in the pathophysiology of several inflammatory diseases, including asthma and chronic obstructive pulmonary disease. A high-affinity LTB4 receptor BLT1 has been shown to exert proinflammatory roles. A cyclooxygenase metabolite, 12(S)-hydroxyheptadeca-5Z, 8E, 10E-trienoic acid (12-HHT), is an endogenous ligand for BLT2, a low-affinity LTB4 receptor. The recent study indicated that BLT2 has a protective role in allergic airway inflammation, suggesting different functions between BLT1 and BLT2 in the pathogenesis of asthma. Selective BLT1 antagonists may have a potential therapeutic application in patients with asthma, and BLT2 may represent a novel therapeutic target for lung diseases.

Leukotriene B4 receptor 1 is differentially expressed on peripheral T cells of steroid-sensitive and -resistant asthmatics

BACKGROUND

Numbers of CD8(+) T cells expressing the leukotriene B4 (LTB4) receptor, BLT1, have been correlated with asthma severity.

OBJECTIVE

To examine the activation and numbers of BLT1-expressing peripheral blood CD4(+) and CD8(+) T cells from patients with steroid-sensitive (SS) and steroid-resistant (SR) asthma.

METHODS

CD4(+) and CD8(+) T cells isolated from peripheral blood of healthy human subjects and patients with SS and SR asthma were stimulated in culture with anti-CD3/anti-CD28 followed by analysis of BLT1 surface expression and cytokine production. Activation of CD8(+) T cells after ligation of BLT1 by LTB4 was monitored by changes in intracellular Ca(2+) concentrations.

RESULTS

The number of BLT1-expressing cells was larger in patients with asthma than in controls and larger on activated CD8(+) than on CD4(+) T cells. Addition of LTB4 to activated CD8(+) T cells resulted in increases in intracellular Ca(2+) concentrations. Expansion of activated CD4(+) T cells, unlike CD8(+) T cells, was significantly decreased in the presence of corticosteroid. In patients with SS asthma, numbers of BLT1-expressing CD8(+) T cells were lower in the presence of corticosteroid, unlike in those with SR asthma in whom cell expansion was maintained. Levels of interleukin-13 were highest in cultured CD8(+) T cells, whereas interleukin-10 levels were higher in CD4(+) T cells from controls and patients with SS asthma. Interferon-γ levels were lowest in patients with SR asthma.

CONCLUSION

Differences in BLT1 expression, steroid sensitivity, and cytokine production were demonstrated in T lymphocytes from patients with SS and SR asthma. The LTB4-BLT1 pathway in CD8(+) cells may play an important role in asthma and serve as an important target in the treatment of patients with SR asthma.

Steroidogenic enzyme Cyp11a1 regulates Type 2 CD8+ T cell skewing in allergic lung disease

Allergic asthma is a heterogeneous inflammatory disorder of the airways characterized by chronic airway inflammation and airway hyperresponsiveness. Numbers of CD8(+)IL-13(+) T cells are increased in asthmatics and during the development of experimental asthma in mice. In an atopic environment rich in IL-4, these CD8(+) T cells mediate asthmatic responses, but the mechanisms regulating the conversion of CD8(+) effector T cells from IFN-γ- to pathogenic IL-13-producing effector cells that contribute to an asthma phenotype have not been defined. Here, we show that cholesterol side-chain cleavage P450 enzyme, Cyp11a1, is a key regulator of CD8(+) T-cell conversion. Expression of the gene, protein, and enzymatic activity of Cyp11a1 were markedly increased in CD8(+) T cells differentiated in the presence of IL-2 plus IL-4 compared with cells differentiated in IL-2 alone. Inhibition of Cyp11a1 enzymatic activity with aminoglutethimide or reduction in the expression of Cyp11a1 using short hairpin RNA prevented the IL-4-induced conversion of IFN-γ- to IL-13-producing cells without affecting expression of the lineage-specific transcription factors T-box expressed in T cells (T-bet) or GATA binding protein 3 (GATA3). Adoptive transfer of aminoglutethimide-treated CD8(+) T cells into sensitized and challenged CD8-deficient recipients failed to restore airway hyperresponsiveness and inflammation. We demonstrate that Cyp11a1 controls the phenotypic conversion of CD8(+) T cells from IFN-γ to IL-13 production, linking steroidogenesis in CD8(+) T cells, a nonclassical steroidogenic tissue, to a proallergic differentiation pathway.