Compartmentalized chemokine-dependent regulatory T-cell inhibition of allergic pulmonary inflammation

Regulatory T cells enhance Th17 migration in psoriatic arthritis which is reversed by anti-TNF

Regulatory T cells (Treg) prevent the migration of effector T cells toward sites of inflammation, thereby limiting disease progression. We investigated this aspect of Treg function using psoriatic arthritis (PsA) as an exemplar of chronic inflammation. Patients with PsA had an increased Th17:Treg ratio which was reversed by anti-tumor necrosis factor (TNF) therapy. Utilizing an in vitro migration assay, Treg from patients with PsA treated with conventional therapy paradoxically boosted CCR6⁺ effector T-cell (a surrogate for Th17) migration toward CCL20. In contrast, Treg from patients with PsA treated with anti-TNF suppressed CCL20-driven effector T-cell migration. The boosting effect of TNF blockade upon Treg suppression of migration was accompanied by increased effector T-cell CCL20 production and enhanced interaction between Treg and effector T cells. This study provides mechanistic insight into Treg modulation of effector T-cell migration in patients with chronic inflammation and how this can be targeted by therapy.

Inflammation in Asthma Pathogenesis: Role of T cells, Macrophages, Epithelial Cells and Type 2 Inflammation

Asthma is a chronic disease with abnormal inflammatory and immunological responses. The disease initiated by antigens in subjects with genetic susceptibility. However, environmental factors play a role in the initiation and exacerbation of asthma attack. Asthma is T helper 2 (Th2)-cell-mediated disease. Recent studies indicated that asthma is not a single disease entity, but it is with multiple phenotypes and endotypes. The pathophysiological changes in asthma included a series of subsequent continuous vicious circle of cellular activation contributed to induction of chemokines and cytokines that potentiate inflammation. The heterogeneity of asthma influenced the treatment response. The asthma pathogenesis driven by varied set of cells such as eosinophils, basophils, neutrophils, mast cells, macrophages, epithelial cells and T cells. In this review the role of T cells, macrophage, and epithelial cells are discussed.

What does elevated TARC/CCL17 expression tell us about eosinophilic disorders?

Eosinophilic disorders encompass a large spectrum of heterogeneous diseases sharing the presence of elevated numbers of eosinophils in blood and/or tissues. Among these disorders, the role of eosinophils can vary widely, ranging from a modest participation in the disease process to the predominant perpetrator of tissue damage. In many cases, eosinophilic expansion is polyclonal, driven by enhanced production of interleukin-5, mainly by type 2 helper cells (Th2 cells) with a possible contribution of type 2 innate lymphoid cells (ILC2s). Among the key steps implicated in the establishment of type 2 immune responses, leukocyte recruitment toward inflamed tissues is particularly relevant. Herein, the contribution of the chemo-attractant molecule thymus and activation-regulated chemokine (TARC/CCL17) to type 2 immunity will be reviewed. The clinical relevance of this chemokine and its target, C-C chemokine receptor 4 (CCR4), will be illustrated in the setting of various eosinophilic disorders. Special emphasis will be put on the potential diagnostic, prognostic, and therapeutic implications related to activation of the TARC/CCL17-CCR4 axis.

Distinct functions of tissue-resident and circulating memory Th2 cells in allergic airway disease

Memory CD4⁺ T helper type 2 (Th2) cells drive allergic asthma, yet the mechanisms whereby tissue-resident memory Th2 (Th2 Trm) cells and circulating memory Th2 cells collaborate in vivo remain unclear. Using a house dust mite (HDM) model of allergic asthma and parabiosis, we demonstrate that Th2 Trm cells and circulating memory Th2 cells perform nonredundant functions. Upon HDM rechallenge, circulating memory Th2 cells trafficked into the lung parenchyma and ignited perivascular inflammation to promote eosinophil and CD4⁺ T cell recruitment. In contrast, Th2 Trm cells proliferated near airways and induced mucus metaplasia, airway hyperresponsiveness, and airway eosinophil activation. Transcriptional analysis revealed that Th2 Trm cells and circulating memory Th2 cells share a core Th2 gene signature but also exhibit distinct transcriptional profiles. Th2 Trm cells express a tissue-adaptation signature, including genes involved in regulating and interacting with extracellular matrix. Our findings demonstrate that Th2 Trm cells and circulating memory Th2 cells are functionally and transcriptionally distinct subsets with unique roles in promoting allergic airway disease.

Shared DNA methylation signatures in childhood allergy: The MeDALL study

BACKGROUND

Differential DNA methylation associated with allergy might provide novel insights into the shared or unique etiology of asthma, rhinitis, and eczema.

OBJECTIVE

We sought to identify DNA methylation profiles associated with childhood allergy.

METHODS

Within the European Mechanisms of the Development of Allergy (MeDALL) consortium, we performed an epigenome-wide association study of whole blood DNA methylation by using a cross-sectional design. Allergy was defined as having symptoms from at least 1 allergic disease (asthma, rhinitis, or eczema) and positive serum-specific IgE to common aeroallergens. The discovery study included 219 case patients and 417 controls at age 4 years and 228 case patients and 593 controls at age 8 years from 3 birth cohorts, with replication analyses in 325 case patients and 1111 controls. We performed additional analyses on 21 replicated sites in 785 case patients and 2124 controls by allergic symptoms only from 8 cohorts, 3 of which were not previously included in analyses.

RESULTS

We identified 80 differentially methylated CpG sites that showed a 1% to 3% methylation difference in the discovery phase, of which 21 (including 5 novel CpG sites) passed genome-wide significance after meta-analysis. All 21 CpG sites were also significantly differentially methylated with allergic symptoms and shared between asthma, rhinitis, and eczema. The 21 CpG sites mapped to relevant genes, including ACOT7, LMAN3, and CLDN23. All 21 CpG sties were differently methylated in asthma in isolated eosinophils, and 10 were replicated in respiratory epithelium.

CONCLUSION

Reduced whole blood DNA methylation at 21 CpG sites was significantly associated with childhood allergy. The findings provide novel insights into the shared molecular mechanisms underlying asthma, rhinitis, and eczema.

The Role of T Cells and Macrophages in Asthma Pathogenesis: A New Perspective on Mutual Crosstalk

Asthma is associated with innate and adaptive immunity mediated by immune cells. T cell or macrophage dysfunction plays a particularly significant role in asthma pathogenesis. Furthermore, crosstalk between them continuously transmits proinflammatory or anti-inflammatory signals, causing the immune cell activation or repression in the immune response. Consequently, the imbalanced immune microenvironment is the major cause of the exacerbation of asthma. Here, we discuss the role of T cells, macrophages, and their interactions in asthma pathogenesis.

Elevated Circulating CD4+CD25+CD127-/low Regulatory T Cells in Patients with Non-asthmatic Eosinophilic Bronchitis

PURPOSE

Non-asthmatic eosinophilic bronchitis (NAEB) is a common cause of chronic cough. It is characterized by sputum eosinophilia like asthma but lacks airway hyperresponsiveness. Regulatory T cells (Tregs) are recognized as immune suppressors and are involved in the pathogenesis of asthma. However, the relationship between Tregs and NAEB remains unknown. This study aimed to preliminarily explore the role of Tregs in NAEB by comparing circulating Tregs levels to asthma and healthy controls.

METHODS

Fractional exhaled nitric oxide (FeNO), spirometry with bronchial provocation test, sputum induction and blood routine test were performed in all subjects. Peripheral blood mononuclear cells were used to detect the Tregs (CD4⁺CD25⁺CD127^-/low) by flow cytometry. Relationship between the levels of circulating Tregs and clinical indexes was also observed.

RESULTS

A total of 15 patients with NAEB, 20 patients with asthma and 11 healthy controls were included. The absolute numbers of circulating Tregs in the NAEB group (49.8 ± 18.9 × 10³ cells/ml) and asthma group (53.3 ± 18.7 × 10³ cells/ml) were higher than that in healthy control group (32.7 ± 11.6 × 10³ cells/ml) (both P < 0.01). In total, the level of circulating Tregs showed positive correlation with FeNO (r = 0.30, P < 0.05).

CONCLUSION

Tregs may play a key role not only in asthmatic patients, but also in patients with NAEB, as reflected by the elevated Tregs in peripheral blood.

Quantitative assessment of airway remodelling and response to allergen in asthma

BACKGROUND AND OBJECTIVE

In vivo evaluation of the microstructural differences between asthmatic and non-asthmatic airways and their functional consequences is relevant to understanding and, potentially, treating asthma. In this study, we use endobronchial optical coherence tomography to investigate how allergic airways with asthma differ from allergic non-asthmatic airways in baseline microstructure and in response to allergen challenge.

METHODS

A total of 45 subjects completed the study, including 20 allergic, mildly asthmatic individuals, 22 non-asthmatic allergic controls and 3 healthy controls. A 3-cm airway segment in the right middle and right upper lobe were imaged in each subject immediately before and 24 h following segmental allergen challenge to the right middle lobe. Relationships between optical airway measurements (epithelial and mucosal thicknesses, mucosal buckling and mucus) and airway obstruction (FEV1 /FVC (forced expiratory volume in 1 s/forced vital capacity) and FEV1 % (FEV1 as a percentage of predictive value)) were investigated.

RESULTS

Significant increases at baseline and in response to allergen were observed for all four of our imaging metrics in the asthmatic airways compared to the non-asthmatic airways. Epithelial thickness and mucosal buckling exhibited a significant relationship to FEV1 /FVC in the asthmatic group.

CONCLUSION

Simultaneous assessments of airway microstructure, buckling and mucus revealed both structural and functional differences between the mildly asthmatic and control groups, with airway buckling seeming to be the most relevant factor. The results of this study demonstrate that a comprehensive, microstructural approach to assessing the airways may be important in future asthma studies as well as in the monitoring and treatment of asthma.

Combined treatment with SB203580 and dexamethasone suppresses non-typeable Haemophilus influenzae-induced Th17 inflammation response in murine allergic asthma

Accumulating evidence suggests that non-typeable Haemophilus influenzae (NTHi) infection drives the development of steroid-resistant allergic airway disease (SRAAD), exacerbates clinical symptoms, worsens quality of life, and accounts for most of the related healthcare burden. The poor understanding of the pathogenesis of SRAAD deters the development of more effective therapeutic strategies. Here, we established a murine model of NTHi infection-induced exacerbation of allergic airway disease. We showed that NTHi infection drove Th 17-mediated pulmonary neutrophilic inflammation, aggravated airway hyper-responsiveness, and upset the balance of MUC5AC and MUC5B expression. Dexamethasone treatment effectively inhibited the features of allergic airway disease but failed to reduce NTHi-induced exacerbation, which was associated with the hyper-phosphorylation of p38 mitogen-activated protein kinase (MAPK). Interestingly, inhibition of p38 using a specific inhibitor (SB203580) only partly suppressed the airway hyper-responsiveness and mucus hyper-secretion but failed to abrogate the infection-induced neutrophilic inflammatory response in SRAAD. However, SB203580 and dexamethasone co-treatment substantially suppressed all the features of NTHi-induced SRAAD. Our findings highlight the importance of p38 MAPK in the pathogenesis of NTHi-induced steroid resistance, and this combined treatment approach may be a novel strategy against steroid-resistant asthma.

Sialyl Glycan Expression on T Cell Subsets in Asthma: a correlation with disease severity and blood parameters

Memory T helper (Th) and regulatory T (Treg) cells play key roles in asthma. Certain sialyl carbohydrate determinants for selectins profoundly affect the migratory properties of memory Th cells, and the suppressive function of Treg cells. Previous studies have shown that the proportion of CCR4⁺ memory Th cells expressing sialyl 6-sulfo Lewis X (Le^X) is elevated in asthma patients. We aim to investigate the roles of different sialyl glycans on T cell subsets in asthma. Using flow cytometry, we assessed the expression of three sialyl glycans, sialyl 6-sulfo Le^X, cyclic sialyl 6-sulfo Le^X, and sialyl Le^X on memory Th and Treg cells, in the peripheral blood of asthmatic children. We also assessed the relationships between glycan-expressing cell percentages and asthma clinical parameters. Compared with controls, asthmatic children showed higher proportions of memory Th cells expressing sialyl Le^X and sialyl 6-sulfo Le^X. The proportions of memory Th cells with sialyl 6-sulfo Le^X and cyclic sialyl 6-sulfo Le^X expression in asthmatic children correlated with absolute eosinophil count and IgE level, respectively. Children with moderate-to-severe asthma had lower numbers of sialyl Le^X positive Treg cells. Our study suggests that sialyl glycans on T cells may play important roles in the pathogenesis of asthma.

Guiding regulatory T cells to the allograft

PURPOSE OF REVIEW

The application of regulatory T cell (Treg) therapy in organ transplantation is actively being pursued using unmodified, typically polyclonal cells. As the results of these ongoing clinical trials emerge, it is time to plan the next wave of clinical trials of Tregs. Here we will review a key strategy to improve Treg effectiveness and reduce side effects, namely increasing Treg specificity - both in terms of antigen recognition and localization to the allograft.

RECENT FINDINGS

Study of chemokine signatures accompanying acute rejection has revealed several chemokines that could be targeted to increase Treg homing. For example, Tregs possessing a Th1-like phenotype and expressing CXCR3 are better able to migrate towards local inflammation. Allografts themselves can be modified to increase Treg-attracting chemokines and Tregs themselves can produce chemokines, facilitating local proximity to their targets of suppression. Finally, tailoring Treg antigen specificity by T-cell or chimeric antigen receptor engineering is another approach to increase the specificity of suppression and optimize localization.

SUMMARY

Treg localization to the graft is important, but the important role of lymph node and germinal center homing cannot be overlooked. There is an opportunity to learn from advances made in cancer immunotherapy to optimize Treg therapy for transplantation.

Enhanced antigen presenting and T cell functions during late-phase allergic responses in the lung

BACKGROUND

Allergic inflammation is a common feature of asthma and may contribute to both development and perpetuation of disease. The interaction of antigen-presenting cells (APC) with sensitized helper T lymphocytes (TC) producing Th2 cytokines may determine the inflammatory response. Recruitment of APC and TC to the lung during allergic responses has been demonstrated, but functional studies in humans have been limited.

OBJECTIVE

This study examined the function of APC and TC accumulating at sites of inflammation after segmental allergen challenge (SAC).

METHODS

Fifteen allergic patients underwent SAC, and cells from bronchoalveolar lavage (BAL) were collected after 24 hours. APC and TC from the blood and BAL were purified based on expression of the monocyte marker, CD14; the plasmacytoid dendritic cell (pDC) marker, BDCA4, identifying neuropilin-1 (NRP1); and the helper T cell marker, CD4. Functional activity was assessed using allergen-induced T cell proliferation. Flow cytometry identified cells expressing CD14 and NRP1.

RESULTS

SAC resulted in a 12-fold increase in mononuclear cells having the morphologic appearance of blood monocytes. Most of these cells co-expressed CD14 and NRP1. After saline challenge, BAL mononuclear cells demonstrated little APC function. Following SAC, BAL mononuclear cells showed function equal to pDC from blood and greater than blood monocytes. Purified NRP1⁺ cells from BAL had even greater function than pDC cells from blood (P = .008). Using consistent sources of APC, enhanced proliferation of TC from lung compared to blood was also demonstrated (P = .002).

CONCLUSIONS

The marked increase in APC function for allergen-specific TC proliferation during allergic inflammation is largely due to the recruitment of monocytes and dendritic cells. There is also an enhanced response in the lung TC population, consistent with recruitment of allergen-specific T cells. Interactions between recruited APC and TC may occur as an early event promoting allergic airway inflammation.

Lung-Infiltrating Foxp3+ Regulatory T Cells Are Quantitatively and Qualitatively Different during Eosinophilic and Neutrophilic Allergic Airway Inflammation but Essential To Control the Inflammation

Understanding functions of Foxp3⁺ regulatory T cells (Tregs) during allergic airway inflammation remains incomplete. In this study, we report that, during cockroach Ag-induced allergic airway inflammation, Foxp3⁺ Tregs are rapidly mobilized into the inflamed lung tissues. However, the level of Treg accumulation in the lung was different depending on the type of inflammation. During eosinophilic airway inflammation, ∼30% of lung-infiltrating CD4 T cells express Foxp3, indicative of Tregs. On the contrary, only ∼10% of infiltrating CD4 T cells express Foxp3 during neutrophilic airway inflammation. Despite the different accumulation, the lung inflammation and inflammatory T cell responses were aggravated following Treg depletion, regardless of the type of inflammation, suggesting regulatory roles for Tregs. Interestingly, however, the extent to which inflammatory responses are aggravated by Treg depletion was significantly greater during eosinophilic airway inflammation. Indeed, lung-infiltrating Tregs exhibit phenotypic and functional features associated with potent suppression. Our results demonstrate that Tregs are essential regulators of inflammation, regardless of the type of inflammation, although the mechanisms used by Tregs to control inflammation may be shaped by environmental cues available to them.

Automated segmentation and quantification of airway mucus with endobronchial optical coherence tomography

We propose a novel suite of algorithms for automatically segmenting the airway lumen and mucus in endobronchial optical coherence tomography (OCT) data sets, as well as a novel approach for quantifying the contents of the mucus. Mucus and lumen were segmented using a robust, multi-stage algorithm that requires only minimal input regarding sheath geometry. The algorithm performance was highly accurate in a wide range of airway and noise conditions. Mucus was classified using mean backscattering intensity and grey level co-occurrence matrix (GLCM) statistics. We evaluated our techniques in vivo in asthmatic and non-asthmatic volunteers.

Effect of follicular helper T cells on the pathogenesis of asthma

Follicular helper T (TFH) cells are considered to be a separate T helper cell subset, specifically to help memory B cell participate in humoral immunity. It has been reported that there is an association between the imbalance of TFH function and certain autoimmune diseases. However, to the best of our knowledge, the effect of TFH cells on the process of bronchial asthma has not been investigated. The aim of the present study was to investigate the associated markers of TFH cells in bronchial asthma-induced mice. In the current study, sensitized and long-term challenges induced a mouse asthmatic model and were used to investigate the associated markers of TFH cells in the pathogenesis of asthma. The results demonstrated that B cell lymphoma 6, inducible T-cell costimulator (ICOS), ICOS ligand, C-X-C chemokine receptor type 5 (CXCR5) and interleukin (IL)-21 protein and mRNA expression levels were higher in the asthma group, as compared with the control group. Furthermore, the ratio of cluster of differentiation (CD) 4⁺CXCR5⁺/CD4⁺ and CD4⁺CXCR5⁺ICOS⁺/CD4⁺CXCR5⁺ was significantly increased in the asthma group. The results of the current study suggest that TFH cells and associated markers may have a role in the pathogenesis of chronic bronchial asthma.

Regulatory T Cells in Allergy and Asthma

The immune system's correct functioning requires a sophisticated balance between responses to continuous microbial challenges and tolerance to harmless antigens, such as self-antigens, food antigens, commensal microbes, allergens, etc. When this equilibrium is altered, it can lead to inflammatory pathologies, tumor growth, autoimmune disorders, and allergy/asthma. The objective of this review is to show the existing data on the importance of regulatory T cells (Tregs) on this balance and to underline how intrauterine and postnatal environmental exposures influence the maturation of the immune system in humans. Genetic and environmental factors during embryo development and/or early life will result in a proper or, conversely, inadequate immune maturation with either beneficial or deleterious effects on health. We have focused herein on Tregs as a reflection of the maturity of the immune system. We explain the types, origins, and the mechanisms of action of these cells, discussing their role in allergy and asthma predisposition. Understanding the importance of Tregs in counteracting dysregulated immunity would provide approaches to diminish asthma and other related diseases in infants.

Allergic asthma is distinguished by sensitivity of allergen-specific CD4+ T cells and airway structural cells to type 2 inflammation

Despite systemic sensitization, not all allergic individuals develop asthma symptoms upon airborne allergen exposure. Determination of the factors that lead to the asthma phenotype in allergic individuals could guide treatment and identify novel therapeutic targets. We used segmental allergen challenge of allergic asthmatics (AA) and allergic nonasthmatic controls (AC) to determine whether there are differences in the airway immune response or airway structural cells that could drive the development of asthma. Both groups developed prominent allergic airway inflammation in response to allergen. However, asthmatic subjects had markedly higher levels of innate type 2 receptors on allergen-specific CD4+ T cells recruited into the airway. There were also increased levels of type 2 cytokines, increased total mucin, and increased mucin MUC5AC in response to allergen in the airways of AA subjects. Furthermore, type 2 cytokine levels correlated with the mucin response in AA but not AC subjects, suggesting differences in the airway epithelial response to inflammation. Finally, AA subjects had increased airway smooth muscle mass at baseline measured in vivo using novel orientation-resolved optical coherence tomography. Our data demonstrate that the development of allergic asthma is dependent on the responsiveness of allergen-specific CD4+ T cells to innate type 2 mediators as well as increased sensitivity of airway epithelial cells and smooth muscle to type 2 inflammation.

T regulatory cell chemokine production mediates pathogenic T cell attraction and suppression

T regulatory cells (Tregs) control immune homeostasis by preventing inappropriate responses to self and nonharmful foreign antigens. Tregs use multiple mechanisms to control immune responses, all of which require these cells to be near their targets of suppression; however, it is not known how Treg-to-target proximity is controlled. Here, we found that Tregs attract CD4+ and CD8+ T cells by producing chemokines. Specifically, Tregs produced both CCL3 and CCL4 in response to stimulation, and production of these chemokines was critical for migration of target T cells, as Tregs from Ccl3-/- mice, which are also deficient for CCL4 production, did not promote migration. Moreover, CCR5 expression by target T cells was required for migration of these cells to supernatants conditioned by Tregs. Tregs deficient for expression of CCL3 and CCL4 were impaired in their ability to suppress experimental autoimmune encephalomyelitis or islet allograft rejection in murine models. Moreover, Tregs from subjects with established type 1 diabetes were impaired in their ability to produce CCL3 and CCL4. Together, these results demonstrate a previously unappreciated facet of Treg function and suggest that chemokine secretion by Tregs is a fundamental aspect of their therapeutic effect in autoimmunity and transplantation.

Donor-derived exosomes induce specific regulatory T cells to suppress immune inflammation in the allograft heart

To inhibit the immune inflammation in the allografts can be beneficial to organ transplantation. This study aims to induce the donor antigen specific regulatory T cells (Treg cell) inhibit the immune inflammation in the allograft heart. In this study, peripheral exosomes were purified from the mouse serum. A heart transplantation mouse model was developed. The immune inflammation of the allograft heart was assessed by histology and flow cytometry. The results showed that the donor antigen-specific T helper (Th)2 pattern inflammation was observed in the allograft hearts; the inflammation was inhibited by immunizing the recipient mice with the donor-derived exosomes. Purified peripheral exosomes contained integrin MMP1a; the latter induced CD4⁺ T cells to express Fork head protein-3 and transforming growth factor (TGF)-β via inhibiting the Th2 transcription factor, GATA binding protein 3, in CD4⁺ T cells. Administration with the donor-derived exosomes significantly prolonged the allograft heart survival. We conclude that the donor-derived peripheral exosomes have the capacity to inhibit the immune inflammation in the allograft heart via inducing specific Treg cells, implicating that administration with the donor-derived exosomes may be beneficial to cardiac transplantation.

IL-4/CCL22/CCR4 axis controls regulatory T-cell migration that suppresses inflammatory bone loss in murine experimental periodontitis

Inflammatory bone resorption is a hallmark of periodontitis, and Tregs and Th2 cells are independently associated with disease progression attenuation. In this study, we employed an infection-triggered inflammatory osteolysis model to investigate the mechanisms underlying Treg and Th2 cell migration and the impact on disease outcome. Aggregatibacter actinomycetemcomitans-infected C57Bl/6 (wild-type [WT]) mice develop an intense inflammatory reaction and alveolar bone resorption, and Treg and Th2 cell migration is temporally associated with disease progression attenuation. Tregs extracted from the lesions preferentially express CCR4 and CCR8, whereas Th2 cells express CCR3, CCR4, and CCR8. The absence of CCR5 and CCR8 did not significantly impact the migration of Tregs and Th2 cells or affect the disease outcome. CCR4KO mice presented a minor reduction in Th2 cells in parallel with major impairment of Treg migration, which was associated with increased inflammatory bone loss and higher proinflammatory and osteoclastogenic cytokine levels. The blockade of the CCR4 ligand CCL22 in WT mice resulted in an increased inflammatory bone loss phenotype similar to that in the CCR4KO strain. Adoptive transfer of CCR4(+) Tregs to the CCR4KO strain revert the increased disease phenotype to WT mice-like levels; also, the in situ production of CCL22 in the lesions is mandatory for Tregs migration and the consequent bone loss arrest. The local release of exogenous CCL22 provided by poly(lactic-co-glycolic acid) (PLGA) microparticles promotes migration of Tregs and disease arrest in the absence of endogenous CCL22 in the IL-4KO strain, characterized by the lack of endogenous CCL22 production, defective migration of Tregs, and exacerbated bone loss. In summary, our results show that the IL-4/CCL22/CCR4 axis is involved in the migration of Tregs to osteolytic lesion sites, and attenuates development of lesions by inhibiting inflammatory migration and the production of proinflammatory and osteoclastogenic mediators.

Regulatory T cells and their roles in immune dysregulation and allergy

The main function of the immune system is to fight off potential infections, but also to maintain its activity below a level that would trigger self-reactivity. Regulatory T cells (Tregs) such as forkhead box P3(+) (FOXP3) Tregs and type 1 regulatory T cells (Tr1) play an essential role in this active process, using several distinct suppressive mechanisms. A wide range of pathologies have been associated with altered Treg cell function. This is best exemplified by the impact of mutations of genes essential for Treg function and the associated autoimmune syndromes. This review summarizes the main features of different subtypes of Tregs and focuses on the clinical implications of their altered function in human studies. More specifically, we discuss abnormalities affecting FOXP3(+) Tregs and Tr1 cells that will lead to autoimmune manifestations and/or allergic reactions, and the potential therapeutic use of Tregs.

Recent progress in the development of antagonists to the chemokine receptors CCR3 and CCR4

INTRODUCTION

The chemokine receptors CCR3 and CCR4 have been shown to be important therapeutic targets for the treatment of a variety of diseases. Although only two chemokine receptor inhibitors have been approved so far, there are numerous compounds that are in various stages of development.

AREAS COVERED

In this review article, the authors provide an update on the progress made in the identification of antagonists against the chemokine receptors CCR3 and CCR4 from 2009 to the present. The rationale of writing this review article is to cover the most important approaches to identifying antagonists to these two receptors, which could prove to be useful therapeutics in treating proinflammatory diseases.

EXPERT OPINION

Pharmaceutical companies have expended a considerable amount of money and effort to identify potent inhibitors of CCR3 and CCR4 for the treatment of asthma and atopic diseases. Although a variety of compounds have been described and several have progressed into the clinic, none have so far made it as approved drugs. There are, however, novel approaches such as mogamulizumab, a monoclonal antibody to CCR4 currently is in clinical trials for cancer and ASM8, an antisense nucleotide to CCR3, which is in Phase II clinical trials for asthma that might still prove to be successful new therapeutics.

Chemokines and chemokine receptors: positioning cells for host defense and immunity

Chemokines are chemotactic cytokines that control the migratory patterns and positioning of all immune cells. Although chemokines were initially appreciated as important mediators of acute inflammation, we now know that this complex system of approximately 50 endogenous chemokine ligands and 20 G protein-coupled seven-transmembrane signaling receptors is also critical for the generation of primary and secondary adaptive cellular and humoral immune responses. Recent studies demonstrate important roles for the chemokine system in the priming of naive T cells, in cell fate decisions such as effector and memory cell differentiation, and in regulatory T cell function. In this review, we focus on recent advances in understanding how the chemokine system orchestrates immune cell migration and positioning at the organismic level in homeostasis, in acute inflammation, and during the generation and regulation of adoptive primary and secondary immune responses in the lymphoid system and peripheral nonlymphoid tissue.

Asthma: the importance of dysregulated barrier immunity

Chronic asthma is an inflammatory disease of the airway wall that leads to bronchial smooth muscle hyperreactivity and airway obstruction, caused by inflammation, goblet cell metaplasia, and airway wall remodeling. In response to allergen presentation by airway DCs, T-helper lymphocytes of the adaptive immune system control many aspects of the disease through secretion of IL-4, IL-5, IL-13, IL-17, and IL-22, and these are counterbalanced by cytokines produced by Treg cells. Many cells of the innate immune system such as mast cells, basophils, neutrophils, eosinophils, and innate lymphoid cells also play an important role in disease pathogenesis. Barrier epithelial cells are being ever more implicated in disease pathogenesis than previously thought, as these cells have in recent years been shown to sense exposure to allergens via pattern recognition receptors and to activate conventional and inflammatory-type DCs and other innate immune cells through the secretion of thymic stromal lymphopoietin, granulocyte-macrophage colony stimulating factor, IL-1, IL-33, and IL-25. Understanding this cytokine crosstalk between barrier epithelial cells, DCs, and immune cells provides important insights into the mechanisms of allergic sensitization and asthma progression as discussed in this review.

Natural regulatory T cells in isolated early responders compared with dual responders with allergic asthma

BACKGROUND

Natural regulatory T (Treg) cells are implicated in the regulation of the inflammatory response in patients with allergic asthma.

OBJECTIVES

We sought to determine changes in Treg cell numbers in the airways and peripheral blood of isolated early responder (IER) versus dual responder (DR) subjects with mild allergic asthma before and after allergen challenge.

METHODS

Induced sputum was collected from 22 subjects with allergic asthma (10 IERs and 12 DRs) and peripheral blood collected from 8 DRs with allergic asthma at 0, 7, and 24 hours after allergen challenge. Treg cells were identified by using fluorescently labeled antibodies to CD4 and forkhead box protein 3 and enumerated by using flow cytometry.

RESULTS

There was a significant increase in the percentage of sputum CD4(+) cells 24 hours after allergen challenge in both IERs and DRs. The percentage of sputum Treg cells significantly decreased 24 hours after challenge in DRs but not IERs. This change was significantly correlated with the magnitude of the late asthmatic response. There was also a significant increase in the absolute number of sputum CD4(+) cells and Treg cells at 24 hours in DRs only. The ratio of the number of Treg cells to CD4(+) cells at 24 hours was significantly smaller in DRs compared with that in IERs. None of the above changes were observed in peripheral blood.

CONCLUSIONS

DRs exhibit a diminished percentage of airway Treg cells after allergen challenge that is not observed in IERs and a significantly lower ratio of Treg cells to CD4(+) cells, which might contribute to the development of the late asthmatic response.

Regulatory T Cells Control Immune Responses through Their Non-Redundant Tissue Specific Features

Regulatory T cells (Treg) are needed in the control of immune responses and to maintain immune homeostasis. Of this subtype of regulatory lymphocytes, the most potent are Foxp3 expressing CD4+ T cells, which can be roughly divided into two main groups; natural Treg cells (nTreg), developing in the thymus, and induced or adaptive Treg cells (iTreg), developing in the periphery from naïve, conventional T cells. Both nTreg cells and iTreg cells have their own, non-redundant roles in the immune system, with nTreg cells mainly maintaining tolerance toward self-structures, and iTreg developing in response to externally delivered antigens or commensal microbes. In addition, Treg cells acquire tissue specific features and are adapted to function in the tissue they reside. This review will focus on some specific features of Treg cells in different compartments of the body.

Lung dendritic cells imprint T cell lung homing and promote lung immunity through the chemokine receptor CCR4

T cell trafficking into the lung is critical for lung immunity, but the mechanisms that mediate T cell lung homing are not well understood. Here, we show that lung dendritic cells (DCs) imprint T cell lung homing, as lung DC-activated T cells traffic more efficiently into the lung in response to inhaled antigen and at homeostasis compared with T cells activated by DCs from other tissues. Consequently, lung DC-imprinted T cells protect against influenza more effectively than do gut and skin DC-imprinted T cells. Lung DCs imprint the expression of CCR4 on T cells, and CCR4 contributes to T cell lung imprinting. Lung DC-activated, CCR4-deficient T cells fail to traffic into the lung as efficiently and to protect against influenza as effectively as lung DC-activated, CCR4-sufficient T cells. Thus, lung DCs imprint T cell lung homing and promote lung immunity in part through CCR4.