Hierarchical IL-5 expression defines a subpopulation of highly differentiated human Th2 cells

Contribution of T cell subsets to different food allergic diseases

Food allergies occur due to a lack of tolerance to the proteins found in foods. While IgE- and non-IgE-mediated food allergies have different clinical manifestations, epidemiology, pathophysiology, and management, they share dysregulated T cell responses. Recent studies have shed light on the contributions of different T cell subsets to the development and persistence of different food allergic diseases. This review discusses the role of T cells in both IgE- and non-IgE-mediated food allergies and considers the potential future investigations in this context.

TL1A priming induces a multi-cytokine Th9 cell phenotype that promotes robust allergic inflammation in murine models of asthma

Multi-cytokine-producing Th9 cells secrete IL-9 and type 2 cytokines and mediate mouse and human allergic inflammation. However, the cytokines that promote a multi-cytokine secreting phenotype have not been defined. Tumor necrosis factor superfamily member TL1A signals through its receptor DR3 to increase IL-9. Here we demonstrate that TL1A increases expression of IL-9 and IL-13 co-expressing cells in murine Th9 cell cultures, inducing a multi-cytokine phenotype. Mechanistically, this is linked to histone modifications allowing for increased accessibility at the Il9 and Il13 loci. We further show that TL1A alters the transcription factor network underlying expression of IL-9 and IL-13 in Th9 cells and increases binding of transcription factors to Il9 and Il13 loci. TL1A-priming enhances the pathogenicity of Th9 cells in murine models of allergic airway disease through the increased expression of IL-9 and IL-13. Lastly, in both chronic and memory-recall models of allergic airway disease, blockade of TL1A signaling decreases the multi-cytokine Th9 cell population and attenuates the allergic phenotype. Taken together, these data demonstrate that TL1A promotes the development of multi-cytokine Th9 cells that drive allergic airway diseases and that targeting pathogenic T helper cell-promoting cytokines could be an effective approach for modifying disease.

TH2 cell compensatory effect following benralizumab treatment for eosinophilic gastritis

BACKGROUND

Eosinophil accumulation is a main feature of eosinophilic gastritis (EoG) and is associated with its histologic diagnosis and pathology. However, a recent clinical trial has demonstrated that EoG endoscopic, noneosinophil histologic, and clinical features remain persistent despite complete eosinophil depletion.

OBJECTIVE

Our aim was to examine gastric T-cell composition and associated cytokine levels of patients with EoG following benralizumab-induced eosinophil depletion versus following administration of placebo.

METHODS

A cohort of subjects with EoG from a subset of subjects who participated in a recent phase 2 benralizumab trial was treated for 12 weeks with administration of 3 doses of benralizumab (anti-IL-5 receptor α antibody [n = 5]) or placebo (n = 4). Single-cell suspensions obtained by gastric biopsy were stimulated with phorbol 12,13-dibutyrate and ionomycin in the presence of brefeldin A and monensin. Harvested cells were fixed, stained, and analyzed by flow cytometry to examine T-cell populations and associated cytokines.

RESULTS

Following benralizumab treatment but not placebo, blood and gastric eosinophil levels decreased 16-fold and 10-fold, respectively. Whereas histologic score and features were significantly decreased, no change was observed in endoscopic score and features. Following complete eosinophil depletion with benralizumab, gastric TH2 cell levels were 3-fold higher than the levels in the patients with EoG who were given placebo; and the levels of associated type 2 cytokine production of IL-4, IL-5, and IL-13 in the benralizumab-treated patients were, respectively, 4-, 5.5-, and 2.5-fold, higher than those in the placebo-treated patients.

CONCLUSION

We have identified a putative positive feedback loop whereby eosinophil depletion results in a paradoxic increase in levels of TH2 cells and derived cytokines; this finding suggests an explanation for the limited success of eosinophil depletion as monotherapy in eosinophil-associated gastrointestinal disorders.

Triggers for eosinophilic esophagitis (EoE): The intersection of food allergy and EoE

Eosinophilic esophagitis and IgE-mediated food allergy are both food-triggered diseases that are increasing in prevalence. They share many clinical links, including significant comorbidity and similar food triggers, and as atopic diseases, they likely share upstream mechanisms related to barrier function and signals leading to TH2 skewing. In this review, we focus on links between eosinophilic esophagitis and IgE-mediated food allergy with an emphasis on what insights may be derived from overlapping food triggers and immune phenotypes. Through further investigation of these connections, we may be able to better understand not only IgE-mediated food allergy and eosinophilic esophagitis but also general atopic response to food proteins and evolution of allergic response to food.

TCF1-LEF1 co-expression identifies a multipotent progenitor cell (TH2-MPP) across human allergic diseases

Repetitive exposure to antigen in chronic infection and cancer drives T cell exhaustion, limiting adaptive immunity. In contrast, aberrant, sustained T cell responses can persist over decades in human allergic disease. To understand these divergent outcomes, we employed bioinformatic, immunophenotyping and functional approaches with human diseased tissues, identifying an abundant population of type 2 helper T (TH2) cells with co-expression of TCF7 and LEF1, and features of chronic activation. These cells, which we termed TH2-multipotent progenitors (TH2-MPP) could self-renew and differentiate into cytokine-producing effector cells, regulatory T (Treg) cells and follicular helper T (TFH) cells. Single-cell T-cell-receptor lineage tracing confirmed lineage relationships between TH2-MPP, TH2 effectors, Treg cells and TFH cells. TH2-MPP persisted despite in vivo IL-4 receptor blockade, while thymic stromal lymphopoietin (TSLP) drove selective expansion of progenitor cells and rendered them insensitive to glucocorticoid-induced apoptosis in vitro. Together, our data identify TH2-MPP as an aberrant T cell population with the potential to sustain type 2 inflammation and support the paradigm that chronic T cell responses can be coordinated over time by progenitor cells.

Th2-skewed peripheral T-helper cells drive B-cells in allergic bronchopulmonary aspergillosis

INTRODUCTION

Patients with allergic bronchopulmonary aspergillosis (ABPA) suffer from repeated exacerbations. The involvement of T-cell subsets remains unclear.

METHODS

We enrolled ABPA patients, asthma patients and healthy controls. T-helper type 1 (Th1), 2 (Th2) and 17 (Th17) cells, regulatory T-cells (Treg) and interleukin (IL)-21+CD4+T-cells in total or sorted subsets of peripheral blood mononuclear cells and ABPA bronchoalveolar lavage fluid (BALF) were analysed using flow cytometry. RNA sequencing of subsets of CD4+T-cells was done in exacerbated ABPA patients and healthy controls. Antibodies of T-/B-cell co-cultures in vitro were measured.

RESULTS

ABPA patients had increased Th2 cells, similar numbers of Treg cells and decreased circulating Th1 and Th17 cells. IL-5+IL-13+IL-21+CD4+T-cells were rarely detected in healthy controls, but significantly elevated in the blood of ABPA patients, especially the exacerbated ones. We found that IL-5+IL-13+IL-21+CD4+T-cells were mainly peripheral T-helper (Tph) cells (PD-1+CXCR5-), which also presented in the BALF of ABPA patients. The proportions of circulating Tph cells were similar among ABPA patients, asthma patients and healthy controls, while IL-5+IL-13+IL-21+ Tph cells significantly increased in ABPA patients. Transcriptome data showed that Tph cells of ABPA patients were Th2-skewed and exhibited signatures of follicular T-helper cells. When co-cultured in vitro, Tph cells of ABPA patients induced the differentiation of autologous B-cells into plasmablasts and significantly enhanced the production of IgE.

CONCLUSION

We identified a distinctly elevated population of circulating Th2-skewed Tph cells that induced the production of IgE in ABPA patients. It may be a biomarker and therapeutic target for ABPA.

T helper cell subsets: diversification of the field

Polarized T helper cell (Th cell) responses are important determinants of host protection. Th cell subsets tailor their functional repertoire of cytokines to their cognate antigens to efficiently contribute to their clearance. In contrast, in settings of immune abrogation, these polarized cytokine patterns of Th cells can mediate tissue damage and pathology resulting in allergy or autoimmunity. Recent technological developments in single-cell genomics and proteomics as well as advances in the high-dimensional bioinformatic analysis of complex datasets have challenged the prevailing Th cell subset classification into Th1, Th2, Th17, and other subsets. Additionally, systems immunology approaches have revealed that instructive input from the peripheral tissue microenvironment can have differential effects on the overall phenotype and molecular wiring of Th cells depending on their spatial distribution. Th cells from the blood or secondary lymphoid organs are therefore expected to follow distinct rules of regulation. In this review, the functional heterogeneity of Th cell subsets will be reviewed in the context of new technological developments and T-cell compartmentalization in tissue niches. This work will especially focus on challenges to the traditional boundaries of Th cell subsets and will discuss the underlying regulatory checkpoints, which could reveal new therapeutic strategies for various immune-mediated diseases.

TSLP shapes the pathogenic responses of memory CD4+ T cells in eosinophilic esophagitis

The cytokine thymic stromal lymphopoietin (TSLP) mediates type 2 immune responses, and treatments that interfere with TSLP activity are in clinical use for asthma. Here, we investigated whether TSLP contributes to allergic inflammation by directly stimulating human CD4+ T cells and whether this process is operational in eosinophilic esophagitis (EoE), a disease linked to variants in TSLP. We showed that about 10% of esophageal-derived memory CD4+ T cells from individuals with EoE and less than 3% of cells from control individuals expressed the receptor for TSLP and directly responded to TSLP, as determined by measuring the phosphorylation of STAT5, a transcription factor activated downstream of TSLP stimulation. Accordingly, increased numbers of TSLP-responsive memory CD4+ T cells were present in the circulation of individuals with EoE. TSLP increased the proliferation of CD4+ T cells, enhanced type 2 cytokine production, induced the increased abundance of its own receptor, and modified the expression of 212 genes. The epigenetic response to TSLP was associated with an enrichment in BATF and IRF4 chromatin-binding sites, and these transcription factors were induced by TSLP, providing a feed-forward loop. The numbers of circulating and esophageal CD4+ T cells responsive to TSLP correlated with the numbers of esophageal eosinophils, supporting a potential functional role for TSLP in driving the pathogenesis of EoE and providing the basis for a blood-based diagnostic test based on the extent of TSLP-induced STAT5 phosphorylation in circulating CD4+ T cells. These findings highlight the potential therapeutic value of TSLP inhibitors for the treatment of EoE.

The ins and outs of innate and adaptive type 2 immunity

Type 2 immunity is orchestrated by a canonical group of cytokines primarily produced by innate lymphoid cells, group 2, and their adaptive counterparts, CD4+ helper type 2 cells, and elaborated by myeloid cells and antibodies that accumulate in response. Here, we review the cytokine and cellular circuits that mediate type 2 immunity. Building from insights in cytokine evolution, we propose that innate type 2 immunity evolved to monitor the status of microbe-rich epithelial barriers (outside) and sterile parenchymal borders (inside) to meet the functional demands of local tissue, and, when necessary, to relay information to the adaptive immune system to reinforce demarcating borders to sustain these efforts. Allergic pathology likely results from deviations in local sustaining units caused by alterations imposed by environmental effects during postnatal developmental windows and exacerbated by mutations that increase vulnerabilities. This framework positions T2 immunity as central to sustaining tissue repair and regeneration and provides a context toward understanding allergic disease.

Distinct roles of ORAI1 in T cell-mediated allergic airway inflammation and immunity to influenza A virus infection

T cell activation and function depend on Ca2+ signals mediated by store-operated Ca2+ entry (SOCE) through Ca2+ release-activated Ca2+ (CRAC) channels formed by ORAI1 proteins. We here investigated how SOCE controls T cell function in pulmonary inflammation during a T helper 1 (TH1) cell-mediated response to influenza A virus (IAV) infection and TH2 cell-mediated allergic airway inflammation. T cell-specific deletion of Orai1 did not exacerbate pulmonary inflammation and viral burdens following IAV infection but protected mice from house dust mite-induced allergic airway inflammation. ORAI1 controlled the expression of genes including p53 and E2F transcription factors that regulate the cell cycle in TH2 cells in response to allergen stimulation and the expression of transcription factors and cytokines that regulate TH2 cell function. Systemic application of a CRAC channel blocker suppressed allergic airway inflammation without compromising immunity to IAV infection, suggesting that inhibition of SOCE is a potential treatment for allergic airway disease.

Distinct spatial and temporal roles for Th1, Th2, and Th17 cells in asthma

Immune response in the asthmatic respiratory tract is mainly driven by CD4⁺ T helper (Th) cells, represented by Th1, Th2, and Th17 cells, especially Th2 cells. Asthma is a heterogeneous and progressive disease, reflected by distinct phenotypes orchestrated by τh2 or non-Th2 (Th1 and Th17) immune responses at different stages of the disease course. Heterogeneous cytokine expression within the same Th effector state in response to changing conditions in vivo and interlineage relationship among CD4⁺ T cells shape the complex immune networks of the inflammatory airway, making it difficult to find one panacea for all asthmatics. Here, we review the role of three T helper subsets in the pathogenesis of asthma from different stages, highlighting timing is everything in the immune system. We also discuss the dynamic topography of Th subsets and pathogenetic memory Th cells in asthma.

Th2 single-cell heterogeneity and clonal distribution at distant sites in helminth-infected mice

Th2 cells provide effector functions in type 2 immune responses to helminths and allergens. Despite knowledge about molecular mechanisms of Th2 cell differentiation, there is little information on Th2 cell heterogeneity and clonal distribution between organs. To address this, we performed combined single-cell transcriptome and T-cell receptor (TCR) clonotype analysis on murine Th2 cells in mesenteric lymph nodes (MLNs) and lung after infection with Nippostrongylus brasiliensis (Nb) as a human hookworm infection model. We find organ-specific expression profiles, but also populations with conserved migration or effector/resident memory signatures that unexpectedly cluster with potentially regulatory Il10^posFoxp3^neg cells. A substantial MLN subpopulation with an interferon response signature suggests a role for interferon signaling in Th2 differentiation or diversification. Further RNA-inferred developmental directions indicate proliferation as a hub for differentiation decisions. Although the TCR repertoire is highly heterogeneous, we identified expanded clones and CDR3 motifs. Clonal relatedness between distant organs confirmed effective exchange of Th2 effector cells, although locally expanded clones dominated the response. We further cloned an Nb-specific TCR from an expanded clone in the lung effector cluster and describe surface markers that distinguish transcriptionally defined clusters. These results provide insights in Th2 cell subset diversity and clonal relatedness in distant organs.

Th2A cells: The pathogenic players in allergic diseases

Proallergic type 2 helper T (Th2A) cells are a subset of memory Th2 cells confined to atopic individuals, and they include all the allergen-specific Th2 cells. Recently, many studies have shown that Th2A cells characterized by CD3+ CD4+ HPGDS+ CRTH2+ CD161high ST2high CD49dhigh CD27low play a crucial role in allergic diseases, such as atopic dermatitis (AD), food allergy (FA), allergic rhinitis (AR), asthma, and eosinophilic esophagitis (EoE). In this review, we summarize the discovery, biomarkers, and biological properties of Th2A cells to gain new insights into the pathogenesis of allergic diseases.

Experimental colonization with Blastocystis ST4 is associated with protective immune responses and modulation of gut microbiome in a DSS-induced colitis mouse model

Background

Blastocystis is a common gut protistan parasite in humans and animals worldwide, but its interrelationship with the host gut microbiota and mucosal immune responses remains poorly understood. Different murine models of Blastocystis colonization were used to examine the effect of a common Blastocystis subtype (ST4) on host gut microbial community and adaptive immune system.

Results

Blastocystis ST4-colonized normal healthy mice and Rag1^−/− mice asymptomatically and was able to alter the microbial community composition, mainly leading to increases in the proportion of Clostridia vadinBB60 group and Lachnospiraceae NK4A136 group, respectively. Blastocystis ST4 colonization promoted T helper 2 (Th2) response defined by interleukin (IL)-5 and IL-13 cytokine production, and T regulatory (Treg) induction from colonic lamina propria in normal healthy mice. Additionally, we observed that Blastocystis ST4 colonization can maintain the stability of bacterial community composition and induce Th2 and Treg immune responses to promote faster recovery from experimentally induced colitis. Furthermore, fecal microbiota transplantation of Blastocystis ST4-altered gut microbiome to colitis mice reduced the severity of colitis, which was associated with increased production of short-chain fat acids (SCFAs) and anti-inflammatory cytokine IL-10.

Conclusions

The data confirm our hypothesis that Blastocystis ST4 is a beneficial commensal, and the beneficial effects of Blastocystis ST4 colonization is mediated through modulating of the host gut bacterial composition, SCFAs production, and Th2 and Treg responses in different murine colonization models.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00018-022-04271-9.

Allergen-specific T cells and clinical features of food allergy: Lessons from CoFAR immunotherapy cohorts

BACKGROUND

Allergen-specific IL-4+ and IL-13+ CD4+ cells (type 2 cells) are essential for helping B cells to class-switch to IgE and establishing an allergic milieu in the gastrointestinal tract. The role of T cells in established food allergy is less clear.

OBJECTIVE

We examined the food allergen-specific T-cell response in participants of 2 food allergen immunotherapy trials to assess the relationship of the T-cell response to clinical phenotypes, including response to immunotherapy.

METHODS

Blood was obtained from 84 participants with peanut allergy and 142 participants with egg allergy who underwent double-blind placebo-controlled food challenges. Peanut- and egg-responsive T cells were identified by CD154 upregulation after stimulation with the respective extract. Intracellular cytokines and chemokine receptors were also detected. The response to peanut epicutaneous immunotherapy (Peanut Epicutaneous Phase II Immunotherapy Clinical Trial [CoFAR6]; 49 participants receiving epicutaneous immunotherapy) and egg oral immunotherapy or a baked egg diet (Baked Egg or Egg Oral Immunotherapy for Children With Egg Allergy [CoFAR7]; 92 participants) was monitored over time.

RESULTS

Peanut-specific type 2 and CCR6+ T cells were negatively correlated with each other and differently associated with immune parameters, including specific IgE level and basophil activation test result. At baseline, type 2 cells, but not CCR6+ cells, were predictive of clinical parameters, including a successfully consumed dose of peanut and baked egg tolerance. Exposure to peanut or egg immunotherapy was associated with a decrease in type 2 cell frequency. At baseline, high egg-specific type 2 cell frequency was the immune feature most predictive of oral immunotherapy failure.

CONCLUSION

Food-specific type 2 T cells at baseline are informative of threshold of reactivity and response to immunotherapy.

Allergic airway recall responses require IL-9 from resident memory CD4+ T cells

Asthma is a chronic inflammatory lung disease with intermittent flares predominately mediated through memory T cells. Yet, the identity of long-term memory cells that mediate allergic recall responses is not well defined. In this report, using a mouse model of chronic allergen exposure followed by an allergen-free rest period, we characterized a subpopulation of CD4+ T cells that secreted IL-9 as an obligate effector cytokine. IL-9-secreting cells had a resident memory T cell phenotype, and blocking IL-9 during a recall challenge or deleting IL-9 from T cells significantly diminished airway inflammation and airway hyperreactivity. T cells secreted IL-9 in an allergen recall-specific manner, and secretion was amplified by IL-33. Using scRNA-seq and scATAC-seq, we defined the cellular identity of a distinct population of T cells with a proallergic cytokine pattern. Thus, in a recall model of allergic airway inflammation, IL-9 secretion from a multicytokine-producing CD4+ T cell population was required for an allergen recall response.

Single-cell characterization of dog allergen-specific T cells reveals TH2 heterogeneity in allergic individuals

BACKGROUND

Allergen-specific type 2 CD4⁺ T_H2 cells are critically involved in the pathogenesis of IgE-mediated allergic diseases. However, the heterogeneity of the T_H2 response has only recently been appreciated.

OBJECTIVE

We sought to characterize at the single-cell level the ex vivo phenotype, transcriptomic profile, and T-cell receptor (TCR) repertoire of circulating CD4⁺ T cells specific to the major dog allergens Can f 1, Can f 4, and Can f 5 in subjects with and without dog allergy.

METHODS

Dog allergen-specific memory CD4⁺ T cells were detected ex vivo by flow cytometry using a CD154-based enrichment assay and single-cell sorted for targeted gene expression analysis and TCR sequencing.

RESULTS

Dog allergen-specific T-cell responses in allergic subjects were dominantly of T_H2 type. T_H2 cells could be phenotypically further divided into 3 subsets, which consisted of T_H2-like (CCR6^-CXCR3^-CRTH2^-), T_H2 (CCR6^-CXCR3^-CRTH2⁺CD161^-), and T_H2A (CCR6^-CXCR3^-CRTH2⁺CD161⁺CD27^-) cells. All these subsets were nonexistent within the allergen-specific T-cell repertoire of healthy subjects. Single-cell transcriptomic profiling confirmed the T_H2-biased signature in allergen-specific T cells from allergic subjects and revealed a T_H1/T_H17 signature in nonallergic subjects. TCR repertoire analyses showed that dog allergen-specific T cells were diverse and allergic subjects demonstrated less clonality compared to nonallergic donors. Finally, TCR and transcriptomic analyses revealed a close relationship between T_H2-like, T_H2, and T_H2A cells, with the last ones representing the most terminally differentiated and highly polarized subtype.

CONCLUSIONS

Our study demonstrates heterogeneity within allergen-specific T_H2 cells at the single-cell level. The results may be utilized for improving immune monitoring after allergen immunotherapy and for designing targeted immunomodulatory approaches.

Is the plasticity of the Th17 subset a key source of allergenic Th2 responses?

This commentary summarizes and discusses a recent study from Tortola et al, which reports the vast plasticity of T helper (Th) 17 cells and suggests that this subset might be an important source of Th2 cells under certain inflammatory conditions.

CD4 + T cells in inflammatory diseases : pathogenic T-helper cells and the CD69-Myl9 system

CD4 + T cells direct immune responses against infectious microorganisms but are also involved in the pathogenesis of inflammatory diseases. In the last two to three decades, various researchers have identified and characterized several functional CD4 + T cell subsets, including T-helper 1 (Th1), Th2, Th9 and Th17 cells and regulatory T (Treg) cells. In this mini-review, we introduce the concept of pathogenic Th cells that induce inflammatory diseases with a model of disease induction by a population of pathogenic Th cells; "pathogenic Th population disease-induction model". We will focus on Th2 cells that induce allergic airway inflammation-pathogenic Th2 cells (Tpath2 cells)-and discuss the nature of Tpath2 cells that shape the pathology of chronic inflammatory diseases. Various Tpath2 cell subsets have been identified and their unique features are summarized in mouse and human systems. Second, we will discuss how Th cells migrate and are maintained in chronic inflammatory lesions. We propose a model known as the "CD69-Myl9 system". CD69 is a cell surface molecule expressed on activated T cells and interaction with its ligand myosin light chain 9 (Myl9) is required for the induction of inflammatory diseases. Myl9 molecules in the small vessels of inflamed lungs may play a crucial role in the migration of activated T cells into inflammatory lesions. Emerging evidence may provide new insight into the pathogenesis of chronic inflammatory diseases and contribute to the development of new therapeutic strategies for intractable inflammatory disorders.

Molecular mechanisms and treatment modalities in equine Culicoides hypersensitivity

Equine Culicoides hypersensitivity (CH) is the most common allergic condition in horses affecting the skin. This review focuses on immunopathology and molecular mechanisms of equine CH. The role of eosinophils is emphasized, as well as disease severity and the influence of long-term chronic allergen exposure on T helper (Th) 2 cells. Using current knowledge from human allergic disorders, similar effects are hypothesized in equine patients. Key aspects of CH diagnosis and treatment are discussed, focusing on allergen specific immunotherapy and allergen-independent approaches, such as targeting hypereosinophilia through interleukin-5 and allergic non-histaminic pruritus though interleukin-31.

Benralizumab Effectiveness in Severe Eosinophilic Asthma with and without Chronic Rhinosinusitis with Nasal Polyps: A Real-World Multicenter Study

BACKGROUND

Chronic rhinosinusitis with nasal polyps (CRSwNP) affects around 60% of patients with severe eosinophilic asthma (SEA). Benralizumab was recently approved for SEA add-on treatment.

OBJECTIVE

To assess the real-world effectiveness of benralizumab in SEA with or without CRSwNP.

METHODS

We conducted a multicenter observational study, including patients with SEA treated with benralizumab for 24 weeks in 12 Italian specialized facilities. Asthma exacerbations, Asthma Control Test (ACT), lung function, oral corticosteroid (OCS) dosage, and eosinophil and basophil count in peripheral blood were recorded at baseline and after 4, 12, and 24 weeks. The 22-item Sino-Nasal Outcome Test (SNOT-22) and Lund-Mackay scores were assessed at baseline and after 24 weeks in SEA+CRSwNP.

RESULTS

A total of 137 patients with late-onset SEA were included; 57.7% (79 of 137) showed the copresence of CRSwNP. Overall, severe asthma exacerbations decreased from 4 (3-6) to 0 (0-2) (P < .0001) after 24 weeks of treatment, and significant improvements were observed as early as 4 weeks in ACT score, OCS dosage, forced expiratory volume in the 1st second (FEV₁)%, FEV₁ (L), forced vital capacity (FVC)%, FEV₁/FVC% (P < .0001), and forced expiratory flow between 25% and 75% of FVC (FEF_25-75)% (P = .0022). Eosinophils and basophils in peripheral blood were rapidly depleted. In patients with SEA+CRSwNP, SNOT-22 decreased from 46 (39.5-64.5) to 32 (19-46) (P < .0001). Furthermore, in comparison with SEA, they showed enhanced responses with regard to ACT minimal clinically important difference (P = .0387), FEV₁% (P = .017), FEV₁ (L) (P = .02), and FEF_25-75% (P = .0362).

CONCLUSIONS

These real-world data suggest that benralizumab can represent a valid add-on therapeutic option for patients with SEA, especially with comorbid CRSwNP.

Clonally expanded, GPR15-expressing pathogenic effector TH2 cells are associated with eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is an allergic disorder characterized by the recruitment of eosinophils to the esophagus, resulting in chronic inflammation. We sought to understand the cellular populations present in tissue biopsies of patients with EoE and to determine how these populations are altered between active disease and remission. To this end, we analyzed cells obtained from esophageal biopsies, duodenal biopsies, and peripheral blood of patients with EoE diagnosed with active disease or remission with single-cell RNA and T cell receptor (TCR) sequencing. Pathogenic effector TH2 (peTH2) cells present in the esophageal biopsies of patients with active disease expressed distinct gene signatures associated with the synthesis of eicosanoids. The esophageal tissue-resident peTH2 population also exhibited clonal expansion, suggesting antigen-specific activation. Peripheral CRTH2+CD161- and CRTH2+CD161+ memory CD4+ T cells were enriched for either a conventional TH2 phenotype or a peTH2 phenotype, respectively. These cells also exhibited substantial clonal expansion and convergence of TCR sequences, suggesting that they are expanded in response to a defined set of antigens. The esophagus-homing receptor GPR15 was up-regulated by peripheral peTH2 clonotypes that were also detected in the esophagus. Finally, GPR15+ peTH2 cells were enriched among milk-reactive CD4+ T cells in patients with milk-triggered disease, suggesting that these cells are an expanded, food antigen-specific population with enhanced esophagus homing potential.

Diversity of T Helper and Regulatory T Cells and Their Contribution to the Pathogenesis of Allergic Diseases

T helper (Th) and regulatory T (Treg) cells represent important effectors of adaptive immunity. They mediate communication between the immune system and tissue sites and thereby coordinate effective defense against environmental threats or maintain tolerance, respectively. Since the discovery of two prototypic T helper cells, Th1 and Th2, additional phenotypic and functional distinct subsets have been described ranging from Th17, Th22, Th9, and T follicular helper cells. The same holds true for regulatory T cells that represent a family with functionally distinct subsets characterized by co-expression of the transcription factors T-bet, Gata3, or RORγt. Here, we summarize the current knowledge on differentiation and function of T helper and regulatory T cell subsets and discuss their lineage stability versus plasticity towards other subsets. In addition, we highlight the direct and indirect contribution of each subset to the pathology of allergies and indicate novel therapies for specific targeting the effector functions of T helper and regulatory T cells.

Interleukin IL-5 alleviates sepsis-induced acute lung injury by regulating the immune response in rats

To study the effect of IL-5 on the immune response and lung injury in rats with sepsis. We constructed a rat model of sepsis by cecal ligation and puncture (CLP). The rats were randomly divided into the control group, the sham group, the CLP group and the IL-5 group, with 6 rats in each group. With the induction of CLP, the lung tissue of rats was severely injured, and the water content of lung tissue was significantly increased. Moreover, the ratio of CD4⁺/CD8⁺ was significantly decreased and Th1/Th2 was significantly increased in the peripheral blood. The content of IL-6, TNF-α, and HMGB1 was found to be increased in the CLP group. However, with the injection of IL-5, the degree of lung tissue injury in CLP rats was alleviated and the water content of lung tissue was significantly reduced. The ratio of CD4⁺/CD8⁺ was increased and Th1/Th2 was significantly down-regulated in the peripheral blood and the levels of IL-6, TNF-α, and HMGB1 in serum were significantly decreased. In conclusion, IL-5 can alleviate lung injury by regulating the immune response and inhibiting the systemic inflammatory response induced by sepsis.

Pathogenic helper T cells

Intractable chronic inflammatory diseases, including autoimmune diseases, autoinflammatory diseases and allergic diseases, are caused by disruption or failure of the immune system. Pathogenic immune cells are presumed to be closely related to the pathogenesis of intractable diseases, but the precise cellular and molecular mechanisms underlying the pathogenesis of these diseases remain unclear. The balance between the T helper type 1 (Th1) and Th2 cell fractions has been believed to be responsible for the differences among inflammatory diseases. However, an analysis of the cells infiltrating inflammatory lesions in mice and humans revealed the generation of pathogenic Th cells with different characteristics at the memory T-cell stage in the peripheral tissues in various inflammatory diseases. In this review, we will summarize and discuss recent progress regarding the characteristics of pathogenic Th cells, their mode of action, and the molecular mechanisms that regulate the pathology of intractable chronic inflammatory diseases, particularly those with tissue fibrosis. We hope this article will help clarify the pathogenesis of these diseases and propose a future direction for research.

Single-cell transcriptomic analysis of allergen-specific T cells in allergy and asthma

CD4⁺ T helper (T_H) cells and regulatory T (T_reg) cells that respond to common allergens play an important role in driving and dampening airway inflammation in patients with asthma. Until recently, direct, unbiased molecular analysis of allergen-reactive T_H and T_reg cells has not been possible. To better understand the diversity of these T cell subsets in allergy and asthma, we analyzed the single-cell transcriptome of ~50,000 house dust mite (HDM) allergen-reactive T_H cells and T_reg cells from asthmatics with HDM allergy and from three control groups: asthmatics without HDM allergy and nonasthmatics with and without HDM allergy. Our analyses show that HDM allergen-reactive T_H and T_reg cells are highly heterogeneous and certain subsets are quantitatively and qualitatively different in individuals with HDM-reactive asthma. The number of interleukin-9 (IL-9)-expressing HDM-reactive T_H cells is greater in asthmatics with HDM allergy compared with nonasthmatics with HDM allergy, and this IL-9-expressing T_H subset displays enhanced pathogenic properties. More HDM-reactive T_H and T_reg cells expressing the interferon response signature (T_HIFNR and T_regIFNR) are present in asthmatics without HDM allergy compared with those with HDM allergy. In cells from these subsets (T_HIFNR and T_regIFNR), expression of TNFSF10 was enriched; its product, tumor necrosis factor-related apoptosis-inducing ligand, dampens activation of T_H cells. These findings suggest that the T_HIFNR and T_regIFNR subsets may dampen allergic responses, which may help explain why only some people develop T_H2 responses to nearly ubiquitous allergens.

Eosinophils: Cells known for over 140 years with broad and new functions

Eosinophils are multifunctional leukocytes, being involved in the host defense against helminth infection, tissue homeostasis and repair of injured tissue. However, eosinophils also play critical roles in shaping the pathogenesis of allergic diseases, including fibrotic responses in allergic diseases. Eosinophils consist of various granules that are a source of cytokines, chemokines, enzymes, extracellular matrix and growth factors. Recent studies have revealed that eosinophil extracellular trap cell death (EETosis) exacerbates eosinophilic inflammation by releasing the products, including Charcot-Leyden crystals (CLCs). In type 2 inflammatory diseases, memory-type pathogenic helper T (Tpath) cells are involved in shaping the pathogenesis of eosinophilic inflammation by recruiting and activating eosinophils in vivo. We herein review the molecular mechanisms underlying the development of eosinophils and the various functions of granules, including CLCs, during eosinophilic inflammation. We also discuss the double-edged roles of eosinophils in tissue repair and type 2 immune inflammation.

Nasal Polyposis: Insights in Epithelial-Mesenchymal Transition and Differentiation of Polyp Mesenchymal Stem Cells

Chronic rhinosinusitis is a common inflammatory disease of paranasal sinuses, which causes rhinorrhea, nasal congestion, and hyposmia. The genetic predisposition or the exposure to irritants can sustain the inflammatory response and the development of nasal polyposis. Nasal polyps are benign and teardrop-shaped growths that project in the nasal cavities, and originate from the ethmoid sinuses. This inflammatory process is associated with high expression of IL-4, IL-5 and IL-13 and IgE. Antibodies targeting these cytokines or receptors represent a therapeutic strategy in the treatment of nasal polyposis in combination with corticosteroids. The molecular pathogenesis of nasal polyps in chronic rhinosinusitis (CRS) patients is associated with remodeling transition, a process in which epithelial cells lose their typical phenotype, acquiring a mesenchymal-like aspect. TGFβ/SMAD, ERK, and Wnt/β-catenin pathways are altered during the nasal tissue remodeling. miRNA and inhibitor molecules targeting these signaling pathways are able to interfere with the process; which could lead to alternative therapies. Nasal polyps are an alternative source of mesenchymal stem cells, which can be isolated from surgical biopsies. A molecular understanding of the biology of PO-MSCs will contribute to the delineating inflammatory process underlying the development of nasal polyps.

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.

Esophageal type 2 cytokine expression heterogeneity in eosinophilic esophagitis in a multisite cohort

BACKGROUND

There is strong evidence for a role of type 2 cytokines in the pathogenesis of eosinophilic esophagitis (EoE); however, heterogeneity in type 2 gene expression has not been examined.

OBJECTIVE

We examined type 2 immunity-associated gene expression in esophageal biopsy specimens, aiming to determine the degree of cytokine heterogeneity and its potential clinical significance.

METHODS

Patients (n = 312) were recruited from 10 sites associated with the Consortium of Eosinophilic Gastrointestinal Disease Researchers. In addition to histologic and endoscopic assessment, esophageal biopsy specimens were examined for expression of 96 genes within the EoE diagnostic panel.

RESULTS

Five subgroups of patients with active EoE were identified by unsupervised clustering based on expression of IL4, IL5, IL13, C-C motif chemokine ligand 26 (CCL26), thymic stromal lymphopoietin (TSLP), Charcot-Leyden crystal (CLC), C-C motif chemokine receptor 3 (CCR3), and CPA3. These groups differed in age (P < .02) and EoE diagnostic panel score (P < 1.08E-30) but not in eosinophil levels. The group V patients had the highest expression of IL5, TSLP, and CCL26 and genes associated with tissue remodeling, such as COL8A1, actin γ-2 (ACTG2), and tetraspanin 12 (TSPAN12). IL5 and IL13 were highly expressed in group IV; however, groups IV and V differed in age (34 vs 14 years [P < .05]). Groups II and III, which exhibited intermediate expression of IL5 and CPA3, were differentiated by high TSLP and IL13 in group III.

CONCLUSION

We observed heterogeneous type 2 gene expression among patients with active EoE. Type 2 gene overexpression was not directly proportional to disease features; this was especially true for tissue remodeling events. These findings highlight a clinical opportunity for leveraging molecular endotypes to implement personalized medicine in EoE.

TCR sequencing paired with massively parallel 3' RNA-seq reveals clonotypic T cell signatures

High-throughput 3' single-cell RNA-sequencing (scRNA-seq) allows cost-effective, detailed characterization of individual immune cells from tissues. Current techniques, however, are limited in their ability to elucidate essential immune cell features, including variable sequences of T cell antigen receptors (TCRs) that confer antigen specificity. Here, we present a strategy that enables simultaneous analysis of TCR sequences and corresponding full transcriptomes from 3'-barcoded scRNA-seq samples. This approach is compatible with common 3' scRNA-seq methods, and adaptable to processed samples post hoc. We applied the technique to identify transcriptional signatures associated with T cells sharing common TCRs from immunized mice and from patients with food allergy. We observed preferential phenotypes among subsets of expanded clonotypes, including type 2 helper CD4⁺ T cell (T_H2) states associated with food allergy. These results demonstrate the utility of our method when studying diseases in which clonotype-driven responses are critical to understanding the underlying biology.

Single-cell analysis to understand the diversity of immune cell types that drive disease pathogenesis

Single-cell next-generation sequencing assays are powerful tools to understand the nature of the immune cells that drive disease pathogenesis. In this brief review we explain the value of performing assays at single-cell resolution to better understand the pathogenesis of allergy, asthma, and other lung diseases. We explain the challenges in performing single-cell studies of airways and lung samples from patients with lung diseases. A major limitation comes from the amount of diseased tissue that can be used for research purposes. Finally, we discuss which sequencing strategies can be used to successfully investigate airway and lung diseases at single-cell resolution.

Signals from the various immune cells in promoting food allergy-induced eosinophilic esophagitis like disease

Eosinophilic esophagitis (EoE) is a recently recognized esophageal inflammatory disease with clinical manifestations arising from esophageal dysfunction. The etiology of EoE is currently being clarified and food allergy is evolving as the central cornerstone of EoE disease pathogenesis. Given the large number of eosinophils in the esophagus of people with EoE verified by data from murine models EoE is widely considered as the hallmark T-helper type 2 (Th2) disease of the esophagus. It is also known that some eosinophilic inflammation is controlled by other subsets of T cells such as Th9 or Th17 and control is also exerted by type 2 innate lymphoid cells acting together with basophils. In this paper we review results from molecular studies of mouse models in light of the results from the first clinical trials targeting key cytokines in humans and present in-depth molecular understanding of EoE.

Neuropeptide CGRP Limits Group 2 Innate Lymphoid Cell Responses and Constrains Type 2 Inflammation

Innate lymphocytes maintain tissue homeostasis at mucosal barriers, with group 2 innate lymphoid cells (ILC2s) producing type 2 cytokines and controlling helminth infection. While the molecular understanding of ILC2 responses has advanced, the complexity of microenvironmental factors impacting ILC2s is becoming increasingly apparent. Herein, we used single-cell analysis to explore the diversity of gene expression among lung lymphocytes during helminth infection. Following infection, we identified a subset of ILC2s that preferentially expressed Il5-encoding interleukin (IL)-5, together with Calca-encoding calcitonin gene-related peptide (CGRP) and its cognate receptor components. CGRP in concert with IL-33 and neuromedin U (NMU) supported IL-5 but constrained IL-13 expression and ILC2 proliferation. Without CGRP signaling, ILC2 responses and worm expulsion were enhanced. Collectively, these data point to CGRP as a context-dependent negative regulatory factor that shapes innate lymphocyte responses to alarmins and neuropeptides during type 2 innate immune responses.

Opposing roles of eosinophils in cancer

Eosinophils are a subset of granulocytes mostly known for their ability to combat parasites and induce allergy. Although they were described to be related to cancer more than 100 years ago, their role in tumors is still undefined. Recent observations revealed that they display regulatory functions towards other immune cell subsets in the tumor microenvironment or direct cytotoxic functions against tumor cells, leading to either antitumor or protumor effects. This paradoxical role of eosinophils was suggested to be dependent on the different factors in the TME. In addition, the clinical relevance of these cells has been recently addressed. In most cases, the accumulation of eosinophils both in the tumor tissue, called tumor-associated tissue eosinophilia, and in the peripheral blood were reported to be prognostic markers for a better outcome of cancer patients. In immunotherapy of cancer, particularly in therapy with immune checkpoint inhibitors, eosinophils were even shown to be a potential predictive marker for a beneficial clinical response. A better understanding of their role in cancer progression will help to establish them as prognostic and predictive markers and to design strategies for targeting eosinophils.

Single-cell RNA sequencing identifies inflammatory tissue T cells in eosinophilic esophagitis

T cell heterogeneity is highly relevant to allergic disorders. We resolved the heterogeneity of human tissue CD3+ T cells during allergic inflammation, focusing on a tissue-specific allergic disease, eosinophilic esophagitis (EoE). We investigated 1088 single T cells derived from patients with a spectrum of disease activity. Eight disparate tissue T cell subtypes (designated T1-T8) were identified, with T7 and T8 enriched in the diseased tissue. The phenotypes of T7 and T8 resemble putative Treg (FOXP3+) and effector Th2-like (GATA3+) cells, respectively. Prodigious levels of IL-5 and IL-13 were confined to HPGDS+ CRTH2+IL-17RB+FFAR3+CD4+ T8 effector Th2 cells. EoE severity closely paralleled a lipid/fatty acid-induced activation node highlighted by the expression of the short-chain fatty acid receptor FFAR3. Ligands for FFAR3 induced Th2 cytokine production from human and murine T cells, including in an in vivo allergy model. Therefore, we elucidated the defining characteristics of tissue-residing CD3+ T cells in EoE, a specific enrichment of CD4+ Treg and effector Th2 cells, confinement of type 2 cytokine production to the CD4+ effector population, a highly likely role for FFAR3 in amplifying local Th2 responses in EoE, and a resource to further dissect tissue lymphocytes and allergic responses.

Allergic components of eosinophilic esophagitis

Eosinophilic esophagitis (EoE) is a disorder of increasing prevalence worldwide, causing clinical symptoms of vomiting, failure to thrive, and dysphagia and complications of esophageal remodeling with strictures and food impactions. Molecular profiling demonstrates EoE to be an eosinophil-predominant disorder with a TH2 cytokine profile reminiscent of other allergic diseases, such as asthma, allergic rhinitis, and atopic dermatitis. Environmental antigens in the form of foods and aeroallergens induce eosinophil, basophil, mast cell, and T-cell infiltration. Pathogenesis depends on local epithelial immune activation with production of thymic stromal lymphopoietin and eotaxin-3. Complications mirror asthmatic airway pathogenesis, with increases in subepithelial collagen deposition, angiogenesis, and smooth muscle hypertrophy. The removal of instigating antigens, especially foods, causes disease resolution in more than 50% of adults and children. The prevalence of concurrent atopic disorders in patients with EoE and the need to control antigen-specific TH2 inflammation underscore the importance of testing for allergens and treating the entire atopic subject to control the potential interplay between organ-specific allergic responses.

Eosinophilic gastrointestinal diseases beyond eosinophilic esophagitis

OBJECTIVE

Eosinophilic gastrointestinal diseases (EGIDs) are a rare group of disorders that can have varied clinical presentations dependent on the involved segment within the gastrointestinal tract. Eosinophilic gastritis presents with abdominal pain or vomiting, eosinophilic gastroenteritis presents with diarrhea and anemia or hypoalbuminemia, and eosinophilic colitis can present with diarrhea or bloody stools. These nonspecific symptoms remain poorly understood in their relation to the underlying pathogenesis, but a significant percentage of patients have atopy. In this review, we discuss the current literature on EGIDs to promote a practical approach to diagnosis and care.

DATA SOURCES

Review of published literature.

STUDY SELECTIONS

Clinically relevant literature from 1900 through 2018 was obtained from a PubMed search. Those that addressed prevalence, diagnosis, clinical manifestations, natural history, and treatment of EGIDs were reviewed and are summarized in this article.

RESULTS

Of the 485 articles found in the search, most of which were case reports, 71 were selected for review. The natural history of EGIDs is based primarily on case series and small numbers of patients, making therapeutic decisions difficult. Treatment remains limited to dietary restriction that is not effective in many patients and topical or systemic corticosteroids whose long-term use is to be avoided if possible.

CONCLUSION

With the seeming increase in all types of EGIDs, phenotypic descriptions are emerging that will likely promote better understanding of the pathogenesis and identification of novel therapeutic targets.

Distinct Helper T Cell Type 1 and 2 Responses Associated With Malaria Protection and Risk in RTS,S/AS01E Vaccinees

Background

The RTS,S/AS01E malaria vaccine has moderate efficacy, lower in infants than children. Current efforts to enhance RTS,S/AS01E efficacy would benefit from learning about the vaccine-induced immunity and identifying correlates of malaria protection, which could, for instance, inform the choice of adjuvants. Here, we sought cellular immunity-based correlates of malaria protection and risk associated with RTS,S/AS01E vaccination.

Methods

We performed a matched case-control study nested within the multicenter African RTS,S/AS01E phase 3 trial. Children and infant samples from 57 clinical malaria cases (32 RTS,S/25 comparator vaccinees) and 152 controls without malaria (106 RTS,S/46 comparator vaccinees) were analyzed. We measured 30 markers by Luminex following RTS,S/AS01E antigen stimulation of cells 1 month postimmunization. Crude concentrations and ratios of antigen to background control were analyzed.

Results

Interleukin (IL) 2 and IL-5 ratios were associated with RTS,S/AS01E vaccination (adjusted P ≤ .01). IL-5 circumsporozoite protein (CSP) ratios, a helper T cell type 2 cytokine, correlated with higher odds of malaria in RTS,S/AS01E vaccinees (odds ratio, 1.17 per 10% increases of CSP ratios; P value adjusted for multiple testing = .03). In multimarker analysis, the helper T cell type 1 (TH1)-related markers interferon-γ, IL-15, and granulocyte-macrophage colony-stimulating factor protected from subsequent malaria, in contrast to IL-5 and RANTES, which increased the odds of malaria.

Conclusions

RTS,S/AS01E-induced IL-5 may be a surrogate of lack of protection, whereas TH1-related responses may be involved in protective mechanisms. Efforts to develop second-generation vaccine candidates may concentrate on adjuvants that modulate the immune system to support enhanced TH1 responses and decreased IL-5 responses.

TSLP signaling in CD4+ T cells programs a pathogenic T helper 2 cell state

Pathogenic T helper 2 (T_H2) cells, which produce increased amounts of the cytokines interleukin-5 (IL-5) and IL-13, promote allergic disorders, including asthma. Thymic stromal lymphopoietin (TSLP), a cytokine secreted by epithelial and innate immune cells, stimulates such pathogenic T_H2 cell responses. We found that TSLP signaling in mouse CD4⁺ T cells initiated transcriptional changes associated with T_H2 cell programming. IL-4 signaling amplified and stabilized the genomic response of T cells to TSLP, which increased the frequency of T cells producing IL-4, IL-5, and IL-13. Furthermore, the TSLP- and IL-4-programmed T_H2 cells had a pathogenic phenotype, producing greater amounts of IL-5 and IL-13 and other proinflammatory cytokines than did T_H2 cells stimulated with IL-4 alone. TSLP-mediated T_H2 cell induction involved distinct molecular pathways, including activation of the transcription factor STAT5 through the kinase JAK2 and repression of the transcription factor BCL6. Mice that received wild-type CD4⁺ T cells had exacerbated pathogenic T_H2 cell responses upon exposure to house dust mites compared to mice that received TSLP receptor-deficient CD4⁺ T cells. Transient TSLP signaling stably programmed pathogenic potential in memory T_H2 cells. In human CD4⁺ T cells, TSLP and IL-4 promoted the generation of T_H2 cells that produced greater amounts of IL-5 and IL-13. Compared to healthy controls, asthmatic children showed enhancement of such T cell responses in peripheral blood. Our data support a sequential cytokine model for pathogenic T_H2 cell differentiation and provide a mechanistic basis for the therapeutic targeting of TSLP signaling in human allergic diseases.

Thymic stromal lymphopoietin drives the development of IL-13+ Th2 cells

T helper 2 (Th2) cells are defined by their ability to produce the hallmark cytokine IL-4. However, to mediate allergic inflammation in tissues, Th2 cells must secrete additional cytokines including IL-13 and IL-5. We used IL-4 and IL-13 dual-reporter mice to show that naive CD4⁺ T cells cultured in the presence of IL-4 and thymic stromal lymphopoietin (TSLP) generate a population of IL-4^negIL-13^pos Th2 cells that develop from IL-4^neg precursors and express the Th2 effector cytokines IL-5 and IL-9. In vivo, high TSLP levels promote the development of a similar population of IL-4^negIL-13^pos T cells that also express Gata3, Il5, and Il3 transcripts. Thus, TSLP drives the early differentiation of a distinct population of effector Th2 cells with pro-inflammatory properties.

T helper 2 (Th2) cells are pivotal in the development of allergy. Allergen exposure primes IL-4⁺ Th2 cells in lymph node, but production of effector cytokines including IL-5 and IL-13 is thought to require additional signals from antigen and the environment. Here we report that a substantial proportion of naive CD4⁺ T cells in spleen and lymph node express receptors for the epithelium-derived inflammatory cytokine thymic stromal lymphopoietin (TSLP). Culture of naive CD4⁺ T cells in anti-(a)CD3, aCD28, and TSLP-supplemented Th2 conditions enabled the development of a unique population of IL-13-single positive (IL-13-SP) CD4⁺ T cells; TSLP and Th2 conditions were both required for their development. Sorting experiments revealed that IL-13-SP Th2 cells originated from IL-4-negative precursors and coexpressed transcripts for the Th2 cytokines IL-5 and IL-9. In vivo, high TSLP levels acted directly on CD4⁺ T cells to induce the development of IL-13-SP and IL-4⁺IL-13⁺ double-positive populations in lymph node. These cells were phenotypically similar to Th2 effector cells and were CXCR5^lowPD1^low and expressed low levels of Bcl6 and Il21 transcripts and high levels of Gata3, Il3, and Il5. Our findings suggest a role of TSLP in directly promoting Th2 cell effector function and support the notion of TSLP as a key driver of Th2 inflammation.

Heterogeneity of Human CD4(+) T Cells Against Microbes

CD4(+) T helper (Th) cells play a central role in the adaptive immune response by providing help to B cells and cytotoxic T cells and by releasing different types of cytokines in tissues to mediate protection against a wide range of pathogenic microorganisms. These functions are performed by different types of Th cells endowed with distinct migratory capacities and effector functions. Here we discuss how studies of the human T cell response to microbes have advanced our understanding of Th cell functional heterogeneity, in particular with the discovery of a distinct Th1 subset involved in the response to Mycobacteria and the characterization of two types of Th17 cells specific for extracellular bacteria or fungi. We also review new approaches to dissect at the clonal level the human CD4(+) T cell response induced by pathogens or vaccines that have revealed an unexpected degree of intraclonal diversification and propose a progressive and selective model of CD4(+) T cell differentiation.

Pathogenic Effector Th2 Cells in Allergic Eosinophilic Inflammatory Disease

There is an absolute requirement for Th2 cells in the pathogenesis of allergen-driven eosinophil-rich type 2 inflammation. Although Th2 cells are generally regarded as a homogeneous population, in the past decade there has been increasing evidence for a minority subpopulation of IL-5+ Th2 cells that have enhanced effector function. This IL-5+ Th2 subpopulation has been termed pathogenic effector Th2 (peTh2), as it exhibits greater effector function and disease association than conventional Th2 cells. peTh2 cells have a different expression profile, differentially express transcription factors, and preferentially use specific signaling pathways. As such, peTh2 cells are a potential target in the treatment of allergic eosinophilic inflammation. This review examines peTh2 cells, both in mouse models and human disease, with an emphasis on their role in the pathogenesis of allergic eosinophilic inflammation.

Dysregulation of interleukin 5 expression in familial eosinophilia

BACKGROUND

Familial eosinophilia (FE) is a rare autosomal dominant inherited disorder characterized by the presence of lifelong peripheral eosinophilia (>1500/μL). Mapped to chromosome 5q31-q33, the genetic cause of FE is unknown, and prior studies have failed to demonstrate a primary abnormality in the eosinophil lineage.

OBJECTIVE

The aim of this study was to identify the cells driving the eosinophilia in FE.

METHODS

Microarray analysis and real-time PCR were used to examine transcriptional differences in peripheral blood mononuclear cells (PBMC), and in purified cell subsets from affected and unaffected family members belonging to a single large kindred. Cytokine levels in serum and PBMC culture supernatants were assessed by suspension array multiplexed immunoassays.

RESULTS

Whereas IL-5 mRNA expression was significantly increased in freshly isolated PBMC from affected family members, this was not accompanied by increased mRNA expression of other Th2 cytokines (IL-4 or IL-13). Serum levels of IL-5 and IL-5 receptor α, but not IgE, were similarly increased in affected family members. Of note, IL-5 mRNA expression was significantly increased in purified CD3+ CD4+, CD14+, CD19+, and ILC2 cells from affected family members, as were IL-5 protein levels in supernatants from both stimulated PBMC and ILC2 cultures.

CONCLUSIONS

These data are consistent with the hypothesis that the eosinophilia in FE is secondary to dysregulation of IL-5 production in PBMC (and their component subsets).

The Regulatory Function of Eosinophils

Eosinophils are a minority circulating granulocyte classically viewed as being involved in host defense against parasites and promoting allergic reactions. However, a series of new regulatory functions for these cells have been identified in the past decade. During homeostasis, eosinophils develop in the bone marrow and migrate from the blood into target tissues following an eotaxin gradient, with interleukin-5 being a key cytokine for eosinophil proliferation, survival, and priming. In multiple target tissues, eosinophils actively regulate a variety of immune functions through their vast arsenal of granule products and cytokines, as well as direct cellular interaction with cells in proximity. The immunologic regulation of eosinophils extends from innate immunity to adaptive immunity and also involves non-immune cells. Herein, we summarize recent findings regarding novel roles of murine and human eosinophils, focusing on interactions with other hematopoietic cells. We also review new experimental tools available and remaining questions to uncover a greater understanding of this enigmatic cell.

A phenotypically and functionally distinct human TH2 cell subpopulation is associated with allergic disorders

Allergen-specific type 2 helper T (TH2) cells play a central role in initiating and orchestrating the allergic and asthmatic inflammatory response pathways. One major factor limiting the use of such atopic disease-causing T cells as both therapeutic targets and clinically useful biomarkers is the lack of an accepted methodology to identify and differentiate these cells from overall nonpathogenic TH2 cell types. We have described a subset of human memory TH2 cells confined to atopic individuals that includes all allergen-specific TH2 cells. These cells are terminally differentiated CD4+ T cells (CD27- and CD45RB-) characterized by coexpression of CRTH2, CD49d, and CD161 and exhibit numerous functional attributes distinct from conventional TH2 cells. Hence, we have denoted these cells with this stable allergic disease-related phenotype as the TH2A cell subset. Transcriptome analysis further revealed a distinct pathway in the initiation of pathogenic responses to allergen, and elimination of these cells is indicative of clinical responses induced by immunotherapy. Together, these findings identify a human TH2 cell signature in allergic diseases that could be used for response-monitoring and designing appropriate immunomodulatory strategies.