Dendritic cells and B cells: unexpected partners in Th2 development

An esophagus cell atlas reveals dynamic rewiring during active eosinophilic esophagitis and remission

Coordinated cell interactions within the esophagus maintain homeostasis, and disruption can lead to eosinophilic esophagitis (EoE), a chronic inflammatory disease with poorly understood pathogenesis. We profile 421,312 individual cells from the esophageal mucosa of 7 healthy and 15 EoE participants, revealing 60 cell subsets and functional alterations in cell states, compositions, and interactions that highlight previously unclear features of EoE. Active disease displays enrichment of ALOX15+ macrophages, PRDM16+ dendritic cells expressing the EoE risk gene ATP10A, and cycling mast cells, with concomitant reduction of TH17 cells. Ligand-receptor expression uncovers eosinophil recruitment programs, increased fibroblast interactions in disease, and IL-9+IL-4+IL-13+ TH2 and endothelial cells as potential mast cell interactors. Resolution of inflammation-associated signatures includes mast and CD4+ TRM cell contraction and cell type-specific downregulation of eosinophil chemoattractant, growth, and survival factors. These cellular alterations in EoE and remission advance our understanding of eosinophilic inflammation and opportunities for therapeutic intervention.

Anti-CD20 treatment attenuates Th2 cell responses: implications for the role of lung follicular mature B cells in the asthmatic mice

BACKGROUND

B cells were believed to act as antigen-presenting cells (APCs) to promote T helper type 2 (Th2) cell responses. However, the role of lung B cells and its subpopulations in Th2 cell responses in asthma remains unclear.

OBJECTIVE

We leveraged an anti-CD20 monoclonal antibody (mAb) treatment that has been shown to selectively deplete B cells in mice and investigated whether this treatment modulates Th2 cell responses and this modulation is related to lung follicular mature (FM) B cells in a murine model of asthma.

METHODS AND RESULTS

We used a house dust mite (HDM)-induced asthma mouse model and found that anti-CD20 mAb treatment attenuates Th2 cell responses. Meanwhile, anti-CD20 mAb treatment did dramatically reduce the number of B cells, especially FM B cells in the lungs, but did not impact the frequency of other immune cell types, including lung T cells, dendritic cells, natural killer cells, and regulatory T cells in wild-type mice. Moreover, we found that the suppressive effect of anti-CD20 mAb treatment on Th2 cell responses could be reversed upon adoptive transfer of lung FM B cells, but not lung CD19+ B cells without FM B cells in asthmatic mice.

CONCLUSIONS

These findings reveal that anti-CD20 mAb treatment alleviates Th2 cell responses, possibly by depleting lung FM B cells in a Th2-driven asthma model. This implies a potential therapeutic approach for asthma treatment through the targeting of lung FM B cells.

Development of Self-Assembled Protein Nanocage Spatially Functionalized with HA Stalk as a Broadly Cross-Reactive Influenza Vaccine Platform

There remains a need for the development of a universal influenza vaccine, as current seasonal influenza vaccines exhibit limited protection against mismatched, mutated, or pandemic influenza viruses. A desirable approach to developing an effective universal influenza vaccine is the incorporation of highly conserved antigens in a multivalent scaffold that enhances their immunogenicity. Here, we develop a broadly cross-reactive influenza vaccine by functionalizing self-assembled protein nanocages (SAPNs) with multiple copies of the hemagglutinin stalk on the outer surface and matrix protein 2 ectodomain on the inner surface. SAPNs were generated by engineering short coiled coils, and the design was simulated by MD GROMACS. Due to the short sequences, off-target immune responses against empty SAPN scaffolds were not seen in immunized mice. Vaccination with the multivalent SAPNs induces high levels of broadly cross-reactive antibodies of only external antigens, demonstrating tight spatial control over the designed antigen placement. This work demonstrates the use of SAPNs as a potential influenza vaccine.

Sensing of protease activity as a triggering mechanism of Th2 cell immunity and allergic disease

CD4 T-helper cell type 2 (Th2) cells mediate host defense against extracellular parasites, like helminths. However, Th2 cells also play a pivotal role in the onset and progression of allergic inflammatory diseases such as atopic dermatitis, allergic rhinitis, asthma, and food allergy. This happens when allergens, which are otherwise harmless foreign proteins, are mistakenly identified as "pathogenic." Consequently, the encounter with these allergens triggers the activation of specific Th2 cell responses, leading to the development of allergic reactions. Understanding the molecular basis of allergen sensing is vital for comprehending how Th2 cell responses are erroneously initiated in individuals with allergies. The presence of protease activity in allergens, such as house dust mites (HDM), pollen, fungi, or cockroaches, has been found to play a significant role in triggering robust Th2 cell responses. In this review, we aim to examine the significance of protease activity sensing in foreign proteins for the initiation of Th2 cell responses, highlighting how evolving a host protease sensor may contribute to detect invading helminth parasites, but conversely can also trigger unwanted reactions to protease allergens. In this context, we will explore the recognition receptors activated by proteolytic enzymes present in major allergens and their contribution to Th2-mediated allergic responses. Furthermore, we will discuss the coordinated efforts of sensory neurons and epithelial cells in detecting protease allergens, the subsequent activation of intermediary cells, including mast cells and type 2 innate lymphoid cells (ILC2s), and the ultimate integration of all signals by conventional dendritic cells (cDCs), leading to the induction of Th2 cell responses. On the other hand, the review highlights the role of monocytes in the context of protease allergen exposure and their interaction with cDCs to mitigate undesirable Th2 cell reactions. This review aims to provide insights into the innate functions and cell communications triggered by protease allergens, which can contribute to the initiation of detrimental Th2 cell responses, but also promote mechanisms to effectively suppress their development.

Interferon Gamma Targeted Therapy: Is It Justified in Primary Sjögren's Syndrome?

Background: The pathomechanism of primary Sjögren syndrome (pSS) is multifactorial. Many cytokines take part in this process, including interferon. The study aimed to quantify certain cytokines involved in the pathomechanism of primary Sjögren syndrome (IL2, IL5, IL6, IL10, IL13, TNFα, IFNγ) and determine their common clinical correlation. On this basis, we discuss the potential use of anti-cytokine drugs in pSS therapy. Methods: The study group consisted of adult patients with a confirmed diagnosis of pSS. Results: The most frequently detected cytokines were IFNγ (82% of patients), TNFα (70%), IL6 (50%), and IL2 (42.5%). In all patients, except for one patient, IFNγ was found in the presence of other specific cytokines. There was no difference in clinical symptoms, age, and laboratory test results between the group of patients with IL-6 + TNFα + IFNγ positive cytokine, and the group of patients in whom they were not detected. There was no correlation between the presence of IL5, IL13, IL2, IL6, IL10, TNFα and musculoskeletal symptoms, skin lesions, glandular domains, pulmonary neurological, lymphadenopathy, biological and hematological domains in ESSDAI (p > 0.05). Conclusions: IFNγ most likely plays a central role in the pathomechanism of the disease. We have not noticed a clinical correlation between the three most common cytokines (IL6, IFNγ and TNFα), preliminary research results open up the possibility of searching for new treatments for pSS. The lower percentage of patients with detectable levels of TNFα and IL6 may explain the ineffectiveness of drugs targeting cytokines in clinical trials to date.

Context-dependent roles of B cells during intestinal helminth infection

The current approaches to reduce the burden of chronic helminth infections in endemic areas are adequate sanitation and periodic administration of deworming drugs. Yet, resistance against some deworming drugs and reinfection can still rapidly occur even after treatment. A vaccine against helminths would be an effective solution at preventing reinfection. However, vaccines against helminth parasites have yet to be successfully developed. While T helper cells and innate lymphoid cells have been established as important components of the protective type 2 response, the roles of B cells and antibodies remain the most controversial. Here, we review the roles of B cells during intestinal helminth infection. We discuss the potential factors that contribute to the context-specific roles for B cells in protection against diverse intestinal helminth parasite species, using evidence from well-defined murine model systems. Understanding the precise roles of B cells during resistance and susceptibility to helminth infection may offer a new perspective of type 2 protective immunity.

The Role of B Cells in Regulation of Th Cell Differentiation in Coxsackievirus B3-Induced Acute Myocarditis

Viral myocarditis (VMC) is the major cause of sudden death in adolescents. To date, no effective treatment has been identified for VMC. Studies have shown that T helper (Th) cells such as Th1, Th2, Th17, and Th22 cells are involved in the pathogenesis of VMC. However, the role of B cells and their impact on Th cells in VMC is unclear. In this study, we investigated the role of B cells in Th cell differentiation in myocardial damage in an animal model of VMC. C57BL/6 mice were infected with Coxsackievirus B3 (CVB3) intraperitoneally or injected with phosphate-buffered saline as a control condition. At day 7, samples from these mice were analyzed by histology, ELISA, flow cytometry, and gene expression assays. We found that TNF-α-, IL-6-, and IL-17-producing B cell numbers were significantly increased, while IL-4-producing B cell population was significantly reduced in acute VMC. Furthermore, we performed B cell knockout (BKO), SCID, and SCID+B cells reconstitution experiments. We found that BKO alleviated the cardiac damage following CVB3 infection, may hamper the differentiation of Th1 and Th17 cells, may promote the differentiation of Th2 cells, and proved ineffective for the differentiation of Th22 cells. In contrast, SCID+B cells reconstitution experiment exacerbated the cardiac damage. Ex vivo studies further revealed that B cells promote the differentiation of Th1 and Th17 cells and inhibit the differentiation of Th2 cells. Our study shows that B cells are activated and have strong abilities of antigen presentation and producing cytokines in VMC; B cells not only play a pathogenic role in VMC independent of T cells but also promote Th1 and Th17 cell differentiation, and hamper Th2 cell differentiation in VMC.

Calcium Dynamics Regulate Protective Responses and Growth of Staphylococcus aureus in Macrophages

Staphylococcus aureus (S. aureus) is a gram-positive bacteria, which causes various fatal respiratory infections including pneumonia. The emergence of Methicillin-Resistance Staphylococcus aureus (MRSA) demands a thorough understanding of host-pathogen interactions. Here we report the role of calcium in regulating defence responses of S. aureus in macrophages. Regulating calcium fluxes in cells by different routes differentially governs the expression of T cell costimulatory molecule CD80 and Th1 promoting IL-12 receptor. Inhibiting calcium influx from extracellular medium increased expression of IFN-γ and IL-10 while blocking calcium release from the intracellular stores inhibited TGF-β levels. Blocking voltage-gated calcium channels (VGCC) inhibited the expression of multiple cytokines. While VGCC regulated the expression of apoptosis protein Bax, extracellular calcium-regulated the expression of Cytochrome-C. Similarly, VGCC regulated the expression of autophagy initiator Beclin-1. Blocking VGCC or calcium release from intracellular stores promoted phagosome-lysosome fusion, while activating VGCC inhibited phagosomelysosome fusion. Finally, calcium homeostasis regulated intracellular growth of Staphylococcus, although using different mechanisms. While blocking extracellular calcium influx seems to rely on IFN-γ and IL-12Rβ receptor mediated reduction in bacterial survival, blocking either intracellular calcium release or via VGCC route seem to rely on enhanced autophagy mediated reduction of intracellular bacterial survival. These results point to fine-tuning of defence responses by routes of calcium homeostasis.

The Role of Thyroid Hormone in the Innate and Adaptive Immune Response during Infection

In the past decades, there has been growing evidence for a functional interaction between the thyroid hormone and the immune system. This article provides an overview of the mechanisms by which thyroid hormones affect the innate and adaptive immune response during infection. The influence of thyroid hormone on the most important players of the innate [neutrophils, macrophages, natural killer (NK) cells, and dendritic cells (DCs)] and adaptive immune system (B- and T-lymphocytes) is reviewed here based on both clinical and preclinical studies. The effects of modulation of the immune system by drugs, such as monoclonal antibodies, tyrosine kinase inhibitors, and interferons on thyroid function, are beyond the scope of this article. Thyroid hormones regulate the activity of neutrophils which is reflected by higher numbers of neutrophils outside the bloodstream and enhanced activity of the respiratory burst following stimulation with thyroid hormone. Hyperthyroidism affects neutrophil function to a larger extent than hypothyroidism. In addition to neutrophil function, macrophage function is strongly affected by thyroid hormones, with triiodothyronine having a pro-inflammatory effect in these cells. NK cell proliferation and cytotoxic activity are also dependent on thyroid hormone levels. Finally, thyroid hormones enhance DC proliferation and maturation. In the adaptive immune system, a hyperthyroid state leads to increased activation of lymphocytes. This effect of thyroid hormone is mediated by various factors including NF-κB and protein kinase C signaling pathways and the β-adrenergic receptor. In general, a hyperthyroid state leads to a more activated immune system whereas hypothyroidism leads to a less activated immune system. © 2020 American Physiological Society. Compr Physiol 10:1277-1287, 2020.

Contributions of Major Cell Populations to Sjögren's Syndrome

Sjögren’s syndrome (SS) is a female dominated autoimmune disease characterized by lymphocytic infiltration into salivary and lacrimal glands and subsequent exocrine glandular dysfunction. SS also may exhibit a broad array of extraglandular manifestations including an elevated incidence of non-Hodgkin’s B cell lymphoma. The etiology of SS remains poorly understood, yet progress has been made in identifying progressive stages of disease using preclinical mouse models. The roles played by immune cell subtypes within these stages of disease are becoming increasingly well understood, though significant gaps in knowledge still remain. There is evidence for distinct involvement from both innate and adaptive immune cells, where cells of the innate immune system establish a proinflammatory environment characterized by a type I interferon (IFN) signature that facilitates propagation of the disease by further activating T and B cell subsets to generate autoantibodies and participate in glandular destruction. This review will discuss the evidence for participation in disease pathogenesis by various classes of immune cells and glandular epithelial cells based upon data from both preclinical mouse models and human patients. Further examination of the contributions of glandular and immune cell subtypes to SS will be necessary to identify additional therapeutic targets that may lead to better management of the disease.

Mild Cytokine Elevation, Moderate CD4+ T Cell Response and Abundant Antibody Production in Children with COVID-19

Children with Coronavirus Disease 2019 (COVID-19) were reported to show milder symptoms and better prognosis than their adult counterparts, but the difference of immune response against SARS-CoV-2 between children and adults hasn’t been reported. Therefore we initiated this study to figure out the features of immune response in children with COVID-19. Sera and whole blood cells from 19 children with COVID-19 during different phases after disease onset were collected. The cytokine concentrations, SARS-CoV-2 S-RBD or N-specific antibodies and T cell immune responses were detected respectively. In children with COVID-19, only 3 of 12 cytokines were increased in acute sera, including interferon (IFN)-γ-induced protein 10 (IP10), interleukin (IL)-10 and IL-16. We observed an increase in T helper (Th)-2 cells and a suppression in regulatory T cells (Treg) in patients during acute phase, but no significant response was found in the IFN-γ-producing or tumor necrosis factor (TNF)-α-producing CD8⁺T cells in patients. S-RBD and N IgM showed an early induction, while S-RBD and N IgG were prominently induced later in convalescent phase. Potent S-RBD IgA response was observed but N IgA seemed to be inconspicuous. Children with COVID-19 displayed an immunophenotype that is less inflammatory than adults, including unremarkable cytokine elevation, moderate CD4⁺ T cell response and inactive CD8⁺ T cell response, but their humoral immunity against SARS-CoV-2 were as strong as adults. Our finding presented immunological characteristics of children with COVID-19 and might give some clues as to why children develop less severe disease than adults.

Bacterial Immunogenicity Is Critical for the Induction of Regulatory B Cells in Suppressing Inflammatory Immune Responses

B cells fulfill multifaceted functions that influence immune responses during health and disease. In autoimmune diseases, such as inflammatory bowel disease, multiple sclerosis and rheumatoid arthritis, depletion of functional B cells results in an aggravation of disease in humans and respective mouse models. This could be due to a lack of a pivotal B cell subpopulation: regulatory B cells (Bregs). Although Bregs represent only a small proportion of all immune cells, they exhibit critical properties in regulating immune responses, thus contributing to the maintenance of immune homeostasis in healthy individuals. In this study, we report that the induction of Bregs is differentially triggered by the immunogenicity of the host microbiota. In comparative experiments with low immunogenic Bacteroides vulgatus and strong immunogenic Escherichia coli, we found that the induction and longevity of Bregs depend on strong Toll-like receptor activation mediated by antigens of strong immunogenic commensals. The potent B cell stimulation via E. coli led to a pronounced expression of suppressive molecules on the B cell surface and an increased production of anti-inflammatory cytokines like interleukin-10. These bacteria-primed Bregs were capable of efficiently inhibiting the maturation and function of dendritic cells (DCs), preventing the proliferation and polarization of T helper (Th)1 and Th17 cells while simultaneously promoting Th2 cell differentiation in vitro. In addition, Bregs facilitated the development of regulatory T cells (Tregs) resulting in a possible feedback cooperation to establish immune homeostasis. Moreover, the colonization of germfree wild type mice with E. coli but not B. vulgatus significantly reduced intestinal inflammatory processes in dextran sulfate sodium (DSS)-induced colitis associated with an increase induction of immune suppressive Bregs. The quantity of Bregs directly correlated with the severity of inflammation. These findings may provide new insights and therapeutic approaches for B cell-controlled treatments of microbiota-driven autoimmune disease.

TLR9 agonist adsorbed to alum adjuvant prevents asthma-like responses induced by Blomia tropicalis mite extract

Blomia tropicalis mite is highly prevalent in tropical and subtropical regions and it is associated with allergic diseases such as rhinitis and asthma. By using an OVA-model of allergic lung disease, we have previously shown that sensitization in the presence of toll like receptors (TLRs) agonists attenuates subsequent OVA-induced allergic responses. Here, we evaluated the effect of CpG-ODN, a specific synthetic TLR-9 agonist, on the development of experimental asthma induced by Blomia tropicalis extract, a relevant source of aeroallergens. Among different protocols of Blomia tropicalis extract sensitization, the subcutaneous sensitization in the presence of alum adjuvant induced the highest Th2 responses, including high IgE levels. Adsorption of CpG to Blomia tropicalis extract/Alum attenuated the airway hyperreactivity, the infiltration of inflammatory cells including eosinophils, and the IL-5 content in BAL. In addition, lung peribronchial inflammatory infiltrate, mucus production and IL-5-producing CD3⁺ CD4⁺ T cells were significantly reduced in the Blomia tropicalis extract/Alum+CpG group. Importantly, CpG inhibited total IgE production as well as active systemic or cutaneous anaphylaxis reactions. Inhibition of pulmonary Th2 responses was associated with increased IL-10 production but not with IFN-γ production. Notably, in IL-10-deficient mice, sensitization with OVA/Alum+CpG resulted in intense lung neutrophilia and IFN-γ production, indicating that IL-10 is necessary to inhibit subsequent Th1 immunity. Our work highlights the mechanisms of allergy attenuation by CpG and it indicates the potential use of Alum-based formulation with CpG to treat allergic processes.

Compartmentalization of dendritic cell and T-cell interactions in the lymph node: Anatomy of T-cell fate decisions

Upon receiving cognate and co-stimulatory priming signals from antigen (Ag)-presenting dendritic cells (DCs) in secondary lymphoid tissues, naïve CD4+ T cells differentiate into distinct effector and memory populations. These alternate cell fate decisions, which ultimately control the T-cell functional attributes, are dictated by programming signals provided by Ag-bearing DCs and by other cells that are present in the microenvironment in which T-cell priming occurs. We know that DCs can be subdivided into multiple populations and that the various DC subsets exhibit differential capacities to initiate development of the different CD4+ T-helper populations. What is less well understood is why different subanatomic regions of secondary lymphoid tissues are colonized by distinct populations of Ag-presenting DCs and how the location of these DCs influences the type of T-cell response that will be generated. Here we review how chemokine receptors and their ligands, which position allergen and nematode-activated DCs within different microdomains of secondary lymphoid tissues, contribute to the establishment of IL-4 committed follicular helper T and type 2 helper cell responses.

The impact of allergen exposure and specific immunotherapy on circulating blood cells in allergic rhinitis

Allergic rhinitis (AR) is an IgE-mediated inflammatory disease of the nasal mucosa with well described local immune responses during allergen exposure. The frequent association of AR with general extra-nasal symptoms and other allergic conditions, such as conjunctivitis and asthma, however, support a more systemic disease impact. In addition to acute elevation of soluble inflammatory mediators in periphery blood, a growing number of studies have reported changes in circulating blood cells after specific nasal allergen challenge or environmental allergen exposure. These findings imply an involvement of specific blood leukocyte subsets, thrombocytes and recently, erythrocytes. This review summarizes the circulating blood cell dynamics associated with allergen exposure in AR subjects reported so far. Additionally, the impact of therapy, particularly allergen-specific immunotherapy (AIT), the only currently available causal treatment reducing AR-related symptoms, is further considered in this context.

Circulating level of Th17 cells is associated with sensitivity to glucocorticoids in patients with immune thrombocytopenia

Glucocorticoids are a widely recognized first-line therapy for immune thrombocytopenia (ITP). However, some patients are unresponsive to glucocorticoid therapy for reasons that remain unclear. Accumulating evidence suggests that CD4⁺ T-cell abnormalities play a crucial role in the development of ITP. In the present study, we investigated peripheral blood CD4⁺ T cells, Th17-associated cytokines, and the mRNA expression level of Th17 transcription factor-RORγt-in patients with newly-diagnosed ITP before glucocorticoid therapy. The study involved 27 newly-diagnosed patients. Th17-cell levels in the peripheral blood of newly-diagnosed ITP patients were associated with responsiveness to glucocorticoid therapy. Newly-diagnosed ITP patients who were not sensitive to glucocorticoid treatment were found to have lower levels of Th17 cells. Quantifying Th17 cells may allow physicians to predict prognosis of glucocorticoid treatment and stratify therapy for those with ITP. This strategy may provide a new approach to the treatment of glucocorticoid-insensitive patients.

Type 2 cytokine responses: regulating immunity to helminth parasites and allergic inflammation

Purpose of Review

It is well established that T helper type 2 (T_H2) immune responses are necessary to provide protection against helminth parasites but also to promote the detrimental inflammation associated with allergies and asthma. Given the importance of type 2 immunity and inflammation, many studies have focused on better understanding the factors that regulate T_H2 cell development and activation. As a result, significant progress has been made in understanding the signaling pathways and molecular events necessary to promote T_H2 cell polarization. In addition to the adaptive compartment, emerging studies are better defining the innate immune pathways needed to promote T_H2 cell responses. Given the recent and substantial growth of this field, the purpose of this review is to highlight recent studies defining the innate immune events that promote immunity to helminth parasites and allergic inflammation.

Recent Findings

Emerging studies have begun to elucidate the importance of cytokine alarmins such as thymic stromal lymphopoietin (TSLP), IL-25 (IL-17E) and IL-33 in promoting type 2 immunity and inflammation following helminth challenge or exposure to allergens. Specifically, recent reports have begun to define the complex cellular networks these alarmins activate and their contribution to type 2 immunity and inflammation.

Summary

Our increased understanding of the pathways that regulate type 2 cytokine-mediated immunity and inflammation have revealed novel therapeutic targets to treat both helminth infections and allergic disease states.

Role of B cells in TH cell responses in a mouse model of asthma

BACKGROUND

The importance of B lymphocytes to present antigens for antibody production is well documented. In contrast, very little is known about their capacity to influence CD4⁺ T-cell activation during a primary or secondary response to allergens.

OBJECTIVE

Using mouse models of asthma, we investigated the role of B cells as antigen-presenting cells in priming and maintenance of T_H cell responses.

METHODS

Mice were immunized through the intranasal route with house dust mite (HDM) extract derived from Dermatophagoides pteronyssinus. B cells were depleted in HDM-sensitized animals to investigate the importance of B cells in maintenance of the allergic response. B cells were depleted before HDM sensitization to investigate the role of B cells in T-cell priming; furthermore, HDM sensitization was performed in mice with MHC class II expression restricted to the B-cell lineage.

RESULTS

We found that B cells serve as potent antigen-presenting cells ex vivo and restimulate in vivo-primed HDM-specific T_H cells. HDM antigens were taken up by B cells independently of B-cell receptor specificity, indicating that HDM uptake and antigen presentation to CD4⁺ T cells is not restricted to rare B cells carrying HDM-specific B cell receptors. B-cell depletion before HDM challenge in HDM-sensitized mice resulted in a dramatic reduction of allergic response, indicating the role of B cells in amplification of T_H2 responses. In contrast, HDM sensitization of mice in which MHC class II expression was restricted to B cells revealed the inability of these cells to prime T_H2 responses but highlighted their unexpected role in priming T_H1 and T_H17 responses.

CONCLUSION

Collectively, these data reveal new mechanisms leading to initiation and exacerbation of the allergic response that might have implications for designing new therapeutic strategies to combat HDM allergy.

Schistosome-induced pulmonary B cells inhibit allergic airway inflammation and display a reduced Th2-driving function

Chronic schistosome infections protect against allergic airway inflammation (AAI) via the induction of IL-10-producing splenic regulatory B (Breg) cells. Previous experiments have demonstrated that schistosome-induced pulmonary B cells can also reduce AAI, but act independently of IL-10. We have now further characterized the phenotype and inhibitory activity of these protective pulmonary B cells. We excluded a role for regulatory T (Treg) cell induction as putative AAI-protective mechanisms. Schistosome-induced B cells showed increased CD86 expression and reduced cytokine expression in response to Toll-like receptor (TLR) ligands compared with control B cells. To investigate the consequences for T cell activation we cultured ovalbumin (OVA)-pulsed, schistosome-induced B cells with OVA-specific transgenic T cells and observed less Th2 cytokine expression and T cell proliferation compared with control conditions. This suppressive effect was preserved even under optimal T cell stimulation by anti-CD3/28. Blocking of the inhibitory cytokines IL-10 or TGF-β only marginally restored Th2 cytokine induction. These data suggest that schistosome-induced pulmonary B cells are impaired in their capacity to produce cytokines to TLR ligands and to induce Th2 cytokine responses independent of their antigen-presenting function. These findings underline the presence of distinct B cell subsets with different stimulatory or inhibitory properties even if induced by the same type of helminth.

Development of eosinophilic inflammation is independent of B-T cell interaction in a chronic house dust mite-driven asthma model

BACKGROUND

Chronic exposure to environmental triggers, such as house dust mite (HDM), drives T helper 2 (Th2) cell-mediated asthma. Recent evidence has shown that B-T cell interaction, and in particular germinal centre reactions and follicular T helper (Tfh) cells are required for the development of eosinophilic airway inflammation in HDM-driven models containing a sensitization and challenge phase. Whether B-T cell interactions are essential for pulmonary eosinophilic inflammation following chronic allergen provocation remains unknown.

AIMS

In this study, we investigated the importance of B-T cell interaction in the development of eosinophilic airway inflammation and pulmonary remodelling in a chronic HDM-driven asthma model.

METHODS

We exposed C57BL/6, Cd40l^-/- , and Mb1^-/- mice to HDM three times a week for five consecutive weeks.

RESULTS

Chronic HDM exposure induced a pronounced eosinophilic allergic airway inflammation in broncho-alveolar lavage fluid (BALf) and lung tissue, associated with the formation of immunologically active inducible bronchus-associated lymphoid tissue (iBALT) in the lungs. The absence of B cells or lack of CD40L signalling did not hamper eosinophilic inflammation in the airways, although the number of Tfh and Th2 cells was substantially reduced in the lungs. Importantly, type 2 innate lymphoid cell (ILC2) numbers in BALf and lung were not affected by the absence of B cells or B-T cell interaction. Furthermore, eosinophilic airway inflammation is not sufficient to induce pulmonary remodelling and airway hyperresponsiveness.

CONCLUSION AND CLINICAL RELEVANCE

From these findings, we conclude that B-T cell interaction is required for robust Tfh and Th2 cell induction, but not essential for eosinophilic airway inflammation during a chronic HDM-driven asthma model.

Efficient Culture of Human Naive and Memory B Cells for Use as APCs

The ability to culture and expand B cells in vitro has become a useful tool for studying human immunity. A limitation of current methods for human B cell culture is the capacity to support mature B cell proliferation. We developed a culture method to support the efficient activation and proliferation of naive and memory human B cells. This culture supports extensive B cell proliferation, with ∼10³-fold increases following 8 d in culture and 10⁶-fold increases when cultures are split and cultured for 8 more days. In culture, a significant fraction of naive B cells undergo isotype switching and differentiate into plasmacytes. Culture-derived (CD) B cells are readily cryopreserved and, when recovered, retain their ability to proliferate and differentiate. Significantly, proliferating CD B cells express high levels of MHC class II, CD80, and CD86. CD B cells act as APCs and present alloantigens and microbial Ags to T cells. We are able to activate and expand Ag-specific memory B cells; these cultured cells are highly effective in presenting Ag to T cells. We characterized the TCR repertoire of rare Ag-specific CD4⁺ T cells that proliferated in response to tetanus toxoid (TT) presented by autologous CD B cells. TCR Vβ usage by TT-activated CD4⁺ T cells differs from resting and unspecifically activated CD4⁺ T cells. Moreover, we found that TT-specific TCR Vβ usage by CD4⁺ T cells was substantially different between donors. This culture method provides a platform for studying the BCR and TCR repertoires within a single individual.

Immune System Modifications Induced in a Mouse Model of Chronic Exposure to (90)Sr

Strontium 90 ((90)Sr) remains in the environment long after a major nuclear disaster occurs. As a result, populations living on contaminated land are potentially exposed to daily ingesting of low quantities of (90)Sr. The potential long-term health effects of such chronic contamination are unknown. In this study, we used a mouse model to evaluate the effects of (90)Sr ingestion on the immune system, the animals were chronically exposed to (90)Sr in drinking water at a concentration of 20 kBq/l, for a daily ingestion of 80-100 Bq/day. This resulted in a reduced number of CD19(+) B lymphocytes in the bone marrow and spleen in steady-state conditions. In contrast, the results from a vaccine experiment performed as a functional test of the immune system showed that in response to T-dependent antigens, there was a reduction in IgG specific to tetanus toxin (TT), a balanced Th1/Th2 response inducer antigen, but not to keyhole limpet hemocyanin (KLH), a strong Th2 response inducer antigen. This was accompanied by a reduction in Th1 cells in the spleen, consistent with the observed reduction in specific IgG concentration. The precise mechanisms by which (90)Sr acts on the immune system remain to be elucidated. However, our results suggest that (90)Sr ingestion may be responsible for some of the reported effects of internal contamination on the immune system in civilian populations exposed to the Chernobyl fallout.

T Follicular Helper Cell Plasticity Shapes Pathogenic T Helper 2 Cell-Mediated Immunity to Inhaled House Dust Mite

Exposure to environmental antigens, such as house dust mite (HDM), often leads to T helper 2 (Th2) cell-driven allergic responses. However, the mechanisms underlying the development of these responses are incompletely understood. We found that the initial exposure to HDM did not lead to Th2 cell development but instead promoted the formation of interleukin-4 (IL-4)-committed T follicular helper (Tfh) cells. Following challenge exposure to HDM, Tfh cells differentiated into IL-4 and IL-13 double-producing Th2 cells that accumulated in the lung and recruited eosinophils. B cells were required to expand IL-4-committed Tfh cells during the sensitization phase, but did not directly contribute to disease. Impairment of Tfh cell responses during the sensitization phase or Tfh cell depletion prevented Th2 cell-mediated responses following challenge. Thus, our data demonstrate that Tfh cells are precursors of HDM-specific Th2 cells and reveal an unexpected role of B cells and Tfh cells in the pathogenesis of allergic asthma.

Systemic sclerosis: New evidence re-enforces the role of B cells

Systemic sclerosis (SSc) is characterized by widespread fibrosis, microangiopathy (vasospasms and stenosis), and formation of autoantibodies. T cell activation has been shown to contribute to fibrosis and microvasculopathy in SSc. However, recent evidence suggests that B cells are also likely to contribute in the pathogenesis of the disease. B cells are hyperactivated in SSc, as indicated by the overexpression of the stimulatory CD19 receptor and impairment of the inhibitory CD22 receptor. They lead to the production of many autoantibodies, some of which induce collagen production and vasoconstriction. They promote fibroblast collagen production through cell contact. Furthermore, B cells can function as antigen-presenting cells to T cells and induce dendritic cell maturation that promotes profibrotic Th2 response. Lately, interleukin (IL)-10-producing B regulatory cells, which induce generation of T regulatory cells and can ameliorate autoimmune diseases, were found to be reduced in SSc, favoring autoaggression of B cells in this disease. Finally, B cell depletion with rituximab improves or stabilizes skin fibrosis and lung function. These finding suggest that new therapeutic strategies targeting B cell function(s) can be developed for SSc.

Short-term consumption of n-3 PUFAs increases murine IL-5 levels, but IL-5 is not the mechanistic link between n-3 fatty acids and changes in B-cell populations

N-3 polyunsaturated fatty acids (PUFAs) exert immunomodulatory effects on B cells. We previously demonstrated that n-3 PUFAs enhanced the relative percentage and/or frequency of select B2 cell subsets. The objectives here were to determine if n-3 PUFAs (a) could boost cytokines that target B-cell frequency, (b) enhance the frequency of the B1 population and (c) to identify the mechanism by which n-3 PUFAs modify the proportion of B cells. Administration of n-3 PUFAs as fish oil to C57BL/6 mice enhanced secretion of the Th2 cytokine IL-5 but not IL-9 or IL-13. N-3 PUFAs had no influence on the percentage or frequency of peritoneal B1 or B2 cells. Subsequent experiments with IL-5(-/-) knockout mice showed n-3 PUFAs decreased the percentage of bone marrow B220(lo)IgM(hi) cells and increased the proportion and number of splenic IgM(+)IgD(lo)CD21(lo) cells compared to the control. These results, when compared with our previous findings with wild-type mice, suggested IL-5 had no role in mediating the effect of n-3 PUFAs on B-cell populations. To confirm this conclusion, we assayed IL-5 secretion in a diet-induced obesity model in which n-3 PUFAs enhanced the frequency of select B-cell subsets. N-3 PUFA supplementation as ethyl esters to obesogenic diets did not alter circulating IL-5 levels. Altogether, the data establish that n-3 PUFAs as fish oil can increase circulating IL-5 in lean mice, which has implications for several disease end points, but this increase in IL-5 is not the mechanistic link between n-3 PUFAs and changes in B-cell populations.

The varieties of immunological experience: of pathogens, stress, and dendritic cells

In the 40 years since their discovery, dendritic cells (DCs) have been recognized as central players in immune regulation. DCs sense microbial stimuli through pathogen-recognition receptors (PRRs) and decode, integrate, and present information derived from such stimuli to T cells, thus stimulating immune responses. DCs can also regulate the quality of immune responses. Several functionally specialized subsets of DCs exist, but DCs also display functional plasticity in response to diverse stimuli. In addition to sensing pathogens via PRRs, emerging evidence suggests that DCs can also sense stress signals, such as amino acid starvation, through ancient stress and nutrient sensing pathways, to stimulate adaptive immunity. Here, I discuss these exciting advances in the context of a historic perspective on the discovery of DCs and their role in immune regulation. I conclude with a discussion of emerging areas in DC biology in the systems immunology era and suggest that the impact of DCs on immunity can be usefully contextualized in a hierarchy-of-organization model in which DCs, their receptors and signaling networks, cell-cell interactions, tissue microenvironment, and the host macroenvironment represent different levels of the hierarchy. Immunity or tolerance can then be represented as a complex function of each of these hierarchies.