Novel mechanisms in immune tolerance to allergens during natural allergen exposure and allergen-specific immunotherapy

The Role of Regulatory T Cells in Allergic Diseases: Collegium Internationale Allergologicum (CIA) Update 2024

BACKGROUND

Allergy represents a major health problem of increasing prevalence worldwide with a high socioeconomic impact. Our knowledge on the molecular mechanisms underlying allergic diseases and their treatments has significantly improved over the last years. The generation of allergen-specific regulatory T cells (Tregs) is crucial in the induction of healthy immune responses to allergens, preventing the development and worsening of allergic diseases.

SUMMARY

In the last decades, intensive research has focused on the study of the molecular mechanisms involved in Treg development and Treg-mediated suppression. These mechanisms are essential for the induction of sustained tolerance by allergen-specific immunotherapy (AIT) after treatment discontinuation. Compelling experimental evidence demonstrated altered suppressive capacity of Tregs in patients suffering from allergic rhinitis, allergic asthma, food allergy, or atopic dermatitis, as well as the restoration of their numbers and functionality after successful AIT.

KEY MESSAGE

The better understanding of the molecular mechanisms involved in Treg generation during allergen tolerance induction might well contribute to the development of novel strategies for the prevention and treatment of allergic diseases.

Serum proteomics identifies S100A11 and MMP9 as novel biomarkers for predicting the early efficacy of sublingual immunotherapy in allergic rhinitis

BACKGROUND

Allergic rhinitis (AR) is a chronic inflammatory disorder, and sublingual immunotherapy (SLIT) is an important therapy. However, SLIT exhibits a wide range of fluctuations and lacks objective monitoring indicators. Therefore, exploring biomarkers for early prediction of the efficacy of SLIT is urgently needed.

METHODS

We recruited two independent cohorts. In the discovery cohort, house dust mite (HDM) -induced AR patients underwent SLIT for at least 1 year, and were categorized into response and no response groups based on early efficacy. Serum proteomics was conducted to detect variations in protein expression levels between the two groups. The candidate proteins were confirmed in the validation cohort with enzyme-linked immunosorbent assay (ELISA), and their predictive values and levels of change before and after treatment were evaluated.

RESULTS

Serum proteomics identified a total of 113 differential proteins between the two groups, including 41 proteins upregulated and 72 downregulated in the no response group than the response group. The top 5 up- and down-regulated proteins were selected for further validation, and ELISA results revealed that serum CCL14, LTA4H, S100A11 and MMP9 levels were significantly elevated, and TGFBI and MASP1 were decreased in the response group than those in the no response group(P < 0.05). Moreover, receiver operating characteristic curves revealed that serum S100A11 and MMP9 exhibited greater ability in predicting the early effectiveness of SLIT (AUC > 0.7, P < 0.05). Furthermore, these two biomarkers exhibited significant reductions 1 year after SLIT, particularly in those patients who responded positively to the treatment (P < 0.05).

CONCLUSION

Serum S100A11 and MMP9 have the potential to serve as biomarkers for early prediction of the effectiveness of SLIT and monitoring the therapeutic effects. The circulating proteomic alterations might contribute to guiding treatment and understanding the mechanism of SLIT in AR patients.

B cells: The many facets of B cells in allergic diseases

B cells play a key role in our immune system through their ability to produce antibodies, suppress a proinflammatory state, and contribute to central immune tolerance. We aim to provide an in-depth knowledge of the molecular biology of B cells, including their origin, developmental process, types and subsets, and functions. In allergic diseases, B cells are well known to induce and maintain immune tolerance through the production of suppressor cytokines such as IL-10. Similarly, B cells protect against viral infections such as severe acute respiratory syndrome coronavirus 2 that caused the recent coronavirus disease 2019 pandemic. Considering the unique and multifaceted functions of B cells, we hereby provide a comprehensive overview of the current knowledge of B-cell biology and its clinical applications in allergic diseases, organ transplantation, and cancer.

Allergen desensitization reduces the severity of relapsed alopecia areata in dust-mite allergic patients

Atopy may be a facilitating factor in some alopecia areata (AA) patients with early disease onset and more severe/extensive AA. The underlying immune mechanisms are unknown, but allergen responses may support a pro-inflammatory environment that indirectly promotes AA. To investigate the long-term effect of allergen immunotherapy (AIT) against house dust mite (HDM) allergy on disease severity and prognosis for AA patients. An observational comparative effectiveness study was conducted on 69 AA patients with HDM allergy. 34 patients received conventional/traditional AA treatment (TrAA) plus AIT (AIT-TrAA), and 35 patients received TrAA alone. Serum total immunoglobulin E (tIgE), HDM specific IgE (sIgE), HDM specific IgG4 (sIgG4) and cytokines (IL-4, IL-5, IL-10, IL-12, IL-13, IL-33, IFNγ) were quantified in these patients, together with 58 non-allergic AA patients and 40 healthy controls. At the end of the 3-year desensitization course, the AIT-TrAA group presented with lower SALT scores than the TrAA group, especially in non-alopecia totalis/universalis (AT/U) patients and pre-adolescent AT/U patients (age ≤ 14). In patients with elevated tIgE levels before AIT, a decrease in tIgE was correlated to reduced extent of AA on completion of the AIT course. After desensitization, elevation of IL-5 and decrease of IL-33 were observed in HDM allergic-AA patients. Desensitization to HDM in allergic AA patients reduces the severity of relapse-related hair loss over the 3-year AIT treatment course, possibly via opposing Th2 dominance. This adjunctive treatment may help reduce disease severity and curtail the disease process in allergic patients with AA.

Clinical and experimental treatment of allergic asthma with an emphasis on allergen immunotherapy and its mechanisms

Allergen immunotherapy (AIT) is currently the only form of treatment that modifies allergic asthma. Pharmacotherapy alone seeks to control the symptoms of allergic asthma, allergic rhinitis, and other atopic conditions. In contrast, AIT can induce long-term physiological modifications through the immune system. AIT enables individuals to live improved lives many years after treatment ends, where they are desensitized to the allergen(s) used or no longer have significant allergic reactions upon allergen provocation. The leading forms of treatment with AIT involve injections of allergen extracts with increasing doses via the subcutaneous route or drops/tablets via the sublingual route for several years. Since the initial attempts at this treatment as early as 1911 by Leonard Noon, the mechanisms by which AIT operates remain unclear. This literature-based review provides the primary care practitioner with a current understanding of the mechanisms of AIT, including its treatment safety, protocols, and long-term efficacy. The primary mechanisms underlying AIT include changes in immunoglobulin classes (IgA, IgE, and IgG), immunosuppressive regulatory T-cell induction, helper T cell type 2 to helper T cell type 1 cell/cytokine profile shifts, decreased early-phase reaction activity and mediators, and increased production of IL-10, IL-35, TGF-β, and IFN-γ. Using the databases PubMed and Embase, a selective literature search was conducted searching for English, full-text, reviews published between 2015 and 2022 using the keywords (with wildcards) "allerg*," "immunotherap*," "mechanis*," and "asthma." Among the cited references, additional references were identified using a manual search.

Chinese Guideline on Allergen Immunotherapy for Allergic Rhinitis: The 2022 Update

In the last few decades, there has been a progressive increase in the prevalence of allergic rhinitis (AR) in China, where it now affects approximately 250 million people. AR prevention and treatment include allergen avoidance, pharmacotherapy, allergen immunotherapy (AIT), and patient education, among which AIT is the only curative intervention. AIT targets the disease etiology and may potentially modify the immune system as well as induce allergen-specific immune tolerance in patients with AR. In 2017, a team of experts from the Chinese Society of Allergy (CSA) and the Chinese Allergic Rhinitis Collaborative Research Group (C2AR2G) produced the first English version of Chinese AIT guidelines for AR. Since then, there has been considerable progress in basic research of and clinical practice for AIT, especially regarding the role of follicular regulatory T (TFR) cells in the pathogenesis of AR and the use of allergen-specific immunoglobulin E (sIgE) in nasal secretions for the diagnosis of AR. Additionally, potential biomarkers, including TFR cells, sIgG4, and sIgE, have been used to monitor the incidence and progression of AR. Moreover, there has been a novel understanding of AIT during the coronavirus disease 2019 pandemic. Hence, there was an urgent need to update the AIT guideline for AR by a team of experts from CSA and C2AR2G. This document aims to serve as professional reference material on AIT for AR treatment in China, thus improving the development of AIT across the world.

Cytokine and Lymphocyte Profiles in Dogs with Atopic Dermatitis after Allergen-Specific Immunotherapy

Canine atopic dermatitis (cAD) is a chronic and recurrent inflammatory and pruritic skin disease in dogs. Currently, allergen-specific immunotherapy (ASIT) is the only identified disease-modifying intervention for allergic diseases. It decreases the symptoms triggered by allergens and prevents recurrence of the disease in the long-term. The aim of our research was to determine how immunotherapy changes the proportion of lymphocyte subsets in dog peripheral blood and the levels of cytokines secreted by these cells during therapy. ASIT was applied for 6 months. Blood samples for further analyses were collected from patients in the third and sixth month of immunotherapy. Six out of seven dogs receiving ASIT showed a positive effect. A reduction in cytokine levels (IL-13, TNF-α) in peripheral blood of cAD patients and changes in the number of specific T cell subpopulations—reduction of Tc cells (CD8+) and increase of activated T cells (CD3+CD25+)—confirmed the beneficial effect of the applied ASIT. In addition, a significantly higher percentage of Treg cells (CD4+CD25+FOXP3+) was noted in cAD patients before treatment compared to healthy dogs. After 3 months of therapy, the percentage of Tregs significantly decreased, and after 6 months, it increased significantly again.

Identification of Robust Biomarkers for Early Predicting Efficacy of Subcutaneous Immunotherapy in Children With House Dust Mite-Induced Allergic Rhinitis by Multiple Cytokine Profiling

Background

Subcutaneous immunotherapy (SCIT) is an effective treatment for children with allergic rhinitis (AR), but its efficacy fluctuates among patients. There are no reliable candidate biomarkers for monitoring and predicting the response to SCIT. The present study aims to identify novel biomarkers for early predicting the efficacy of SCIT in pediatric AR patients based on multiple cytokine profiling.

Methods

We prospectively recruited 72 children with house dust mite (HDM)-induced AR who were assigned to receive SCIT. The serum samples were collected and multiple cytokine profiling was conducted by Luminex assay at baseline. All patients were followed-up for 1 year and then categorized into effective and ineffective group based on their efficacy, and levels of 48 selected cytokines were tested and compared between the two groups. The potential cytokines were further validated by enzyme-linked immunosorbent assay (ELISA) in a cohort with 54 responders and 26 non-responders.

Results

Sixty-nine of 72 children completed one-year follow-up schedule with 46 included in effective group and 23 in ineffective group. The results of multiple cytokine profiling showed that 15 cytokines (eotaxin, G-CSF, GM-CSF, IFN-γ, IL-12(p40), IL-13, IL-15, IL-16, IL-4, MIF, MIP-1α, RANTES, SCF, SDF-1α and VEGF) were dysregulated between effective and ineffective group (all P < 0.05). Unadjusted and adjusted multivariate analysis models highlighted that serum eotaxin, IFN-γ, IL-4 and MIF levels closely associated with the efficacy of SCIT in pediatric HDM-induced AR patients. In addition, receiver operating characteristic (ROC) curves revealed potential values of these four biomarkers in predicting the response to SCIT. Further ELISA validation results in the cohort of 80 pediatric patients demonstrated that serum eotaxin and IL-4 levels were elevated in responders while IFN-γ levels decreased in responders (all P < 0.05). ROC curves demonstrated that serum IL-4 exhibited more reliable accuracy in predicting SCIT efficacy than eotaxin and IFN-γ.

Conclusion

Our discover–validation study suggested that cytokines including IL-4, eotaxin and IFN- γ may serve as robust biomarkers for early predicting response of SCIT in children with HDM-induced AR. These results strengthen the evidence that cytokines were associated with the response of SCIT and contributed to understand its underlying therapeutic mechanisms.

Does the Use of Asthma-Controller Medication in Accordance with Guidelines Reduce the Incidence of Acute Exacerbations and Healthcare Costs?

Background

In asthma, consistent control of chronic airway inflammation is crucial, and the use of asthma-controller medication has been emphasized. Our purpose in this study is to compare the incidence of acute exacerbation and healthcare costs related to the use of asthma-controller medication.

Methods

By using data collected by the National Health Insurance Review and Assessment Service, we compared one-year clinical outcomes and medical costs from July 2014 to June 2015 (follow-up period) between two groups of patients with asthma who received different prescriptions for recommended asthma-controller medication (inhaled corticosteroids or leukotriene receptor antagonists) at least once from July 2013 to June 2014 (assessment period).

Results

There were 51,757 patients who satisfied our inclusion criteria. Among them, 13,702 patients (26.5%) were prescribed a recommended asthma-controller medication during the assessment period. In patients using a recommended asthma-controller medication, the frequency of acute exacerbations decreased in the follow-up period, from 2.7% to 1.1%. The total medical costs of the controller group decreased during the follow-up period compared to the assessment period, from $3,772,692 to $1,985,475. Only 50.9% of patients in the controller group used healthcare services in the follow-up period, and the use of asthma-controller medication decreased in the follow-up period.

Conclusion

Overall, patients using a recommended asthma-controller medication showed decreased acute exacerbation and reduced total healthcare cost by half.

Multiple-Cytokine Profiling: A Novel Method for Early Prediction of the Efficacy of Sublingual Immunotherapy in Allergic Rhinitis Patients

Background

Methods

Results

Conclusion

Comparison of Overall Immunity Levels among Workers at Grape Orchard, Rose Greenhouse, and Open-Field Onion Farm

Background

Methods

Results

Conclusion

New Insights into the Role of PD-1 and Its Ligands in Allergic Disease

Programmed cell death 1 (PD-1) and its ligands PD-L1 and PD-L2 are receptors that act in co-stimulatory and coinhibitory immune responses. Signaling the PD-1/PD-L1 or PD-L2 pathway is essential to regulate the inflammatory responses to infections, autoimmunity, and allergies, and it has been extensively studied in cancer. Allergic diseases include asthma, rhinoconjunctivitis, atopic dermatitis, drug allergy, and anaphylaxis. These overactive immune responses involve IgE-dependent activation and increased CD4+ T helper type 2 (Th2) lymphocytes. Recent studies have shown that PD-L1 and PD-L2 act to regulate T-cell activation and function. However, the main role of PD-1 and its ligands is to balance the immune response; however, the inflammatory process of allergic diseases is poorly understood. These immune checkpoint molecules can function as a brake or a kick-start to regulate the adaptive immune response. These findings suggest that PD-1 and its ligands may be a key factor in studying the exaggerated response in hypersensitivity reactions in allergies. This review summarizes the current understanding of the role of PD-1 and PD-L1 and PD-L2 pathway regulation in allergic diseases and how this immunomodulatory pathway is currently being targeted to develop novel therapeutic immunotherapy.

Allergic Rhinitis: What Do We Know About Allergen-Specific Immunotherapy?

Allergic rhinitis (AR) is an IgE-mediated disease that is characterized by Th2 joint inflammation. Allergen-specific immunotherapy (AIT) is indicated for AR when symptoms remain uncontrolled despite medication and allergen avoidance. AIT is considered to have been effective if it alleviated allergic symptoms, decreased medication use, improved the quality of life even after treatment cessation, and prevented the progression of AR to asthma and the onset of new sensitization. AIT can be administered subcutaneously or sublingually, and novel routes are still being developed, such as intra-lymphatically and epicutaneously. AIT aims at inducing allergen tolerance through modification of innate and adaptive immunologic responses. The main mechanism of AIT is control of type 2 inflammatory cells through induction of various functional regulatory cells such as regulatory T cells (Tregs), follicular T cells (Tfr), B cells (Bregs), dendritic cells (DCregs), innate lymphoid cells (IL-10⁺ ILCs), and natural killer cells (NKregs). However, AIT has a number of disadvantages: the long treatment period required to achieve greater efficacy, high cost, systemic allergic reactions, and the absence of a biomarker for predicting treatment responders. Currently, adjunctive therapies, vaccine adjuvants, and novel vaccine technologies are being studied to overcome the problems associated with AIT. This review presents an updated overview of AIT, with a special focus on AR.

New Insights in Therapy for Food Allergy

Food allergy is an increasing problem worldwide, with strict avoidance being classically the only available reliable treatment. The main objective of this review is to cover the latest information about the tools available for the diagnosis and treatment of food allergies. In recent years, many efforts have been made to better understand the humoral and cellular mechanisms involved in food allergy and to improve the strategies for diagnosis and treatment. This review illustrates IgE-mediated food hypersensitivity and provides a current description of the diagnostic strategies and advances in different treatments. Specific immunotherapy, including different routes of administration and new therapeutic approaches, such as hypoallergens and nanoparticles, are discussed in detail. Other treatments, such as biologics and microbiota, are also described. Therefore, we conclude that although important efforts have been made in improving therapies for food allergies, including innovative approaches mainly focusing on efficacy and safety, there is an urgent need to develop a set of basic and clinical results to help in the diagnosis and treatment of food allergies.

Mechanisms of Drug Desensitization: Not Only Mast Cells

Drug desensitization (DD) allows transient clinical tolerance to the drug in reactive patients and it is frequently and successfully used in the management of both IgE and non IgE-mediated hypersensitivity reactions (HRs). The underlying mechanisms behind this process is not well understood. The desensitization procedure is associated with the inhibition of mast cells degranulation and cytokine production, that, is attributable, at least partially, to the abrogation of Ca2+ mobilization; in vitro findings and in vivo mouse models of rapid desensitization show that the organization and spatial distribution of actin is critical for Ca2+ mobilization. Some clinical observations may suggest the induction of a longer memory of tolerance by DD and they raise the suspicion that other cells and mechanisms are involved in DD. Some data are emerging about the modifications of immune responses during DD in patients with previous immediate HRs. In particular, an increase of regulatory cytokines, mainly represented by IL-10, has been shown, and more importantly, the appearance of IL-35 producing T regulatory cells has been described during DD. The release of controlled cellular mediators by mast cells over time and the development of the antigen-specific regulation of adaptive response allow to safely and successfully reach the target dose of a first line drug during DD.

B regulatory cells in allergy

B cells have classically been recognized for their unique and indispensable role in the production of antibodies. Their potential as immunoregulatory cells with anti-inflammatory functions has received increasing attention during the last two decades. Herein, we highlight pioneering studies in the field of regulatory B cell (Breg) research. We will review the literature on Bregs with a particular focus on their role in the regulation of allergic inflammation.

Expression of CD27 and CD28 on γδ T cells from the peripheral blood of patients with allergic rhinitis

The costimulatory receptors CD27 and CD28 have pivotal and non-redundant roles in the activation and differentiation of γδ T-cells. However, the roles of CD27 and CD28 on γδ T-cells in allergic rhinitis (AR) have remained elusive. The aim of the present study was to investigate the expression of CD27 and CD28 on γδ T cells in patients with AR. Peripheral blood mononuclear cells from 14 patients with AR and 12 healthy subjects were isolated and analyzed by flow cytometry to determine the percentage of γδ T cells and regulatory T cells (Tregs), and the expression of IFN-γ, IL-17A, CD27 and CD28 on γδ T cells. The correlations between the expression of CD27 and CD28, and the percentages of IFN-γ⁺ and IL-17A⁺ γδ T-cell subsets and Tregs in AR were analyzed. It was observed that the percentages of γδ T cells, and the IL-17A⁺, CD27^-CD28⁺ and CD27^-CD28^- γδ T-cell subsets were significantly increased, while the percentages of Tregs and IFN-γ⁺ and CD27⁺CD28⁺ γδ T-cell subsets were significantly decreased in AR. Of note, the percentage of CD27⁺CD28⁺ γδ T-cell subsets was positively correlated with that of the IFN-γ⁺ γδ T-cell subset and the percentage of the CD27^-CD28⁺ γδ T-cell subset was positively correlated with that of the IL-17A⁺ γδ T-cell subset. Furthermore, the percentages of γδ T cells and the CD27^-CD28⁺ γδ T-cell subset were both negatively correlated with that of Tregs. Therefore, the results of the present study indicate that CD27 and CD28 may be the key signals for activation of different γδ T-cell subsets and may contribute to the immune regulatory function of γδ T cells in the peripheral blood of patients with AR.

Immunological Outcomes of Allergen-Specific Immunotherapy in Food Allergy

IgE-mediated food allergies are caused by adverse immunologic responses to food proteins. Allergic reactions may present locally in different tissues such as skin, gastrointestinal and respiratory tract and may result is systemic life-threatening reactions. During the last decades, the prevalence of food allergies has significantly increased throughout the world, and considerable efforts have been made to develop curative therapies. Food allergen immunotherapy is a promising therapeutic approach for food allergies that is based on the administration of increasing doses of culprit food extracts, or purified, and sometime modified food allergens. Different routes of administration for food allergen immunotherapy including oral, sublingual, epicutaneous and subcutaneous regimens are being evaluated. Although a wealth of data from clinical food allergen immunotherapy trials has been obtained, a lack of consistency in assessed clinical and immunological outcome measures presents a major hurdle for evaluating these new treatments. Coordinated efforts are needed to establish standardized outcome measures to be applied in food allergy immunotherapy studies, allowing for better harmonization of data and setting the standards for the future research. Several immunological parameters have been measured in food allergen immunotherapy, including allergen-specific immunoglobulin levels, basophil activation, cytokines, and other soluble biomarkers, T cell and B cell responses and skin prick tests. In this review we discuss different immunological parameters and assess their applicability as potential outcome measures for food allergen immunotherapy that may be included in such a standardized set of outcome measures.

[Systemic reactions to subcutaneous immunotherapy for bronchial asthma and/or allergic rhinitis in children and their risk factors]

OBJECTIVE

To investigate the incidence of systemic reactions (SR) to subcutaneous immunotherapy (SCIT) for bronchial asthma and/or allergic rhinitis in children and their risk factors.

METHODS

A retrospective analysis was performed on 198 children with bronchial and/or allergic rhinitis. According to the presence or absence of SR and local reactions (LR) during SCIT, the patients were divided into two groups: SR (with SR and LR, n=31) and control (without SR or LR, n=142). A multivariate logistic regression analysis was used to determine the risk factors associated with SR.

RESULTS

Among the 198 patients who received 8 157 injections of SCIT, 25 (12.6%) experienced SR (31 times, 0.38%), including grade I SR (18 times, 58%), grade II SR (10 times, 32%), grade III SR (3 times, 10%), and no grade IV SR. The multivariate logistic regression analysis showed that multiple sensitization with both food and inhaled allergens, specific IgE to dust mites (grade 6), total IgE (grade 6), and a history of LR were independent risk factors for SR (P<0.05).

CONCLUSIONS

SCIT is a safe treatment for bronchial asthma and/or allergic rhinitis in children, with a low incidence of SR. Children with multiple sensitization with both food and inhaled allergens, a hypersensitive state (specific IgE to dust mites, grade 6; total IgE, grade 6), and a history of LR have an increased risk of SR to SCIT.

Tolerance mechanisms in allergen immunotherapy

PURPOSE OF REVIEW

Allergen immunotherapy is the only treatment modality which alters the natural course of allergic diseases by restoring immune tolerance against allergens. Deeper understanding of tolerance mechanisms will lead to the development of new vaccines, which target immune responses and promote tolerance.

RECENT FINDINGS

Successful allergen immunotherapy (AIT) induces allergen-specific peripheral tolerance, characterized mainly by the generation of allergen-specific Treg cells and reduction of Th2 cells. At the early phase, AIT leads to a decrease in the activity and degranulation of mast cells and basophils and a decrease in inflammatory responses of eosinophils in inflamed tissues. Treg cells show their effects by secreting inhibitory cytokines including interleukin (IL)-10, transforming growth factor-β, interfering with cellular metabolisms, suppressing antigen presenting cells and innate lymphoid cells (ILCs) and by cytolysis. AIT induces the development of regulatory B cells producing IL-10 and B cells expressing allergen-specific IgG4. Recent investigations have demonstrated that AIT is also associated with the formation of ILC2reg and DCreg cells which contribute to tolerance induction.

SUMMARY

Research done so far, has shown that multiple molecular and cellular factors are dysregulated in allergic diseases and modified by AIT. Studies should now focus on finding the best target and ideal biomarkers to identify ideal candidates for AIT.

Allergen immunotherapy in children and adolescents with respiratory diseases

To date, the only disease-modifying treatment strategy for allergic rhinitis and asthma is allergen immunotherapy (AIT). There is evidence that AIT improves allergic rhinitis and asthma, such as reducing symptom severity and medication use and improving of quality of life, with a long-lasting effect after the end of the course. The recent clinical trials evidenced AIT effectiveness and safety in allergic asthma. Consequently, the current version of the GINA (Global Initiative for Asthma) guidelines recommend AIT as an add-on therapy for asthma. There is also evidence that AIT may exert preventive activity on the possible progression from allergic rhinitis to asthma in children and the onset of new sensitizations.

B-cell responses in allergen immunotherapy

PURPOSE OF REVIEW

The establishment of long-term clinical tolerance in AIT requires the involvement of basophils, mast cells, allergen-specific regulatory T and B cells, downregulation of effector type 2 responses, and increase in production of specific IgG, particularly immunglobulin G4 (IgG4) antibodies. This review aims to provide an overview of the role of B cells in AIT, their mechanism of action, and their potential for improving AIT.

RECENT FINDINGS

In-depth research of B cells has paved the way for improved diagnosis and research on allergic diseases. B cells play a central role in allergy and allergen tolerance through the production of immunglobulin E (IgE)-blocking antibodies. However, an increasing body of evidence has emerged supporting a role for B cells in regulating immune responses that extends beyond the production of antibodies. Regulatory B cells play an important role in immunosuppression, mediated by secretion of anti-inflammatory cytokines.

SUMMARY

Successful AIT establishes the reinstatement of immune tolerance toward allergens, reduces allergic symptoms, and improves clinical treatments in patients. B cells play a central role in this process through antibody-independent immune regulatory processes in addition to the production of IgE-blocking antibodies.

Der p 1-based immunotoxin as potential tool for the treatment of dust mite respiratory allergy

Immunotoxins appear as promising therapeutic molecules, alternative to allergen-specific-immunotherapy. In this work, we achieved the development of a protein chimera able to promote specific cell death on effector cells involved in the allergic reaction. Der p 1 allergen was chosen as cell-targeting domain and the powerful ribotoxin α-sarcin as the toxic moiety. The resultant construction, named proDerp1αS, was produced and purified from the yeast Pichia pastoris. Der p 1-protease activity and α-sarcin ribonucleolytic action were effectively conserved in proDerp1αS. Immunotoxin impact was assayed by using effector cells sensitized with house dust mite-allergic sera. Cell degranulation and death, triggered by proDerp1αS, was exclusively observed on Der p 1 sera sensitized-humRBL-2H3 cells, but not when treated with non-allergic sera. Most notably, equivalent IgE-binding and degranulation were observed with both proDerp1αS construct and native Der p 1 when using purified basophils from sensitized patients. However, proDerp1αS did not cause any cytotoxic effect on these cells, apparently due to its lack of internalization after their surface IgE-binding, showing the complex in vivo panorama governing allergic reactions. In conclusion, herein we present proDerp1αS as a proof of concept for a potential and alternative new designs of therapeutic tools for allergies. Development of new, and more specific, second-generation of immunotoxins following proDerp1αS, is further discussed.

Allergen Immunotherapy in Pediatric Asthma: A Pragmatic Point of View

To date, the only disease-modifying treatment strategy for allergic rhinitis and asthma is allergen immunotherapy (AIT). There is evidence that AIT improves allergic rhinitis and asthma, such as reducing symptom severity and medication use and improving of quality of life, with a long-lasting effect after the end of the course. The recent clinical trials evidenced AIT effectiveness and safety in allergic asthma. Consequently, the current version of the GINA (Global Initiative for Asthma) guidelines recommend AIT as an add-on therapy for asthma. There is also evidence that AIT may exert preventive activity on the possible progression from allergic rhinitis to asthma in children and the onset of new sensitizations. The present review provides a pragmatic summary of the clinical indications of AIT in pediatric asthma, including the immunological mechanisms, the predictive biomarkers, and the safety issues in clinical practice.

EAACI Allergen Immunotherapy User's Guide

Allergen immunotherapy is a cornerstone in the treatment of allergic children. The clinical efficiency relies on a well-defined immunologic mechanism promoting regulatory T cells and downplaying the immune response induced by allergens. Clinical indications have been well documented for respiratory allergy in the presence of rhinitis and/or allergic asthma, to pollens and dust mites. Patients who have had an anaphylactic reaction to hymenoptera venom are also good candidates for allergen immunotherapy. Administration of allergen is currently mostly either by subcutaneous injections or by sublingual administration. Both methods have been extensively studied and have pros and cons. Specifically in children, the choice of the method of administration according to the patient's profile is important. Although allergen immunotherapy is widely used, there is a need for improvement. More particularly, biomarkers for prediction of the success of the treatments are needed. The strength and efficiency of the immune response may also be boosted by the use of better adjuvants. Finally, novel formulations might be more efficient and might improve the patient's adherence to the treatment. This user's guide reviews current knowledge and aims to provide clinical guidance to healthcare professionals taking care of children undergoing allergen immunotherapy.

A novel proangiogenic B cell subset is increased in cancer and chronic inflammation

B cells contribute to immune responses through the production of immunoglobulins, antigen presentation, and cytokine production. Several B cell subsets with distinct functions and polarized cytokine profiles have been reported. In this study, we used transcriptomics analysis of immortalized B cell clones to identify an IgG4⁺ B cell subset with a unique function. These B cells are characterized by simultaneous expression of proangiogenic cytokines including VEGF, CYR61, ADM, FGF2, PDGFA, and MDK. Consequently, supernatants from these clones efficiently promote endothelial cell tube formation. We identified CD49b and CD73 as surface markers identifying proangiogenic B cells. Circulating CD49b⁺CD73⁺ B cells showed significantly increased frequency in patients with melanoma and eosinophilic esophagitis (EoE), two diseases associated with angiogenesis. In addition, tissue-infiltrating IgG4⁺CD49b⁺CD73⁺ B cells expressing proangiogenic cytokines were detected in patients with EoE and melanoma. Our results demonstrate a previously unidentified proangiogenic B cell subset characterized by expression of CD49b, CD73, and proangiogenic cytokines.

Mechanisms of allergen-specific immunotherapy for allergic rhinitis and food allergies

Allergen-specific immunotherapy (AIT) is currently the only potential treatment for allergies including allergic rhinitis (AR) and food allergies (FA) that can modify the underlying course of the diseases. Although AIT has been performed for over a century, the precise and detailed mechanism for AIT is still unclear. Previous clinical trials have reported that successful AIT induces the reinstatement of tolerance against the specific allergen. In this review, we aim to provide an updated summary of the knowledge on the underlying mechanisms of IgE-mediated AR and FA as well as the immunological changes observed after AIT and discuss on how better understanding of these can lead to possible identification of biomarkers and novel strategies for AIT.

Approaches to inducing antigen-specific immune tolerance in allergy and autoimmunity: Focus on antigen-presenting cells and extracellular vesicles

Increasing prevalence of allergic and autoimmune diseases urges clinicians and researchers to search for new and efficient treatments. Strategies that activate antigen-specific immune tolerance and simultaneously maintain immune reactivity to all other antigens deserve special attention. Accordingly, antigen-presenting cells (APCs) seem to be the best suited for orchestrating these mechanisms by directing T cell immune responses towards a tolerant subtype. Recent advances in understanding cell-to-cell communication via extracellular vesicles (EVs) make the latter promising candidates for reprogramming APCs towards a tolerant phenotype, and for mediating tolerogenic APC function. Thus, comprehensive studies have been undertaken to describe the interactions of APCs and EVs naturally occurring during immune tolerance induction, as well as to develop EV-based manoeuvres enabling the induction of immune tolerance in an antigen-specific manner. In this review, we summarize the findings of relevant studies, with a special emphasis on future perspectives on their translation to clinical practice.

Early Life Domestic Pet Ownership, and the Risk of Pet Sensitization and Atopic Dermatitis in Preschool Children: A Prospective Birth Cohort in Shanghai

Background: Although domestic pet ownership is on the rise, the impact of early life pet ownership on children's pet sensitization and atopic dermatitis (AD) remains controversial. Methods: Shanghai Allergy Cohort is an ongoing prospective study followed up to the age of 5 years. Pregnant mothers were recruited and their offspring were followed up every year by a group of pediatricians. Information on furred pet ownership was collected by the questionnaire. AD was diagnosed by dermatologists according to disease history and Williams criteria at 5 years ± 1 months. Skin prick test (SPT) was performed to determine sensitization to specific allergens. Multiple logistic regression models were used to evaluate the associations between pet ownership and AD, dog/cat sensitization. Results: In the 538 children at preschool age, 112 (20.82%) were diagnosed with AD. Dermatophagoides pteronyssinus and Dermatophagoides farina were the most common allergens, and almost 10% of children were positive to dog and cat. The percentage of positive SPT reactors at 5-year old was 65.28% in the group of children with AD, higher than that in non-AD group (44.57%). Domestic pet ownership at both infant and preschool period was positively associated with an increased risk of sensitization to dog (OR _adjusted = 2.85 [95% CI: 1.08-7.50 for infant exposure], OR _adjusted = 2.73 [95% CI: 1.33-5.61] for preschool exposure), and interestingly, pet ownership at infant period negatively associated with higher risk of AD at 5-year old (OR adjusted = 0.33 [95% CI: 0.12-0.88]). Conclusion: This is the first prospective birth cohort study in Shanghai that found half of preschool children had positive allergen sensitization even in the non-AD children. Although early life exposure to dog may increase the risk of dog sensitization, it significantly decreased the risk of AD. The underlying mechanisms warrant further investigations.

Il-10 producing T and B cells in allergy

The molecular and cellular mechanisms of allergen tolerance in humans have been intensively studied in the past few decades. The demonstration of epitope-specific T cell tolerance, particularly mediated by the immune suppressor functions of IL-10 led to a major conceptual change in this area more than 20 years ago. Currently, the known essential components of allergen tolerance include the induction of allergen-specific regulatory of T and B cells, the immune suppressive function of secreted factors, such as IL-10, IL-35, IL-1 receptor antagonist and TGF-β, immune suppressive functions of surface molecules such as CTLA-4 and PD-1, the production IgG4 isotype allergen-specific blocking antibodies, and decreased allergic inflammatory responses by mast cells, basophils, and eosinophils in inflamed tissues. In this review, we explain the importance of the role of IL-10 in allergen tolerance.

Mechanisms of Subcutaneous and Sublingual Aeroallergen Immunotherapy: What Is New?

Allergen immunotherapy (AIT) is considered to be the only treatment option with the promise of healing and induction of long-lasting allergen tolerance, persisting even after discontinuation of therapy. Despite a more than 100-year-long history, still only a minority of patients are being treated with AIT. Substantial developments took place in the last decade to overcome problems in standardization, efficacy, safety, high costs, long duration of treatment; and new guidelines have also been implemented. Major advancements in the understanding of AIT mechanisms with the focus on recent findings of subcutaneous and sublingual AIT have been summarized.

Serum cytokines elevated during gluten-mediated cytokine release in coeliac disease

Cytokines have been extensively studied in coeliac disease, but cytokine release related to exposure to gluten and associated symptoms has only recently been described. Prominent, early elevations in serum interleukin (IL)-2 after gluten support a central role for T cell activation in the clinical reactions to gluten in coeliac disease. The aim of this study was to establish a quantitative hierarchy of serum cytokines and their relation to symptoms in patients with coeliac disease during gluten-mediated cytokine release reactions. Sera were analyzed from coeliac disease patients on a gluten free-diet (n = 25) and from a parallel cohort of healthy volunteers (n = 25) who underwent an unmasked gluten challenge. Sera were collected at baseline and 2, 4 and 6 h after consuming 10 g vital wheat gluten flour; 187 cytokines were assessed. Confirmatory analyses were performed by high-sensitivity electrochemiluminescence immunoassay. Cytokine elevations were correlated with symptoms. Cytokine release following gluten challenge in coeliac disease patients included significant elevations of IL-2, chemokine (C-C motif) ligand 20 (CCL20), IL-6, chemokine (C-X-C motif) ligand (CXCL)9, CXCL8, interferon (IFN)-γ, IL-10, IL-22, IL-17A, tumour necrosis factor (TNF)-α, CCL2 and amphiregulin. IL-2 and IL-17A were earliest to rise. Peak levels of cytokines were generally at 4 h. IL-2 increased most (median 57-fold), then CCL20 (median 10-fold). Cytokine changes were strongly correlated with one another, and the most severely symptomatic patients had the highest elevations. Early elevations of IL-2, IL-17A, IL-22 and IFN-γ after gluten in patients with coeliac disease implicates rapidly activated T cells as their probable source. Cytokine release after gluten could aid in monitoring experimental treatments and support diagnosis.

Update in Pediatric Asthma: Selected Issues

Asthma is a complex condition that affects 14% of the world's children and the approach to management includes both pharmacologic as well as non-pharmacologic strategies including attention to complex socioeconomic status phenomena. After an historical consideration of asthma, allergic and immunologic aspects of asthma in children and adolescents are presented. Concepts of socioeconomic aspects of asthma are considered along with environmental features and complications of asthma disparities. Also reviewed are links of asthma with mental health disorders, sleep disturbances and other comorbidities. A stepwise approach to asthma management is discussed that includes pharmacologic and non-pharmacologic strategies in the pediatric population. The role of immunotherapy and use of various immunomodulators are considered as well.

Options of immunotherapeutic treatments for children with asthma

Introduction: Asthma is the most common chronic disease in children. Avoiding triggers, and pharmacologic treatment with short acting beta-agonist, inhaler corticosteroids and anti-leukotriene are often enough to obtain symptoms control. Nevertheless, there is a subset of children with severe asthma and poor symptom control despite maximal therapy. In these patients, anti-IgE and anti-IL5 monoclonal antibodies are suggested as the fifth step of Global Initiative for Asthma guidelines. Area covered: Immunotherapeutic treatments are now suggested for asthma management. This article will discuss the available evidence on allergen immunotherapy and biologic drugs in pediatric asthma treatment. Expert opinion: Previously published studies demonstrated a good efficacy and safety profile of Allergen Immunotherapy in patients with mild-moderate asthma and sensitization to one main allergen. New understanding of mechanisms underlying severe asthma inflammation has allowed the identifications of specific biomarkers guiding the clinician in the choice of patient specific drug. Among the suggested immunotherapeutic options, omalizumab (blocking IgE) remains the first choice for atopic 'early onset' asthma in patients aged over 6 years. Instead, mepolizumab (blocking the IL5 ligand) should be considered for 'eosinophilic' asthma. Other biologic drugs are under consideration but data on the pediatric population are still lacking.

The use of biologics for immune modulation in allergic disease

The rising prevalence of allergies represents an increasing socioeconomic burden. A detailed understanding of the immunological mechanisms that underlie the development of allergic disease, as well as the processes that drive immune tolerance to allergens, will be instrumental in designing therapeutic strategies to treat and prevent allergic disease. Improved characterization of individual patients through the use of specific biomarkers and improved definitions of disease endotypes are paving the way for the use of targeted therapeutic approaches for personalized treatment. Allergen-specific immunotherapy and biologic therapies that target key molecules driving the Th2 response are already used in the clinic, and a wave of novel drug candidates are under development. In-depth analysis of the cells and tissues of patients treated with such targeted interventions provides a wealth of information on the mechanisms that drive allergies and tolerance to allergens. Here, we aim to deliver an overview of the current state of specific inhibitors used in the treatment of allergy, with a particular focus on asthma and atopic dermatitis, and provide insights into the roles of these molecules in immunological mechanisms of allergic disease.

Butyrate Enhances Desensitization Induced by Oral Immunotherapy in Cow's Milk Allergic Mice

Background

In previous studies, we showed that a fructo-oligosaccharide- (FOS-) supplemented diet enhanced oral immunotherapy (OIT) efficacy in a mouse model for cow's milk allergy. Fermentation of FOS by intestinal bacteria leads to production of short-chain fatty acids (SCFA) including butyrate.

Aim

To investigate the contribution of butyrate in the enhanced efficacy of OIT + FOS.

Methods

C3H/HeOuJ mice were sensitized and received OIT with or without FOS or butyrate supplementation. After treatment, whole blood was collected to conduct a basophil activation test (BAT) and allergen challenges were performed to measure acute allergic symptoms. CD4 + CD25 + regulatory T cells (Tregs) were isolated from treated mice or differentiated in vitro and used in a bone marrow-derived mast cell (BMMC) suppression assay. Cecum content was collected to analyze SCFA concentrations.

Results

Allergen-induced basophil activation was reduced in OIT + butyrate samples compared to OIT. Accordingly, the acute allergic skin response and mast cell degranulation upon challenge were reduced in OIT + butyrate and OIT + FOS mice compared to sensitized controls. Butyrate was increased in the cecum content of OIT + FOS mice compared to OIT mice and sensitized controls. Treg-mediated BMMC suppression was enhanced after in vivo butyrate and FOS exposure in combination with OIT but with a more pronounced effect for butyrate.

Conclusion

Butyrate supplementation enhanced OIT-induced desensitization of basophils and mast cells and Treg functionality. Only OIT + FOS treatment induced potential microbial alterations, shown by increased butyrate levels in cecum content. Both butyrate and FOS are promising candidates to improve OIT efficacy in human studies to treat food allergies.

Immunomodulation in Pediatric Asthma

Childhood asthma is actually defined as a heterogeneous disease, including different clinical variants and partially sharing similar immune mechanisms. Asthma management is mainly focused on maintaining the control of the disease and reducing the risk of adverse outcomes. Most children achieve good control with standard therapies, such as low doses of inhaled corticosteroids (ICS) and/or one or more controller. These medications are targeted to suppress bronchial inflammation and to restore airway responsiveness. However, they are not disease-modifying and do not specifically target inflammatory pathways of asthma; in addition, they are not significantly effective in patients with severe uncontrolled asthma. The aim of this review is to update knowledge on current and novel therapeutic options targeted to immunomodulate inflammatory pathways underlying pediatric asthma, with particular reference on biologic therapies.

Antigen-specific regulatory T-cell responses against aeroantigens and their role in allergy

The mucosal immune system of the respiratory tract is specialized to continuously monitor the external environment and to protect against invading pathogens, while maintaining tolerance to innocuous inhaled particles. Allergies result from a loss of tolerance against harmless antigens characterized by formation of allergen-specific Th2 cells and IgE. Tolerance is often described as a balance between harmful Th2 cells and various types of protective "regulatory" T cells. However, the identity of the protective T cells in healthy vs. allergic individuals or following successful allergen-specific therapy is controversially discussed. Recent technological progress enabling the identification of antigen-specific effector and regulatory T cells has significantly contributed to our understanding of tolerance. Here we discuss the experimental evidence for the various tolerance mechanisms described. We try to integrate the partially contradictory data into a new model proposing different mechanism of tolerance depending on the quality and quantity of the antigens as well as the way of antigen exposure. Understanding the basis of tolerance is essential for the rational design of novel and more efficient immunotherapies.

Clinical efficacy of sublingual immunotherapy is associated with restoration of steady-state serum lipocalin 2 after SLIT: a pilot study

Background

So far, only a few biomarkers in allergen immunotherapy exist that are associated with a clinical benefit. We thus investigated in a pilot study whether innate molecules such as the molecule lipocalin-2 (LCN2), with implications in immune tolerance demonstrated in other fields, may discriminate A) between allergic and non-allergic individuals, and B) between patients clinically responding or non-responding to sublingual allergen immunotherapy (SLIT) with house dust mite (HDM) extract. Moreover, we assessed haematological changes potentially correlating with allergic symptoms.

Methods

LCN2-concentrations were assessed in sera of healthy and allergic subjects (n = 126) as well as of house dust mite (HDM) allergics before and during HDM- sublingual immunotherapy (SLIT) in a randomized, double-blind, placebo-controlled trial for 24 weeks. Sera pre-SLIT (week 0), post-SLIT (week 24) and 9 months after SLIT were assessed for LCN2 levels and correlated with total nasal symptom scores (TNSS) obtained during chamber challenge at week 24 in patients receiving HDM- (n = 31) or placebo-SLIT (n = 10).

Results

Allergic individuals had significantly (p < 0.0001) lower LCN2-levels than healthy controls. HDM-allergic patients who received HDM-SLIT showed a significant increase in LCN2 9 months after termination of HDM-SLIT (p < 0.001), whereas in subjects receiving placebo no increase in LCN2 was observed. Among blood parameters a lower absolute rise in the lymphocyte population (p < 0.05) negatively correlated with symptom improvement (Pearson r 0.3395), and a lower relative increase in the neutrophils were associated with improvement in TNSS (p < 0.05). LCN2 levels 9 months after immunotherapy showed a low positive correlation with the relative improvement of symptoms (Pearson r 0.3293). LCN2-levels 9 months off-SLIT were significantly higher in patients whose symptoms improved during chamber challenge than in those whose symptoms aggravated (p < 0.01).

Conclusion

Serum LCN2 concentrations 9 months off-SLIT correlated with clinical reactivity in allergic patients. An increase in the LCN2 levels 9 months after HDM-SLIT was associated with a clinical benefit. Serum LCN2 may thus contribute to assess clinical reactivity in allergic patients.

Trial registration

Part of the data were generated from clinicaltrials.gov Identifier NCT01644617.

Development of a skin-friendly microemulsion for dermal allergen-specific immunotherapy

Due to their role in immune responses, the skin dendritic cells (i.e. epidermal Langerhans cells and dermal dendritic cells) have become of great interest to researchers in the past decades. A dermal administration of allergens could target these professional antigen-presenting cells directly and build up immunotolerance. Additionally, many of the adverse side effects, which are seen in the current state of the art specific immunotherapy routes, could be avoided. Therefore, in this study a penetration enhancing microemulsion was developed and its physicochemical properties were determined under several storage conditions. The influence of different preservatives on the microemulsion stability was observed. We examined epidermal penetration of Alexa Fluor-647 labelled bee-venom phospholipase A2 (Api m 1) using the Franz diffusion cell set up and confocal laser-scanning microscopy. First results of an in-vivo Api m 1-allergic mouse model indicated the protective efficacy of dermal AIT with our newly developed microemulsion. Summarily, the developed microemulsion is a suitable, stable drug delivery system for the topical administration of proteogenic allergens into the epidermis and is able to reach dendritic cells in the skin.

Worms: Pernicious parasites or allies against allergies?

Type 2 immune responses are most commonly associated with allergy and helminth parasite infections. Since the discovery of Th1 and Th2 immune responses more than 30 years ago, models of both allergic disease and helminth infections have been useful in characterizing the development, effector mechanisms and pathological consequences of type 2 immune responses. The observation that some helminth infections negatively correlate with allergic and inflammatory disease led to a large field of research into parasite immunomodulation. However, it is worth noting that helminth parasites are not always benign infections, and that helminth immunomodulation can have stimulatory as well as suppressive effects on allergic responses. In this review, we will discuss how parasitic infections change host responses, the consequences for bystander immunity and how this interaction influences clinical symptoms of allergy.

Biomarkers of immunotherapy response in patients with allergic rhinitis

INTRODUCTION

Allergen immunotherapy represents the only disease-modifying therapy available for immunoglobulin E-mediated diseases such as allergic rhinitis and asthma. Allergen immunotherapy induces allergen tolerance by interfering with the immune-pathogenic mechanisms of the allergic response and is potentially able to provide long-term relief of symptoms of allergic rhinitis and asthma and alter the natural course of allergic diseases. Areas covered: Since allergen immunotherapy (AIT) is actually considered an individualized treatment on patient's clinical and immunological profile, the identification of specific biomarkers, which may guide diagnosis, management, and predict response to AIT treatment in allergic rhinitis (AR) patients, is essential and is currently an active field of research. Expert commentary: The identification and validation of biomarkers of successful AIT for AR is an urgent need to definitively establish the role of AIT as a therapeutic tool of personalized medicine.

Involvement of T-Helper 9 Activation in a Mouse Model of Allergic Rhinitis

Background

We aimed to investigate the role of T-Helper (TH) 9 cells in the pathogenesis of allergic rhinitis (AR) in mice.

Material/Methods

An AR model was produced in BALB/c mice, and the viral encoding interleukin (IL)-9 silencing sequence was used to reduce IL-9 expression. The experiment was divided into a control group, an AR group, an IL-9 shRNA+AR group, and a vector+AR group. Hematoxylin and eosin (H&E) staining was used to detect pathological changes. The cytokine expression was detected by ELISA method. Cellular typing was detected by flow cytometry.

Results

Cells in the control group were regularly arranged, with clear layers and no congestion, edema, or necrosis observable. By contrast, in the AR model group and the vector treatment group, nasal mucosa showed clear hyperemia and edema in upper tissues and infiltration of inflammatory cells, which were ameliorated by IL-9 silencing. Compared with the control group, interferon-γ (IFN-γ) was significantly down-regulated, while IL-4, IL-17, and IL-9 were significantly elevated in the AR model group. TH1 cells in nasal mucosa, lymph, nasal lavage, spleen, and peripheral blood were significantly reduced, while TH2, TH9, TH17, and Treg cells were significantly elevated in the AR group compared with the control group. Importantly, all these changes in AR model were ameliorated by IL-9 silencing.

Conclusions

AR is related to the changes of cytokines in TH1, TH2, TH9, TH17, and Treg, which are improved by IL-9 silencing. Activation of TH9 cells is involved in the pathogenesis of AR.

Mechanisms of allergen-specific immunotherapy: Diverse mechanisms of immune tolerance to allergens

OBJECTIVE

The aim of this review is to provide an overview of the current knowledge on the mechanisms of allergen immunotherapy based on the recent publications and clinical trials.

DATA SOURCES

PubMed literature review.

STUDY SELECTIONS

In this review, we focus on diverse mechanisms of AIT and provide an insight into alternative routes of administration. Additionally, we review and discuss the most recent studies investigating potential biomarkers and highlight their role in clinical settings.

RESULTS

Successful allergen-specific immunotherapy (AIT) induces the reinstatement of tolerance toward allergens and represents a disease-modifying treatment. In the last decades, substantial progress in understanding the mechanisms of AIT has been achieved. Establishment of long-term clinical tolerance to allergens engages a complex network of interactions, modulating the functions of basophils, mast cells, allergen-specific regulatory T and B cells, and production of specific antibodies. The reduction of symptoms and clinical improvement is achieved by skewing the immune response away from allergic inflammation.

CONCLUSION

Although the complex nature of AIT mechanisms is becoming more clear, the need to discover reliable biomarkers to define patients likely to respond to the treatment is emerging.

Highlights in immune response, microbiome and precision medicine in allergic disease and asthma

Several recent key findings in immunology of allergic diseases that have led to a need of reassessment of our current thinking are reviewed in this issue of the journal. Recently developed strong evidence on the role of hygiene hypothesis in protection from allergic disease and its immune mechanisms is reviewed by Ober et al. The authors pointed out immunologic mechanisms of lower prevalence of asthma and allergic sensitization observed among Amish children living on traditional farms with higher endotoxin levels as compared to Hutterite children living on industrialized farms. Barcik et al. reviewed that biologically active histamine in humans is produced by certain bacteria in the gut in addition to several cells, and has broad immunoregulatory functions. Turcanu et al. reviewed immune mechanisms of a revolutionary change to protect from food allergy. The immunologic window of opportunity in the infants can be used to enable oral tolerance in severe allergy predisposed children. Accordingly, van de Veen et al. reviewed general mechanisms of allergen tolerance highlighting recent findings. Extensive usage of precision medicine due to emerging biologics is knocking the doors of allergic diseases and asthma. Boyd et al. reviewed the existing and future "immune monitoring" approaches in the multiple omics perspective with the hope of identifying better correlates of disease status, predictors of therapeutic outcomes, and potential side-effects of treatment. Paul et al. reviewed newly uncovered innate and adaptive immunologic mechanisms that contribute to the pathogenesis of eosinophilic esophagitis. Further highlighting newly developing disease subgroups and precision medicine, Guttman-Yassky & Kruger reviewed clinical subtypes of atopic dermatitis and psoriasis, which may potentially benefit from newly developing highly efficient biologicals. Complementing this paper, Kabashima & Nomura reviewed similarities and distinctions in mouse models of atopic dermatitis and psoriasis.