Immune responses to inhalant Mammalian allergens

Hussein S, Abdalhabib EK, Nabi SU. The critical impacts of cytokine storms in respiratory disorders

Cytokine storm (CS) refers to the spontaneous dysregulated and hyper-activated inflammatory reaction occurring in various clinical conditions, ranging from microbial infection to end-stage organ failure. Recently the novel coronavirus involved in COVID-19 (Coronavirus disease-19) caused by SARS-CoV-2 (Severe Acute Respiratory Syndrome Coronavirus 2) has been associated with the pathological phenomenon of CS in critically ill patients. Furthermore, critically ill patients suffering from CS are likely to have a grave prognosis and a higher case fatality rate. Pathologically CS is manifested as hyper-immune activation and is clinically manifested as multiple organ failure. An in-depth understanding of the etiology of CS will enable the discovery of not just disease risk factors of CS but also therapeutic approaches to modulate the immune response and improve outcomes in patients with respiratory diseases having CS in the pathogenic pathway. Owing to the grave consequences of CS in various diseases, this phenomenon has attracted the attention of researchers and clinicians throughout the globe. So in the present manuscript, we have attempted to discuss CS and its ramifications in COVID-19 and other respiratory diseases, as well as prospective treatment approaches and biomarkers of the cytokine storm. Furthermore, we have attempted to provide in-depth insight into CS from both a prophylactic and therapeutic point of view. In addition, we have included recent findings of CS in respiratory diseases reported from different parts of the world, which are based on expert opinion, clinical case-control research, experimental research, and a case-controlled cohort approach.

Molecular sensitization patterns to cat and dog allergens in Lithuanian children population

Background

Over the last few decades, there was observed an increase of asthma and allergic rhinitis cases caused by allergy to pets.

Objective

This study aimed to analyze molecular sensitization patterns to dog and cat allergens in Lithuanian children who were experiencing allergy-like symptoms.

Materials and methods

A total of 574 children (0-18 years) were tested for allergen-specific immunoglobulin E (sIgE) levels with ALEX2 (ALEX2®, Allergy Explorer Test System). Positive sera were further analyzed for sensitization to cat (Fel d 1, Fel d 2, Fel d 4, and Fel d 7) and dog (Can f 1, Can f 2, Can f 3, Can f 4, Can f 5, and Can f 6) allergen components.

Results

Two hundred forty-seven children tested positive (sIgE ≥0.3 kUA/L) to at least 1 dog or cat allergen component. There were 61.1% children sensitized to components from both sources, 29.2% - exclusively to cat, and 9.7% - to dog components. The major sensitizers were Fel d 1 (84.8%) and Can f 1 (59.4%). There were 42.9% patients sensitized to 3 or more different mammalian protein families and 40.4% - to 3 or more lipocalins. There were 5.7% of children sensitized both to Fel d 1 + Fel d 4 and Can f 1/2 + Can f 5, indicating the high risk of severe asthma. Monosensitization to Fel d 1 was the dominant pattern among Lithuanian children (26.3%).

Conclusion

The majority of children were cat/dog-polysensitized, although sensitization only to cat allergens was most observed. Extensive molecular profiling can be an useful tool for accurate true sensitization diagnosis and prognosis of disease severity.

Component-Resolved Diagnosis Based on a Recombinant Variant of Mus m 1 Lipocalin Allergen

Exposure to the Mus m 1 aeroallergen is a significant risk factor for laboratory animal allergy. This allergen, primarily expressed in mouse urine where it is characterized by a marked and dynamic polymorphism, is also present in epithelium and dander. Considering the relevance of sequence/structure assessment in protein antigenic reactivity, we compared the sequence of the variant Mus m 1.0102 to other members of the Mus m 1 allergen, and used Discotope 2.0 to predict conformational epitopes based on its 3D-structure. Conventional diagnosis of mouse allergy is based on serum IgE testing, using an epithelial extract as the antigen source. Given the heterogeneous and variable composition of extracts, we developed an indirect ELISA assay based on the recombinant component Mus m 1.0102. The assay performed with adequate precision and reasonable diagnostic accuracy (AUC = 0.87) compared to a routine clinical diagnostic test that exploits the native allergen. Recombinant Mus m 1.0102 turned out to be a valuable tool to study the fine epitope mapping of specific IgE reactivity to the major allergen responsible for mouse allergy. We believe that advancing in its functional characterization will lead to the standardization of murine lipocalins and to the development of allergen-specific immunotherapy.

Concordance of skin test reactivity between indoor inhalant allergens among children with allergic respiratory disease

Background

In vitro studies have demonstrated cross-reactivity among indoor allergen proteins in children with allergic respiratory diseases. However, there are only few studies evaluating in vivo response. A skin prick test (SPT) with commercial indoor solutions is widely used in clinical practice. We aimed to evaluate SPT agreement in children with allergic respiratory disease between pairs of common indoor allergens.

Methods

We reviewed SPT results of children 2 to 18 years old, diagnosed with respiratory allergic disease. Results from house dust mite (Dermatophagoides farinae, Dermatophagoides pteronyssinus), cockroach (Periplaneta americana, Blatella germanica), cat and dog were collected. Sensitization was defined as ≥ 3 mm in wheal diameter. Kappa coefficient (κ) was used to analyze sensitization concordance for each allergen pair.

Results

The charts of 300 children, 187 (62.33%) males, were reviewed. Mean age was 7.43 ± 3.29 years with 183 (61%), 140 (46.67%), 45 (15%), 30 (10%) sensitizations to house dust mite (HDM), cockroach, cat and dog, respectively. Sensitization concordance between HDM and cockroach was moderate: κ = 0.53 (95% CI: 0.42–0.64). Moderate agreement occurred between dog and cat: κ = 0.41 (95%CI: 0.30–0.52). HDM-sensitized children showed poor concordance with both cat κ = 0.17 (95%CI: 0.09–0.24) and dog κ = 0.09 (95%CI: 0.03–0.14). There was also poor concordance between cockroach-sensitized children to cat κ = 0.19 (95%CI; 0.11–0.28) and dog κ = 0.11 (95%CI; 0.04–0.18).

Conclusion

We demonstrated moderate agreement of SPT response between HDM and cockroach as well as dog and cat. This may be due to cross-reactivity. Component-resolved diagnosis should be considered in children with co-sensitization of these allergen pairs.

Real-life effects of benralizumab on allergic chronic rhinosinusitis and nasal polyposis associated with severe asthma

The aim of this study has been to evaluate the efficacy of the IL-5 receptor blocker benralizumab on chronic rhinosinusitis with nasal polyposis (CRSwNP), associated with severe eosinophilic allergic asthma. Ten patients with severe eosinophilic allergic asthma and CRSwNP were enrolled. Sino-nasal outcome test (SNOT-22), numerical rating scale (NRS), endoscopic nasal polyp score, Lund Mackey CT (computed tomography) score, and blood eosinophil count were measured at baseline and after 24 weeks of treatment with benralizumab. All the above clinical, endoscopic, imaging, and hematological parameters significantly improved after 24 weeks of treatment with benralizumab. In particular, SNOT-22 decreased from 61.10 ± 17.20 to 26.30 ± 19.74 (P < 0.001), NRS decreased from 7.20 ± 1.55 to 3.40 ± 2.22 (P < 0.001), the endoscopic polyp nasal score decreased from 4.20 ± 1.32 to 2.50 ± 1.78 (P < 0.001), the Lund-Mackay CT score decreased from 16.60 ± 5.50 to 6.90 ± 5.99 (P < 0.001), and blood eosinophil count decreased from 807.3 ± 271.1 cells/μL to 0 cells/μL (P < 0.0001). These results strongly suggest that benralizumab exerted a very effective therapeutic action on CRSwNP associated with severe asthma, thus improving nasal symptoms and decreasing polyp size.

Phage-display reveals interaction of lipocalin allergen Can f 1 with a peptide resembling the antigen binding region of a human γδT-cell receptor

Although some progress has been achieved in understanding certain aspects of the allergenic mechanism of animal lipocalins, they still remain largely enigmatic. One possibility to unravel this property is to investigate their interaction with components of the immune system. Since these components are highly complex we intended to use a high-throughput technology for this purpose. Therefore, we used phage-display of a random peptide library for panning against the dog allergen Can f 1. By this method we identified a Can f 1 binding peptide corresponding to the antigen-binding site of a putative γδT-cell receptor. Additional biochemical investigations confirmed this interaction.

Therapeutic Effects of Benralizumab Assessed in Patients with Severe Eosinophilic Asthma: Real-Life Evaluation Correlated with Allergic and Non-Allergic Phenotype Expression

Background

Benralizumab can be utilized as add-on biological treatment of severe eosinophilic asthma. However, so far only a few real-life studies have been published with regard to the use of this anti-IL-5 receptor humanized monoclonal antibody.

Objective

The primary aim of this multicenter observational investigation has been to assess the therapeutic effects of benralizumab in patients with severe uncontrolled, corticosteroid refractory eosinophilic asthma. The secondary objective was to evaluate the efficacy of benralizumab with regard to positive or negative skin prick test (SPT).

Methods

Clinical, functional, and laboratory parameters were evaluated in order to verify the therapeutic actions of benralizumab in atopic and non atopic subjects with difficult-to-treat eosinophilic asthma. Moreover, a comparative evaluation was carried out in relation to the presence or absence of SPT positivity.

Results

After 6 months of add-on biological therapy with benralizumab, our 111 patients experienced a marked improvement of their severe eosinophilic asthma, expressed by significant changes in asthma exacerbation rate, prednisone intake, daily use of short-acting β₂-adrenergic agonists (SABA), asthma control test (ACT) score, asthma quality of life questionnaire (AQLQ) score (56 patients), forced expiratory volume in one second (FEV₁), forced vital capacity (FVC), blood eosinophil count, blood basophil count (59 patients), and fractional exhaled nitric oxide (FeNO) levels (39 patients). In addition, significantly more effective outcomes were detected in patients with positive SPT, when compared to subjects with negative SPT, only in regard to asthma exacerbation number, ACT score, and daily SABA utilization. No significant correlation was found between serum IgE concentrations and each of all measured parameters.

Conclusion and Clinical Relevance

Taken together, the results of this real-world study indicate that in both allergic and non-allergic subjects benralizumab can be used as a valuable pharmacotherapeutic option for add-on biological therapy of severe eosinophilic asthma, regardless of SPT positivity or negativity.

Immunologic Pathophysiology and Airway Remodeling Mechanism in Severe Asthma: Focused on IgE-Mediated Pathways

Despite the expansion of the understanding in asthma pathophysiology and the continual advances in disease management, a small subgroup of patients remains partially controlled or refractory to standard treatments. Upon the identification of immunoglobulin E (IgE) and other inflammatory mediators, investigations and developments of targeted agents have thrived. Omalizumab is a humanized monoclonal antibody that specifically targets the circulating IgE, which in turn impedes and reduces subsequent releases of the proinflammatory mediators. In the past decade, omalizumab has been proven to be efficacious and well-tolerated in the treatment of moderate-to-severe asthma in both trials and real-life studies, most notably in reducing exacerbation rates and corticosteroid use. While growing evidence has demonstrated that omalizumab may be potentially beneficial in treating other allergic diseases, its indication remains confined to treating severe allergic asthma and chronic idiopathic urticaria. Future efforts may be bestowed on determining the optimal length of omalizumab treatment, seeking biomarkers that could better predict treatment response and as well as extending its indications.

Molecular Targets for Biological Therapies of Severe Asthma

Asthma is a heterogeneous respiratory disease characterized by usually reversible bronchial obstruction, which is clinically expressed by different phenotypes driven by complex pathobiological mechanisms (endotypes). Within this context, during the last years several molecular effectors and signalling pathways have emerged as suitable targets for biological therapies of severe asthma, refractory to standard treatments. Indeed, various therapeutic antibodies currently allow to intercept at different levels the chain of pathogenic events leading to type 2 (T2) airway inflammation. In addition to pro-allergic immunoglobulin E (IgE), that chronologically represents the first molecule against which an anti-asthma monoclonal antibody (omalizumab) was developed, today other targets are successfully exploited by biological treatments of severe asthma. In particular, pro-eosinophilic interleukin 5 (IL-5) can be targeted by mepolizumab or reslizumab, whereas benralizumab is a selective blocker of IL-5 receptor. Moreover, dupilumab behaves as a dual receptor antagonist of pleiotropic interleukins 4 (IL-4) and 13 (IL-13). Besides these drugs that are already available in medical practice, other biologics are under clinical development such as those targeting innate cytokines, also including the alarmin thymic stromal lymphopoietin (TSLP), which plays a key role in the pathogenesis of type 2 asthma. Therefore, ongoing and future biological therapies are significantly changing the global scenario of severe asthma management. These new therapeutic options make it possible to implement phenotype/endotype-specific treatments, that are delineating personalized approaches precisely addressing the individual traits of asthma pathobiology. Such tailored strategies are thus allowing to successfully target the immune-inflammatory responses underlying uncontrolled T2-high asthma.

Real-Life effects of benralizumab on exacerbation number and lung hyperinflation in atopic patients with severe eosinophilic asthma

BACKGROUND

The humanized monoclonal antibody benralizumab targets the α subunit of the interleukin-5 (IL-5) receptor and the FcγRIIIa receptor expressed by natural killer cells. Through this dual mechanism of action, benralizumab neutralizes the pro-eosinophil functions of IL-5 and promotes eosinophil apoptosis.

OBJECTIVES AND METHODS

The present real-life study aimed to evaluate, in 22 allergic patients with severe eosinophilic asthma, the effects of benralizumab on asthma exacerbations and lung hyperinflation.

RESULTS

In this regard here we show that, after 24 weeks of add-on treatment, benralizumab completely depleted peripheral blood eosinophils (from 810 to 0 cells/μL; p < 0.0001), and significantly decreased both asthma exacerbation number (from 4 to 0; p < 0.0001) and residual volume (from 2720 to 2300 mL; p < 0.01). Moreover, at the same time point (24 weeks) benralizumab also increased pre-bronchodilator FEV₁ (from 1295 to 1985 mL; p < 0.0001), FVC (from 2390 to 2974 mL; p < 0.0001), FEF_25-75 (from 0.6 to 1.42 L/sec; p < 0.0001), IC (from 1940 to 2460 mL; not significant), and ACT score (from 14.73 to 22.95; p < 0.0001), as well as reduced prednisone intake (from 25 to 0 mg; p < 0.0001).

CONCLUSION

In conclusion, our results suggest that via its anti-eosinophil actions benralizumab improved airflow limitation, lung hyperinflation, and respiratory symptoms, as well as lowered asthma exacerbation rate and abrogated OCS consumption in most patients.

Real-life evaluation of mepolizumab efficacy in patients with severe eosinophilic asthma, according to atopic trait and allergic phenotype

BACKGROUND

Anti-interleukin-5 (IL-5) monoclonal antibodies can be used as add-on biological therapies in allergic and non-allergic patients with severe eosinophilic asthma. However, within such a therapeutic context real-life investigations are lacking.

OBJECTIVE

Therefore, the aim of the present observational study was to evaluate the effects of mepolizumab in allergic and non-allergic subjects with severe eosinophilic asthma.

METHODS

Relevant clinical, functional, laboratory, and pharmacotherapeutic parameters were assessed in the above patient subgroups.

RESULTS

After one year of add-on biological treatment with mepolizumab, our 88 patients experienced a remarkable improvement of their severe asthma, documented by a better symptom control, expressed by a significant improvement in asthma control test (ACT) score. Indeed, the mean value (±standard deviation) of ACT score increased from 12.55 (±3.724) to 21.08 (±3.358). Moreover, significant improvements were also detected with regard to the median values (interquartile range) of forced expiratory volume in one second (FEV₁ ), blood eosinophil numbers, annual rate of disease exacerbations, and daily intake of oral corticosteroids (OCS). In particular, FEV₁ enhanced from 1640 mL (1110-2275) to 1920 mL (1525-2615), blood eosinophil count dropped from 711.0 cells/μL (500.0-1022) to 90.00 cells/μL (50.00-117.5), the annual rate of asthma exacerbations decreased from 3.000 (2.000-6.000) to 0.000 (0.000-1.000), and the daily prednisone intake fell from 6.250 mg (0.000-25.00) to 0.000 mg (0.000-0.000). After one year of mepolizumab treatment, the improvements in clinical, functional, and haematological parameters were quite similar in patient subgroups characterized by skin prick test (SPT) negativity or positivity, respectively. A significant correlation was observed between serum IgE levels and OCS intake decrease (r = -0.2257; P < .05).

CONCLUSION AND CLINICAL RELEVANCE

Hence, our real-life data suggest that mepolizumab can represent a valid add-on therapeutic option for patients with severe eosinophilic asthma, irrespective of IgE serum concentrations, and allergic sensitization.

Critical aspects in dog allergen immunotherapy (DAI). May Component Resolved Diagnosis (CRD) play a role in predicting the efficacy?

We hypothesize that a pivotal condition determining the efficacy of dog allergen immunotherapy (DAI) might be the mono-sensitization to dog lipocalins (Can f 1-2) in individuals not directly or indirectly exposed to other furry animals. In fact, the concomitant sensitization to lipocalins and/or albumins, especially in those patients directly exposed to furry animals, may potentially stimulate patient's airways by inducing persistent inflammation and, thus, clinical symptoms. In these conditions, it is likely that DAI alone could be inadequate to reduce airway inflammation mediated by inhalation of dog allergens in patients with simultaneous exposure to other furry animals. Can f 5 has been found as exclusive allergen in about one third of dog-sensitized individuals. Considering the presence of different allergenic materials in extract of mammalian origin, it is evident that a standard DAI is not likely to be effective in Can f 5 prevalent or mono-sensitized individuals. Moreover, we would underline the need of collecting detailed information on the possible exposures to furry animals (other than the common pets), an information that usually is neglected in clinical practice. Furthermore, a detailed clinical history exploring the real significance of dog sensitization (mono or poly-sensitization, induction of clinical symptoms after exposure etc.) should be performed before prescribing DAI. In some patients, with potential high susceptibility to animal allergens, the use of CRD is essential to verify the presence of concomitant allergic sensitization to lipocalins and/or albumins belonging to other furry animals. The availability of CRD introduced the possibility of a better targeted prescription of DAI because it might be useful for point out the primary allergens and for the exclusion of cross-reactive ones.

Consensus document on dog and cat allergy

The prevalence of sensitization to dogs and cats varies by country, exposure time and predisposition to atopy. It is estimated that 26% of European adults coming to the clinic for suspected allergy to inhalant allergens are sensitized to cats and 27% to dogs. This document is intended to be a useful tool for clinicians involved in the management of people with dog or cat allergy. It was prepared from a consensus process based on the RAND/UCLA method. Following a literature review, it proposes various recommendations concerning the diagnosis and treatment of these patients, grounded in evidence and clinical experience. The diagnosis of dog and cat allergy is based on a medical history and physical examination that are consistent with each other and is confirmed with positive results on specific IgE skin tests. Sometimes, especially in polysensitized patients, molecular diagnosis is strongly recommended. Although the most advisable measure would be to avoid the animal, this is often impossible and associated with a major emotional impact. Furthermore, indirect exposure to allergens occurs in environments in which animals are not present. Immunotherapy is emerging as a potential solution to this problem, although further supporting studies are needed.

Omalizumab, the first available antibody for biological treatment of severe asthma: more than a decade of real-life effectiveness

Omalizumab was the first, and for a long time the only available monoclonal antibody for the add-on treatment of severe allergic asthma. In particular, omalizumab selectively targets human immunoglobulin (Ig)E, forming small-size immune complexes that inhibit IgE binding to its high- and low-affinity receptors. Therefore, omalizumab effectively blunts the immune response in atopic asthmatic patients, thus significantly improving the control of asthma symptoms and successfully preventing disease exacerbations. These very positive effects of omalizumab make it possible to drastically decrease both referrals to the emergency room and hospitalizations for asthma exacerbations. Such important therapeutic actions of omalizumab have been documented by several randomized clinical trials, and especially by more than 10 years of real-life experience in daily clinical practice. Omalizumab can also interfere with airway remodelling by inhibiting the activation of IgE receptors located on structural cells such as bronchial epithelial cells and airway smooth muscle cells. Moreover, omalizumab is characterized by a very good safety and tolerability profile. Hence, omalizumab represents a valuable therapeutic option for the add-on biological treatment of severe allergic asthma.

Diagnosis of Allergy to Mammals and Fish: Cross-Reactive vs. Specific Markers

PURPOSE OF REVIEW

Allergen extracts are still widely used in allergy diagnosis as they are regarded as sensitive screening tools despite the fact that they may lack some minor allergens. Another drawback of extracts is their low specificity, which is due to the presence of cross-reactive allergens. Progress in allergen identification has disclosed a number of allergenic molecules of homologous sequence and structure which are present in different animal species. This review summarizes recent advances in mammalian and fish allergen identification and focuses on their clinical relevance.

RECENT FINDINGS

Serum albumins and parvalbumins are well-known animal panallergens. More recently several members of the lipocalin family were found to be cross-reactive between furry animals whereas in fish, additional allergens, enolase, aldolase and collagen, were found to be important and cross-reactive allergens. New epidemiological studies have analysed the prevalence and clinical relevance of mammalian and fish components. Primary sensitization can be distinguished from cross-sensitization by using marker allergens. Although substantial progress has been made in allergen identification, only few markers are commercially available for routine clinical practice.

Allergy to pets and new allergies to uncommon pets

Abstract. Animal dander is an important source of respiratory allergens, and sensitization to allergens from cat and/or dog during childhood represents a risk factor for the development of asthma and rhinitis later in life. The identification and characterization of allergenic components is crucial to improve diagnosis and therapy in patients with allergy to pets. Allergens from furry animals belong to a restricted number of protein families, a large majority are lipocalins or albumins, some are secretoglobins or latherins. Animal dander contains cross-reactive molecules and current efforts aim at defining species-specific allergens that have a high diagnostic sensitivity. Component-resolved diagnosis allows to discriminate genuine sensitization from cross-sensitization. This review contains a detailed description of allergenic components of cat, dog, horse, and small mammalian pets. Sensitizations to exotic pets, a newly emerging issue, are also discussed.

Sensitization to Common and Uncommon Pets or Other Furry Animals: Which May Be Common Mechanisms?

Exposure to animal allergens constitutes a relevant risk factor for the development of allergic sensitization. Moreover, an increasing number of people become owners of less common animals. In this article we summarize aspects related to sensitization to cat/dog which may be applied also to uncommon pets or other furry animals. The data discussed here suggest that several different factors may induce allergic sensitization to furry animals with or without previous contact. Allergic sensitization without animal exposure is a relevant risk for patients because they are not aware about the possibility that even severe respiratory symptoms may develop after an occasional animal contact. This aspect should be taken into account by susceptible individuals before acquiring pets or beginning a contact for working/leisure activity with a common as well as uncommon animal. As a consequence, skin prick test and/or evaluation of specific IgE antibodies (by classic ImmunoCAP or micro-array technique ImmunoCAP ISAC) also to less common ("new") mammalian allergens could be recommended in individuals already sensitized to common pets to identify the occurrence of allergic sensitization and consequently to avoid future exposures to uncommon animal allergens.

EAACI Molecular Allergology User's Guide

The availability of allergen molecules ('components') from several protein families has advanced our understanding of immunoglobulin E (IgE)-mediated responses and enabled 'component-resolved diagnosis' (CRD). The European Academy of Allergy and Clinical Immunology (EAACI) Molecular Allergology User's Guide (MAUG) provides comprehensive information on important allergens and describes the diagnostic options using CRD. Part A of the EAACI MAUG introduces allergen molecules, families, composition of extracts, databases, and diagnostic IgE, skin, and basophil tests. Singleplex and multiplex IgE assays with components improve both sensitivity for low-abundance allergens and analytical specificity; IgE to individual allergens can yield information on clinical risks and distinguish cross-reactivity from true primary sensitization. Part B discusses the clinical and molecular aspects of IgE-mediated allergies to foods (including nuts, seeds, legumes, fruits, vegetables, cereal grains, milk, egg, meat, fish, and shellfish), inhalants (pollen, mold spores, mites, and animal dander), and Hymenoptera venom. Diagnostic algorithms and short case histories provide useful information for the clinical workup of allergic individuals targeted for CRD. Part C covers protein families containing ubiquitous, highly cross-reactive panallergens from plant (lipid transfer proteins, polcalcins, PR-10, profilins) and animal sources (lipocalins, parvalbumins, serum albumins, tropomyosins) and explains their diagnostic and clinical utility. Part D lists 100 important allergen molecules. In conclusion, IgE-mediated reactions and allergic diseases, including allergic rhinoconjunctivitis, asthma, food reactions, and insect sting reactions, are discussed from a novel molecular perspective. The EAACI MAUG documents the rapid progression of molecular allergology from basic research to its integration into clinical practice, a quantum leap in the management of allergic patients.

The mannose receptor negatively modulates the Toll-like receptor 4-aryl hydrocarbon receptor-indoleamine 2,3-dioxygenase axis in dendritic cells affecting T helper cell polarization

BACKGROUND

Dendritic cells (DCs) are key players in the induction and re-elicitation of TH2 responses to allergens. We have previously shown that different C-type lectin receptors on DCs play a major role in allergen recognition and uptake. In particular, mannose receptor (MR), through modulation of Toll-like receptor (TLR) 4 signaling, can regulate indoleamine 2,3-dioxygenase (IDO) activity, favoring TH2 responses. Interestingly, the aryl hydrocarbon receptor (AhR), a ligand-dependent transcription factor with an emerging role in immune modulation, has been implicated in IDO activation in response to TLR stimulation.

OBJECTIVE

Here we investigated how allergens and lectins modulate the TLR4-AhR-IDO axis in human monocyte-derived DCs.

METHODS

Using a combination of genomics, proteomics, and immunologic studies, we investigated the role of MR and AhR in IDO regulation and its effect on T helper cell differentiation.

RESULTS

We have demonstrated that LPS induces both IDO isoforms (IDO1 and IDO2) in DCs, with partial involvement of AhR. Additionally, we found that, like mannan, different airborne allergens can effectively downregulate TLR4-induced IDO1 and IDO2 expression, most likely through binding to the MR. Mannose-based ligands were also able to downregulate IL-12p70 production by DCs, affecting T helper cell polarization. Interestingly, AhR and some components of the noncanonical nuclear factor κB pathway were shown to be downregulated after MR engagement, which could explain the regulatory effects of MR on IDO expression.

CONCLUSION

Our work demonstrates a key role for MR in the modulation of the TLR4-AhR-IDO axis, which has a significant effect on DC behavior and the development of immune responses against allergens.

Cross-reactivity between aeroallergens and food allergens

In patients with respiratory allergy, cross-reactivity between aeroallergens and foods may induce food allergy, symptoms ranging from oral allergy syndrome to severe anaphylaxis. Clinical entities due to IgE sensitization to cross-reactive aeroallergen and food allergen components are described for many sources of plant origin (pollen-food syndromes and associations, such as birch-apple, cypress-peach and celery-mugwort-spice syndromes, and mugwort-peach, mugwort-chamomile, mugwort-mustard, ragweed-melon-banana, goosefoot-melon associations), fungal origin (Alternaria-spinach syndrome), and invertebrate, mammalian or avian origin (mite-shrimp, cat-pork, and bird-egg syndromes). Clinical cases of allergic reactions to ingestion of food products containing pollen grains of specific plants, in patients with respiratory allergy to Asteraceae pollen, especially mugwort and ragweed, are also mentioned, for honey, royal jelly and bee polen dietary supplements, along with allergic reactions to foods contaminated with mites or fungi in patients with respiratory allergy to these aeroallergens. Medical history and diagnosis approach may be guided by the knowledge about the diverse cross-reacting allergens involved, and by the understanding of these clinical entities which may vary significantly or may be overlapping. The association between primary IgE sensitization with respiratory symptoms to inhaled allergens and food allergy due to cross-reactive allergen components is important to assess in allergy practice. The use of molecular-based diagnosis improves the understanding of clinically relevant IgE sensitization to cross-reactive allergen components from aeroallergen sources and foods.