In vitro allergy tests compared to intradermal testing in horses with recurrent airway obstruction

Towards personalized medicine for the treatment of equine asthma

Although horses with asthma share similar clinical signs, the heterogeneity of the disease in terms of severity, triggering factors, inflammatory profile, and pathological features has hindered our ability to define biologically distinct subgroups. The recognition of phenotypes and endotypes could enable the development of precision medicine, including personalized, targeted therapy, to benefit affected horses. While in its infancy in horses, this review outlines the phenotypes of equine asthma and discusses how knowledge gained from targeted therapy in human medicine can be applied to evaluate the potential opportunities for personalized medicine in equine asthma and to suggest avenues for research to advance this emerging field.

Microarray molecular mapping of horses with severe asthma

BACKGROUND

Severe asthma (SA) in horses, resembling human asthma, is a prevalent, debilitating allergic respiratory condition marked by elevated allergen-specific immunoglobulin E (IgE) against environmental proteins; however, research exploring the exposome's influence on IgE profiles is currently limited but holds paramount significance for diagnostic and therapeutic developments.

ANIMALS

Thirty-five sports horses were analyzed, consisting of environmentally matched samples from France (5 SA; 6 control), the United States (6 SA; 6 control), and Canada (6 SEA; 6 control).

METHODS

This intentional cross-sectional study investigated the sensitization profiles of SA-affected and healthy horses via serological antigen microarray profiling. Partial least square-discriminant analysis (PLS-DA) was used to identify and rank the importance of allergens for class separation (ie, affected/non-affected) as variable influence of projection (VIP), and allergen with commonality internationally established via frequency analysis.

RESULTS

PLS-DA models showed high discriminatory power in predicting SA in horses from Canada (area under the curve [AUC] 0.995) and France (AUC 0.867) but poor discriminatory power in horses from the United States (AUC 0.38). Hev b 5.0101, Cyn D, Der p 2, and Rum cr were the only shared allergens across all geographical groups.

CONCLUSIONS AND CLINICAL IMPORTANCE

Microarray profiling can identify specific allergenic components associated with SA in horses, while mathematical modeling of this data can be used for disease classification, highlighting the variability of sensitization profiles between geographical locations and emphasizing the importance of local exposure to the prevalence of different allergens. Frequency scoring analysis can identify important variables that contribute to the classification of SA across different geographical regions.

Decision Making in Severe Equine Asthma-Diagnosis and Monitoring

Decision making consists of gathering quality data in order to correctly assess a situation and determine the best course of action. This process is a fundamental part of medicine and is what enables practitioners to accurately diagnose diseases and select appropriate treatment protocols. Despite severe equine asthma (SEA) being a highly prevalent lower respiratory disease amongst equids, clinicians still struggle with the optimization of routine diagnostic procedures. The use of several ancillary diagnostic tests has been reported for disease identification and monitoring, but many are only suitable for research purposes or lack practicality for everyday use. The aim of this paper is to assist the equine veterinarian in the process of decision making associated with managing SEA-affected patients. This review will focus on disease diagnosis and monitoring, while also presenting a flow-chart which includes the basic data that the clinician must obtain in order to accurately identify severely asthmatic horses in their everyday routine practice. It is important to note that European and American board-certified specialists on equine internal medicine can provide assistance in the diagnosis and treatment plan of SEA-affected horses.

Immunoproteomics reveal increased serum IgG3/5 binding to Dermatophagoides and yeast protein antigens in severe equine asthma in a preliminary study

Introduction

Severe equine asthma (SEA) is a common, chronic respiratory disease of horses characterized by hyperreactivity to hay dust which has many similarities to severe neutrophilic asthma in humans. SEA-provoking antigens have not been comprehensively characterized, but molds and mites have been suggested as relevant sources. Here, we identified relevant antigen candidates using immunoproteomics with IgG isotype-binding analyses.

Methods

Proteins from Dermatophagoides pteronyssinus (Der p) were separated by two-dimensional gel electrophoresis followed by immunoblotting (2D immunoblots) resulting in a characteristic pattern of 440 spots. After serum incubation, antibody (Ig)-binding of all Ig (Pan-Ig) and IgG isotypes (type-2-associated IgG3/5, type-1-associated IgG4/7) was quantified per each spot and compared between asthmatic and healthy horses' sera (n=5 per group).

Results

Ig binding differences were detected in 30 spots. Pan-Ig binding was higher with asthmatics compared to healthy horses' sera on four spots, and IgG3/5 binding was higher on 18 spots. Small IgG4/7 binding differences were detected on 10 spots with higher binding with asthmatics' sera on four but higher binding with healthy horses' sera on six spots. Proteins from the spots with group differences including mite and yeast proteins were identified by liquid chromatography mass spectrometry. The latter likely originated from the feeding substrate of the Der p culture. Prioritized antigen candidates amongst the proteins identified were Der p 1, Der p 11, group 15 allergens, myosin heavy chain, and uncharacterized Der p proteins. Additionally, yeast enolases, alcohol dehydrogenase (ADH), phosphoglycerate kinase (PGK), glyceraldehyde-3-phosphate dehydrogenase, and heat shock proteins were prioritized. Eleven antigen candidates were tested for confirmation by ELISAs using the respective proteins separately. Differences in asthmatics vs. healthy horses' serum Ig binding to Der p 1, Der p 18, and three yeast enzymes (enolase, ADH, and PGK) confirmed these as promising antigens of immune responses in SEA.

Discussion

Antigens with relevance in SEA were newly identified by immunoproteomics, and yeast antigens were considered for SEA for the first time. Serum IgG3/5 binding to relevant antigens was increased in SEA and is a novel feature that points to increased type-2 responses in SEA but requires confirmation of the corresponding cellular responses.

Comparison of Skin Prick Tests (SPT), Intradermal Tests (IDT) and In Vitro Tests in the Characterization of Insect Bite Hypersensitivity (IBH) in a Population of Lusitano Horses: Contribution for Future Implementation of SPT in IBH Diagnosis

Thirty controls (C) and 30 IBH-affected (T) Lusitano horses were evaluated. T horses were included based on anamnesis and physical examination, supported by questionnaires. All horses were submitted to skin tests, Intrademal (IDT) and Skin Prick Tests (SPT), on the neck with 14 specific allergens, 13 recombinant proteins (r-proteins) from Culicoides nubeculosus (Cul n) and Culicoides obsoletus (Cul o) salivary glands and Culicoides nubeculosus Whole Body Extract (Cul n WBE). Addicionally, a cluster of six T and six C horses were also tested with Cul n 3 and Cul n 4 produced in insect cells and barley, as well as E. coli produced Cul o 3 and Cul o WBE. Allergen concentrations were 10 µg/mL for IDT and 100 µg/mL for SPT, and wheal diameters assessed at 20 min, 6 and 48 h. IDTs were considered positive when wheal diameter was ≥50% of the histamine wheal and SPT's ≥ 0.9 cm. In vitro tests, allergen-specific serum IgE and sulfidoleukotriene (sLT) release assay were also carried out. Results showed that Cul n WBE, Cul n 7, 8, 9, Cul o1P and Cul o 2P were the best performing allergens for SPTs (p ≤ 0.0001) for the 1st allergen panel and Cul o WBE, Cul n 3 Bar and Cul n 4 Bac (p ≤ 0.05) for the 2nd, presenting a higher discriminatory diagnostic potential than IDTs, at a concentration of 100 µg/mL, with readings assessed at 20 min. Regarding in vitro tests overall, the sLT release assay performed best.

Protein microarray allergen profiling in bronchoalveolar lavage fluid and serum of horses with asthma

BACKGROUND

The diagnostic value of allergen-specific immunoglobulin E (IgE) in horses with asthma is uncertain. A recently developed protein microarray detected abnormally high latex-specific IgE concentrations in the serum of horses with severe asthma.

OBJECTIVES

The main objective was to characterize the IgE profiles of asthmatic horses in Switzerland using a protein microarray platform in serum and bronchoalveolar lavage fluid (BALF). The secondary objective was to determine whether serological and BALF allergen-specific IgE concentrations correlated.

ANIMALS

Forty-four asthmatic and 39 control horses ≥5 years of age.

METHODS

This prospective cross-sectional study investigated the sensitization profiles of horses with asthma compared with environmentally matched healthy controls. Both serum and BALF were analyzed using the protein microarray. Partial least square-discriminant analysis (PLS-DA) was used to identify and rank the importance of the allergens for class detection (ie, asthma vs control), with a variable influence on the projection (VIP) >1 considered significant.

RESULTS

The allergens that best discriminated (VIP >1) asthmatic horses from controls were proteins derived from fungi (Aspergillus fumigatus), insects (Culicoides spp.), and latex (Hevea brasiliensis). The serological model predictive ability was markedly inferior (area under the curve [AUC] 0.585, 95% confidence interval [CI]: 0.454-0.747) to that of the BALF (AUC 0.751, 95% CI: 0.582-0.866). The two models shared nine allergens, of which eight showed significant weak to moderate correlations.

CONCLUSION AND CLINICAL IMPORTANCE

The concentrations of several allergen-specific IgE were higher in asthmatic horses. The protein microarray performed better on BALF than serum for detection of asthma. Serological IgE concentrations do not closely correlate with BALF concentrations and should be interpreted with caution.

Intradermal Testing Results in Horses Affected by Mild-Moderate and Severe Equine Asthma

Simple Summary

Equine asthma is a respiratory syndrome sharing several similarities with human asthma and represents the most common cause of chronic coughing in horses. Based on the severity and recurrence of the conditions, it is classified as mild-moderate or severe equine asthma. Although a precise pathogenetic mechanism has not yet been identified, it is generally agreed that environmental allergens behave as triggers of a hypersensitivity response (HR), culminating in asthmatic exacerbations. In human medicine, the skin prick test is considered the gold standard of allergy testing; similarly, in equine medicine, intradermal testing is used to identify hypersensitivities to specific allergens. The present study describes and compares the results of intradermal testing in horses affected by either mild-moderate or severe equine asthma to evaluate the responsiveness of asthmatic horses and to identify the most frequently involved allergens. Type-I HR was shown to play a major role in the pathogenesis of severe equine asthma, while type-IV HR seems to be involved mostly in milder forms. Insects represented the antigens inducing the most frequent and strongest reactions among asthmatic horses, followed by Dermatophagoides spp. and dog epithelium; these allergens should therefore be considered for avoidance strategies and the future development of desensitizing allergen-specific immunotherapy.

Abstract

Equine asthma is an inflammatory respiratory disorder, classified as mild-moderate (MEA) and severe (SEA). SEA is characterized by recurrent exacerbations, consisting of dyspnea, coughing and exercise intolerance; MEA causes poor performance, occasional cough and mucus hypersecretion. Although a precise pathogenesis is not completely understood, allergic mechanisms are considered an important pathophysiological feature of equine asthma. In equine medicine, intradermal testing (IDT) is effective in identifying hypersensitivity to specific allergens. However, to date, the studies about IDT in asthmatic horses obtained contradictory results. This study aims to evaluate IDT responses in MEA and SEA horses and to identify the most significant allergens. Thirty-eight asthmatic horses were enrolled and underwent IDT using 50 allergens; reactions were evaluated at 30 min, 4, 24 and 48 h and were assigned a score from 0 to 4. In SEA horses, the most frequent and strongest reactions were observed at 30 min and 4 h, suggesting the involvement of type I hypersensitivity; in MEA horses, also type IV hypersensitivity seemed to play a major role. Insects, Dermatophagoides spp. and dog epithelium induced in MEA and SEA horses the most significant hypersensitivity responses and could therefore be considered as the main allergenic antigens in our geographic area.

Comparison of Four Different Allergy Tests in Equine Asthma Affected Horses and Allergen Inhalation Provocation Test

Potential triggers for equine asthma are allergens from hay and straw dusts, mold spores and storage mites. The contribution of these environmental trigger factors to equine asthma is still largely uncertain. The aim of this study was to compare results of four allergy tests from healthy and asthma-affected horses, and to evaluate the clinical relevance of allergens tested positive via specific inhalation provocation test. Fifteen horses were classified using a clinical scoring system as asthmatic (n = 9) or control (n = 6). Four different allergy tests (functional in vitro test, intradermal test, Fc-epsilon receptor test, and ELISA for allergen-specific IgE) were compared. A histamine inhalation provocation test as positive control was performed in all horses and the interpleural pressure was measured. In addition, two individual allergens were chosen for the allergen inhalation provocation test based on the results of the allergy tests and inhaled in increasing concentrations, until signs of dyspnea occurred. None of the four allergy tests could differentiate reliably between controls and asthma-affected horses. There was no agreement among the results of the four allergy tests. The interpleural pressure results showed a large individual variability. A clear positive reaction on the allergen inhalation provocation test was only detected in two asthma-affected horses 6 hours after allergen inhalation with Aspergillus fumigatus and Cladosporium herbarum. In most cases a purely type I immediate reaction is unlikely to be involved in causing the clinical signs of equine asthma. Because of a delayed reaction after allergen provocation in two horses, the involvement of cell-mediated type III or IV hypersensitivity may be possible. As all allergy tests used in this study can only detect IgE-mediated hypersensitivity, these tests are probably not suitable for an etiological diagnosis of equine asthma.

Evaluation of multiple allergen simultaneous (sIgE) testing compared to intradermal testing in the etiological diagnosis of atopic dermatitis in horses

Although intradermal testing (IDT) is commonly used in the etiological diagnosis of allergies, in vitro testing for specific IgE (sIgE) is an attractive alternative. Currently, new laboratory techniques in veterinary allergological practice, including multiple allergen simultaneous tests (MASTs), gradually supersede in vivo tests. Both, serological (sIgE) and IDTs in fourteen atopic Malopolski horses were performed. Correlation and agreement between test results were evaluated. Receiver operating characteristic analysis showed that sIgE to Acarus siro had the best diagnostic performance (Area under the ROC curve [AUC] = 0.969), followed by Dermatophagoides pteronyssinus (AUC = 0.844), Dermatophagoides farinae (AUC = 0.813) and Tyrophagus putrescentiae (AUC = 0.803). A significant positive correlation between IDT and MAST was found for A. siro (r_S = 0.870; p = 0.00005), and D. farinae (r_S = 0.657; p = 0.011). There was significant moderate agreement for 2 of 5 allergens, A. siro (κ = 0.569) and D. farinae (κ = 0.485) in semiquantitative assessment and significant fair to substantial agreement for 3 of 5 allergens, D. pteronyssinus (κ = 0.689), A. siro (κ = 0.569), D. farinae (κ = 0.432) in dichotomic assessment. Sensitivity ranged from 44% to 89%, depending on the allergen, while specificity was significantly higher for all allergens in MAST (60%–100%); the mean accuracy was 73% (manufacturer cut-off) and 77.4% (optimal cut-off) based on the Youden index. Compared with IDT, serological MAST showed good detection performance for 60% allergen sIgE in dichotomic assessment with substantial diagnostic capability, but careful clinical interpretation is needed for some allergens.

A Comparison of Multiple Allergen Simultaneous Tests Using Allergen-Specific IgE Concentration and Intradermal Skin Tests in Atopic Horses With Pollen Allergy

Intradermal tests (IDTs) and measurement of specific immunoglobulin E class (sIgE) levels in sera are the most common and reliable methods used in allergological clinical practice. The purpose of this study was to explore the sensitization of pollen allergy in atopic horses with pollinosis and to assess the diagnostic value of the multiple allergen simultaneous tests (MASTs) compared with that of the IDT. Twenty-one Malopolski horses with typical skin hypersensitivity symptoms during pollen seasons were enrolled. Intradermal tests were performed, and allergen-specific IgE concentrations in sera were measured using a monoclonal anti-IgE antibody to pollens of grass, weeds, trees, and cultivated plants. The highest sensitization rate was for Secale cereale (IDT, 76%; MAST, 66.7%), grass (IDT, 71%; MAST, 57%), and Brassica napus (IDT, 52.4%; MAST, 57%). Receiver operating characteristic (ROC) curve analysis and the area under the ROC curve (AUC) showed that Betula spp., Alnus spp., and Corylus spp. had the highest AUC at 0.854, followed by Secale cereale (AUC = 0.796), Plantago lanceolata (AUC = 0.726), Brassica napus (AUC = 0.704), and a grass allergen mixture (AUC = 0.695). The mean AUC for all allergens was 0.712 (0.604-0.867). The overall sensitivity of the sIgE plant horse panel was 78% (range, 68%-90%), the specificity was 86.3% (range, 64%-100%), and the accuracy was 79% (range, 64%-87%). Statistical kappa (κ) agreement between the MAST and IDT was reached for tree (κ = 0.767), rye (κ = 0.687), colza (κ = 0.671), and grass (κ = 0.664) pollen. The MAST showed a favorable agreement with the IDT and can be used for the detection of sIgE in atopic horses with pollinosis.

Bronchoalveolar lavage fluid cytokine, cytology and IgE allergen in horses with equine asthma

The pathophysiology of equine asthma (EA) is still not fully described, but the involvement of an allergic reaction is strongly suspected. This theory has led to the use of allergen-specific immunoglobulin (Ig)E tests to support a diagnosis of asthma. The objective of this descriptive study was to evaluate the correlation between four subgroups of EA (mastocytic mild equine asthma [MEA], neutrophilic MEA, mixed MEA, and severe equine asthma [SEA]), allergen specific IgE (measured in both serum and BALF) and mRNA expression of selected genes in bronchoalveolar lavage fluid (BALF). Serum and BALF were collected from 64 horses with a history of lower airway problems with or without poor performance. Differential cell counts from BALF were used to assign horses to one of four groups (mastocytic MEA; neutrophilic MEA, mixed MEA, and SEA). The expression of messenger RNA (mRNA) coding for IL4, IL5, IL8, IL10, TGFB, TNFA, toll-like receptor (TLR)4, IL1RA, IL1B, matrix metalloproteinase 8 (MMP8), TLR9, chemokine ligand 5 (CCL5) and cluster of differentiation (CD)14 in BALF were measured using reverse transcriptase (RT) quantitative PCR (qPCR). Allergen-specific IgE was measured in serum and BALF using an allergen-specific IgE ELISA test with the screening panel: house mites, storage mites, mould and pollen. As expected, the BALF neutrophil differential count correlated with mRNA expression of MMP-8 (r = 0.611, p < 0.001), TLR-4 (r = 0.540, p < 0.001), IL-1RA (r = 0.490, p < 0.001), IL-1β (r = 0.463, p < 0.001) and IL-8 (r = 0.302, p = 0.015). Cytokine expression of IL-1β (p = 0.014), MMP8 (p = 0.028) and IL-1RA (p = 0.037) was significantly higher in the SEA group compared to the MEA subgroups. The BALF mast cell count was correlated with allergen-specific IgE for insects (r = 0.370, p = 0.002) and pollen (r = 0.313, p = 0.011). Eosinophils in BALF were correlated with BALF mRNA expression of IL-4 (r = 0.340, p = 0.006) together with a significant correlation between BALF eosinophils and allergen-specific IgE for mites (r = 0.930, p < 0.001) and pollen in BALF (r = 0.837, p < 0.001). No correlation was found between allergen-specific IgE in serum and BALF for any of the allergen in the screening panel. Based on these results from allergen-specific IgE in horses with EA is not found in systemic circulation, and only the mastocytic and mixed subgroups of horses with EA had allergen-specific IgE in BALF. Further studies are needed to clarify the relationships identified here.

Antigen array for serological diagnosis and novel allergen identification in severe equine asthma

Severe equine asthma (sEA), which closely resembles human asthma, is a debilitating and performance-limiting allergic respiratory disorder which affects 14% of horses in the Northern Hemisphere and is associated with increased allergen-specific immunoglobulin E (IgE) against a range of environmental proteins. A comprehensive microarray platform was developed to enable the simultaneous detection of allergen-specific equine IgE in serum against a wide range of putative allergenic proteins. The microarray revealed a plethora of novel pollen, bacteria, mould and arthropod proteins significant in the aetiology of sEA. Moreover, the analyses revealed an association between sEA-affected horses and IgE antibodies specific for proteins derived from latex, which has traditionally been ubiquitous to the horse’s environment in the form of riding surfaces and race tracks. Further work is required to establish the involvement of latex proteins in sEA as a potential risk factor. This work demonstrates a novel and rapid approach to sEA diagnosis, providing a platform for tailored management and the development of allergen-specific immunotherapy.

Comparative Review of Asthma in Farmers and Horses

PURPOSE OF REVIEW

Farmers are routinely exposed to organic dusts and aeroallergens that can have adverse respiratory health effects including asthma. Horses are farm-reared large animals with similar exposures and can develop equine asthma syndrome (EAS). This review aims to compare the etiology, pathophysiology, and immunology of asthma in horses compared to farmers and highlights the horse as a potential translational animal model for organic dust-induced asthma in humans.

RECENT FINDINGS

Severe EAS shares many clinical and pathological features with various phenotypes of human asthma including allergic, non-allergic, late onset, and severe asthma. EAS disease features include variable airflow obstruction, cough, airway hyperresponsiveness, airway inflammation/remodeling, neutrophilic infiltrates, excess mucus production, and chronic innate immune activation. Severe EAS is a naturally occurring and biologically relevant, translational animal disease model that could contribute to a more thorough understanding of the environmental and immunologic factors contributing to organic dust-induced asthma in humans.

Development of a comprehensive protein microarray for immunoglobulin E profiling in horses with severe asthma

BACKGROUND

Severe asthma in horses, known as severe equine asthma (SEA), is a prevalent, performance-limiting disease associated with increased allergen-specific immunoglobulin E (IgE) against a range of environmental aeroallergens.

OBJECTIVE

To develop a protein microarray platform to profile IgE against a range of proven and novel environmental proteins in SEA-affected horses.

ANIMALS

Six SEA-affected and 6 clinically healthy Warmblood performance horses.

METHODS

Developed a protein microarray (n = 384) using protein extracts and purified proteins from a large number of families including pollen, bacteria, fungi, and arthropods associated with the horses, environment. Conditions were optimized and assessed for printing, incubation, immunolabeling, biological fluid source, concentration techniques, reproducibility, and specificity.

RESULTS

This method identified a number of novel allergens, while also identifying an association between SEA and pollen sensitization. Immunolabeling methods confirmed the accuracy of a commercially available mouse anti-horse IgE 3H10 source (R2 = 0.91). Biological fluid source evaluation indicated that sera and bronchoalveolar lavage fluid (BALF) yielded the same specific IgE profile (average R2 = 0.75). Amicon centrifugal filters were found to be the most efficient technique for concentrating BALF for IgE analysis at 40-fold. Overnight incubation maintained the same sensitization profile while increasing sensitivity. Reproducibility was demonstrated (R2 = 0.97), as was specificity using protein inhibition assays. Arthropods, fungi, and pollens showed the greatest discrimination for SEA.

CONCLUSIONS AND CLINICAL IMPORTANCE

We have established that protein microarrays can be used for large-scale IgE mapping of allergens associated with the environment of horses. This technology provides a sound platform for specific diagnosis, management, and treatment of SEA.

Assessment of serum allergen-specific IgE levels in horses with seasonal allergic dermatitis and recurrent airway obstruction in Spain

Allergic conditions are prevalent equine diseases that can be diagnosed by clinical examination alone, but definitive diagnosis is more likely with laboratory testing. The ELISA Allercept^© test was used to analyse the serum samples of 73 horses with allergic diseases. Sixty-one horses (83.5%) had allergen-specific IgE levels ≥ 150 ELISA Units (EU), the cut-off defined by the assay. Fifty-four horses had allergic dermatitis (AD) with high IgE levels to Tyrophagus putrescentiae (51.9%), Rumex crispus (48.1%), Tabanus (46.3%) and Dermatophagoides farinae/ D. pteronyssinus (40.7%). Seven horses with recurrent airway obstruction (RAO) had a high prevalence of T. putrescentiae (85.7%), followed by that of Acarus siro (57.1%) and D. farinae/D. pteronyssinus (57.1%). Horses affected with RAO had more positive reactions to mites (2.22 ± 0.84) than did horses with AD (1.51 ± 0.61, P < 0.05). A strong correlation of serum allergen-specific IgE level was found between Culex tarsalis and Stomoxys (r = 0.943) and between Dactylis glomerata and both Secale cereale (r = 0.79) and R. crispus (r = 0.696). These results indicate that among horses with allergic diseases in Spain, ELISA tests demonstrated a high prevalence of serum allergen-specific IgE in response to mites. Our study emphasises the importance of laboratory testing and updating allergy panels to improve the likelihood of a definitive diagnosis and the identification of allergens that should be included in allergic disease treatment.

Equine asthma: Integrative biologic relevance of a recently proposed nomenclature

The term “equine asthma” has been proposed as a unifying descriptor of inflammatory airway disease (IAD), recurrent airway obstruction (RAO), and summer pasture‐associated obstructive airway disease. Whilst the term will increase comprehensibility for both the lay and scientific communities, its biologic relevance must be compared and contrasted to asthma in human medicine, recognizing the limited availability of peer‐reviewed equine‐derived data, which are largely restricted to clinical signs, measures of airway obstruction and inflammation and response to therapy. Such limitations constrain meaningful comparisons with human asthma phenotypes. Suggested minimum inclusion criteria supporting the term asthma, as well as similarities and differences between IAD, RAO, and multiple human asthma phenotypes are discussed. Furthermore, differences between phenotype and severity are described, and typical features for equine asthma subcategories are proposed. Based on shared features, we conclude that mild/moderate (IAD) and severe (RAO) equine asthma are biologically appropriate models for both allergic and non‐allergic human asthma, with RAO (severe equine asthma) also being an appropriate model for late‐onset asthma. With the development of new biologic treatments in humans and the application of more targeted therapeutic approaches in the horse, it would appear appropriate to further investigate the allergic (Th‐2) and non‐allergic (non‐Th‐2) phenotypes of equine asthma. Further research is required to more fully determine the potential clinical utility of phenotype classification.

Molecular allergen profiling in horses by microarray reveals Fag e 2 from buckwheat as a frequent sensitizer

Background

Companion animals are also affected by IgE‐mediated allergies, but the eliciting molecules are largely unknown. We aimed at refining an allergen microarray to explore sensitization in horses and compare it to the human IgE reactivity profiles.

Methods

Custom‐designed allergen microarray was produced on the basis of the ImmunoCAP ISAC technology containing 131 allergens. Sera from 51 horses derived from Europe or Japan were tested for specific IgE reactivity. The included horse patients were diagnosed for eczema due to insect bite hypersensitivity, chronic coughing, recurrent airway obstruction and urticaria or were clinically asymptomatic.

Results

Horses showed individual IgE‐binding patterns irrespective of their health status, indicating sensitization. In contrast to European and Japanese human sensitization patterns, frequently recognized allergens were Aln g 1 from alder and Cyn d 1 from Bermuda grass, likely due to specific respiratory exposure around paddocks and near the ground. The most prevalent allergen for 72.5% of the tested horses (37/51) was the 2S‐albumin Fag e 2 from buckwheat, which recently gained importance not only in human but also in horse diet.

Conclusion

In line with the One Health concept, covering human health, animal health and environmental health, allergen microarrays provide novel information on the allergen sensitization patterns of the companion animals around us, which may form a basis for allergen‐specific preventive and therapeutic concepts.

Role of neutrophils in equine asthma

Neutrophilic bronchiolitis is the primary lesion in asthma-affected horses. Neutrophils are key actors in host defense, migrating toward sites of inflammation and infection, where they act as early responder cells toward external insults. However, neutrophils can also mediate tissue damage in various non-infectious inflammatory processes. Within the airways, these cells likely contribute to bronchoconstriction, mucus hypersecretion, and pulmonary remodeling by releasing pro-inflammatory mediators, including the cytokines interleukin (IL)-8 and IL-17, neutrophil elastase, reactive oxygen species (ROS), and neutrophil extracellular traps (NETs). The mechanisms that regulate neutrophil functions in the tissues are complex and incompletely understood. Therefore, the inflammatory activity of neutrophils must be regulated with exquisite precision and timing, a task achieved through a complex network of mechanisms that regulates neutrophil survival. The discovery and development of compounds that can help regulate ROS, NET formation, cytokine release, and clearance would be highly beneficial in the design of therapies for this disease in horses. In this review, neutrophil functions during inflammation will be discussed followed by a discussion of their contribution to airway tissue injury in equine asthma.

Determination of irritant threshold concentrations of multiple tree, grass, weed and mould allergens for intradermal testing of horses residing in the southern USA

BACKGROUND

Appropriate allergen threshold concentrations (TCs) for intradermal testing (IDT) have not been established in horses for many pollen and mould allergens.

OBJECTIVES

To determine the TCs in non-allergic horses and describe the frequency of late phase reactions for 26 allergens, including trees, grasses, weeds and moulds in horses residing in the southern Unites States.

ANIMALS

Twenty four clinically normal horses in the southern United States.

METHODS

Threshold concentrations for different allergens were determined using IDT subjective measurements at 30 minutes. Delayed reactions were evaluated at 4 and 24 h.

RESULTS

Threshold concentrations (all PNU/mL) were established for eight tree allergens (black willow 1,000, box elder 1,000, live oak 1,000, pecan 2,000, white ash 4,000, red oak 4,000, red mulberry 2,000 and green ash 2,000); two grass allergens (Johnson grass 250 PNU/mL and Kentucky blue grass 500 PNU/mL); two weeds (carelessweed 1,000 PNU/mL, great ragweed 500 PNU/mL) and one mould (Curvularia 8,000 PNU/mL). The TC was not determined due to excessive reactivity at the lowest concentration tested (1,000 PNU/mL) for bahia and perennial rye grass. Eleven other allergens did not meet the criteria to establish a TC when evaluated at 30 min due to lack of positive reactions. Multiple allergens caused positive reactions in ≥10% of horses at 4 h. Reactions at 24 h were rare with the exception of one horse.

CONCLUSIONS AND CLINICAL IMPORTANCE

This study identified intradermal TC for multiple pollen and mould allergens in horses. These values may prove useful for optimizing allergen concentrations for IDT of allergic horses.

Allergens in veterinary medicine

Allergic diseases in animals are increasingly gaining importance in veterinary practice and as research models. For intradermal testing and allergen immunotherapy, a good knowledge of relevant allergens for the individual species is of great importance. Currently, the knowledge about relevant veterinary allergens is based on sensitization rates identified by intradermal testing or serum testing for allergen-specific IgE; crude extracts are the basis for most evaluations. Only a few studies provide evidence about the molecular structure of (particularly) dust mite, insect and mould allergens in dogs and horses, respectively. In those species, some major allergens differ from those in humans. This position paper summarizes the current knowledge about relevant allergens in dogs, cats and horses.

Serum concentrations of allergen-specific IgE in horses with equine recurrent airway obstruction and healthy controls assessed by ELISA

BACKGROUND

Equine recurrent airway obstruction (RAO), also known as heaves, is one of the most common respiratory problems in older horses. When RAO-affected horses stay pastured or in a dust-free environment for a prolonged time, clinical signs as well as airway inflammation wane. A number of environmental, immunologic, infectious, and genetic factors play an important role in the pathogenesis of RAO, and the immunologic basis of this disease is still poorly understood.

OBJECTIVES

The aim of this study was to investigate the concentrations of allergen-specific IgE in the serum of horses suffering from RAO and healthy controls.

MATERIAL AND METHODS

The study included a group of 14 adult Polish Konik horses, kept in a standardized environment, and divided into 2 groups: 7 horses which did not have any respiratory problems comprised the control group and 7 horses with a history of RAO constituted the study group. A clinical and laboratory evaluation, endoscopic examination, and bronchoalveolar lavage (BAL) were performed in all horses. Sera of all horses were tested against allergens from 9 molds and 3 mites using the Heska Allercept assay.

RESULTS

In the serologic tests, a statistically significant difference between both groups was found for specific IgE against mites, wherein Tyrophagus putrescentia correlated most clearly with RAO. There was no difference between groups for IgE specific against molds.

CONCLUSION

On the basis of our observations and results, we conclude that RAO is associated with increased serum concentrations of specific serum IgE against mites, in particular T putrescentia.

Update on noninfectious inflammatory diseases of the lower airway

Inflammatory airway disease and recurrent airway obstruction are 2 nonseptic diseases of the equine respiratory system with a shared cause of exposure to particulate matter. They appear to occupy 2 ends of a spectrum of disease, but are differentiated by history, clinical signs, and response to treatment. Diagnosis can be made by sampling of respiratory fluids and lung function testing. Treatment consists of environmental modification and pharmacologic treatment with systemic or inhaled corticosteroids and bronchodilators.

Pollen Allergies in Humans and their Dogs, Cats and Horses: Differences and Similarities

Both humans and their most important domestic animals harbor IgE and a similar IgE receptor repertoire and expression pattern. The same cell types are also involved in the triggering or regulation of allergies, such as mast cells, eosinophils or T-regulatory cells. Translational clinical studies in domestic animals could therefore help cure animal allergies and at the same time gather knowledge relevant to human patients. Dogs, cats and horses may spontaneously and to different extents develop immediate type symptoms to pollen allergens. The skin, nasal and bronchial reactions, as well as chronic skin lesions due to pollen are in principle comparable to human patients. Pollen of various species most often causes allergic rhinitis in human patients, whereas in dogs it elicits predominantly eczematous lesions (canine atopic dermatitis), in horses recurrent airway obstruction or hives as well as pruritic dermatitis, and in cats bronchial asthma and so-called cutaneous reactive patterns (eosinophilic granuloma complex, head and neck pruritus, symmetric self-induced alopecia). In human allergy-specific IgE detection, skin tests or other allergen provocation tests should be completed. In contrast, in animals IgE and dermal tests are regarded as equally important and may even replace each other. However, for practical and economic reasons intradermal tests are most commonly performed in a specialized practice. As in humans, in dogs, cats and horses allergen immunotherapy leads to significant improvement of the clinical symptoms. The collected evidence suggests that canines, felines and equines, with their spontaneous allergies, are attractive model patients for translational studies.

Comparative immunology of allergic responses

Allergic responses occur in humans, rodents, non-human primates, avian species, and all of the domestic animals. These responses are mediated by immunoglobulin E (IgE) antibodies that bind to mast cells and cause release/synthesis of potent mediators. Clinical syndromes include naturally occurring asthma in humans and cats; atopic dermatitis in humans, dogs, horses, and several other species; food allergies; and anaphylactic shock. Experimental induction of asthma in mice, rats, monkeys, sheep, and cats has helped to reveal mechanisms of pathogenesis of asthma in humans. All of these species share the ability to develop a rapid and often fatal response to systemic administration of an allergen--anaphylactic shock. Genetic predisposition to development of allergic disease (atopy) has been demonstrated in humans, dogs, and horses. Application of mouse models of IgE-mediated allergic asthma has provided evidence for a role of air pollutants (ozone, diesel exhaust, environmental tobacco smoke) in enhanced sensitization to allergens.

Development of an in vitro model system for studying the interaction of Equus caballus IgE with its high-affinity receptor FcεRI

The interaction of IgE with its high-affinity Fc receptor (FcεRI) followed by an antigenic challenge is the principal pathway in IgE mediated allergic reactions. As a consequence of the high affinity binding between IgE and FcεRI, along with the continuous production of IgE by B cells, allergies usually persist throughout life, with currently no permanent cure available. Horses, especially race horses, which are commonly inbred, are a species of mammals that are very prone to the development of hypersensitivity responses, which can seriously affect their performance. Physiological responses to allergic sensitization in horses mirror that observed in humans and dogs. In this paper we describe the development of an in situ assay system for the quantitative assessment of the release of mediators of the allergic response pertaining to the equine system. To this end, the gene encoding equine FcεRIα was transfected into and expressed onto the surface of parental Rat Basophil Leukemia (RBL-2H3.1) cells. The gene product of the transfected equine α-chain formed a functional receptor complex with the endogenous rat β- and γ-chains. The resultant assay system facilitated an assessment of the quantity of mediator secreted from equine FcεRIα transfected RBL-2H3.1 cells following sensitization with equine IgE and antigenic challenge using β-hexosaminidase release as a readout. Mediator release peaked at 36.68% ± 4.88% at 100 ng ml(-1) of antigen. This assay was modified from previous assays used to study human and canine allergic responses. We have also shown that this type of assay system has multiple applications for the development of diagnostic tools and the safety assessment of potential therapeutic intervention strategies in allergic disease.

Recurrent airway obstruction: a review

Recurrent airway obstruction is a widely recognised airway disorder, characterised by hypersensitivity-mediated neutrophilic airway inflammation and lower airway obstruction in a subpopulation of horses when exposed to suboptimal environments high in airborne organic dust. Over the past decade, numerous studies have further advanced our understanding of different aspects of the disease. These include clarification of the important inhaled airborne agents responsible for disease induction, improving our understanding of the underlying genetic basis of disease susceptibility and unveiling the fundamental immunological mechanisms leading to establishment of the classic disease phenotype. This review, as well as giving a clinical overview of recurrent airway obstruction, summarises much of the work in these areas that have culminated in a more thorough understanding of this debilitating disease.

Apoptotic effects of tamoxifen on leukocytes from horse peripheral blood and bronchoalveolar lavage fluid

A reduction in inflammatory cell apoptosis is an important concept in the maintenance of inflammation and a potential target for the resolution of inflammation in many inflammatory diseases. Dysregulation of apoptosis has been implicated in a range of diseases, including tumors, neurodegenerative disorders and autoimmunity, and may also be implicated in allergic asthma. In horses, recurrent airway obstruction (RAO) is an asthma-like condition that is characterized increased survival neutrophil bronchial. Tamoxifen is a synthetic, non-steroidal, anti-estrogen agent that is widely used for treating all stages of breast cancer and has been approved for the prevention of breast cancer in high-risk women. The observed efficacy of tamoxifen has been attributed to both growth arrest and the induction of apoptosis. Therefore, the aim of our study was to evaluate the ability of tamoxifen to induce apoptosis in vitro in granulocytic cells from peripheral blood and in mononuclear cells from bronchoalveolar lavage fluid (BALF) in horses. Flow cytometry using commercial AnnexinV-FITC and propidium iodide was used to quantify early and late apoptotic leukocytes, respectively. The results showed a significant increase in early apoptosis in peripheral blood and bronchial granulocytic cells treated with tamoxifen. The rate of early apoptosis of mononuclear cells from blood and BALF when incubated with tamoxifen was significantly lower compared with granulocytic cells. We did not observe a direct effect of tamoxifen on late apoptosis in any of the in vitro assays in the cell types used here. These results indicate that the apoptotic mechanisms under these experimental conditions would affect only blood and BALF granulocytic cells, particularly in early apoptosis. Finally, further in vitro and in vivo studies are needed to better understand apoptotic mechanisms because tamoxifen could be used to treat chronic, inflammatory pathologies associated with granulocytes and allergic diseases, such as asthma or equine RAO.

Heaves, an asthma-like disease of horses

Animal models have been developed to investigate specific components of asthmatic airway inflammation, hyper-responsiveness or remodelling. However, all of these aspects are rarely observed in the same animal. Heaves is a naturally occurring disease of horses that combines these features. It is characterized by stable dust-induced inflammation, bronchospasm and remodelling. The evaluation of horses during well-controlled natural antigen exposure and avoidance in experimental settings allows the study of disease mechanisms in the asymptomatic and symptomatic stages, an approach rarely feasible in humans. Also, the disease can be followed over several years to observe the cumulative effect of repeated episodes of clinical exacerbation or to evaluate long-term treatment, contrasting most murine asthma models. This model has shown complex gene and environment interactions, the involvement of both innate and adaptive responses to inflammation, and the contribution of bronchospasm and tissue remodelling to airway obstruction, all occurring in a natural setting. Similarities with the human asthmatic airways are well described and the model is currently being used to evaluate airway remodelling and its reversibility in ways that are not possible in people for ethical reasons. Tools including antibodies, recombinant proteins or gene arrays, as well as methods for sampling tissues and assessing lung function in the horse are constantly evolving to facilitate the study of this animal model. Research perspectives that can be relevant to asthma include the role of neutrophils in airway inflammation and their response to corticosteroids, systemic response to pulmonary inflammation, and maintaining athletic capacities with early intervention.

Increased apoptosis of CD4 and CD8 T lymphocytes in the airways of horses with recurrent airway obstruction

Recurrent airway obstruction (RAO, also known as equine heaves) is an inflammatory condition similar to human asthma caused by exposure of susceptible horses to poorly ventilated stable environments. The disease is characterized by neutrophilic airway inflammation, mucus hypersecretion and reversible bronchoconstriction. This inflammatory process is mediated by several factors, including antibodies, cytokines, resident cells of the airway and inflammatory cellular components that arrive in the respiratory tract. An increasing body of evidence has lent support to the concept that a dysregulation of T cell apoptosis may play a central role in the development of airway inflammation and the associated asthma. Therefore, the aim of this study was to investigate early and late apoptosis of CD4 and CD8 T cell subpopulations obtained from the airways of acute RAO-positive animals after exposure to hay/straw. The percentages of CD4 and CD8 T cells and their associated frequencies of apoptosis were quantified using flow cytometry. Hay/straw exposure induced clinical airway obstruction, airway neutrophilia and increased airway mucus production in RAO-positive horses. In addition, allergen exposure increased the percentage of CD4 T cells in RAO-positive horses as well as the frequency of early and late apoptosis in both CD4 and CD8 lymphocyte subpopulations. These results suggest that the higher frequency of lymphocyte apoptosis may play a role in disease progression of horses afflicted with RAO and may partially explain the characteristic remission of this pathological condition once the allergen source is removed. However, further studies are needed to clarify the role of T cell apoptosis in RAO-affected horses.

Detection of reaginic antibodies against Faenia rectivirgula from the serum of horses affected with Recurrent Airway Obstruction by an in vitro bioassay

Reaginic antibodies, mainly of the IgE and some IgG subclasses, play an important role in the induction of type I immediate hypersensitivity reactions. These antibodies bind through their Fc fragment to high affinity receptors (FcεRI) present in the membrane of mast cells and basophils. Previously, several studies have investigated the role of reaginic antibodies in the pathogenesis of RAO. However, whereas immunological aspects of RAO have been extensively studied, the precise sequence of events is still not well understood and role of IgE in this disease still remains controversial. Therefore, in this study a bioassay was developed for reaginic antibody determination in serum from RAO-affected horses in order to determine the etiology of disease. The technique involves measuring in vitro calcium mobilization in RBL-2H3 cells following incubation with horse serum from RAO-affected or unaffected horses and one of the RAO antigens (Faenia rectivirgula). Results demonstrated that 15% of samples from the RAO-affected horses reacted positively in this in vitro bioassay, whereas the samples from unaffected horses did not. This bioassay indicates that reaginic antibodies could be involved in the immunological mechanism leading to RAO; and this technique may facilitate future research in other allergic diseases in horses.