The Dynamics of Circulating Immune Complexes in Horses with Severe Equine Asthma

The Most Common Environmental Risk Factors for Equine Asthma-A Narrative Review

Equine asthma is a popular subject of research. Many factors influencing the methods used to improve the welfare of asthmatic horses remain unclear. This study reviews scientific articles published after 2000 to collect the most important information on the terminology, symptoms, and potential environmental factors influencing the development and course of equine asthma. Our work highlights the impact of environmental factors on the severity of equine asthma and why these factors should be controlled to improve treatment outcomes. The present article provides horse owners and veterinarians with valuable information on how to improve the well-being of horses that are at risk of developing asthma symptoms.

Neutrophil gelatinase-associated lipocalin as a potential biomarker for equine asthma

BACKGROUND

Studies in people have found neutrophil gelatinase-associated lipocalin (NGAL) concentrations are increased in asthma and can be used to distinguish between asthma subtypes. NGAL has not yet been investigated in equine asthma (EA).

OBJECTIVES

To investigate the ability of NGAL concentrations in bronchoalveolar lavage (BAL) fluid and serum to distinguish between control horses, horses with mild-moderate EA (MEA) and horses with severe EA (SEA).

STUDY DESIGN

Retrospective cross-sectional study.

METHODS

Details of endoscopic examination including tracheal mucus score (TMS, scale 0-5) and BAL cytology performed on 227 horses were extracted from records and NGAL concentrations were measured on stored serum and BAL fluid samples. The horses were divided into groups (control group n = 73, MEA n = 98, SEA n = 56) based on clinical signs and BAL cytology results. Differences between groups were evaluated with the Mann-Whitney test and correlation between BAL NGAL, serum NGAL, and BAL cytology were evaluated using Spearman's correlation.

RESULTS

BAL NGAL concentrations were higher in EA than in control horses (median: 25.6 and 13.3 μg/L, respectively, p < 0.001). Concentrations of NGAL in BAL differed between groups, with higher concentrations in MEA than in control horses (median: 18.5 and 13.3 μg/L, respectively, p < 0.001), and higher concentrations in SEA than in MEA horses (median: 54.1 and 18.5 μg/L, respectively, p < 0.001). BAL NGAL concentration differed between horses with TMS ≤2 an >2 (median 15.6 and 21.1 μg/L, respectively, p = 0.004). No differences were found in serum NGAL concentration between any of the groups.

MAIN LIMITATION

Only 66 of the 227 (29%) horses had haematology and serum NGAL measured.

CONCLUSION

BAL NGAL concentration differed between control and EA and reflected severity of disease. These results justify further research into the potential of NGAL as a biomarker of EA.

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.

The Immune Mechanisms of Severe Equine Asthma-Current Understanding and What Is Missing

Severe equine asthma is a chronic respiratory disease of adult horses, occurring when genetically susceptible individuals are exposed to environmental aeroallergens. This results in airway inflammation, mucus accumulation and bronchial constriction. Although several studies aimed at evaluating the genetic and immune pathways associated with the disease, the results reported are inconsistent. Furthermore, the complexity and heterogeneity of this disease bears great similarity to what is described for human asthma. Currently available studies identified two chromosome regions (ECA13 and ECA15) and several genes associated with the disease. The inflammatory response appears to be mediated by T helper cells (Th1, Th2, Th17) and neutrophilic inflammation significantly contributes to the persistence of airway inflammatory status. This review evaluates the reported findings pertaining to the genetical and immunological background of severe equine asthma and reflects on their implications in the pathophysiology of the disease whilst discussing further areas of research interest aiming at advancing treatment and prognosis of affected individuals.

Some Genetic and Environmental Effects on Equine Asthma in Polish Konik Horses

Simple Summary

Equine Asthma (EA) is a blanket term covering inflammatory diseases of the lower airways in horses. It includes mild-to-moderate equine asthma, which affects horses of any age, and severe equine asthma, which is typically seen in horses older than 7 years of. Relationships of the disease’s occurrence with sex or breed have been proven. However, some authors consider genetic background a predisposing factor, due to the fact that in some bloodlines a clinical form of asthma is more frequently observed. This indicates serious breeding and economic consequences. This study aimed to identify the factors affecting predisposition to severe equine asthma in the population of Polish Konik horses and some environmental and inbreeding effects on the disease. Generally, in the observed population, EA is negligibly affected by the factors analysed. Individual inbreeding effects on asthma were not confirmed by various statistical approaches, but significant maternal inbreeding effects were observed. These results are very important from the perspective of the currently implemented genetic resource conservation programme.

Abstract

Current knowledge of the genetic and environmental backgrounds of equine asthma seems to be insufficient, especially for primitive horse breeds. The main objectives of this study were to estimate the effects of sex, birth period, stud, parentage line and inbreeding on asthma morbidity in Polish Konik horses. Records of 274 horses (housed in two studs) were analysed. These animals were allocated to maternal and paternal lines. Individual inbreeding coefficients were extracted from the additive relationship matrix. Horses underwent diagnosis based on observation of the basic symptoms (high frequency of coughing and excessive nasal discharge). Subsequently, some horses (28 individuals) were clinically examined to confirm the earlier observations. Generally, no significant effects of parentage line on heaves morbidity were identified by the use of logistic regression, although the Pearson’s chi-squared test had shown that individuals of some maternal and paternal lines had a predisposition to severe equine asthma. It was concluded that the individual inbreeding level is not associated with the incidence of EA, but a significant effect of the maternal inbreeding coefficient may be observed. It was also found that there is some variability in the incidence of this disease between studs.