Abstract
Simple SummarySevere equine asthma (EA) syndrome, formerly termed Recurrent Airway Obstruction (RAO) or heaves, is one of the most common respiratory diseases in adult horses and a frequent cause of poor equine performance. The affected animals may show periods of clinical remission followed by periods of exacerbation over months to years. Therefore, the aim of the present study was to investigate the histological features, and the Neurokinin-A (NKA) and Interleukin-8 (IL-8) immunoreactivity on bronchoscopic biopsies in horses, obtained during different phases of the disease (asymptomatic, exacerbation and remission). Histological samples of EA-affected horses appeared significantly different from those of non-EA-affected horses (control group) throughout the experimental phase, from inclusion to exacerbation and remission, and intensity of NKA immunopositivity of horses with severe EA was significantly higher than that of control horses in late exacerbation and in remission phase. No significant difference between horses with severe EA in each phase and control horses was noticed for IL-8 immunoreactivity. Moreover, no influence of bronchial sampling position on histological and immunohistochemistry results was found, and it suggests that bronchial structural and functional modification during severe equine asthma tends to be distributed homogeneously throughout the respiratory tree.Severe equine asthma (EA) syndrome is a chronic obstructive disease characterized by exaggerated contraction, inflammation, and structural alteration of the airways in adult horses, when exposed to airborne molds and particulate material. However, little is known about the relationship between the degree and type of inflammation on one hand, and the severity of the disease and the response to treatment on the other. Furthermore, to date, very few studies evaluate the diagnostic value of histology and immunohistochemical features of endoscopic biopsies on subjects with severe equine asthma. To investigate the expression of two inflammatory markers (NKA and IL-8) before, during, and after the exacerbation of severe EA, a histological and immunohistochemical study was carried out on a series of biopsy samples collected by bronchoscopy from six EA-affected horses subjected to process exacerbation through environmental stimuli and then to pharmacological treatment. The application of a histological biopsy scoring system revealed a significant difference between control cases and the EA-affected horses in all experimental phases (asymptomatic, early exacerbation phase, late exacerbation phase, and remission phase). For immunohistochemistry (IHC), only the intensity of NKA positivity increases significantly between control horses and the EA horses at late exacerbation and remission phases. In EA-affected horses, a difference was detected by comparing histology between asymptomatic and remission phase, meanwhile, NKA and IL-8 showed no differences between the experimental phases. Based on these results we can assert that: (1) The endoscopic biopsies generate reliable and homogeneous samples in the entire bronchial tree; (2) the clinical improvement associated with treatment is characterized by a significant worsening of the histological findings; and (3) the NKA immunopositivity seems to increase significantly rather than decrease, as one would have expected, after pharmacological treatment. Further studies are necessary both to implement the number of samples and to use other markers of inflammation to characterize the potential role of cytokines in the diagnosis and therapeutic approach of severe equine asthma.
Highlights
Disorders of the respiratory system, the lower airways, are the most frequently diagnosed conditions in sport horses evaluated for poor performance [1]
Histological score, and NKA and interleukins 8 (IL-8) immunohistochemistry scores of bronchial biopsies revealed no significant differences between the different biopsy sites nor in EAaffected horses in every experimental time, and in slaughtered horses (Table 1)
With the exception of the first sampling performed, endoscopic biopsies in equine asthma (EA)-affected horses were found to be evaluable in at least one of the four samples each horse in each phase, and samples of all phases in all cases were included in the statistical evaluation, both for histology and for immunohistochemistry
Summary
Disorders of the respiratory system, the lower airways, are the most frequently diagnosed conditions in sport horses evaluated for poor performance [1]. EA is being recommended to describe horses with chronic respiratory signs ranging in severity from mild to severe: they were previously referred as inflammatory airway disease (IAD). RAO is considered as one of the main features of horses with a severe form of equine asthma ( defined as severe equine asthma syndrome) [2,3,4,5,6], which resembles human asthma in many aspects [3,4]. Horses affected by severe equine asthma syndrome show labored breathing at rest following exposure to specific airborne agents, and reversible and reproducible airway obstruction related to the level of environmental exposures [4]. The exposure to hay and dust leading to heaves is rather a consequence of the human influence on the horses’
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