Bronchoalveolar lavage fluid neutrophilia is associated with the severity of pulmonary lesions during equine asthma exacerbations.

Abstract

The severe form of equine asthma is associated with pathological changes of the peripheral airways and pulmonary parenchyma that are only partly described. Also, the relationship between these structural alterations and the percentage of neutrophils found within the airway lumen, assessed by bronchoalveolar lavage fluid (BALF) cytology, remains ill-defined. To examine the histological lesions associated with equine asthma during disease exacerbation and remission, and their relationship with lung function and BALF neutrophilia. Observational retrospective study. Peripheral lung tissues, BALF cytology and lung function data from 61 horses (22 controls, 24 asthma exacerbations and 15 asthma remission) were obtained from an equine pulmonary tissue bank. Two pathologists semi-quantitatively assessed histological features, including airway wall inflammation, interstitial fibrosis, mucus cell hyperplasia, mucostasis, peribronchiolar metaplasia, presence of granuloma and the overall severity of these lesions. Mucostasis, mucus cell hyperplasia, peribronchiolar metaplasia and interstitial fibrosis were associated with disease exacerbation (P≤0.05), and these changes were all attenuated during remission. Airway wall inflammation was greater in horses with asthma in exacerbation compared with horses with asthma in remission and control horses (P≤0.05). Acute (neutrophilic) airway wall inflammation was more frequently detected in asthmatic cases compared with control horses (P<0.0001) and was associated with BALF neutrophilia >5% in control horses (P = 0.002). The degree of bronchiolar inflammation was higher in asthmatic horses in remission stabled and treated pharmacologically compared with those kept on pasture (P = 0.04). Samples obtained from a convenient cohort of horses were studied. Severely asthmatic horses present parenchymal and peribronchial/peribronchiolar lesions possibly contributing to the obstructive nature of the disease.