Epsilon Open Archive

Abstract

Non-infectious airway inflammation in horses is a common problem worldwide when horses are housed indoors. In this thesis the inflammatory pathways in equine airways, with special regards to the role of bronchial epithelium, were investigated in horses with highly reactive airways (recurrent airway obstruction, RAO) and in clinically normal race horses under conventional management. In the former group the cytokine mRNA and protein expression in bronchial epithelium and were examined, whereas only the cytokine mRNA expression of bronchoalveolar lavage (BAL) cells and BAL cytology were included in the work on the stabled race horses. These latter horses unexpectedly developed transient pulmonary eosinophilia which allowed deeper investigation of eosinophil kinetics in horses. These studies showed that endobronchial biopsy was a safe and readily performed procedure to obtain airway tissue samples from the live horse. Moreover, biopsies were of sufficient size and quality for evaluation of cytokine mRNA expression, airway morphology and for immunohistochemical analysis. The work on RAO horses strengthened earlier findings of increased mRNA expression of the neutrophil chemotaxic cytokine IL-8 in RAO horses in both BAL cell and bronchial tissues. Thus, use of bronchial tissues can provide a valued complementary tool to study serial events of inflammation in equine airway at closely timed intervals not possible with the sampling technique of BAL. In the group of race horses, prolonged winter stabling was associated with subtlepulmonary alterations reflective of increased inflammatory response in equine airways.Specifically there was increased expression of IL-6 mRNA in BAL cells along with a trend for increased neutrophils in the BAL. No underlying cause of the transient pulmonary eosinophilia could be identified. Surprisingly, expression of mRNA of eosinophil associated IL-4 and IL-5 was not detectably altered in these horses. It appears that eosinophil influx to the equine lung can be subclinical apart from temporary exercise intolerance, and abate without specific treatment other than deworming. These combined studies introduce and demonstrate future potential in examination of bronchial tissues as a complement to BAL cells studies in molecular biological analysis to increase the understanding of mechanisms of noninfectious airway inflammation in the horse.