Evaluation of cytokine mRNA expression in bronchoalveolar lavage cells from horses with inflammatory airway disease

Inflammatory airway disease (IAD) is a common disorder of performance horses and is associated with poor performance and accumulation of mucus and inflammatory cells in lower airway secretions. Horses with IAD frequently have increased relative counts of neutrophils in bronchoalveolar lavage fluid (BALF); less commonly relative counts of eosinophils and/or mast cells may be increased. The aetiopathogenesis of IAD is unknown and may involve innate and/or acquired immune responses to various factors including respirable dust constituents, micro-organisms, noxious gases and unconditioned air. The molecular pathways and role of the immune system in the pathogenesis of IAD remain poorly defined and it is unknown whether polarised T cell responses occur in the disease, as have been reported to occur in equine recurrent airway obstruction and asthma in humans. Elucidating cytokine responses that develop in horses with IAD may allow a greater understanding of the possible aetiopathological pathway(s) involved and could contribute to development of novel treatments. We compared the mRNA expression of tumour necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), interleukin (IL)-1β, IL-2, IL-4, IL-8, IL-13, IL-17 and IL-23 in cell pellets extracted from BALF of horses with IAD (n=21) and horses free of respiratory tract disease (n=17). Horses with IAD had significantly increased levels of TNF-α, IL-1β and IL-23 mRNA; no significant differences in the other cytokine mRNAs were detected. The results of this study indicate that IAD of horses is associated with increased mRNA expression of pro-inflammatory cytokines in BALF cells, which may reflect stimulation of the innate immune responses to inhaled antigens. There was no evidence of a polarised T-cell cytokine response suggesting hypersensitivity responses may not be involved in the aetiopathogenesis of IAD.