Abstract
Recurrent airway obstruction (RAO) is a pulmonary inflammatory condition that afflicts certain mature horses exposed to organic dust particulates in hay. Its clinical and pathological features, manifested by reversible bronchoconstriction, excessive mucus production and airway neutrophilia, resemble the pulmonary alterations that occur in agricultural workers with occupational asthma. The immunological basis of RAO remains uncertain although its chronicity, its localization to a mucosal surface and its domination by a neutrophilic, non-septic inflammatory response, suggest involvement of Interleukin-17 (IL-17). We examined global gene expression profiles in mediastinal (pulmonary-draining) lymph nodes isolated from RAO-affected and control horses. Differential expression of > 200 genes, coupled with network analysis, supports an IL-17 response centered about NF-κB. Immunohistochemical analysis of mediastinal lymph node sections demonstrated increased IL-17 staining intensity in diseased horses. This result, along with the finding of increased IL-17 concentrations in lymph node homogenates from RAO-affected horses (P = 0.1) and a down-regulation of IL-4 gene and protein expression, provides additional evidence of the involvement of IL-17 in the chronic stages of RAO. Additional investigations are needed to ascertain the cellular source of IL-17 in this equine model of occupational asthma. Understanding the immunopathogenesis of this disorder likely will enhance the development of therapeutic interventions beneficial to human and animal pulmonary health.
Highlights
Certain mature horses, when exposed to hay particulates and stable dust, spontaneously develop a pulmonary disorder called recurrent airway obstruction (RAO)
We are unaware of any other studies in which the global gene expression profiles of mediastinal lymph nodes from RAO-affected horses have been examined
We evaluated transcriptomes of mediastinal lymph node cells as a reflection of the immunological events occurring within the lung
Summary
Certain mature horses, when exposed to hay particulates and stable dust, spontaneously develop a pulmonary disorder called recurrent airway obstruction (RAO). This disease, characterized by reversible airflow obstruction, bronchial hyper-responsiveness, excessive mucus production and airway neutrophilia [1] shares many of the clinical and pathological features of occupational asthma in humans [2]. This similarity, coupled with the finding that horses have more similar life spans and lung anatomy to humans than do mice, makes the equine species an attractive animal model for investigations of human asthma [3]. Hypotheses regarding the genes responsible for certain disease phenotypes can more be generated and tested [12]
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