Mucus and inflammation in equine heaves

Abstract

Accumulation of mucus within the airways is a consistent feature of the chronic inflammatory airway disease known as heaves or recurrent airway obstruction (RAO). Accumulations are greatest when heaves-affected horses are stabled and have neutrophilic inflammation in their airways but accumulations persist when horses are at pasture and inflammation is less severe. Mucus consists of an apoprotein core and oligosaccharide side chains that include α- 1,2 fucose. Persistence of mucus accumulation has been demonstrated by measurement of leveis of α-1,2 fucose within the bronchoalveolar lavage fluid. When heaves-affected animals are stabled, mucus accumulation is due in part to decreased clearability (increased viscoelasticity) and to increased production as evidenced by increased expression of the gene eqMUC5AC. When horses return to pasture, clearability is not different from that of control animals and accumulation must therefore be due to persistently increased secretion that is facilitated by delayed apoptosis of mucous cells. The stimulus for increased mucus production and secretion in stabled horses is most likely neutrophil products including elastase and reactive oxygen species. Persistent secretion when horses are at pasture is probably due to persistent low-level inflammation within the epithelium as evidenced by continued expression of nuclear factor-kappaB.