Persistent mucus accumulation: a consequence of delayed bronchial mucous cell apoptosis in RAO-affected horses?

This study examined the contribution of delayed apoptosis of bronchial mucous cells to mucus accumulation in equine recurrent airway obstruction (RAO). In pilot studies, Bcl-2, an apoptosis inhibitor, was detected in airway mucous cells of RAO-affected horses in remission and during acute disease, when most mucus was secreted. To study whether delayed apoptosis results in an increase in the number of mucous cells during disease recovery, six RAO-affected and six control horses were fed hay for 5 days to induce inflammation and then pellets for 7 days to partially resolve RAO before euthanasia. RAO- affected horses had more airway obstruction and luminal mucus than control horses under both management systems. At the time of euthanasia, RAO-affected horses had more inflammation and Bcl-2-positive bronchial mucous cells than control animals. In horses with >10 and 50% and