That we observed increased expression of KL may indicate that smoke exposed ferrets are responding to delayed mucociliary clearance, as recently shown [34], The discordant expression of KL in ferrets compared to humans could be due to the possibility that higher expression of KL acts as a compensatory response to oxidative stress due to smoking, a finding reported by other studies [41], including in human smokers without COPD [42]. The gene discussed is KL; the disease is chronic obstructive pulmonary disease.