In a mouse model of COPD induced by chronic cigarette smoke (CS) exposure for 4 and 24 weeks, mice chronically exposed to CS showed higher lung Th17 prevalence, increased retinoic acid orphan receptor (ROR)-γt mRNA, and Th17-related cytokines (IL-17A, IL-6, and IL-23) compared to control mice [27]. This evidence concerns the gene IL17A and chronic obstructive pulmonary disease.