CTSK and chronic obstructive pulmonary disease: Besides the changes observed in the expression of Mmp12, Gpnmb, Ctsk, Cd68, Spp1, and Ccl22 in both murine lung tissues and lung tissues of COPD patients, other COPD characteristics, such as an enlarged mean linear intercept (Lm) and increased number of neutrophils and macrophages in the bronchoalveolar lavage fluid, were also observed in this murine model of cigarette smoke-induced COPD [32].