TIMP1 and chronic obstructive pulmonary disease: Given that prior reports suggest that circulating MMP or TIMP expression can be altered in smoking-related respiratory diseases such as chronic obstructive pulmonary disease and emphysema [21, 22], and a substantial proportion of the patients with IPF and controls in our study were former smokers, we investigated whether there were differences in MMP or TIMP expression by current/past versus never smoking status.