MDK and chronic obstructive pulmonary disease: Correlation analyses between each of the 15 proteins and major clinical determinants of COPD demonstrated that our signature reflected mainly the prevalence of emphysema, rather than the incidence of exacerbations and of unscheduled medical visits, although 5 to 7 proteins out of the 15 and related to cell fate, remodeling and repair (14-3-3 protein β/α, eIF-4H and tropomyosin 4) and to immunity and defense (BTK, midkine and lactadherin) were associated with these two latter clinical parameters.