We did this for historic (pack-years) and current (number of cigarettes smoked per day within the last 6 months) tobacco load by relating it to the extracellular concentration of IL-26 protein in BAL and BW samples of smokers with or without COPD from the COSMIC cohort and in the IS of smokers with COPD during stable conditions and during COPD exacerbations from the BALO cohort. The gene discussed is IL26; the disease is chronic obstructive pulmonary disease.