Healthy non-smoking subjects were never smokers with normal spirometry and did not have a history of lung disease or chronic respiratory symptoms.

Information about respiratory symptoms and comorbidities were collected. Healthy subjects underwent pulmonary function tests (Spirometry). Induced sputum was collected to determine total and differential inflammatory cells counts as well as inflammatory mediators (Interleukin-8 and tumor necrosis factor-alpha).

Never smokers referred to subjects who had never smoked Airflow limitation in COPD was defined as a post-bronchodilator forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) ratio <70% and FEV1 reversibility of <12% and 200 mL from baseline values after inhalation of 400 µg of Salbutamol.

Information about respiratory symptoms and comorbidities were collected. Never smoking subjects with COPD underwent pulmonary function tests (Spirometry). Induced sputum was collected to determine total and differential inflammatory cells counts as well as inflammatory mediators (Interleukin-8 and tumor necrosis factor-alpha).

Smokers were defined as persons who had smoked > 20 packs of cigarettes in a lifetime and who continue smoking every day.

Airflow limitation in COPD was defined as a post-bronchodilator forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC) ratio <70% and FEV1 reversibility of <12% and 200 mL from baseline values after inhalation of 400 µg of Salbutamol.

Information about respiratory symptoms and comorbidities were collected. Smoking subjects with COPD underwent pulmonary function tests (Spirometry). Induced sputum was collected to determine total and differential inflammatory cells counts as well as inflammatory mediators (Interleukin-8 and tumor necrosis factor-alpha).

Induced sputum was collected and analysed in the three arms (Healthy subjects, Never smokers with COPD and smokers with COPD) The volume of the sputum sample, was treated with an equal volume of 0.1% dithiothreitol. The samples were then vortexed and placed in a shaking water bath at 37°C for 15 min to ensure complete homogeneisation. The suspensions were centrifuged at 400× g and the sputum supernatant stored at -80°C until cytokines analysis. The cell pellet was resuspended in 0.5% bovine serum albumin in phosphate buffered saline and cytospin were made by putting 100 µL of the cell suspension in the funnels.

Slides for differential cell counts were stained with May-Grünwald Giemsa.

Weight was measured in kilograms for all the participants.

Height was measured in meters for all the participants.

FVC was measured using a portable spirometer (Easy One ndd. Medizintechnik; Zurich, Switzerland) according to the American Thoracic Society criteria.

FEV1 was measured using a portable spirometer (Easy One ndd. Medizintechnik; Zurich, Switzerland) according to the American Thoracic Society criteria.

Sputum induction was conducted by inhalation of nebulised sterile hypertonic saline solution followed by coughing and expectoration of airway secretions. For nebulisation, an ultrasound nebulizer was used for 5-20 min to provide an adequate amount of sample. The subject is asked to cough and expectorate at 5 min intervals.

Weight and height values were combined to report BMI in kg/m2

The calculation of FEV1/FVC allows the identification of obstructive ventilatory defect. A FEV1/FVC < 70 % where FEV1 is reduced more than FVC signifies an obstructive defect.