COPD is a significant health problem worldwide. It affects more than 10% of patients over the age of 40. According to the World Health Organization, it is the third most common cause of death among adults in the world, and the number of patients is continuously growing. Hence, all measures aimed at a better understanding of COPD pathogenesis, the course of the disease, and limitations in treatment efficacy seem critically important. Since 2008 our team has provided a substantial output in understanding the pathophysiology of airway inflammation in obstructive lung diseases. In our studies, we systematically evaluated selected cytokines concentrations in different respiratory samples to determine their mutual relations and to determine the role of cytokines in airway inflammation more precisely. However, there is still a large gap in our understanding of COPD. It is hypothesized that in COPD pathogenesis, additional factors, like genetics, autoimmune processes or deviated microbiota are involved. Each of the mentioned factors leads to a different type of immune response with a different effect on the airways. We believe that using more advanced laboratory methods (i.e. metabolomics and airway microbiome analysis) alongside the well-established ones (i.e. cellular and cytokine composition) will allow for an adequate characterization of inflammation.

The study will include 50 COPD subjects and 50 smokers without COPD and 20 control subjects (never smokers) who meet the inclusion and exclusion criteria (Table 1) and give an informed written consent to participate in the study. All study participants will undergo the following procedures: peripheral blood sample collection, chest HRCT imaging (without contrast), lung function assessment (spirometry with a bronchial obstruction reversibility test, bodyplethismography, diffusion lung capacity for carbon monoxide (DLCO), sputum induction with sterile hypertonic saline (NaCl).

Inclusion Criteria:

• age ⩾ 40 years,
• written informed history of smoking ⩾ 10 pack-years
• COPD diagnosis (post- bronchodilator FEV1/FVC < LLN)
• stable COPD (min. 3 months)

Exclusion Criteria:

• history of asthma or current lung disease (exception: solitary nodules), respiratory failure
• use of inhaled or oral steroids in the 3 months prior to the study,
• infection of the respiratory tract or exacerbation in the 3 months prior the study
• uncontrolled comorbidities such as: systemic connective tissue diseases, malignancy, uncontrolled cardiovascular diseases, chronic paranasal sinusitis,
• contraindications to sputum induction

Each subject visiting the outpatient clinic at our department presenting exertional dyspnoea and/or chronic cough will be screened for eligibility to participate in the study. A control group (never-smokers) will consist of volunteers matched by age and sex to the study group. Inclusion and exclusion criteria are presented in Table 1. Subjects who gave their written informed consent will be divided into three groups (Table 1). The assignment to a specific study group will be based on past medical history, clinical signs and symptoms, and the results of spirometry with a bronchial obstruction reversibility test.