The objective of this study was to investigate structural changes of the lower respiratory tract using clinical and functional characteristics and biomarkers of inflammation in patients with acute exacerbation of chronic obstructive pulmonary disease (COPD). Methods . This observational cohort study involved 101 symptomatic patients with acute exacerbation of COPD who met 2 or 3 Anthonisen's criteria. According to high resolution computed tomography (HRCT) findings patients were divided into two groups: 57 patients with COPD and bronchiolitis and 44 people with COPD and no signs of bronchiole lesion. Clinical manifestation, lung function, respiratory failure, structural changes in the lung parenchyma and biomarkers of adaptive immune response were analyzed. Results . Inflammatory changes in small bronchi and bronchioles in patients with acute COPD exacer bation was associated with more severe exacerbation, occurrence of the respiratory failure, need in respiratory support, lung parenchyma consolidation, increased sputum purulence, lower total serum immunoglobulin E as a marker of humoral immune response. Conclusion . Inflammation in bronchioles in patients with acute exacerbation of COPD is associated with more severe respiratory failure and need in respiratory support. Consolidation of the lung parenchyma is noted more often in patients with COPD and co existing bronchiolitis. Exacerbation of COPD accompanied by bronchiolitis is characterized by less prominent humoral immune hypersensitivity response that could be diagnosed by the total serum immunoglobulin E level.