Toll-like receptor expression in smokers with and without COPD.

INTRODUCTION: Chronic obstructive pulmonary disease (COPD) is characterized by non-reversible airflow limitation and systemic engagement. Bacterial colonization in the lungs is common in COPD-patients and may be associated with frequent acute exacerbations. Pattern-recognition receptors (PRRs), like Toll-like receptor 2 (TLR2), TLR4 and CD14 are expressed on most immunologic active cell types and are most likely of importance in COPD patho-physiology.
MATERIAL AND METHODS: Twenty smokers with and 20 without COPD and 20 healthy non-smokers participated in the study. At two visits, induced sputum was collected after spirometry, blood was sampled and bronchoscopy with bronchoalveolar lavage was performed. Expression of TLR2, TLR4 and CD14 on different cell types and soluble receptors were assessed in the different compartments.
RESULTS: Expression of TLR2 was lower on sputum neutrophils and soluble TLR2 (sTLR2) was higher in the supernatant in the COPD group, indicating a down regulation of TLR2 at the transit from blood to sputum. Expression of CD14 on sputum neutrophils and gene expression of CD14 on alveolar macrophages was up-regulated in the two smoking groups compared with non-smokers. No differences between the groups were found regarding TLR4 expression.
CONCLUSIONS: Pattern-recognition receptors (PRRs), that are expected to make a first line of defense against invading micro-organisms, are differently regulated in smokers with COPD compared with smokers without airflow limitation and non-smokers. This is likely of importance in COPD patho-physiology, in particular for exacerbations, which often are caused by micro-organisms.