The study measured the natural antimicrobial peptide LL‑37 in lung fluids of people with COPD and healthy folks. It found that early‑stage COPD patients have higher LL‑37 levels, while those with severe disease have lower levels, hinting that the body’s innate immunity changes as the disease progresses.

Innate immunity is currently under scope of interest concerning its role in the development of chronic obstructive pulmonary disease (COPD). Antimicrobial peptides constitute a potent part of this fast response system. Here, we focus on the role of a specific antimicrobial peptide, the only human cathelicidin, the pleiotropic LL-37 peptide, in the development of COPD under clinical conditions. A cross-sectional study was conducted in groups of 43 patients with COPD (previously classified according to GOLD) and 12 healthy individuals. Bronchoalveolar lavage fluid (BALF) sampling, followed by LL-37 measurements by mass spectrometry combined with previous immunoaffinity purification, was performed. Based on urea levels, concentrations of LL-37 in epithelial lining fluid (ELF) were calculated. Additionally, an antimicrobial assay of growth inhibition of two bacterial species, often involved in COPD development mechanisms, by purchased LL-37 was conducted. Altogether, 55 BALF samples were analyzed. LL-37 levels were significantly higher in BALF from patients in early stages of COPD (GOLD I-II) compared to BALFs from healthy individuals. The same was true for ELF. Cathelicidin’s concentration was significantly lower in both BALF and ELF from patients in advanced COPD (GOLD III-IV). The significantly elevated LL-37 levels both in BALF and ELF in patients with COPD at stage GOLD I-II together with reduced levels in advanced (COPD stage III-IV) further supports the innate immunity involvement in COPD pathology and suggests a profound change in non-specific immunity during the disease progression.