In people with cystic fibrosis, higher levels of the antimicrobial peptide LL‑37 in lung fluid are linked to more inflammation and worse lung function, while lower levels of other peptides (beta‑defensins) show up as the disease gets worse.

The antimicrobial peptides human beta-defensin 1 and 2 (hBD-1 and 2) and the cathelicidin LL-37/hCAP-18 are key factors in innate immune responses of the respiratory tract. The aim of this study was to determine the concentrations of these peptides in airway surface fluid of CF patients with mild lung disease. We measured the concentrations of hBD-1, hBD-2, and LL-37 in bronchoalveolar lavage fluid of 20 patients (5-34 years) participating in the prospective BEAT-study (bronchoalveolar lavage for the evaluation of anti-inflammatory treatment) using an immuno-dot blot-assay. All three peptides could be detected in lavage fluid of the study population. Increased levels of inflammatory markers in bronchoalveolar lavage fluid were associated with elevated concentrations of LL-37/hCAP-18 (total cell count, P = 0.006; relative neutrophil count, P = 0.002). Deterioration of lung function, measured by MEF25 (maximal flow rate at 25% of residual forced vital capacity), correlated with decreased hBD-2 (P = 0.026), but increased LL-37/hCAP-18 concentrations (P = 0.016). The data suggest that concentrations of antimicrobial peptides are correlated with severity of CF lung disease: Levels of LL-37/hCAP-18 are associated with bronchial inflammation and, therefore disease severity, whereas decreased levels of beta-defensins in advanced lung disease likely contribute to a secondary defect of the local host defense.