The study shows that the antimicrobial peptide LL‑37 normally spikes in the nose when Staph aureus is present, but this boost is missing in people with chronic sinus inflammation and nasal polyps, suggesting a weakened local defense. The other peptide hBD‑3 didn’t change, and nasal cells can still make LL‑37 when directly exposed to the bacteria.

Nasal carriage of Staphylococcus aureus in patients with chronic rhinosinusitis with nasal polyps (NP) is hypothesized to have pathophysiological impact on the disease. Antimicrobial peptides (AMP), especially human beta-defensin-3 (hBD-3) and LL-37, are an important part of the multifactorial defence against microorganisms in barrier organs like the nasal mucosa. The interaction of S. aureus colonization and AMP in nasal secretions and mucosa of NP were investigated in this study. AMP were quantified in nasal secretions of 13 normal controls (NC) and 12 NP patients, each with and without S. aureus colonization, by ELISA. Immunohistochemistry was used to investigate the cellular sources of AMP in the nasal mucosa. To explore the AMP response of primary nasal epithelial cell cultures (NEC) towards S. aureus stimulation, a functional assay was established. AMP could be demonstrated in nasal secretions of all groups without differences in hBD-3 concentrations comparing S. aureus carriers vs. non-carriers. In NC, higher LL-37 concentrations were observed in S. aureus colonized as compared to non-colonized patients. This effect was not detectable in NP patients. Epithelial cells, submucosal glands and cells of the connective tissue could be identified as sources of AMP by immunohistochemistry. An AMP response of NEC towards S. aureus stimulation was detected in all groups. In NP patients, LL-37 response towards S. aureus colonization is disturbed while the ability of NEC to respond on S. aureus challenge is preserved. This deregulation of the nasal barrier could be involved in the multifactorial pathophysiology of NP.