The study found that the natural antimicrobial peptide LL‑37 is more abundant in the noses of people with chronic sinus inflammation compared to healthy noses, and it shows up alongside other inflammation signals like IL‑1β and IL‑8.

LL-37 is one of the antimicrobial peptides and the only member of the cathelicidin family identified so far in humans. We attempted to find a correlation between LL-37 peptide and inflammation of the nasal mucosa. Nasal mucosa specimens were obtained from 15 chronic infective rhinitis patients and 6 normal controls. Immunohistochemical staining was used to examine the localization of LL-37 and reverse transcriptase polymerase chain reaction (RT-PCR) was used to determine the levels of LL-37, IL-1beta and IL-8 in tissue. LL-37 peptide was primarily localized in the surface of the epithelia, in the serous and mucous cells of the submucosal glands and in stromal inflammatory cells. The number of LL-37 immunoreactive cells in inflammatory nasal mucosa was significantly increased compared with normal nasal tissue. Using RT-PCR, LL-37 mRNA was detected in 3/6 normal turbinate samples but in all cases with inflammatory nasal tissues. IL-1beta and IL-8 transcripts exhibited a similar pattern to that of LL-37. We suggest that LL-37 is one of the antimicrobial peptides found in human nasal mucosa and that it participates in the innate immune system of the nasal mucosa.