Fungus is thought to play an important role in some subgroups of chronic rhinosinusitis (CRS) patients with eosinophilic mucus (EMCRS). The cathelicidin LL-37 is an important innate defense peptide with antimicrobial activity but its responses in CRS and EMCRS patients have not been established. We investigated the innate immune responses of LL-37 in nasal tissue from CRS and EMCRS patients to fungal allergen challenge.

The levels of LL-37 produced by nasal tissue and secreted in response to fungal allergen challenge were determined by a nasal tissue explant in vitro model. LL-37 mRNA and protein levels were quantified by real-time reverse-transcriptase–polymerase chain reaction and immunoassay methods.

LL-37 mRNA expression in CRS, but not EMCRS patients, is significantly upregulated by Aspergillus (mean fourfold increase) and Alternaria (mean sixfold increase) extracts in a dose-response manner (p < 0.001). LL-37 peptide levels in the nasal tissue from CRS patients are increased in response to Alternaria (p < 0.05). In contrast, with EMCRS patients, the expression of LL-37 peptide in nasal tissue is increased with Aspergillus (p < 0.001) but is reduced with Alternaria. We also observed a trend where levels of secreted LL-37 were decreased with higher doses of Alternaria and Aspergillus extracts.

LL-37 is significantly up-regulated at the mRNA and protein level in CRS patients in response to fungal allergens. However, EMCRS patients do not show increased LL-37 at either the mRNA or the protein level in response to Alternaria.