Up-regulation of IL-18 in allergic rhinitis

Background: This paper reports a study on the concentrations of the pro-inflammatory cytokines IL-18 and IL-1beta in nasal secretions of allergic rhinitis patients in relation to ECP and nasal symptoms. Methods: We measured IL-18 and IL-1beta concentrations using ELISA, and eosinophilic cationic protein (ECP) using the CAP system, in nasal secretions of 15 seasonal allergic rhinitis (SAR) patients at six visits throughout the pollen season. Pollen exposure, nasal and ocular symptoms were monitored daily. Furthermore, we measured IL-18, IL-1beta and ECP concentrations in nasal secretions of 19 controls and 20 symptomatic persistent allergic rhinitis (PAR) patients with house dust mite allergy. Results: In SAR, the increase of IL-18, IL-1beta and ECP paralleled the pollen flight with a time delay. IL-18 and IL-1beta significantly increased during the pollen season compared to baseline, and differently from ECP, remained elevated until 4 weeks after the season. In PAR, the concentrations of IL-18 and ECP, but not IL-1beta, were significantly higher compared to controls, with IL-18 concentrations also being significantly higher than in SAR. Conclusions: This is the first study to demonstrate the up-regulation of IL-18 in nasal secretions in allergic rhinitis. The persistence of elevated IL-18 concentrations until after the season and the high concentrations in PAR compared to SAR suggests its role in persistent allergic inflammation.