The effects of natural pollen exposure on inflammatory cytokines and their relationship with nonspecific bronchial hyperresponsiveness in seasonal allergic rhinitis

The exact mechanism of bronchial hyperresponsiveness (BHR) is not clear in allergic rhinitis (AR); an increase of BHR in pollen season suggests that natural pollen exposure causes airway inflammation in seasonal AR (SAR). This study was designed to investigate the effects of natural pollen exposure on inflammatory cytokines and their relationship with BHR. Sixty-six SAR patients with grass pollen sensitivity and 26 nonallergic rhinitis (NAR) patients were included. Peripheral blood samples for cytokine levels were taken and a nonspecific bronchial provocation test was performed during pollen season between May and August. The same measurements were repeated off-season between November and February. These measurements were done in NAR patients once. During the pollen season, SAR patients had significantly more increased levels of IL-13 than NAR patients (11.45 ± 12.54 versus 5.19 ± 4.02; p = 0.005). Blood eosinophil numbers were higher in those patients with BHR during pollen season than those without BHR (399.0 ± 255.8 versus 278.9 ± 193.2 mm⁻³; p = 0.046). Blood eosinophil numbers during off-season were not different in those with and without BHR (respectively, 261.4 ± 202.3 mm⁻³ versus 205.9 ± 116.9 mm⁻³; p = 0.53). IL-10 levels were higher in the patients without BHR (n = 28) than those patients with BHR (n = 22) during off-season (8.12 ± 13.1 versus 3.28 ± 0.37; p = 0.04). Having higher levels of IL-10 than threshold value was more frequent in SAR patients without BHR than those patients with BHR during off-season (7/28 versus 1/22; ² = 4.34; p = 0.04). IL-10 has a role in the continuation of BHR during off-season in SAR patients.