Introduction:
To study the concentrations of human β-2 defensin (HβD-2) and cathelicidin (hCAP-18/LL-37) in the mucosal secretions of the upper respiratory tract (URT) in children with asthma and allergic rhinitis, and to identify factors potentially affecting the levels of given antimicrobial peptides (AMP).

Material and methods:
We performed a clinical and laboratory examination of 76 children aged 7 to 17 years with a verified diagnosis of asthma and/or allergic rhinitis lasting at least one year. The control group consisted of 20 gender-matched, clinically healthy peers. Levels of HβD-2 and hCAP-18/LL-37 in the URT secretions were determined beyond the exacerbation of the allergic disease using ELISA.

Results:
We registered a significant decrease in the AMP concentrations in the URT secretions in atopic children: when compared with the controls’ values, levels of HβD-2 concentrations in children with allergic rhinitis were on average 1.2 times lower, in asthmatics ‒ 1.6 times lower, and in children with a combination of asthma and rhinitis – 2 times lower. Similarly, hCAP-18/LL-37 concentrations in children with allergic rhinitis were 2 times lower, in asthmatics – 2.9 times lower, and in patients with both diseases they were 2.4 times lower than in controls. The severity of allergic diseases, lack of symptom control, passive smoking, and the presence of family history burdened with atopic diseases seem to have a potential negative impact on the levels of AMPs in the URT secretions. In contrast, the concentrations of the AMPs were positively associated with breastfeeding duration, full symptom control, and adherence to maintenance therapy. An inverse correlation between levels of AMPs and the frequency (r = –0.65, p < 0.05) and duration (r = –0.48, p < 0.05) of viral URT infections in asthmatic children was also found.

Conclusions:
Asthma and allergic rhinitis are associated with an altered mucosal innate immune response in the upper airways.