Background: Allergic rhinitis is induced by an IgE-mediated inflammation after allergen exposure of the membranes lining the nose which, in predisposed individuals, may constitute a risk factor for the occurrence of asthma.

Objective: To detect early changes in nasal inflammation after allergen exposure, 11 children [9.0 (7, 11) yrs], sensitized to house dust mites (HDM), with rhinoconjunctivitis and asthma and an age- and gender-matched control group (Ctr) were studied.

Methods: The following parameters were evaluated: i) pulmonary function; ii) bronchial reactivity to methacholine (MCh), expressed as Pd20MCh; iii) nasal brushing (NB) ‘at baseline’ and, on a separate day, 30 min after nasal allergen challenge (NAC). On NBs, the following markers of inflammation were evaluated: a) neutrophil and eosinophil proportion, b) ‘intact to degranulated eosinophil’ ratio, and c) expression of intercellular adhesion molecule (ICAM)-1 and HLA-DR by nasal epithelial cells.

Results: ‘At baseline’, allergic children showed elevated nasal eosinophilia and increased ICAM-1 and HLA-DR expression (p<0.05), as compared to Ctr. In allergic children, nasal eosinophilia correlated with Pd20MCh (p=0.002). The significant decrease in nasal eosinophilia observed after NAC (p=0.002) was associated with a significant decrease in the ‘intact to degranulated eosinophil’ ratio (p=0.001). Interestingly, correlations were still present between Pd20MCh and ‘post NAC’ eosinophilia (p=0.004) or the NAC-induced decrease in eosinophilia (p=0.010).

Conclusions: In children sensitized to HDM, experimental allergen exposure is followed by an early depletion of nasal eosinophils. The correlation between allergen-induced changes in nasal eosinophilia and bronchial reactivity to MCh further supports the concept of a tight link between upper and lower respiratory tract involvement in respiratory allergy.

Key words: Nasal eosinophils, bronchial hyperreactivity, allergen challenge, childhood, rhinoconjunctivitis, allergic asthma, house dust mites.