Background Local airway inflammation and airway remodelling are considered important in the clinical expression of allergic asthma.

Objective The aim of this study was to compare airway inflammation and remodelling in nasal and bronchial mucosa of subjects with allergic rhinitis with or without asthma.

Methods Four experimental groups were formed: allergic asthma and rhinitis (n = 19); allergic rhinitis, no asthma (n = 18); atopic subjects, no asthma, no rhinitis (n = 8) and non‐allergic healthy control subjects (n = 16). Blood samples, nasal and bronchial biopsy specimens were collected during stable disease. Immunohistochemistry was performed for eosinophils (MBP), mast cells (CD117) and vascular endothelium (CD31). Epithelial loss, reticular basement membrane (RBM) thickness and subepithelial vascularity was assessed with a computer‐assisted image analysis system.

Results In nasal and bronchial mucosa, numbers of eosinophils were significantly higher in rhinitis patients with and without asthma than in asymptomatic atopics (P < 0.05) and controls (P ≤ 0.01). In bronchial mucosa, the RBM was significantly thickened in rhinitis patients with and without asthma compared to asymptomatic atopics (P < 0.05) and controls (P < 0.01), while in nasal mucosa no differences were seen. Patients with asthma and rhinitis had increased numbers of blood eosinophils (P = 0.05) and skin test reactivity (P = 0.01) compared to patients with rhinitis only. No significant differences could be found between the investigated groups with respect to serum IL‐5 and eotaxin levels, the number of mucosal mast cells and the degree of epithelial loss and subepithelial vascularity. Epithelial desquamation was significantly increased in the bronchial mucosa compared to nasal mucosa, not only in asthmatics (P < 0.001), but also in atopics without asthma and rhinitis (P = 0.02).

Conclusions This study shows that allergic inflammation, increased basement membrane thickness and epithelial desquamation are present in the lower airways of atopic subjects, even before the onset of clinical symptoms. Despite the presence of inflammatory cells, no structural changes could be assessed in nasal mucosa of allergic patients.