Increased numbers of dendritic cells in the bronchial mucosa of atopic asthmatic patients: downregulation by inhaled corticosteroids.

BACKGROUND: Dendritic cells (DC) are the most potent antigen-presenting cells (APC) and stimulators of T cells. Dendritic cells are also likely to be essential for the initiation of allergic immune responses in the lung. However, there are not many data on the presence of dendritic cells in the airways of patients with atopic asthma and on the effects of corticosteroid-treatment on such dendritic cells. OBJECTIVE: We investigated the distribution of dendritic cells in the bronchial epithelium and mucosa of 16 non-smoking atopic asthmatic patients and eight healthy control subjects using detailed immunohistochemistry (CD1a, HLA-DR, L25 as markers for dendritic cells). METHODS: Eleven asthmatics were treated for 2.5 years with bronchodilators only and five with bronchodilators and inhaled beclomethasone dipropionate (BDP), 800 micrograms daily. The patients were randomly sampled from a double-blind multicentre study. RESULTS: There were higher numbers of CD1a+ DC (P = 0.003), L25+ DC (P = 0.002) and HLA-DR expression (P = 0.042) in the bronchial mucosa of asthmatic patients compared with healthy controls. After 2.5 years of treatment, we found a significant increase in flow expiratory volume in 1 second (FEV1) (P = 0.009) and a significant decrease in hyperresponsiveness (PC20 histamine) (P = 0.013) in the corticosteroid group (n = 5) compared with the bronchodilator group (n = 11). This clinical improvement in the corticosteroid-treated group was accompanied by significantly lower numbers of CD1a+ DC (P = 0.008), and HLA-DR expression (P = 0.028) in the bronchial mucosa than in the bronchodilator-treated group. CONCLUSION: Our data suggest that dendritic cells are involved in asthmatic inflammation and that corticosteroids may downregulate the number of dendritic.