Dendritic cells in normal and asthmatic airways: Expression of the alpha subunit of the high affinity immunoglobulin E receptor (Fc epsilon RI-alpha)

Background Immunoglobulin E (IgE) plays an important role in asthma, with total serum IgE levels closely related to both clinical expression of the disease and airway hyperresponsiveness. IgE binds to a high affinity cell-surface receptor (Fc epsilon RI) which is present on mast cells and which has also recently been demonstrated on cutaneous dendritic cells. If pulmonary dendritic cells were also able to express this receptor, this would have important implications with regard to their potential role in asthma. Objectives The aims of the study were to investigate the expression of the alpha subunit of the high affinity IgE receptor (Fc epsilon RI-alpha) in normal and asthmatic airways, and to analyse its cellular provenance with particular emphasis on the dendritic cell. Methods Bronchial biopsy specimens were obtained using fibreoptic bronchoscopy from 10 atopic asthmatics and nine non-atopic non-asthmatic control subjects. Specimens were processed into glycolmethacrylate resin and analysed by immuno-histochemistry using specific monoclonal antibodies against Fc epsilon RI-alpha, and against tryptase and CD1a, markers for mast cells and dendritic cells, respectively. Results The numbers of dendritic cells were significantly higher in the airways of asthmatics compared with those of control subjects (P < 0.02). Analysis of sequential sections revealed that the alpha subunit of Fc epsilon RI was localized to both mast cells and dendritic cells. The proportion of dendritic cells expression Fc epsilon RI-alpha was significantly increased in the asthmatic group (P < 0.003). Conclusions These results support the hypothesis that dendritic cells play an important role in allergic asthma although the functional significance of Fc epsilon RI-alpha expression needs further investigation.