Enhanced expression of high-affinity IgE receptor (FcεRI) α chain in human allergen-induced rhinitis with co-localization to mast cells, macrophages, eosinophils, and dendritic cells

Background: IgE-dependent activation of mast cells and basophils through the high-affinity IgE receptor (FcεRI) is involved in the pathogenesis of allergen-induced immediate and late responses. Objective: We investigated the expression and cellular distribution of FcεRI in the nasal mucosa after allergen challenge in patients with summer hay fever. Methods: Fourteen grass pollen-sensitive patients and seven normal control subjects underwent nasal challenge with grass pollen and allergen diluent in random order separated by 2 weeks. Nasal airway caliber was monitored by acoustic rhinometry, and nasal biopsy was performed at 6 hours. Messenger RNA for FcεRI was determined by using reverse-transcription polymerase chain reaction, and FcεRI protein expression was determined by immunohistology with a mouse monoclonal antibody (22E7) and a rabbit polyclonal antibody (997) directed against the α subunit. Co-localization of FcεRI receptors was performed by using double- immunostaining methods. Results: In atopic subjects, there was a significant early decrease in nasal airway caliber, which extended up to 6 hours after allergen challenge. FcεRI mRNA levels were elevated at 6 hours (p = 0.03). Cells expressing FcεRI protein were increased in patients with atopic rhinitis compared with normal control subjects (p = 0.03). Further increases in FcεRI⁺ cells were observed after allergen challenge only in the atopic group (p = 0.02). Double immunohistochemistry revealed that the majority of FcεRI⁺ cells were mast cells (64%), followed by macrophages (20%), eosinophils (4%), and dendritic cells (2%), with 10% FcεRI⁺ cells being unidentified. Conclusions: Our results demonstrate increased FcεRI expression during allergen-induced rhinitis and highlight a potential target for treatment.