Increased Expression of High Affinity IgE (Fc ɛ RI) Receptor- α Chain mRNA and Protein-bearing Eosinophils in Human Allergen-induced Atopic Asthma

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Abstract
Fc ɛ RI receptors play an important role in allergen-induced mediator release and antigen presentation by mast cells, basophils, and monocyte / macrophages in atopic disorders. The expression of Fc ɛ RI by tissue eosinophils in atopic asthma after allergen challenge has not been established. For this reason we attempted to identify mRNA and protein product + Fc ɛ RI α eosinophils in cytospins made from bronchoalveolar lavage (BAL) from atopic asthmatics (n = 9) and nonatopic normal subjects (n = 4) 24 h after segmental challenge with allergen or diluent. Messenger RNA for Fc ɛ RI α was determined using in situ hybridization and Fc ɛ RI α protein expression by immunocytochemistry using a mouse monoclonal antibody 22E7. Colocalization of Fc ɛ RI α receptors to eosinophils was performed using chromotrope 2R. When compared with a control challenge, segmental challenge with Dermatophagoides pteronyssinus induced significant BAL eosinophilia (p = 0.007). The total number of BAL Fc ɛ RI α mRNA and protein-positive cells also increased in asthmatics, median values 2 (0.7–7.2) and 11.5 (0.6–65.0) × 106 cells (p = 0.02) and 0 (0–0.3 × 106) and 3.1 × 106 (0.45 − 162.5 × 106) cells (p = 0.007), respectively, for mRNA and protein. Net increases in Fc ɛ RI α+ cells correlated with the net increases in BAL eosinophils (r = 0.98, p = 0.0001 for mRNA and r = 0.72, p = 0.02 for protein). Colocalization studies with chromotrope 2R revealed that only 4% of Fc ɛ RI α+ cells were eosinophils after control challenge and, in contrast, 85 to 95% of Fc ɛ RI α+ cells were eosinophils after allergen. There were no differences in the numbers of Fc ɛ RI α+ cells or eosinophils in normal control subjects. Our results demonstrated that local endobronchial allergen provocation in atopic asthmatics results in increased synthesis and expression of Fc ɛ RI α predominantly on BAL eosinophils.