Increased expression of high affinity IGE receptor (FCεRI) α chain mRNA and protein bearing eosinophils in human allergen-induced atopic asthma

FcεRI 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 FcεRI by tissue eosinophils in atopic asthma after allergen challenge has not been established. For this reason we attempted to identify mRNA and protein product+ FcεRIα eosinophils in cytospins made from bronchoalveolar lavage (BAL) from atopic asthmatics (n=9) and non-atopic normals (n=4) 24 hours after segmental challenge with allergen or diluent. Messenger RNA for FcεRIα was determined using in situ hybridisation and FcεRIα protein expression by immunocytochemistry using a mouse monoclonal antibody 22E7. Co-localisation of FcεRIα 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 FcεRIα 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 FcεRIα+ 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). Co-localisation studies with chromotrope 2R revealed that only 4% of FcεRIα+ cells were eosinophils following control challenge and, in contrast, 85 - 95% of FcεRIα+ cells were eosinophils following allergen. There were no difference in the numbers of FcεRIα+ 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 FcεRIα predominantly on BAL eosinophils.