Heterogeneous expression of CD23 epitopes by eosinophils from patients. Relationships with IgE‐mediated functions

The receptor for IgE (FcϵRII) on human eosinophils presents some common characteristics with CD23, a differentiation marker of B cells. We have used flow cytometry for evaluating the expression of various epitopes of CD23 on purified eosinophils from patients with eosinophilia. A correlation was found between the binding of myeloma IgE protein and the binding of a monoclonal antibody (mAb 135), directed against the IgE‐binding site of B cell CD23. Using two additional anti‐CD23 mAb, directed (8‐30) or not (3‐5) against the IgE‐binding site, a low expression of these CD23 epitopes was observed on eosinophils from different eosinophilic patients. Northern blot analysis of eosinophil RNA with the cDNA probe of CD23 revealed a low‐abundancy transcript in three of the six patients expressing membrane CD23. The inhibition by all anti‐CD23 mAb of IgE‐mediated cytotoxicity and IgE binding to eosinophils clearly indicated the participation of a CD23‐related molecule in IgE‐dependent eosinophil functions.