Eosinophils: from low- to high-affinity immunoglobulin E receptors

Several experimental approaches have been used to identify immunoglobulin (IgE) binding molecules expressed by human eosinophils. After the description that Fee RII/CD23 identified on eosinophils could participate in IgE binding and IgE‐mediated cytotoxicity, Mac2/ε binding proteins belonging to the S‐type lectin family were also detected on human eosinophits. Anti‐Mac2 monoclonal antibodies inhibited eosinophil‐dependent cytotoxicity towards parasitic targets. More recently, Fcε RI was demonstrated on human eosinophils from hypereosinophilic patients. The 3 components of Fcε RI, α, β and γ chains, were detected in eosinophils. The α chain of Fcε RI was shown to be involved in IgE binding to eosinophils and in the selective release of eosinophil peroxidase. The participation of Fcε RI‐bearing eosinophils in a protective immune response against a parasitic infection indicates a so far unsuspected function of Fcε RI. The interactions between the different types of IgE binding molecules are discussed.