Expression of IgE Receptors on Eosinophils

DAVID DOMBROWICZ, ANDRE CAPRON, and MONIQUE CAPRON 

INSERM U547 Institut Pasteur de Lille Lille, France 

IgE receptors bind either to the Fc portion of the immunoglobulin, and thus belong to the Fc receptor superfamily, or to carbohydrate moieties. The high-affinity receptor (FceRI) and the low-affinity receptor (FceRII/CD23) fall in the first group, while, Mac2/galectin-3, a member of the S-type lectin family, falls in the second one. 

Over the last 8 years, several important findings, mainly due to the new experimental approaches involving molecular biology and genetically engineered animals, have modified our concepts of the role of eosinophils in immune re- 

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Surface FceRI expression on peripheral blood eosinophils has been variably observed in vivo since the first report of the high-affinity receptor on blood eosinophils (90) and remains a topic of controversy (91). The initial description involved blood eosinophils from subjects with hypereosinophilic syndromes (90), but subsequent studies have failed to reproduce these observations (85,92). Blood eosinophils express both mRNA and intracellular protein for the a and y subunits of the FceRI receptor complex but lack the P subunit protein. Eosinophils in culture with IL-5 release the a subunit protein into the culture supernatant, but the addition of IgE failed to induce expression of the receptor on the cell surface... 

The controversies concerning eosinophil IgE receptors have taught us several important lessons. Eirst, transcription of mRNA or even the presence of synthesized receptor protein within the cells does not necessarily indicate the expression of the receptor on cell surfaces. Potential discrepancies between receptor expression and actual receptor function need to be resolved. 

The initial report for the expression of low-affinity IgE receptors on human eosinophils goes back to the mid-1980s. In this report (18), the investigators generated... 

Sihra BS, Kon OM, Grant JA, Kay AB. Expression of high-affinity IgE receptors (FceRI) on peripheral blood basophils, monocytes, and eosinophils in atopic and nonatopic subjects relationship to total serum IgE concentrations. J Allergy Chn Immunol 1997 99 699—706. 

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