Eosinophils: receptors and mediators in hypersensitivity.

The presence of receptors for IgE on eosinophils has drawn attention to their direct participation in IgE-dependent hypersensitivity reactions. Surface IgE antibodies were detected on eosinophils from parasite-infected or allergic patients. The addition of the specific antigen or anti-IgE antibodies to such purified eosinophils induced the release of eosinophil peroxidase (EPO) and major basic protein (MBP), but not of eosinophil cationic protein (ECP). In contrast, ECP was detected after the addition of anti-IgG antibodies. Moreover, PAF-acether was only produced after IgE-dependent activation of hypodense eosinophils but not after IgG triggering. These results suggest a selectivity in the mediators (pre-formed and newly formed) released in response to IgE- or IgG-dependent activation of human hypodense eosinophils. Associated with preliminary findings obtained by using electron microscopy and immunogold staining, they bring new information concerning the mechanisms of release of eosinophil mediators. Finally, they underline the essential role of eosinophils in hypersensitivity reactions.