INTERLEUKIN-5 SYNTHESIS BY EOSINOPHILS - ASSOCIATION WITH GRANULES AND IMMUNOGLOBULIN-DEPENDENT SECRETION

Interleukin 5 (IL-5) is the main factor that promotes the terminal dif ferentiation of eosinophil progenitors (as indicated by colony formati on assays), and enhances the effector capacity of mature eosinophils. IL-5 is produced by T lymphocytes, CD4(-)/CD8(-) and mast cells and re cently, messenger (m)RNA of this cytokine has been identified in eosin ophils from patients with coeliac disease, asthma, or eosinophilic hea rt diseases. In this study, IL-5 mRNA and immunoreactive IL-5 protein were detected in tissue and blood eosinophils from patients with eosin ophilic cystitis or hypereosinophilic syndromes but not in Crohn's dis ease. By electron microscopy associated to immunogold staining, immuno reactive IL-5 was identified in eosinophilic granules. After stimulati on with IgA-, IgE-, or IgG-immune complexes, blood eosinophils were sh own, by immunocytochemistry and by enzyme-linked immunosorbent assay, to secrete IL-5. These observations demonstrate that eosinophils, unde r physiological stimulation, can release significant amounts of IL-5, which may contribute to local eosinophil recruitment and activation.