IDENTIFICATION OF MESSENGER-RNA FOR IL-4 IN HUMAN EOSINOPHILS WITH GRANULE LOCALIZATION AND RELEASE OF THE TRANSLATED PRODUCT

Human eosinophils are cytokine-producing cells that are prominent in I gE-dependent allergic tissue reactions. IL-4 promotes the development of the Th2-type phenotype in T cells and is an essential cofactor for IgE production by B cells. We detected mRNA for IL-4 by reverse transc ription-PCR in blood eosinophils from atopic asthmatics. By specific E LISA, 108 +/- 20 pg of IL-4 protein/10(6) cells could be extracted fro m whole cells, and approximately 30% of the IL-4 was released after in cubation with serum-coated particles. Using immunocytochemistry, eosin ophils from atopic asthmatics and nonatopic controls showed IL-4 immun oreactivity using an anti-IL-4 mAb. IL-4 was located predominantly in the eosinophil granules, as shown by both immunogold electron microsco py and a cell fractionation technique that dissociated cell granules f rom membrane and cytosolic components. IL-4 mRNA colocalized with eosi nophils (using sequential immunocytochemistry with an eosinophil-speci fic (EC2) mAb and in situ hybridization using an IL-4-specific antisen se riboprobe) in both cell cytospins from bronchoalveolar lavage fluid from asthmatics as well as skin biopsies obtained from allergen-induc ed late phase (6-h) reactions in atopic subjects. Using double immunoc ytochemistry on skin biopsies with eosinophil- and IL-4-specific mAb, 83.5 +/- 3.5% of eosinophils were IL-4(+). Conversely, eosinophils acc ounted for 46.5 +/- 3.9% of the total cells expressing IL-4 immunoreac tivity. Thus, human eosinophils express mRNA for IL-4, and the transla ted product is contained within the crystalloid granule from which it is released after stimulation with serum-coated particles. These obser vations are consistent with the hypothesis that eosinophils contribute to the development of the Th2 phenotype by T cells infiltrating atopi c allergic reactions as well as to IgE synthesis.