INTRACELLULAR-LOCALIZATION OF INTERLEUKIN-6 IN EOSINOPHILS FROM ATOPIC ASTHMATICS AND EFFECTS OF INTERFERON-GAMMA

Eosinophils, prominent cells in asthmatic inflammation, have been show n to synthesize, store, and release an array of up to 18 cytokines and growth factors, including interleukin-6 (IL-6). In this report, we sh ow that IL-6 immunofluorescence localizes to the matrix of the crystal loid granule in peripheral blood eosinophils from atopic asthmatics us ing confocal laser scanning microscopy (CLSM). Granule localization of IL-6 was confirmed using dot-blot analysis and enzyme-linked immunoso rbent assay (ELISA) on subcellular fractions of highly purified eosino phils produced from density centrifugation across a 0% to 45% Nycodenz gradient. IL-6 was found to coelute with eosinophil crystalloid granu le marker proteins, including eosinophil peroxidase (EPO), major basic protein (MBP), arylsulfatase B, and beta-hexosaminidase. Immunoreacti vity to IL-6 colocalized with granule-associated IL-2 and IL-5 in subf ractionated eosinophils. We also made the novel and compelling observa tion that interferon gamma (IFN gamma), a Th1-type cytokine, stimulate d an early elevation in eosinophil IL-6 immunoreactivity. A 2.5 fold e nhancement of IL-6 immunoreactivity in eosinophil granules was observe d within 10 minutes of IFN gamma treatment (500 U/mL), as determined b y subcellular fractionation and CLSM. These findings suggest that IFN gamma has short-term effects on human eosinophil function and imply th at a physiologic role exists for Th1-type cytokine modulation of Th2-t ype responses in these cells. (C) 1998 by The American Society of Hema tology.