Regulation of Cellular Activation (B) Int Arch Allergy Immunol 1999;118:447–449 Effects of Interferon- γ on Mobilization and Release of Eosinophil-Derived RANTES J.R. Velazquez P. Lacy S. Mahmudi-Azer R. Moqbel Pulmonary Research Group, Department of Medicine, University of Alberta, Edmonton, Canada Abstract Eosinophils synthesize and release a number of cy- tokines and chemokines, including RANTES, a potent chemoattractant particularly for memory T cells and eosinophils. Long-term (c 12 h) incubation with interfer- on-γ (IFN-γ) has been shown to activate eosinophils and induce expression of membrane receptors. We hypo- thesized that IFN-γ mobilizes intracellular RANTES in eosinophils in advance of mediator release. Highly puri- fied peripheral blood eosinophils were obtained from asthmatics and stimulated with IFN-γ at 500 U/ml for time course analysis up to 2 h. By specific ELISA, RANTES was detected in supernatants (80B15 pg per 2 E 10 6 cells) following 120 min of stimulation. Immu- noreactive RANTES in resting cells (5 E 10 7 eosinophils) was detected in two intracellular compartments in stud- ies of subcellular fractionation by density gradient cen- trifugation. After 10 min IFN-γ stimulation, RANTES im- munoreactivity was confined to crystalloid granules. RANTES was redistributed from secretory granules to light-membrane fractions after 60 min of IFN-γ incuba- tion. Our data suggest that rapid mobilization and re- lease of RANTES occurs from stimulated eosinophils. These findings may have important implications for the role of IFN-γ in activating human eosinophils, particular- Key Words Asthma · Granulocytes · Crystalloid granules · Chemokines Fax +41 61 306 12 34 E-Mail karger @ karger.ch www.karger.com  1999 S. Karger AG, Basel 1018–2438/99/1184–0447 $17.50/0 Accessible online at: http://BioMedNet.com/karger Correspondence to: Dr. Redwan Moqbel Pulmonary Research Group, 574 Heritage Medical Research Center, University of Alberta Edmonton, Alberta T6G 2S2 (Canada) Tel. +1 403 492 1909, Fax +1 403 492 5329 E-Mail redwan.moqbel@ualberta.ca Introduction Eosinophil activation in allergic inflammation potential- ly involves the release of up to 19 different cytokines and growth factors [reviewed in 1], including RANTES [2]. RANTES is a CC chemokine and acts as a potent in vitro chemoattractant for memory T cells and eosinophils [3, 4]. Release of RANTES into biological fluids during allergic inflammation correlates strongly with the intensity of in- flammatory cell infiltrate and symptoms of allergy and asth- ma [5]. An earlier study has shown that peripheral blood eosinophils express RANTES mRNA and apparently store RANTES intracellularly [2]. Interferon-γ (IFN-γ) stimula- tion, in vitro, induced upregulation of RANTES transcrip- tion and translation in eosinophils [2]. We hypothesized that intracellular RANTES is rapidly mobilized and secreted following stimulation by IFN-γ in a time-dependent manner. RANTES release was analyzed in eosinophils purified from atopic subjects using RANTES- specific ELISA and subcellular fractionation, and its sites of storage were compared with the crystalloid granule protein eosinophil peroxidase (EPO). ly in severe chronic asthma or viral exacerbation of asthmatic inflammation, where this cytokine may play a role. International Archives of Allergyand Immunology