Identification of interleukin-2 in human peripheral blood eosinophils

F. Levi-Schaffer, J. Barkans, T. M. Newman, S. Ying, M. Wakelin, R. Hohenstein, V. Barak, P. Lacy, A. B. Kay, R. Moqbel*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

76 Scopus citations

Abstract

Interleukin-2 (IL-2) is an essential growth factor for T cells. Previous studies have shown that human peripheral eosinophils respond to IL-2 in chemotaxis and express the IL-2 receptor (CD25). In addition, eosinophils have been shown to transcribe messenger RNA for IL-2. The aim of the present study was to determine whether eosinophils translate mRNA for IL-2 and to determine the site of intracellular localization. By immunocytochemistry, an average of 9% of cells showed cytoplasmic staining for IL-2 in freshly isolated unstimulated blood eosinophils obtained from asthmatic subjects who were not receiving oral corticosteroid treatment (n = 5). Freshly isolated, disrupted, highly purified eosinophils (>99%, by CD16- immunomagnetic selection) contained an average of 6 pg/106 cells of IL-2 measured by a specific enzyme linked immunosorbent assay (ELISA) (n = 7). Purified eosinophil incubated with serum-coated Sephadex beads showed an increase in the amount of intracellularly-retained IL-2 (26.2 ± 7.2 pg/106 cells) with some evidence for release of this cytokine but only in three out of six eosinophil preparations (range 1.3-5.8 pg/106 cells). The intracellular localization of IL-2 was determined by fractionation of the cells on a linear (0-45%) Nycodenz gradient in sucrose buffer followed by detection of IL-2 in the fractions using an IL-2-specific ELISA and dot blotting. The majority of the IL-2 detected co-eluted with known eosinophil granule markers (i.e. major basic protein (MBP), eosinophil cationic protein (ECP), eosinophil peroxidase (EPO) and β-hexosaminidase) but small quantities were also detected in the cytosolic (lactate dehydrogenase (LDH) associated) and membrane (CD9+) fractions. Immunogold labelling of intact eosinophils using an anti-IL-2 monoclonal antibody confirmed IL-2 immunoreactivity in association with the eosinophil crystalline granule cores. These data are consistent with the hypothesis that eosinophils synthesize, release and store IL-2 largely within cystalloid granules. This stored IL-2 may serve as a reservoir for rapid release of IL-2 in inflammatory reactions associated with eosinophilia.

Original languageAmerican English
Pages (from-to)155-161
Number of pages7
JournalImmunology
Volume87
Issue number1
StatePublished - 1996

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