Identification of interleukin-2 in human peripheral blood eosinophils.
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/10(6) 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/10(6) cells) with some evidence for release of this cytokine but only in three out of six eosinophil preparations (range 1.3-5.8 pg/10(6) 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 beta-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.
Levi-Schaffer
F
F
Department of Allergy and Clinical Immunology, National Heart and Lung Institute, London, UK.
Barkans
J
J
Newman
T M
TM
Ying
S
S
Wakelin
M
M
Hohenstein
R
R
Barak
V
V
Lacy
P
P
Kay
A B
AB
Moqbel
R
R
D001249:Asthma / Q000276:immunology*; D002458:Cell Fractionation; D003594:Cytoplasmic Granules / Q000276:immunology; D004804:Eosinophils / Q000276:immunology* / Q000648:ultrastructure; D006801:Humans; D015151:Immunoblotting; D007124:Immunoenzyme Techniques; D007376:Interleukin-2 / Q000097:blood*; D016253:Microscopy, Immunoelectron
D007376:Interleukin-2