Human eosinophils from hypereosinophilic patients spontaneously express the p55 but not the p75 interleukin 2 receptor subunit

The expression of interleukin 2 receptor (IL 2R) on eosinophils was investigated in patients with hypereosinophilia. Hypodense activated eosinophils have been described in various diseases such as parasitic or allergic diseases, hypereosinophilic syndrome (HES) associated in some cases to myeloproliferative markers, and more recently described in patients undergoing recombinant IL 2 treatment. The presence of p55 α chain of IL 2R (CD25) on purified eosinophils collected from blood of hypereosinophilic patients was detected by flow cytometry. In 10 out of 19 cases, more than 10% of eosinophils were CD25+. Cross-linking studies on enriched eosinophils showed one 64–75-kDa band, consisting of IL 2 (15 kDa) cross-linked to the IL2R p55 subunit. In Northern blot analysis the two messenger mRNA (3.5 and 1.5 kb) encoding the IL2R p55 subunit were identified after hybridization with a CD25 cDNA probe. In contrast, the presence of the IL2R p75 subunit was not detected. These data provide preliminary evidence for the expression of a low-affinity receptor for IL 2 on in vivo activated eosinophils and raise the question of the role played by this cytokine in eosinophil differentiation and activation.