ACTIVATION OF HUMAN EOSINOPHILS BY IL-13 - INDUCTION OF CD69 SURFACE-ANTIGEN, ITS RELATIONSHIP TO MESSENGER-RNA EXPRESSION, AND PROMOTION OF CELLULAR VIABILITY

To study the effect of IL-13 on CD69 expression and cell viability in human eosinophils, purified human peripheral blood eosinophils from he althy donors were incubated with increasing concentrations of IL-13. T he expression of CD69 was analyzed by flow cytometry (FAGS). Surface e xpression of CD69, which was absent on untreated eosinophils, was indu ced by IL-13 at concentrations ranging from 1 ng/ml to 1 mu g/ml in a concentration-dependent manner. In contrast, neutrophils expressed CD6 9 neither spontaneously nor following incubation with IL-13. Semiquant itative reverse transcription-PCR for CD69 mRNA showed constitutive CD 69 mRNA expression in purified human eosinophils. Incubation of eosino phils with IL-13 further increased CD69-specific mRNA. Analysis of int racellularly stored CD69 in eosinophils permeabilized with saponin rev ealed intracellular binding of anti-CD69 Abs in all isolated eosinophi ls. After stimulation with 100 ng/ml IL-13 for 24 h, the concentration of intracellular CD69 decreased by 41 +/- 9%, Furthermore, IL-13 at a concentration of 100 ng/ml enhanced eosinophil viability, as assessed by propidium iodide staining after 4 days in culture from 8.6 +/- 5.5 % in control medium to 50.7 +/- 6.8% following stimulation with IL-13 treatment. The effect of IL-13 on eosinophil viability as well as that on CD69 expression were both neutralized by anti-IL-13 Abs, In conclu sion, our results demonstrate that IL-13 specifically activates human eosinophils, as determined by the expression of CD69 cell surface prot ein and mRNA expression. Furthermore, IL-13 significantly prolongs eos inophil survival in vitro, The data suggest that IL-13 may play a role in the activation of eosinophils.