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 healthy donors were incubated with increasing concentrations of IL-13. The expression of CD69 was analyzed by flow cytometry (FACS). Surface expression of CD69, which was absent on untreated eosinophils, was induced by IL-13 at concentrations ranging from 1 ng/ml to 1 microgram/ml in a concentration-dependent manner. In contrast, neutrophils expressed CD69 neither spontaneously nor following incubation with IL-13. Semiquantitative reverse transcription-PCR for CD69 mRNA showed constitutive CD69 mRNA expression in purified human eosinophils. Incubation of eosinophils with IL-13 further increased CD69-specific mRNA. Analysis of intracellularly stored CD69 in eosinophils permeabilized with saponin revealed intracellular binding of anti-CD69 Abs in all isolated eosinophils. 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 conclusion, our results demonstrate that IL-13 specifically activates human eosinophils, as determined by the expression of CD69 cell surface protein and mRNA expression. Furthermore, IL-13 significantly prolongs eosinophil survival in vitro. The data suggest that IL-13 may play a role in the activation of eosinophils.