Cytokine priming of the respiratory burst in human eosinophils is Ca2+ independent and accompanied by induction of tyrosine kinase activity.

We report that pretreatment of human eosinophils with GM-CSF, IL-3, or IL-5 enhanced the respiratory burst induced by opsonized particles. In order to gain more insight into the intracellular mechanism(s) involved in cytokine priming, the role of [Ca2+]i and tyrosine kinases was studied. Optimal priming concentrations of GM-CSF, IL-3, and IL-5 did not induce a rise in [Ca2+]i, and Ca(2+)-depleted eosinophils ([Ca2+]i < 20 nM) were still primed after preincubation with these cytokines. GM-CSF, IL-3, and IL-5 induced phosphorylation of two proteins (102 and 122 kd) on tyrosine residues, as deduced from Western blot analysis with an antiphosphotyrosine monoclonal antibody (4G10). This cytokine-stimulated tyrosine phosphorylation was not inhibited under Ca(2+)-depleted conditions. In conclusion, this study demonstrates that GM-CSF, IL-3, and IL-5 priming of the opsonized particle-induced respiratory burst in human eosinophils is completely Ca2+ independent. Moreover the tyrosine phosphorylation of a 102-kd and a 122-kd protein is Ca2+ independent, suggesting that this event might be involved in cytokine priming.