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 Ca²⁺-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 withan antiphosphotyrosine monoclonal antibody (4G10). This cytokine stimulated tyrosine phosphorylation was not inhibited under Ca²⁺-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.