THE ACTIVATION OF THE JAK-STAT-1 SIGNALING PATHWAY BY IL-5 IN EOSINOPHILS

The intracellular signal transduction of IL-5 in eosinophils is unknow n. The objective of this study was to investigate the involvement of t he newly discovered lak-STAT pathway in the IL-5 signal transduction m echanism. Eosinophils were purified from peripheral blood by discontin uous Percoll gradients and stimulated with IL-5. The involvement of Ja k 2 was investigated by immunoprecipitation followed by immunoblotting for tyrosine phosphorylation. The activation of lak 2 was studied by autophosphorylation of the immunoprecipitated kinase. Jak 2 was tyrosi ne phosphorylated within 1 to 3 min after stimulation of eosinophils w ith IL-5. Further, the immunoprecipitated lak 2 obtained from IL-5-sti mulated cells underwent autophosphorylation. Jak 2 coprecipitated with the beta-subunit of the IL-5 receptor, suggesting a physical associat ion of the kinase with the receptor. The nuclear factor STAT-1 (p91) w as investigated by immunoprecipitation followed by immunoblotting for tyrosine phosphorylation. STAT-1 was tyrosine phosphorylated within 15 min of IL-5 stimulation. The presence of STAT-1 in the nuclear extrac t was studied by electrophoretic mobility shift assay. IL-5 induced tw o proteins that bound to the gamma-activating sequence. In the presenc e of an anti-STAT-1 Ab, the band was supershifted. Thus, we demonstrat ed that IL-5 activated the Jak 2-STAT 1 signaling pathway in eosinophi ls. We speculate that the Jak 2-STAT 1 pathway may be involved in the activation of IL-5-inducible genes in eosinophils.