IL-3 and IL-33 activate distinct signal transduction pathways leading to differential regulation of LTC4 synthesis. (A) IL-3 and IL-33 activate distinct signaling pathways in basophils. Cells were stimulated with IL-3 or IL-33 at concentrations and for the time periods indicated. Activation of MAP-kinases, Erk, and p38, and transcriptional regulators, Stat3/Stat5 and IκB-α, and phosphorylation of cPLA2 (P-cPLA2) were analyzed by Western blotting. A representative experiment is shown. Analysis by densitometry of Western blots of 5 independent experiments showed that ERK activation by IL-3 was at least 9 times higher as compared with that induced by IL-33, while p38 activation in response to IL-33 was at least 4 times higher than that promoted by IL-3. The ratio of cPLA2 phosphorylation of cells treated with IL-3 versus cells treated with IL-33 ranged between 1.5 and 2.1. (B) IL-33 does not efficiently prime basophils for C5a-induced LTC4 formation. Cells were primed with 10 ng/mL IL-3 or 50 ng/mL IL-33 for the time periods indicted (priming time) followed by stimulation with 10 nM C5a for 30 minutes. NA / none: nonprimed cells stimulated with C5a alone. (C) Culture with IL-33 does not potentiate IgE-dependent or -independent mediator release. Cells were cultured for 24 hours with IL-3 or IL-33 as indicated, followed by stimulation for 30 minutes with C5a or by IgER-crosslinking using anti-IgER mAb. LTC4 levels (mean values + SEM of 3 experiments) in the cell supernatants are shown in panels B and C.
