IL-3 up-regulates ST2 in basophils, while IL-18 receptors are constitutively expressed. (A) Constitutive and inducible expression of IL-18R and ST2. Basophils were cultured overnight in the absence (nil) or presence of IL-3 (10 ng/mL) and analyzed by flow cytometry for cell surface IL-18R and ST2 expression. The histograms show an overlay of unstimulated (nil) and IL-3–stimulated basophils including isotype control. (B) Time course of IL-3–induced ST2 expression. Freshly isolated (f.i.) basophils were analyzed immediately or cultured for the time indicated without (nil) or with IL-3. Cell surface ST2 expression was analyzed by flow cytometry (top panel) and total protein expression of IL-3–treated cells by Western blotting (bottom panel). (C) Kinetics of induction of mRNA of ST2-isoforms. Basophils were cultured with IL-3 for the time indicated and mRNA was quantified by real-time RT-PCR using specific primers for ST2-isoforms: transmembrane/long, ST2L; soluble, sST2; all isoforms ST2, ST2 (all). The expression of ST2 in comparison to the reference gene β2M is given as RQ (relative quantity). Mean values of duplicates are shown. Representative experiments are shown in all panels.