Figure 3.

IL-4 does not bind to opioid receptors in HEK cells. A, C, E, IL-4 did not displace binding of [³H]-diprenorphine to δ-receptors (A), [³H]-DAMGO to µ-receptors (C), and of [³H]-naloxone to κ-receptors (E). B, D, F, In contrast, selective agonists of δ-receptors (DPDPE; B), µ-receptors (fentanyl; D), and κ-receptors (U50,488; F) displaced binding of [³H]-diprenorphine to δ-receptors (B), [³H]-DAMGO to µ-receptors (D), and of [³H]-naloxone to κ-receptors (F). Experiments were performed in HEK cells stably expressing µ-receptors or transiently transfected with δ-receptors or κ-receptors. [³H]-ligand binding in the absence of the competitor (opioid or IL-4) was set to 100% binding (baseline, depicted by dashed lines) and the data in the presence of the competitor were normalized accordingly and presented as mean ± SEM N = 6 independent experiments per group.