Interleukin (IL)-13 is a T helper 2-derived cytokine that has recently been implicated in allergic airway responses. We hypothesized that IL-13 may regulate expression of eotaxin in airway epithelium. We found that IL-13 upregulated eotaxin messenger RNA and protein synthesis in the airway epithelial cell line BEAS-2B; this effect showed synergy with tumor necrosis factor (TNF)-alpha and also was inhibited by the glucocorticoid budesonide. To establish the mechanisms of eotaxin upregulation by IL-13, cells were transfected with an eotaxin promoter-luciferase reporter plasmid and transcription was activated by IL-13 (1.7-fold) and TNF-alpha (2.8-fold). The combination of IL-13 and TNF-alpha additively activated the promoter constructs (4.1-fold). Activation of signal transducer and activator of transcription (STAT) 6 by IL-13 was confirmed by nuclear protein binding to a DNA probe derived from the eotaxin promoter. Activation of eotaxin transcription by IL-13 and the additive effect with TNF-alpha were lost in plasmids mutated at a putative STAT6 binding site. Cotransfection with a wild-type STAT6 expression vector significantly enhanced activation of the eotaxin promoter after IL-13 stimulation (6-fold induction). A significant increase of eotaxin protein secretion in the supernatant of STAT6 wild-type-transfected cells was observed after IL-13 stimulation. Cotransfection with a dominant negative STAT6 mutant expression vector inhibited activation of the eotaxin promoter by IL-13. These results indicate that IL-13 stimulates eotaxin expression in airway epithelial cells and that STAT6 plays a pivotal role in this response.

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Previous studies have indicated a redundancy in the effects of the cytokines, IL-3, IL-5, and nerve growth factor (NGF) on acute priming of human basophils. In the current study, we have examined the effects of these three cytokines on 18-h priming for leukotriene C4 generation, their ability to induce FcεRIβ mRNA expression, or their ability to sustain basophil viability in culture. We also examine a variety of the signaling steps that accompany activation with these cytokines. In contrast with the ability of IL-3 to alter secretagogue-mediated cytosolic calcium responses following 18-h cultures, 18-h treatment with IL-5 or NGF did not affect C5a-induced leukotriene C4 generation or alter C5a-induced intracellular Ca2+ concentration elevations. IL-3 and IL-5, but not NGF, induced FcεRIβ mRNA expression and all three improved basophil viability in culture with a ranking of IL-3 > IL-5 ≥ NGF. All three cytokines acutely activated the extracellular signal-regulated kinase pathway and the signaling elements that preceded extracellular signal-regulated kinase and cytosolic phospholipase A2 phosphorylation, consistent with their redundant ability to acutely prime basophils. However, only IL-3 and IL-5 induced Janus kinase 2 and STAT5 phosphorylation. This pattern of signal element activation among the three cytokines most closely matched their ability to induce expression of FcεRIβ mRNA. Induction of the sustained calcium signaling that follows overnight priming with IL-3 appeared to be related to the strength of the early signals activated by these cytokines but the relevant pathway required was not identified. None of the signaling patterns matched the ability of the cytokines to promote basophil survival.

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