Activation of interleukin-1 family receptor ST2L by its ligand interleukin-33 (IL-33) is an important component in inflammatory responses. Peripheral blood basophils, recognized as major effector cells in allergic inflammation that play a role in both innate and adaptive immunity, are activated by IL-33 through ST2L. However, studies are challenging due to the paucity of this cell population, representing less than 1% of peripheral blood leukocytes. We identified a basophil-like chronic myelogenous leukemia cell line, KU812, that constitutively expresses ST2L and demonstrates functional responses to IL-33 stimulation. IL-33 induced production of multiple inflammatory mediators in KU812 cells that were blocked by anti-ST2L and anti-IL-33 antibodies. The interaction of IL-33 and ST2L activated NF-kappaB, JNK, and p38 MAPK, but not ERK1/2 signaling pathways. Studies using pharmacological inhibitors to IKK-2 and MAP kinases revealed that one of the functional responses, IL-33-induced IL-13 production, was regulated through NF-kappaB, but not JNK or p38 MAPK signaling. The requirement of NF-kappaB was confirmed by IKK-2 knockdown using shRNA. KU812 represents the first human cell line-based in vitro model of the IL-33/ST2L axis and provides a valuable tool to aid in understanding the mechanism and significance of IL-33 and ST2L interaction and function.
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