Expression and Effects of IL-33 and ST2 in Allergic Bronchial Asthma: IL-33 Induces Eotaxin Production in Lung Fibroblasts

Abstract

Background: Interleukin (IL)-33, a new member of the IL-1 cytokine family, has been recognized as a key cytokine that enhances T helper 2-balanced immune regulation through its receptor ST2; however, the function and relationship of the IL-33 and ST2 pathways in bronchial asthma are still unclear. We investigated the cellular origin and regulation of IL-33 and ST2 in allergic bronchial asthma in vivo and in vitro. Methods: BALB/c mice were sensitized by intraperitoneal injections of ovalbumin (OVA) with alum. Mice were exposed to aerosolized 1% OVA for 30 min a day for 7 days. These mice were then challenged with aerosolized 1% OVA 2 days after the last day of exposure. After the OVA challenge, the mice were sacrificed and their lung tissues were obtained. Mouse lung fibroblasts were cultured and treated with IL-33 or IL-13. Results: The levels of IL-33 mRNA and IL-33 protein in lung tissue increased after the OVA challenge. Most IL-33-expressing cells were CD11c+ cells and epithelial cells, and many ST2-expressing cells were stained lung fibroblasts and inflammatory cells. IL-33 induced eotaxin/CCL11 production in lung fibroblasts. IL-33 and IL-13 synergistically induced eotaxin expression. Conclusions: IL-33 may contribute to the induction and maintenance of eosinophilic inflammation in the airways by acting on lung fibroblasts. IL-33 and ST2 may play important roles in allergic bronchial asthma.