IL-33 is a member of the
IL-1 family and mediates its biological effects via the ST2 receptor, which is selectively expressed on Th2 cells and mast cells. Although polymorphic variation in ST2 is strongly associated with
asthma, it is currently unclear whether
IL-33 acts directly on lung tissue cells at sites of
airway remodeling. Therefore, we aimed to identify the IL-33-responsive cells among primary human lung tissue cells. ST2
mRNA was expressed in both endothelial and epithelial cells but not in fibroblasts or smooth muscle cells. Correspondingly,
IL-33 promoted
IL-8 production by both endothelial and epithelial cells but not by fibroblasts or smooth muscle cells. Transfection of ST2 small interference RNA into both endothelial and epithelial cells significantly reduced the IL-33-dependent upregulation of
IL-8, suggesting that IL-33-mediated responses in these cells occur via the ST2 receptor. Importantly, Th2
cytokines, such as
IL-4, further enhanced ST2 expression and function in both endothelial and epithelial cells. The IL-33-mediated production of
IL-8 by epithelial cells was almost completely suppressed by
corticosteroid treatment. In contrast, the effect of
corticosteroid treatment on the IL-33-mediated responses of endothelial cells was only partial.
IL-33 induced activation of both ERK and
p38 MAPK in endothelial cells but only ERK in epithelial cells.
p38 MAPK was required for the IL-33-mediated responses of endothelial cells, whereas ERK was required for IL-33-mediated
IL-8 production by epithelial cells. Taken together, these findings suggest that IL-33-mediated inflammatory responses of lung tissue cells may be involved in the chronic allergic
inflammation of the asthmatic airway.