IgE in the absence of allergen induces the expression of monocyte chemoattractant protein-1 in the rat basophilic cell-line RBL-2H3

Recently, basophils have been suggested to produce inflammatory mediators in response to IgE in the absence of allergens. Monocyte chemoattractant protein-1 (MCP-1) plays an important role in the initiation of inflammatory responses by recruiting various immune cells to the site of allergic inflammation. In the present study, we examined whether IgE under allergen-free conditions could stimulate basophils and lead to the production of MCP-1. Exposure of the rat basophilic cell-line RBL-2H3 to IgE without allergen resulted in a dose- and time-dependent induction of MCP-1 expression at both the mRNA and protein level. Although allergen was not necessary for IgE-induced MCP-1 expression, it was essential for degranulation as determined by β-hexosaminidase release assay. IgE enhanced phosphorylation of MAP kinases including ERK, p38 kinase, and JNK. However, IgE-induced MCP-1 expression was attenuated by inhibitors for JNK and PKC. Concomitantly, IgE induced activation of AP-1, which is an important transcription factor for MCP-1 gene expression in RBL-2H3 cells. Taken together, our results suggest that IgE alone is sufficient to stimulate basophils to increase expression of MCP-1, which in turn might contribute to the inflammatory response.