Upregulated expression of substance P (SP) and NK1R in eczema and SP-induced mast cell accumulation

Substance P (SP) was reported to be associated with eczema and acts as a potent skin mast cell secretagogue. However, little is known of its expression in inflammatory cells in eczema and its ability in induction of mast cell accumulation. In the present study, we investigated expression of SP and neurokinin-1 receptor (NK1R) on peripheral blood leukocytes and mast cells from patients with eczema and influence of SP on mast cell accumulation by using flow cytometry analysis, trans-epithelial cell migration assay and mouse peritoneal model. The results showed that plasma SP and IL-17A levels in eczema patients were higher than that in healthy control subject. The percentages of SP+ and NK1R+ expression populations of monocytes, helper T cells, natural killer T cells and basophils in peripheral blood of eczema patients were markedly elevated. It was observed that not only absolute number of mast cells but also SP+ and NK1R+ mast cells are enhanced in the lesion skin of eczema. SP showed a potent chemoattractant action on mast cells as assessed by a mouse peritoneal model and a trans-endothelium cell migration assay. SP-induced mast cell accumulation appears a CD18/CD11a complex, l -selectin and ICAM-1-dependent event which can be blocked by a NK-1R antagonist RP67580. In conclusion, elevated expression of SP in patients with eczema and the ability of SP in induction of mast cell accumulation indicate strongly that SP is a potent proinflammatory mediator, which contributes to the pathogenesis of eczema. Inhibitors of SP and blockers of NK1R are likely useful agents for treatment of eczema.