Functional expression of neurokinin 1 receptors on mast cells induced by IL-4 and stem cell factor

It is widely accepted that neurokinin 1 (NK1) receptors are not generally expressed on mast cells but little is known about their expression in inflammation. The present study shows expression of NK1 receptors on bone marrow-derived mast cells (BMMC) under the influence of IL-4 or stem cell factor (SCF). Highest expression was found when both cytokines are present. Six days of coculture with the cytokines IL-4 and SCF showed significant expression of NK1 receptors (NK1 receptor(+)/c-kit(+) BMMC; control: 7%, IL-4/SCF: 16%), while 12 days of cytokine coculture increased this expression to 37% positive cells. A longer coculture with IL-4 and SCF did not give an additional effect. Increased expression in IL-4/SCF-treated BMMC was further confirmed using Western blot analysis. Next, we demonstrated the functional relevance of NK1 receptor expression for mast cell activation, resulting in an enhanced degranulation upon stimulation by substance P. BMMC activation was significantly diminished by the NK1 receptor antagonist RP67580 (10 muM) when stimulated with low concentrations of substance P. The inactive enantiomer RP65681 had no effect. In addition, BMMC cultured from bone marrow of NK1 receptor knockout mice showed significantly decreased exocytosis to low concentrations of substance P. The present study clearly shows that NK1 receptor-induced activation contributes significantly at low physiological substance P concentrations (<100 muM). In conclusion, BMMC were shown to express NK1 receptors upon IL-4/SCF coculture. This expression of NK1 receptors has been demonstrated to be of functional relevance and leads to an increase in the sensitivity of BMMC to substance P.