Stem cell factor and interleukin-4 increase responsiveness of mast cells to Substance P

Objective The response of mast cells (MC) to non–IgE-mediated stimulation is critically dependent on the population of MC examined. The neuropeptide Substance P (SP) has been reported to activate connective tissue–type MC (CTMC), while mucosal MC (MMC) are not activated by SP. We examined the effect of stem cell factor (SCF) plus interleukin-4 (IL-4) on SP-initiated activation of bone marrow-derived MC (BMMC). Materials and Methods Mouse MC, derived from a culture of BM cells with IL-3, were subsequently treated with recombinant SCF plus IL-4 for 6 days. Responsiveness to SP was monitored measuring β-hexosaminidase and lipid mediator release. Histochemical staining, histamine analysis, and granule protease expression were achieved to characterize the cells. Results In contrast to IL-3 grown cells, SCF/IL-4-exposed cells showed functional responsiveness to release β-hexosaminidase (42.25% ± 1.46% at SP concentration of 100 μM) and produce leukotriene C4 (LTC4) (7.4 ± 1.5 ng/106 cells)/prostaglandin D2 (PGD2) (2.0 ± 0.3 ng/106 cells) upon stimulation by SP. The increase in sensitivity of the cells to SP was not due to differentiation into CTMC, as the cells remained heparin negative. Both SCF and IL-4 were needed because SCF or IL-4 alone were insufficient to keep cells viable after 3 to 4 days post coculture. SP-induced secretion from BMMC cultured in medium containing SCF plus IL-4 (25.76% ± 1.83%) was higher in comparison with cells cultured with SCF plus IL-3 (8.85% ± 0.68%). Conclusion These findings indicate that temporal changes in cytokine expression can influence the sensitivity of MC to non-immunologic stimuli. Local cytokine production leading to an increase in MC responsiveness to SP and inducing secretion of granule content and lipid generation may, therefore, propagate and worsen inflammatory conditions.