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

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). 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 beta-hexosaminidase and lipid mediator release. Histochemical staining, histamine analysis, and granule protease expression were achieved to characterize the cells. In contrast to IL-3 grown cells, SCF/IL-4-exposed cells showed functional responsiveness to release beta-hexosaminidase (42.25% +/- 1.46% at SP concentration of 100 microM) and produce leukotriene C(4) (LTC(4)) (7.4 +/- 1.5 ng/10(6) cells)/prostaglandin D(2) (PGD(2)) (2.0 +/- 0.3 ng/10(6) 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%).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.