Stem cell factor enhances IgE-mediated histamine and TNF-α release from dispersed canine cutaneous mast cells

Stem cell factor (SCF), the c- kit receptor ligand, plays a critical role in mast cell (MC) development and differentiation. In addition, SCF has recently been found to both modulate and induce MC activation. To investigate the effect of SCF on canine cutaneous MC function, we have characterized the ability of SCF to modulate the release by mature canine MC of preformed (histamine) and newly generated (TNF-α) mediators. Mature MC were isolated from skin and cultured in the absence or presence of exogenous SCF (6 ng/ml) for up to 5 days and then challenged with anti-IgE (1 μg/ml) alone for 30 min or with a combination of SCF (50 ng/ml) and anti-IgE. SCF alone failed to trigger either histamine or TNF-α release at any time. However, we observed that SCF used as a co-stimulus significantly potentiated histamine and TNF-α release in canine MC activated through FcεRI regardless of whether or not SCF was added to the medium during culturing. Thus, the mean histamine release (%) and TNF-α production (pg/ml) were found to be significantly higher if cells were maintained in culture in SCF-supplemented medium compared with cells cultured in the absence of exogenous SCF. We also observed that MC responsiveness to immunological stimulation increased with culture time, the percentage of histamine released being higher in cells cultured for at least 3 days when compared to freshly isolated MC. Taken together these findings suggest that canine skin MC releasability can be enhanced independently either through prolonged incubation with SCF and/or through anti-IgE and SCF co-stimulation.