Stem cell factor - A possible paradigm between mast cells, eosinophils, and fibroblasts

Background: There is increasing evidence for the association of mast cells, eosinophils, and fibroblasts during the latephase allergic reactions and in fibrotic tissues. Interactions of these cell types, either by direct cell-cell contac or through their soluble mediators, leads to their enhanced survival, chemotaxis, activation, and consequently perpatuation of the allergic and of the repair reations. Stem cell factor (SCF) is important in allergy because it is the only factor essential for human mast cell development and it enhances survival, activation, adhesion, and mediator release of mature mast cells. It is produced by a plethora of cells including mast cells and fibroblasts. In the present work, we reviewed the literature on the importance of SCF in this context and summarized our recent findings on eosinophils as SCF producers. Methods/data base: Eosinophils were purified from the peripheral blood of mildly allergic patients as described [25]. To study production of SCF, reverse transcriptase polymerase chain reaction (RT-PCR), Western Blot, and confocal laser microscopy were performed on freshy isolated and cultured eosinophils. Results: Eosinophils variably expressed mRNA for the soluble and uncleaved forms of SCF and produced the 18.5 kd protein backbone of SCF. After overnight incubation in medium, eosinophils also produced SCF of higher molecular weight (42-45 kd) that might represent its glycosylated forms. Eosinophils expressed cytoplasmic SCF that colocalized with major basic protein. Overnight incubation of eosinophils in culture medium containing chymase, induced SCF release.