Mast cell activation can be induced by multiple mechanisms, including IgE-, complement-, and stem cell factor (SCF)-mediated pathways. In addition, the interaction of mast cells with particular cell populations, such as fibroblasts, have also demonstrated increased mast cell reactivity. In these studies, we have investigated the role of fibroblast-mast cell interaction for induction of histamine release and chemokine production and the specific role of SCF during this interaction. Primary pulmonary fibroblast cell lines were grown in culture and used throughout these studies. Mast cells were grown in parallel with fibroblasts by incubation of bone marrow cells with SCF and IL-3. During mast cell-fibroblast coculture, increased histamine release could be attenuated either by separation of the cell populations using a Trans-Well setup, which did not allow cellular contact, or by specific anti-SCF Ab. In addition, a significant increase in eotaxin, a potent eosinophil-specific CC chemokine, was also observed during fibroblast-mast cell interaction. The production of eotaxin was cell contact dependent and could be inhibited using an anti-SCF Ab or specific antisense therapy. SCF was constitutively produced from fibroblasts in its transmembrane form and could be induced by TNF. SCF-coated plates induced significant mast cell-derived eotaxin production, whereas soluble SCF induced little or no eotaxin, suggesting a necessity for receptor cross-linking for activation. These studies indicate that fibroblast-mast cell contact plays a role in exacerbation of histamine release and eotaxin production.