Human keratinocytes release mast cell differentiation factors other than stem cell factor

Besides stem cell factor (SCF), additional fibroblast-derived mast cell growth factors have previously been described. Since keratinocytes have also been shown to produce SCF, we have studied the ability of culture supernatants from the human HaCaT keratinocyte cell line to induce SCF-independent mast cell differentiation. The immature human mast cells of the HMC-1 line which express a mutant continuously activated SCF receptor were used as model target cells. Culture supernatants from differentiating keratinocytes (at day 11 of culture), and far less so those from proliferating keratinocytes (day 4 of culture), caused a marked, dose-dependent increase of histamine and tryptase in HMC-1 cells. This suggests that human HaCaT keratinocytes release mast cell differentiation factors other than SCF, to a degree related to their state of differentiation.