HUMAN MAST-CELLS EXPRESS STEM-CELL FACTOR

Stem cell factor (SCF) is a major cytokine regulator of mast cell grow th and function. The present study demonstrates that human mast cells are able to produce SCF. Constitutive synthesis of SCF mRNA was seen i n the mast cells isolated from human lung and skin by RT-PCR, This was confirmed by in situ hybridization in conjunctival mast cells of both tryptase-only (MCT) and tryptase/chymase (MCTC) subsets. SCF protein product was found in conjunctival MCT and MCTC mast cells by immunohis tochemistry. Soluble SCF protein was detected in the culture supernata nt of isolated lung mast cells by ELISA, and cross-linkage of IgE rece ptor (Fc epsilon-RI) on the lung mast cells in culture did not alter S CF mRNA expression, or the secreted soluble SCF protein. This was cons istent with the finding that levels of SCF mRNA expression in conjunct ival mast cells mere similar between normal subjects and patients with seasonal allergic conjunctivitis (SAC), This study shows that human m ast cells themselves are a cellular source of SCF, as well as being ta rget cells for this growth factor. SCF may regulate mast cell growth a nd function via both paracrine and autocrine mechanisms. The productio n of SCF by mast cells may be regulated via mechanisms other than IgE receptor-mediated pathways. (C) 1998 John Wiley & Sons, Ltd.