Background：

Stem Cell Factor (SCF)， also known as c-Kit ligand (KL)， steel factor (SLF) and mast cell growth factor (MGF)， is a 30 kDa glycoprotein with broad activities on various tissues， including hematopoietic cells， pigment cells， and primordial germ cells. SCF is secreted by endothelial cells， fibroblasts， and bone marrow stromal cells as a membrane-bound form which may be cleaved to release the soluble form. Both forms are active in promoting colony formation from murine bone marrow cells， but membrane-bound SCF is more effective in promoting hematopoieses in vivo， suggesting a role in cellular interactions between hematopoietic and stromal cells.