SCF (Stem cell factor), also known as MGF (mast cell growth factor), SF (steel factor) and KL (kit ligand), is a 18.5 kDa transmembrane glycoprotein. SCF promotes survival, differentiation, and mobilization of multiple cell types including lymphoid, germ cell, and melanocyte progenitors. SCF is a primary growth and activation factor for mast cells and eosinophils.