Ligand for the receptor-type protein-tyrosine kinase KIT. Plays an essential role in the regulation of cell survival and proliferation, hematopoiesis, stem cell maintenance, gametogenesis, mast cell development, migration and function, and in melanogenesis. KITLG/SCF binding can activate several signaling pathways. Acts synergistically with other cytokines, probably interleukins (By similarity). Homodimer, non-covalently linked. Also exists as a secreted soluble form (isoform 1 only). A soluble form is produced by proteolytic processing of isoform 1 in the extracellular domain. Belongs to the SCF family.