Description: Flt3 (or FMS-related tyrosine kinase 3) Ligand, also known as Flk2 Ligand, is a growth factor that regulates proliferation of early hematopoietic cells. Flt3 Ligand binds to cells expressing the tyrosine kinase receptor Flt3. By itself, Flt3 Ligand does not stimulate proliferation of early hematopoietic cells. Instead, it synergizes with other colony-stimulating factors (CSFs) and interleukins to induce growth and differentiation. Unlike CSFs, however, Flt3 Ligand exerts no activity on mast cells. Multiple isoforms of Flt3 Ligand have been identified. The predominant biologically active form is anchored to the cell surface as the extracellular domain of a transmembrane protein (209 a.a.). The membrane-bound isoform can be proteolytically cleaved to generate a biologically active soluble isoform. Human Flt3 Ligand shares 71% and 65% amino acid sequence identity with mouse and rat Flt3 Ligand, respectively. Human and mouse Flt3 Ligand show cross-species activity. Recombinant human Flt3 Ligand is a soluble 17.6 kDa protein consisting of 155 amino acid residues.