Fms-related tyrosine kinase 3 ligand (Flt3L) is growth fator stimulates the proliferation and differentiation of hematopoietic multipotent progenitors and promotes proliferation of NK cells and dendritic cell subgroups by combination with other growth factors. Flt3L is produced by T cells and stromal fibroblasts, and targeted various cells including hematopoietic stem cells, B cells, T cells, dendritic cells, and NK cells. Flt3L binds to it cognate tyrosine kinase receptor Flt3 and activates JAK/STAT signaling pathway.Flt3L is a hematopoietic four helical bundle cytokine with structurally homologous to stem cell factor (SCF) and colony stimulating facor 1 (CSF-1) demonstrated four conserved cysteines and two glycosylation sites. Flt3L naturally as a non-disulfide-linked homodimer with multiple isoforms. The extracellular portion is approximately 160 amino acid residues in length and the cytoplasmic segment is approximately 20-30 amino acid residues in length.