FMS-like tyrosine kinase 3 ligand (FLT3L) is an endogenous small molecule that functions as a cytokine and growth factor that increases the number of immune cells (lymphocytes (B cells and T cells)) by activating the hematopoietic progenitors. It acts by binding to and activating FLT3 (CD135) which is found on what (in mice) are called multipotent progenitor (MPP) and common lymphoid progenitor (CLP) cells. It also induces the mobilization of the hematopoietic progenitors and stem cells in vivo which may help the system to kill cancer cells.
FLT3L is crucial for steady-state plasmacytoid dendritic cell (pDC) and classical dendritic cell (cDC) development. A lack of FLT3L results in low levels of dendritic cells.
FLT3L in parasite clearance
FLT3L and its receptor are involved in the mammalian immune response to malaria. In strains of plasmodium, FLT3L was shown to be released from mast cells and cause the expansion of dendritic cells, leading to the activation of CD8+ T cells. The same paper suggested that FLT3L release was caused by stimulation of mast cells with uric acid, produced from a precursor secreted by the plasmodium parasite. .