Recombinant human Flt3 ligand exerts both direct and indirect effects on hematopoiesis.
OBJECTIVE
To investigate the direct effects of the Flt3 ligand (FL) on hematopoiesis, such as the stimulation of the formation of hematopoietic colonies and the proliferation of dendritic cells, as well as the indirect stimulation of hematopoiesis, especially via the proliferation of endothelial cells.


METHODS
Mononuclear cells from human cord blood were plated in methylcellulose medium containing different cytokines to induce hematopoietic colony formation. Dendritic cells (DCs) were induced from the mononuclear cells with a cytokine cocktail with or without recombinant human soluble FL (rhFL; 100 ng/ml). The Flt3 receptors on the surface of a human microvascular endothelial cell line (ECV) were analyzed by flow cytometry. The proliferation of ECV stimulated by rhFL was measured with the microculture tetrazolium assay. The levels of FL, IL-6, IL-8, G-CSF and GM-CSF in the supernatant of ECV cultures were measured by enzyme linked immunoabsorbent assay (ELISA).


RESULTS
rhFL stimulates colony formation from cord blood when used as a sole stimulant. FL in combination with other cytokines increased colony formation significantly. The number of DCs was approximately 2.5 times higher when rhFL was used. rhFL stimulates the proliferation of ECV on which Flt3 receptors are expressed. Furthermore, ECV secretes FL, IL-6, IL-8, G-CSF and GM-CSF, which were augmented by tumor necrosis factor-alpha and rhFL.


CONCLUSIONS
rhFL enhances hematopoietic colony formation and DC proliferation from human cord blood cells. FL not only stimulates the proliferation of ECV, but is also secreted by ECV. FL may exert direct and indirect effects on hematopoiesis.
Xu
Zhixiang
Z
Department of Immunology, Medical Biotechnology Institute, Suzhou Medical College, Suzhou 215007, China.
Xu
Ying
Y
Zhu
Jiankun
J
Shi
Qin
Q
Li
Ying
Y
Zhang
Xueguang
X
D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D003713:Dendritic Cells / Q000166:cytology / Q000187:drug effects / Q000276:immunology; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D005312:Fetal Blood / Q000166:cytology / Q000187:drug effects; D006410:Hematopoiesis / Q000187:drug effects*; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000187:drug effects; D006801:Humans; D016130:Immunophenotyping; D008565:Membrane Proteins / Q000494:pharmacology*; D011994:Recombinant Proteins / Q000494:pharmacology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D008565:Membrane Proteins; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; C084881:flt3 ligand protein; D003907:Dexamethasone