Umbilical vein endothelial cells are an important source of c-kit and stem cell factor which regulate the proliferation of haemopoietic progenitor cells

The expression and production of c-kit and its ligand, stem cell factor (SCF), in card brood and neonates were studied. Serum SCF levels were significantly higher in cord blood, neonates aged 1-30 d, and in 4-month-old infants than in the maternal serum (P < 0.01). SCF levels decreased in children from 7 months to 15 years of age (P < 0.01). The serum soluble c-kit levels were significantly higher in cord (P < 0.01) and neonatal blood (P < 0.05) than in the maternal blood. SCF and c-kit levels in placental tissue homogenates and the culture media of decidual cells and trophoblasts were low. To determine the sites of high SCF and c-kit production in cord blood and in early neonates, SCF and c-kit mRNA expression was analysed in various tissues by polymerase chain reaction. High SCF mRNA expression was observed in human umbilical vein endothelial cells (HUVEC). Moderate c-kit mRNA expression was detected in HUVEC, the bone marrow, and cord blood. These findings suggest that endothelial cells mainly produce the SCF in cord blood and in early neonates. To confirm the role of endothelial cells in haemopoiesis, colony-forming assays were performed in the presence of HUVEC culture media, which induced the formation of high numbers of granulocyte and erythroid colonies in cord blood. IL-3, IL-6 and SCF levels were elevated in the media. Our findings suggest that endothelial cells have an important role in the maintenance and proliferation of progenitor cells in neonatal blood via the interaction of c-kit and SCF with other factors. The ex vivo expansion of cord progenitor cells in the presence of endothelial cells needs to be investigated further.