ROLE OF UMBILICAL VEIN ENDOTHELIAL-CELLS IN HEMATOPOIESIS

Effective hematopoiesis is usually induced by interactions between hem atopoietic progenitor cells (HPC) and stromal cells. In cord blood (CB ), umbilical vein endothelial cells (HUVEC) can support HPC as a strom al microenvironment. EC activated mainly by IL-1 and TNF alpha produce a variety of cytokines and growth factors such as IL-1, IL-4, IL-6, G M-CSF and G-CSF. Since HPC express c-kit on their surface, the SCF pro duced by HUVEC plays an important role in the hematopoiesis of CB. WE examined the expression of cytokines and growth factors on HUVEC by PC R. Resting HUVEC expressed high level of SCF, and low levels of IL-6, IL-7, and IL-8. Thus, a. variety of cytokines and growth factors are p roduced by EC, and this cytokine network is thought to play an importa nt role in regulating hematopoiesis. Activated EC can also express var ious adhesion molecules including E-selectin, VCAM-1 and ICAM-1, and f acilitate the adhesion of hematopoietic cells to the endothelium. Furt hermore, the interaction of CB cells with HUVEC has recently been show n in vitro. We previously showed that the culture media of HUVEC induc ed high numbers of colony formation. Suitable cytokine productions are thus provided to HPC by the interaction of HUVEC and cord MNC. On the basis of these findings, several mechanisms to support hematopoiesis in CB can be considered. Specific growth factors produced by EC bind t o HPC to induce proliferation. While cell-cell interactions involve ad hesion of HPC to HUVEC via adhesion molecules, and the adhesion of HPC to EC will facilitate interaction with cytokines and growth factors. Thus HPC in CB proliferate and are maintained by growth factors, and a dhesion molecules produced by HUVEC, and HPC themselves.