TNFα as a Physiological Regulator of Hematopoietic Progenitor Cells：Increase of Early Hematopoietic Progenitor Cells in TNFR55--／-mice in vivo and Potent Inhibition of Progenitor Cell Proliferation by TNFα in Vitro

Murine lineage marker (Lin)^--Sca-1^+c-kit^+and Lin^-Sca-1^-c-kit^+ cens represent the primitive hematopoietic stem cells (HSC)and coommitted hematopoietic progenitor cells(HPC),respectively. The number of Lin^-Sca-1^+c-kit^+HSCs in bone marrow was significantly increased (2.9folds) in tumor necrosis factor(TNF)-receptor-55(TNF-R55)-deficient mice compared with that of wildtype ones without marked change in cellularity of bone marrow.