Inhibition of human colony-forming-unit erythroid by tumor necrosis factor requires accessory cells

Recombinant tumor necrosis factor (rTNF) inhibits erythropoiesis in vivo and in vitro. To study the mechanism of this inhibition, the effect of rTNF on highly purified human CFU-erythroid (E) (mean purity 63.5%), which were generated from peripheral blood burst-forming units-erythroid (BFU-E), was compared to its effect on unpurified human marrow CFU-E (mean purity 0.21%). Although growth of colonies from marrow CFU-E was inhibited by rTNF, no significant effect on purified BFU-E-derived CFU-E colony growth was found. Removal of accessory marrow cells by soy bean agglutinin (SBA) ablated the inhibition of marrow CFU-E colonies by rTNF. Inhibition of colony growth was then restored by adding back SBA+ cells, but not by adding T lymphocytes or adherent cells. Conditioned medium prepared from bone marrow mononuclear cells stimulated by rTNF inhibited the growth of colonies from highly purified BFU-E derived CFU-E resistant to direct inhibition by rTNF. These findings indicate that rTNF does not directly inhibit CFU-E, but requires accessory cells to decrease erythropoiesis. These accessory cells reside in the SBA+ cell fraction, but are neither T cells nor adherent cells. Therefore, in order to produce anemia, TNF must induce release or production of a factor that directly inhibits erythroid colony growth.