Objective: The inhibitory effects of tumor necrosis factor-alpha (TNF-alpha) on cytokine-induced proliferation and differentiation of normal human erythroid progenitors have been characterized extensively, yet little is known about the maturation level of erythroid progenitors that are sensitive to TNF-alpha or of the expression of TNF receptors (TNFRs) in erythroid lineage. The aim of this study was to determine the extent to which human erythroid progenitor cells are sensitive to TNF-alpha, and to relate this to the expression of TNFRs in the erythroid lineage.
Materials and methods: Highly purified human CD34+ cells underwent erythroid differentiation, with or without TNF-alpha. We used colony assay as well as a method by which colony-forming unit-erythroid (CFU-E) and glycophorin A (GPA; a specific marker for erythroid lineage) positive cells can be generated in liquid phase from purified human CD34+ cells in the presence of multiple cytokines, including stem cell factor (SCF), interleukin-3 (IL-3), and erythropoietin (EPO). During erythroid differentiation of CD34+ cells, TNFRs expression were monitored.
Results: TNF-alpha inhibited the generation of GPA+ cells by CD34+ cells as well as the proliferative capacity of GPA+ cells supported by EPO, IL-3, and SCF. Erythroid progenitors became resistant to the inhibitory effect of TNF-alpha as they matured. The detectable expression of TNFR-I was transient in the early phase of erythroid differentiation, whereas TNFR-II was expressed through the entire course of erythroid differentiation of CD34+ cells.
Conclusions: TNF-alpha suppresses erythropoiesis by inhibiting the generation of GPA+ cells derived from CD34+ cells as well as by inhibiting the proliferative capacity of GPA+ cells. Although the presence of TNFRs does not directly indicate that the receptor(s) mediates death signaling, altered expression of TNFRs depending on the level of maturation may imply altered sensitivities to TNF-alpha in various stage of erythroid progenitors.