| Research Abstract |
Tumor necrosis factor-a (TNF-α) inhibits erythropoiesis and enhances non-erythroid colony formation. The present study examines the nature of these non-erythroid cells and investigates their physiological role in relation to erythroid progenitor cells. Highly purified human CD34^+ cells underwent erythroid differentiation in the presence of multiple cytokines, including stem cell factor (SCF), interleukin-3 (IL-3) and erythropoietin (EPO) with and without TNF-α. We enumerated colony-forming unit-erythroid (CFU-E) and glycophorin A (GPA ; a specific marker for erythroid lineage) positive cells in semisolid phase as well as in liquid suspension culture. The character and roles of co-developing non-erythroid cells in the presence of TNF-α were also analyzed using fluorescent activating cell sorter, enzyme immunohistochemistry and confocal microscopy. TNF-α inhibited the generation of GPA^+ cells and conversely enhanced the generation of GPA cells. The GPA cells were comprised of cells wit
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h excentric cell shape and were positive for HLA class I, HLA class II, CD1a, CD4, CD11c, CD14, CD40, CD80, CD83 and CD86, but not CD3, CD8, CD19, CD20 and CD56, indicating the co-development of dendritic cells (DC) along with erythroid differentiation. Developing DC/DC precursors were detected within 3 days of culture. Only in the presence of TNF-α, CD34^+ cells proliferated by forming aggregates where both GPA^+ and CD11c+ DC/DC precursors were present. During culture period, immature CD11c^+ DC were capable of endocytosing damaged GPA^+ cells. In conclusion, GPA cells co-generated from human CD34^+ cells during erythroid differentiation express DC phenotypes. CD11c^+ DC subset physically and selectively associates with developing immature erythorid cells and damaged self-GPA^+ cells and then obtains and captures self-substances. TNF-α is one of the earliest mediators of the acute phase response of inflammation and/or tissue damage. Therefore, our findings suggest that any acute phase response can facilitate rapid DC development from CD34^+ cells in bone marrow. Less
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