Neutralization of Tumor Necrosis Factor Activity Shortly After the Onset of Dendritic Cell Hematopoiesis Reveals a Novel Mechanism for the Selective Expansion of the CD14-Dependent Dendritic Cell Pathway

Tumor necrosis factor alpha-stimulated endothelium: an inducer of dendritic cell development from hematopoietic progenitors and myeloid leukemic cells

Especially when exposed to inflammatory stimuli, endothelial cells (EC) have been shown to promote the maturation of monocytes into dendritic cells (DC) and the long-term proliferation of CD34+ cells by constitutive cytokine production and direct cellular contact. We therefore hypothesized that cytokine-stimulated EC would induce hematopoietic progenitor cells to develop into mature dendritic cells. To test this theory, human CD34+ cells derived from cord blood or leukapheresis products were cultured with a monolayer of either interleukin (IL)-1beta, IL-4, or tumor necrosis factor (TNF)-alpha-stimulated human umbilical cord EC. The cells in suspension were analyzed weekly over a period of 6 weeks. IL-1beta supported cell expansion, whereas IL-4 had no effect on cell expansion or DC differentiation. Only TNF-alpha-stimulated EC induced the development of mature, allostimulatory DC with a high expression of CD83, HLA-DR, CD1a, and costimulatory molecules like CD80 and CD86. Acute myeloid leukemia cells from the cell line Kasumi-1 also developed DC-like features when cocultured with TNF-alpha-stimulated EC. Direct contact between endothelial and progenitor cells increased the number of developing DC. Cell cycle analysis and apoptosis studies demonstrated a reduced G2M fraction, an increased S fraction, and a decrease in TNF-alpha-dependent apoptosis of DC developing in the presence of endothelial cells. As shown by electron and confocal microscopic studies, intimate interactions between EC and DC occurred, resulting in the internalization of the developing DC within the EC monolayer and a bidirectional exchange of proteins. We conclude that, via the action of TNF-alpha, inflamed human endothelium can induce CD34+ and leukemic cells to differentiate into dendritic cells.

Distinct signals control the hematopoiesis of lymphoid-related dendritic cells

The molecular and cellular requirements for the development of different populations of human dendritic cells (DC) were studied. Conditions were defined that support DC production from lymphoid progenitors but that fail to induce DC formation from peripheral monocytes. The production of these lymphoid-related DC was severely blocked when hematopoietic progenitors overexpressed Ik7, a mutant dominant-negative Ikaros protein. In contrast, Ik7 did not block the formation of DC in conditions supporting the development of monocyte-derived DC. Furthermore, Ik7 did not block the formation of monocyte/macrophages and enhanced granulopoiesis. One of the molecular mechanisms mediated by Ik7 appears to be down-regulation of the flt3-receptor mRNA. Thus, distinct signals control the formation of DC demonstrating that some aspects of DC diversity are determined in part by distinct molecular cues at the hematopoietic level. (Blood. 2000;95:128-137)