Monocytes express high amounts of Notch and undergo cytokine specific apoptosis following interaction with the Notch ligand, Delta-1

Notch signaling has been shown to play a key role in cell fate decisions in numerous developmental systems. Using a reverse transcriptase-polymerase c hain reaction (RT-PCR) assay, we reported the expression of human Notch-1 i n CD34+ progenitors. In this study, we evaluated the expression of human No tch-1 and Notch-a protein by hematopoietic cells. In immunofluoresence stud y, we detected low amounts of Notch-1 and Notch-2 protein in both CD34+ and CD34+Lin- cells, high amounts in CD14+ monocytes as well as B and T cells, but no expression in CD15+ granulocytes. We further found that an immobili zed truncated form of the Notch ligand, Delta-1, induced apoptosis in monoc ytes in the presence of macrophage colony-stimulating factor (M-CSF), but n ot granulocyte-macrophage colony-stimulating factor (GMCSF). The widespread expressions of Notch proteins suggest multiple functions for this receptor during hematopoiesis. These studies further indicate a novel role for Notc h in regulating monocyte survival, (Blood. 2000;95:2847-2854) (C) 2000 by T he American Society of Hematology.