Notch2, Bcl6, and IRF2 govern differentiation and survival of murine nonclassical monocytes.

Abstract Nonclassical (patrolling) monocytes are a population of monocytes which monitor the vasculature and participate in tissue repair. Though nonclassical monocytes are thought to be developmentally derived from classical monocytes, the mechanisms that control the differentiation of classical monocytes into nonclassical monocytes are still not completely understood. Signaling through the Notch2 receptor appears to trigger development of nonclassical monocytes. Also, the transcription factors C/EBPβ and Nur77 (Nr4a1) are required for nonclassical monocyte development in vivo. We have now identified additional transcription factor requirements for the differentiation and/or survival of nonclassical monocytes in vivo. We find that mice with conditional deletion of Bcl6 in myeloid cells or germline IRF2 deficiency show a severe loss of nonclassical monocytes. Both Bcl6 and IRF2 are induced during the transition from classical to nonclassical monocyte. In vitro culture of myeloid progenitors on stromal cells expressing DLL1, a Notch2 ligand, recapitulates aspects of nonclassical monocyte development seen in vivo, confirming Notch signaling as a key initiating event in the development of nonclassical monocytes. This system allows for the identification of the downstream targets of Notch2 signaling that drive nonclassical monocyte development, as well as the analysis of the impact of other transcription factors on the differentiation and survival of these cells in vivo. We present a model of the steps required for development of murine nonclassical monocytes. Supported by NIH (RO1 AI150297, RO1 CA248919)