IRF8 regulates lymphoid-myeloid lineage priming and commitment defined by an IRF8-EGFP reporter mouse (P4374)

Abstract

Abstract IRF8 is a transcription factor critically involved in the differentiation of dendritic cells (DCs) and B cells. IRF8 is expressed in early hematopoietic progenitors, but it is not clear how IRF8 promotes these progenitors to commit to one lineage while preventing the development of alternative lineages. To better understand the functions of IRF8, we generated an IRF8-EGFP reporter mouse by replacing the stop codon of the Irf8 locus with the EGFP sequence. Flow cytometric analyses revealed progressive increases in expression of IRF8-EGFP from hematopoietic stem cells to progenitors destined to the granulocyte-macrophage pathway and to the common lymphoid progenitor pathway but not to the megakaryocytic-erythroid progenitor pathway. Cells committed to the B lineage expressed high levels of IRF8-EGFP, which is in sharp contrast with thymic T cells that expressed negligible levels of IRF8-EGFP. Unexpectedly, IRF8-EGFP expression in pre-pro-B cells was extremely heterogeneous, ranging from background to 4 logs above background. Furthermore, we identified an IRF8-EGFPbri population that expresses B220 with the potential to generate B cells, plasmacytoid DCs and myeloid cells in vivo. Finally, DC progenitors including common DC progenitors and pre-cDCs were marked by extremely high expression of IRF8-EGFP. Taken together, these data revealed a sequential expression pattern of IRF8-EGFP in early hematopoietic progenitors coinciding with lineage priming and commitment.