Irf8 deficiency induces functional, transcriptional and epigenetic reprogramming of cDC1 into the cDC2 lineage

Conventional dendritic cells (cDC) consist of two functionally and phenotypically distinct subsets, cDC1 and cDC2, whose development is dependent on distinct sets of transcription factors. Interferon regulatory factor 8 (IRF8) is required at multiple stages of cDC1 development, but its role in mature cDC1 remains unclear. Here we used XCR1-cre to delete Irf8 in committed cDC1 and demonstrate that Irf8 is required for maintaining the identify of cDC1 but not their survival. In the absence of Irf8, committed cDC1 (“ex-cDC1”) acquired the transcriptional, functional and chromatin accessibility properties of cDC2. This conversion was independent on Irf4 and was associated with decreased accessibility in putative IRF8, Batf3 and composite AP-1-IRF (AICE) binding elements, together with increased accessibility of cDC2 associated transcription factor binding elements. Thus, IRF8 expression by committed cDC1 is required for preventing their conversion into cDC2. Bulk RNA-seq and ATAC-seq was used to compare murine conventional dendritic cells sorted from mesenteric lymph nodes (MLN) in steady state from conditional knockout strains lacking IRF4 and/or IRF8 transcription factors.