Abstract
Classical dendritic cells (cDC) are specialized antigen-presenting cells mediating immunity and tolerance. cDC cell-lineage decisions are largely controlled by transcriptional factor regulatory cascades. Using an in vivo cell-specific targeting of Runx3 at various stages of DC lineage development we show that Runx3 is required for cell-identity, homeostasis and function of splenic Esam(hi) DC. Ablation of Runx3 in DC progenitors led to a substantial decrease in splenic CD4(+)/CD11b(+) DC. Combined chromatin immunoprecipitation sequencing and gene expression analysis of purified DC-subsets revealed that Runx3 is a key gene expression regulator that facilitates specification and homeostasis of CD11b(+)Esam(hi) DC. Mechanistically, loss of Runx3 alters Esam(hi) DC gene expression to a signature characteristic of WT Esam(low) DC. This transcriptional reprogramming caused a cellular change that diminished phagocytosis and hampered Runx3(-/-) Esam(hi) DC capacity to prime CD4(+) T cells, attesting to the significant role of Runx3 in specifying Esam(hi) DC identity and function.