Transcriptome-based profiling of yolk sac-derived macrophages reveals a role for Irf8 in macrophage maturation.

Recent studies have shown that tissue macrophages (MΦ) arise from embryonic progenitors of the yolk sac (YS) and fetal liver and colonize tissues before birth. Further studies have proposed that developmentally distinct tissue MΦ can be identified based on the differential expression of F4/80 and CD11b, but whether a characteristic transcriptional profile exists is largely unknown. Here, we took advantage of an inducible fate-mapping system that facilitated the identification of CD45(+)c-kit(-)CX3CR1(+)F4/80(+) (A2) progenitors of the YS as the source of F4/80(hi) but not CD11b(hi) MΦ. Large-scale transcriptional profiling of MΦ precursors from the YS stage to adulthood allowed for building computational models for F4/80(hi) tissue macrophages being direct descendants of A2 progenitors. We further identified a distinct molecular signature of F4/80(hi) and CD11b(hi) MΦ and found that Irf8 was vital for MΦ maturation. Our data provide new cellular and molecular insights into the origin and developmental pathways of tissue MΦ.