RelB and C/EBPα critically regulate the development of Peyer's patch mononuclear phagocytes.

To establish protection against harmful foreign antigens, the small intestine harbors guardian sites called Peyer's patches (PPs). PPs take up antigens through microfold (M) cells and transfer them to the sub-epithelial dome (SED), which contains a high density of mononuclear phagocytes (MPs), for T cell-priming. Accumulating evidence indicates that SED-MPs have unique functions other than T cell-priming to facilitate mucosal immune responses; however, the crucial factors regulating the functions of SED-MPs have not been determined. Here we performed transcriptome analysis, and identified the gene signatures of SED-MPs. Further data interpretation with transcription factor (TF) enrichment analysis estimated TFs responsible for the functions of SED-MPs. Among them, we found that RelB and C/EBPα were preferentially activated in SED-MPs. RelB-deficiency silenced the expression of IL-22BP and S100A4 by SED-MPs. On the other hand, C/EBPα-deficiency decreased the expression of lysozyme by SED-MPs, resulting the increased invasion of orally administered pathogenic bacteria into PPs and mesenteric lymph nodes. Our findings thus demonstrate that RelB and C/EBPα are essential to regulate the functions of SED-MPs.