Mononuclear phagocytes in neonatal Peyer's patches

The small intestine contains lymph node-like structures termed Peyer’s patches (PP). In adult mice they contain active germinal centers reminiscent of active crosstalk with microbiota. In neonatal mice, however, homeostatic immune activation does not take place. We wanted to test whether immune maturation in neonatal mice is stalled due to a reduced presence or function of antigen presenting mononuclear phagocytes (MNP). Thus we subjected PP MNP of postnatal day (PND) 11 and adult mice to scRNAseq in steady state or after immune activation with the TLR7 agonist R848 that induces type I interferon and TNFa after oral gavage. Our results show an altered subset distribution of MNP in neonatal mice (predominance of cDC1 and cDC2b, reduced proportion of cDC2a) and a reduced potential to take up microorganisms and process/present antigen as well as decreased type I interferon mediated gene expresseion. R848 administration could partly overcome this maturation defect of neonatal MNP by increasing the proportion of CCR7+ mature cDC as well as upregulation of interferon I dependent genes. We used scRNA 3' RNA sequencing product from 10x Genomics to investigate to investigate the landscape of mononuclear phagocytes in neonatal Peyer's patches in steady state and after oral R848 (TLR7 agonist) treatment