The postnatal immune system shows certain functional impairment, yet priming during a short time window after birth can have lifelong effects on the immune system. In Nature Communications, Hornef and colleagues characterize the mucosal immune system of neonatal mice. Systematic analysis of leukocytes in the gut shows that myeloid populations are already stably present at birth, whereas thymus-derived T cells appear as a spike after 2 days. A subsequent spike in T cells then occurs around weaning. The presence of these T cells is independent of signaling via TLRs and TCRs and does not require the gut microbiota. Functional and transcriptomic analysis shows these neonatal T cells to be in a relatively inactive state. This unresponsiveness is maintained by both regulatory T cells (Treg cells) and the sequestration of antigens from the neonate by maternal IgA ingested during breastfeeding. This study therefore sheds light on active mechanisms that mediate neonatal suppression of T cells.

Nat. Commun. (21 July 2015) doi:10.1038/ncomms8725