Transitory accumulation of myeloid-derived suppressor cells in neonates is critical for maintenance of homeostasis

Myeloid-derived suppressor cells (MDSC) are potent negative regulators of immune responses at many pathological conditions. It is widely accepted that these cells are not present under steady state condition. Here, we report that MDSC with highly potent ability to suppress T cells accumulate during first two weeks of life in mice. MDSC suppressive activity in neonates was triggered by lactoferrin, a component of milk, and mediated by nitric oxide and up-regulation of PGE2 regulated by S100A9/A8 proteins. Newborn MDSC had transcriptome similar to that of tumor MDSC. However, they had strong up-regulation of antimicrobial gene network. This was associated with enhanced antimicrobial activity of these cells. MDSC played a critical role in control of experimental necrotizing enterocolitis in newborn mice. In humans, MDSC in cord blood of low-weight preterm infants prone to the development of NEC had significantly lower suppressive activity than the cells from cord blood of infants with normal weight. Thus, transitory presence of MDSC after birth is critical for the maintenance of immune homeostasis. RNA-seq on PMN-MDSC and M-MDSC cells from adult and neonate mice