Targeted deletion of HIF-1 in myeloid cells of neonatal mice: decreased accumulation of myeloid-derived suppressor cells and altered microbiome

The newborn's immune system is faced with the challenge of having to learn quickly to fight off infectious agents, but tolerating the colonization of the body surfaces with commensals without reacting with an excessive inflammatory response. Myeloid-derived suppressor cells (MDSC) are innate immune cells with suppressive activity on other immune cells that regulate fetal-maternal tolerance during pregnancy and control intestinal inflammation in neonates. Until now, nothing is known about the role of MDSC in microbiome establishment. One of the transcription factors regulating MDSC homeostasis is the hypoxia-inducible factor 1a (HIF-1a). We investigated the impact of HIF-1a on MDSC accumulation and microbiome establishment during the neonatal period in a mouse model with targeted deletion of HIF-1a in myeloid cells (Hif1a (loxP/loxP)LysMCre+). We show that in contrast to wildtype mice, where an extensive expansion of MDSC was observed, MDSC expansion in neonatal Hif1a (loxP/loxP)LysMCre+ mice was dramatically reduced both systemically and locally in the intestine. This was accompanied by an altered microbiome composition and intestinal T-cell homeostasis. Our results point toward a role of MDSC in inflammation regulation in the context of microbiome establishment and thus reveal a new aspect of the biological role of MDSC during the neonatal period.