The Impact of Maternal Microbes and Microbial Colonization in Early Life on Hematopoiesis

All body surfaces are colonized by microbes, which occurs through a dynamic process over the first few years of life. Initial colonizing microbes are transferred from the maternal microbiota to the newborn through vertical transmission. Postnatal maturation of the immune system is heavily influenced by these microbes, particularly during early life. Although microbial-mediated education of the immune system is better understood at mucosal sites, recent data indicate that the systemic immune system is also shaped by the microbiota. Bacterial products and metabolites produced through microbial metabolism can reach distal sites, and metabolites derived from the maternal microbiota can cross the placenta and are present in milk. Recent studies show that the microbiota can even influence immune development in primary lymphoid organs like the bone marrow. This review outlines our current knowledge of how the microbiota can impact hematopoiesis, with a focus on the effects of maternal and early-life microbiota.