Gut Microbiota, Host Gene Expression, and Cell Traffic via Milk.

Contrary to common belief, the human neonate is often born with a nonsterile gastrointestinal tract, suggesting fetal colonization. This has been substantiated by numerous studies showing microbes in meconium. Shortly after birth, the infant is further colonized by microbes that reflect the diet, which in the newborn consists of milk. When fed milk from the mother's breast, the infant derives a set of live microbes that have the capability of colonizing the gastrointestinal tract. This milk also provides a source of enzymes, such as lipase and alkaline phosphatase. Milk also provides a multitude of proteins, microRNAs, and other components that putatively interact with the host intestinal innate mucosal immune system to control infection, modulate intestinal inflammation, and provide signaling to distal sites for the development of adaptive immunity as well as growth and communication with the central nervous system. Colostrum differs from transitional and mature milk by being particularly rich in immunoglobulins as well as leukocytes. Live microbes found in fresh mother's milk may be personalized for her infant and thus provide an impetus for either ensuring delivery of this personalized milk to the infant or, if that is not possible, to develop the means to personalize donor milk or formula.