Abstract
Objective: The early window of opportunity describes the timeframe after birth in which essentialinteractions of the immune system and the newly developing microbiota take place. The infant’simmune system has to be reactive to invading pathogens and at the same time tolerant to dietaryantigens. If the mechanisms of defense and tolerance induction are disturbed, the risk of infectionsor allergies is increased.Method: This is a narrative review of the recently published information on the topic of neonatalintestinal development and mechanisms of oral tolerance and summarizes the discussions andconclusions from the 8th Human Milk Workshop.Results: The early postnatal period sets the stage for life-long host-microbiome interaction. In thisearly phase, specific developmental mechanisms ensure physiologic interaction with the devel-oping microbiota. Innate and adaptive immune cells interact in a concerted way to induce anduphold oral tolerance. Factors in human milk can support this induction of tolerance and simul-taneously protect against infection and allergy development.Conclusion: Understanding the developmental mechanisms in this early phase of immune sys-tem development is the first step to develop strategies of pathology prevention. As human milkprotects the infant from infections, and aids to develop a tolerogenic immune response, furtherknowledge on the protective factors in human milk and their effect on the immune system isrequired