[Implementation of the intestinal micro flora in the early stage and adequate immunity later on].

The pre and postnatal development of human immunity are remarkably continuous. The feto-placental unit builds up to promote a climate of immune tolerance specifically driven in this way by the maternal immunity. The process of birth triggers the development of the infant's postnatal immunity, in first place through the bacterial colonisation of a sterile intestinal mucosa. The progressive immune response stabilisation at the sub-mucosa level during the first year of life will arise from the interface between the host and its microflora. It will take place progressively and will occur thanks to a variety of successive and complementary very complex immune mechanisms, under the influence of a rich and diversified intestinal microbiotia. Solid scientific arguments allow hypothesising that immune deviances later in life could be the consequence of an inadequate bacterial pressure on the intestinal mucosa at the early stage. A variety of epigenetic modifications taking place in this early stage could account for the deviant programming of later immunity. Each health care provider should acknowledge that some therapeutic and nutritional interventions during the first year of life may interfere with this complex immune development, giving rise to a risk of increasing immune deviancies later on.