The role of breastfeeding in prevention of neonatal infection.

The immune system of the human newborn is of very limited size. It expands rapidly, especially due to the exposure to the gut microflora. Normally the newborn is colonized with microbes from the mother's intestinal flora at and after delivery. The many defence factors of the mother's milk include large amounts of secretory IgA antibodies produced by lymphocytes which have migrated from the mother's gut to the mammary glands. Therefore the SIgA antibodies are mainly directed against the mother's previous and recent gut microflora. Thus breastfeeding modulates the early exposure of the neonate's intestinal mucosa to microbes and limits bacterial translocation through the gut mucosa. This may be a major reason why breastfeeding protects efficiently against neonatal septicaemia, as well as several other infections. The defence factors of the milk prevent infections already at the mucosal level. The transplacentally obtained maternal IgG antibodies protect primarily in tissues and do so at the cost of cytokine-induced clinical symptoms, tissue engagement and high energy consumption.