Last update:
10-May-2010

Immaturity of the neonatal immune system has been suggested in the past as the factor underlying the high rates of morbidity and mortality from infections in newborn infants and the impairment of the neonatal immune response to most vaccines. A biased TH1/TH2 differentiation favoring TH2- rather than TH1-polarization has been incriminated in the susceptibility of newborns to allergic reactions and microbial infections, respectively. Over the last decade, increasing evidence has been produced which indicates that the neonatal immune system has been shaped to accommodate the abrupt transition of the newborn infant from a sterile intrauterine environment into a world rich in foreign antigens, with the concomitant avoidance of harmful inflammatory responses. At the same time, neonatal immunity appears to have a high degree of plasticity and flexibility, allowing mature responses when the infant is faced with life-threatening infectious agents. Deviations from this equilibrium are responsible for many aspects of neonatal mortality. Improving the understanding of neonatal immune function, provides the possibility of developing targeted therapeutic interventions against infections, allergies and other pathological mechanisms related to intrauterine inflammation. In addition, the documented ability of newborn infants to achieve mature immune functions under certain conditions of antigen exposure has provided incentive for the development of novel approaches to enhancing the efficacy of neonatal vaccination.

Key words: Breastfeeding, Endotoxin tolerance, Hygiene hypothesis, Maternal antibodies, Neonatal immune system, Vaccines.