Fundamentals of feto-neonatal immunology and its clinical relevance

The transition from fetal to neonatal life at birth forms an important functional watershed in the developing immune system. In utero, the fetus is exposed to a steady stream of foreign antigens that are derived mainly from the mother, and must down-regulate its immune response to survive. After birth, however, the neonatal immune system is exposed to a new, more diverse set of antigens and must evolve dichotomous responses to contain the micro-organisms on various cutaneous and mucosal surfaces, and at the same time, develop tolerance to other commensal microbes and dietary macromolecules. During this remarkable transition, while some components of the immune system perform at par with adults, immaturity of the other arms results in a developmentally- regulated state of immunodeficiency. This chapter highlights major quantitative and qualitative differences in the innate and adaptive arms of the neonatal and adult immune systems and provides a brief review of the developing mucosal immune system.