Understanding the growth of the fetus in utero from the immunologists’ angle

Abstract

Developmental immunology can be defined as the study of how adaptive host defense blood cells within an individual sequentially respond to repetitive environmental challenges in a way that promotes the health and survival of an individual. According to classical principles an individual becomes immune or protected from re-infection in response to an antigenic encounter during an initial infection. Mature immunological competence is ultimately achieved through cumulative adaptive changes stimulated by exposure to a large repertoire of foreign antigenic material. Since the in utero fetal environment is sequestered from frequent encounters with micro-organisms, the host defense system of the human newborn is inexperienced. This partially accounts for why the human newborn is vulnerable to human microbial attacks during the first 6 weeks of life. Furthermore although many components of the immune system of the fetus are present early in gestation some are immature and do not become fully functional (compared with the activity of immune defenses of adult subjects) until sometime after birth. Despite these limitations fetal host defense systems are capable of active engagement and an immune response does occur when the fetus is infected or immunologically challenged in utero.