14 - THE ACQUISITION OF IMMUNITY BY THE FETUS

Abstract

This chapter discusses the acquisition of immunity by the fetus. It also discusses anatomical transport pathway. There are two possible pathways that IgG, synthesized in the mother, might use as routes to reach the fetal tissue. As the fetus is entirely surrounded by the chorionic vesicle, both routes commence by crossing the trophoblastic epithelium. The first possibility involves the antibody entering the network of capillaries within the cores of chorionic villi and passing via cotyledonary, chorionic and umbilical vessels to the circulatory system of the fetus. The second suggested route is from the connective tissue matrix in the chorionic villus tree across the chorionic plate of the placenta into amniotic fluid. In this hypothesis amniotic fluid would then be swallowed by the fetus. Thereafter, antibodies in amniotic fluid might pass across the intestinal epithelium and so reach the body of the fetus. The latter part of this route is analogous to the neonatal trans-enterocyte transport of antibodies that occurs in the rat. The chapter highlights that the second of these two theoretically possible routes does not seem to be of any major significance in the human because children born with esophageal atresia do not on average have lower serum antibody levels than other children.