Does the Maternal Immune System Regulate the Embryo’s Response to External Toxins?

The maternal immune system, in addition to regulating embryonic development, may determine the tolerance of the embryo to environmental teratogens1 and other toxins. In the first edition of this book, we described some of the mechanisms determining the susceptibility of the embryo to teratogens, and the possible mechanisms whereby immune responses may affect the ability of the embryo to resist teratogenic insults. Chapters 11 and 12 describe the malformations affecting human fetuses which can present as miscarriage and possibly recurrent miscarriage. Chapter 11 shows examples of early embryos which cease development due to major malformations which are incompatible with life. Some of these early fetal demises can only be diagnosed by embryoscopy, and not by conventional techniques such as ultrasound. Philipp et al.2 have reported that 30% of these malformed embryos are eukaryotypic. There are few explanations as to why these malformations may occur. In addition, Chapter 3 describes the genetic factors responsible for recurrent pregnancy loss. Today we know that there are compounds which affect genetic integrity such as ionizing radiation, and Bisphenol A (used to make certain plastics and epoxy resins). However, in the last five years, there have been few reports of the mechanisms whereby immune responses may affect the embryo’s resistance or susceptibility to teratogens and other toxins. Therefore, further studies are necessary in order to determine whether the knowledge accumulated so far will have clinical applications allowing targeted therapies to be developed, which will increase the embryo’s resistance to those agents.