Understanding the complexity of the immune system during pregnancy

Abstract

Progress in our understanding of the role of the maternal immune system during healthy pregnancy will help us better understand the role of the immune system in adverse pregnancy outcomes. In this review, we discuss our present understanding of the 'immunity of pregnancy' in the context of the response to cervical and placental infections and how these responses affect both the mother and the fetus. We discuss novel and challenging concepts that help explain the immunological aspects of pregnancy and how the mother and fetus respond to infection.

Keywords: Immune regulation; macrophages; pregnancy; trophoblast.

Figure 1

The placenta as an immune regulatory organ. Contrary to non pregnant women (A); the presence of the placenta during pregnancy modifies the immunologic response of the mother to microorganisms. The old model (B) conceives the maternal immune system as the major player in response to the fetus and microorganisms (red arrow). Fetal responses (fetus and placenta) are considered limited. The new integrational model takes in consideration the fetal-placental immune response and the maternal immune system as integrated.

Figure 2

Role of the cervix controlling bacterial migration to the upper reproductive tract. A viral infection of the cervix alters the expression and function of TLRs and Defensins, therefore altering the protective role of the cervix.

Figure 3

Role of the placenta as a modulator of fetal and maternal responses. Inflammation at the placenta has a bi-directional effect. Activates the maternal immune system as well as the fetus by creating an inflammatory environment. The inflammatory response may also influence the development of the fetal immune system with important consequences during post-natal age.