Alternative theories: Pregnancy and immune tolerance.

For some time, reproductive immunologists have worked to understand the balance between maternal tolerance of the fetus, maternal health, and fetal protection which leads to successful pregnancy in mammalian species. We have always understood the potential importance of multiple factors, including nutrition, genetics, anatomy, hormonal regulation, environmental insult and many others. Yet, we still struggle to combine our knowledge of these factors and immunology to finally understand complex diseases of pregnancy, such as preeclampsia. Data, and potentially other factors (e.g. politics, economics), support the work to fit pregnancy into classical immune theory driven by the concept of self-non-self-discrimination. However, based on data, many classical theorists call pregnancy "a special case." This review is a first-pass suggestion to attempt to view three models of immune system activation and tolerance as potential alternatives to classical self-non-self-discrimination and to propose a theoretical framework to view them in the context of pregnancy.