| Summary: | The immune system functions on two levels: innate and adaptive. Innate immunity is more primitive and forms a rapid early warning system for global immunity. It evolved to protect single and multicellular organisms from danger. The innate immune system depends on a network of "danger" receptors, called pattern recognition receptors (PRRs), which are germ line encoded and recognize many different danger signals. Adaptive immunity develops slowly but delivers precise antigen-specific responses with immunological memory. The innate and adaptive systems are asymmetrically interdependent. The two stages of preeclampsia involve two different immune interfaces with different interactions between different types of trophoblast: invasive (Interface 1) and syncytiotrophoblast (Interface 2). Recognition of the foreign fetus can only occur at Interface 1, and may involve T-regs or a very pleiomorphic interaction between uNK cells and HLA-C on extravillous trophoblast. Pregnancy imposes a substantial systemic inflammatory stress on all gravidas in the second half of pregnancy. This generates many features that are considered to be physiological responses to pregnancy but are best considered as components of an acute phase response, for example, reduced plasma albumin, hypercoagulability, or leukocytosis. Preeclampsia occurs when this response is increased to the point of decompensation. © 2009 Elsevier Inc. All rights reserved.
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