ABSTRACT
In addition to acting as a barrier by limiting transfer of potentially damaging cells and molecules to the fetus, the trophoblast layers serve to protect the fetus from the maternal immune system. The two main mechanisms involved are production of various molecules with immunosuppressive properties (i.e., progesterone, estrogens, cytokines, and chemokines) and production of nonclassical major histocompatibility complex (MHC) molecules (e.g., HLA-G) that are thought to inhibit activities of natural killer (NK) and T cells in the decidua. Thus, the trophoblast is capable of limiting the effectiveness of the maternal immune system in both recognizing and attacking the conceptus.
