A hormone known for its involvement in the brain's response to stress also plays a
key role in shielding the developing embryo from its mother's immune system. In
its newly identified function, corticotropin-releasing hormone (CRH) stimulates
the production of a protein previously found to prevent maternal immune cells from
attacking embryonic tissue.
The immune system is primed to reject any cells, even those of an embryo, that
display an immune chemistry distinct from their host's. Yet in most pregnant
women, embryos are spared by a poorly understood mechanism that holds her immune
cells at bay.
Earlier research suggested that the interaction between proteins called Fas and
Fas ligand (FasL) keeps potentially dangerous maternal immune cells safely away
from the embryo (SN: 6/14/97, p. 371). Fas resides on the surface of immune cells
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