MOTHERS AND ALIEN CHILDREN
Exasperated parents may facetiously wonder: 'why don't we kick our kids out?' In fact, that very question has perplexed immunologists for decades! Embryos developing within the womb express antigens from their father that are foreign to the mother's immune system, yet unlike any other graft of foreign tissue, they are not rejected. Chrousos and colleagues report a possible explanation for maternal tolerance in the November issue of Nature Immunology.
Embryo implantation in the uterus, which occurs very early in pregnancy, resembles a localized inflammatory lesion. Mothers who experience recurrent early miscarriages fail to control these immune reactions to their offspring. Researchers at the National Institute of Child Health and Human Development and the University of Crete, Greece, report that production of corticotrophin-releasing hormone (CRH; a hormone released by both the developing early embryo and the maternal endometrium that envelops the womb) induces the expression of a "cell suicide" signal called FasL. When activated lymphocytes, a potential threat to the developing embryo, engage FasL, they are triggered to die. Thus, rejection of the developing embryo by maternal lymphocytes is prevented by the protective FasL shield. Blocking CRH diminished embryo implantation and reduced the number of successful pregnancies. Thus, a potential cause for infertility in women may be due to a lack of CRH to inhibit immune reactions to their fetus.
Pediatric and Reproductive Endocrinology Branch, National Institute of Child Health and Human Development, NIH
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(C) Nature Immunology press release.
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