The concept of pregnancy makes no sense-at least not from an immunological point of view. After all, a fetus, carrying half of its father's genome, is biologically distinct from its mother. The fetus is thus made of cells and tissues that are very much not "self"-and not-self is precisely what the immune system is meant to search out and destroy.
Women's bodies manage to ignore this contradiction in the vast majority of cases, making pregnancy possible. Similarly, scientists have generally paid little attention to this phenomenon-called "pregnancy tolerance"-and its biological details.
Now, a pair of scientists from the California Institute of Technology (Caltech) have shown that females actively produce a particular type of immune cell in response to specific fetal antigens-immune-stimulating proteins-and that this response allows pregnancy to continue without the fetus being rejected by the mother's body.
Their findings were detailed in a recent issue of the Proceedings of the National Academy of Sciences (PNAS).
"Our finding that specific T regulatory cells protect the mother is a step to learning how the mother avoids rejection of her fetus. This central biological mechanism is important for the health of both the fetus and the mother," says David Baltimore, Caltech's Robert Andrews Millikan Professor of Biology, recipient of the 1975 Nobel Prize in Physiology or Medicine, and the principal investigator on the research.
Scientists had long been "hinting around at the idea that the mother's immune system makes tolerance possible," notes paper coauthor Daniel Kahn, a visiting associate in biology at Caltech, and an assistant professor of maternal-fetal medicine at the University of California, Los Angeles (UCLA). What they didn't have were the details of this tolerance-or proof that it was immune-related.
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