From The New York Times:
Researchers have long wondered how pregnant women might shape their fetuses’ development — by protecting them against later disease, perhaps, or instilling an appreciation of Mozart. Now a group in California has discovered a surprising new mechanism by which women train their fetuses’ budding immune systems: the mother’s cells slip across the placenta, enter the fetus’s body and teach it to treat these cells as its own. A crucial task of the developing immune system is to learn to distinguish between foreign substances and the self. It is tricky: the system must respond to outside threats but not overreact to harmless stimuli or the body’s own tissues.
The new findings show “how Mom is helping to tune that whole system early on,” said William J. Burlingham, an immunologist at the University of Wisconsin, who is not connected with the research. “It’s a major advance, very new and very exciting.” The work could have relevance to research on topics as diverse as organ transplantation, mother-to-child transmission of H.I.V. and autoimmune disorders like Type 1 diabetes.