How active immune tolerance makes pregnancy possible

ScienceDaily (2010-07-07) -- How a pregnant body tolerates a fetus that is biologically distinct from its mother has long been a mystery. Now, a pair of scientists 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.
http://www.sciencedaily.com/releases/2010/07/100701103437.htm