In the United States alone, women represent 80 percent of all cases of autoimmune disease.
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Some scientists now think the placenta itself might be the reason why women are so disproportionately affected. In a paper published last week in the journal Trends in Genetics, Melissa Wilson, an evolutionary biologist, along with her colleagues from Arizona State University, put forward an explanation called the “pregnancy-compensation hypothesis.” It suggests that women’s immune systems are engaged in a fierce tug of war with placentas.
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When the placenta grows during pregnancy, the organ sends signals to the mother’s immune system to change its activity so that the mother’s body doesn’t eject the placenta and the fetus. This might even mean turning down the immune system in some ways, or for some periods of time. Turning down the immune system too much, though, risks leaving women sensitive to pathogens, which would also be bad for the fetus. So instead the mother’s immune system ramps up in other ways throughout adulthood.
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[T]he immune system can get too aggressive, too ramped up. It starts looking for things to attack that aren’t dangerous, which is how autoimmune diseases set in.
Read full, original post: A Breakthrough in the Mystery of Why Women Get So Many Autoimmune Diseases