Researchers at Yale University have been shifting through gene expression among placental mammals to study how pregnancy evolved, Nature reports.
It notes that researchers suspect that ancient mammals laid eggs like platypuses do, with marsupials in which fetuses hatch from a shelled egg coming along later. Yale's Arun Chavan and his colleagues reported this past summer in the Proceedings of the National Academy of Sciences that when opossum fetuses hatch and hold on to the mothers' uterine lining, an immune response is triggered.
Chavan tells Nature that something similar happens during implantation in placental mammals. By studying the immune responses of rabbits, armadillos, and tenrecs, Chavan and his team found that the immune response that occurs during implantation in placental mammals doesn't include the inflammatory protein interleukin-17 that was present in high amounts in the opossums. He further found that cells lining the uterus suppress it, and since IL-17 usually attracts white blood cells, its suppression likely prevents the embryo from being destroyed. Nature notes that he presented this work at the Society for Integrative and Comparative Biology conference.
"Mammals have figured out a way to keep some aspects of the inflammatory process that are favorable to the fetus, but stop the destructive parts of the response," co-author Gunter Wagner from Yale adds at Nature.