Your Alien Baby

Babies are aliens. And I don’t mean metaphorically. I mean that the fetus growing inside the mother—the host—is an alien body within it. “Like a germ. Or an organ transplant,” as Randi Hutter Epstein compares it to in this essay.

Scientists have long wondered why T cells—immune cells that protect the body—don’t attack a growing baby in a mammal’s womb, precisely because it is an independent, foreign organism.

One NYU team did a set of experiments on pregnant mice, discovering that a chemical attaches itself to the placental tissue to change how the actual genes look, which disguises them to T cells. When it comes to humans, one scientist “suspects that a specific protein in pregnant women, called PP13, acts as a decoy of sorts to trick the mom’s immune system to stay away from the baby”.

Better understanding why some foreign or aberrant tissue goes undetected by the immune system and why some doesn’t is fundamental to understanding how the body reacts. Tumors, for instance, are faulty cells that are for some reason not attacked by T cells. Reconsidering the fetus by denaturalizing it has opened up a whole new realm of scientific study.