Researchers have shown for the first time that the human fetal immune system arises from an entirely different source than the adult immune system. The finding could lead to a better understanding of why many newborns are born with impairments due to toxic overloads from mothers who chose to be vaccinated during their pregnancy.
It also could help scientists better understand how childhood allergies develop, as well as how to manage adult organ transplants, the researchers said. The findings are described in the Dec. 17 issue of Science.
Until now, the fetal and infant immune system had been thought to be simply an immature form of the adult system, one that responds differently because of a lack of exposure to immune threats from the environment. The new research has unveiled an entirely different immune system in the fetus at mid-term that is derived from a completely different set of stem cells than the adult system.
“In the fetus, we found that there is an immune system whose job it is to teach the fetus to be tolerant of everything it sees, including its mother and its own organs,” said Joseph M. McCune, MD, PhD, a professor in the UCSF Division of Experimental Medicine who is a co-senior author on the paper. “After birth, a new immune system arises from a different stem cell that instead has the job of fighting everything foreign.”
The team previously had discovered that fetal immune systems are highly tolerant of cells foreign to their own bodies and hypothesized that this prevented fetuses from rejecting their mothers’ cells during pregnancy.
The adult immune system, by contrast, is programmed to attack anything it considers “other,” which allows the body to fight off infection.
“The adult immune system’s typical role is to see something foreign and to respond by attacking and getting rid of it. The fetal system was thought in the past to fail to ‘see’ those threats, because it didn’t respond to them,” said Jeff E. Mold, first author on the paper and a postdoctoral fellow in the McCune laboratory. “What we found is that these fetal immune cells are highly prone to ‘seeing’ something foreign, but instead of attacking it, they allow the fetus to tolerate it.”