By Heidi Ledford
A human fetus in its second trimester is extraordinarily busy. It is developing skin and bones, the ability to hear and swallow, and working on its first bowel movement. Now, a study published on 14 June in Nature finds that fetuses are also acquiring a functioning immune system — one that can recognize foreign proteins, but is less inclined than a mature immune system to go on the attack (N. McGovern et al. Nature http://dx.doi.org/10.1038/nature22795; 2017).
The results add to a growing body of literature showing that the fetal immune system is more active than previously appreciated. “In general textbooks, you see this concept of a non-responsive fetus is still prevailing,” says immunologist Jakob Michaelsson at the Karolinska Institute in Stockholm. But the fetal immune system is unique, he says. “It’s not just immature, it’s special.”
A developing fetus is constantly exposed to foreign proteins and cells, which are transferred from the mother through the placenta. In humans, this exposure is more extensive than in many other mammals, says immunologist Mike McCune at the University of California, San Francisco. As a result, laboratory mice have proved a poor model for studying the developing human fetal immune system.
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