Welcome to the quantum science podcast.

Each episode we bring you stories about developments in science and mathematics.

I'm Susan Vallett.

Cells in the placenta have an unusual trick for activating gentle immune defenses

and keeping them turned on when no infection is present.

It involves crafting and deploying a fake virus. That's next.

It's season three of the joy of why, and I still have a lot of questions.

Like, what is this thing we call time? Why does altruism exist? And where is Jan 11? I'm here. Astrophysicist and co-host. Ready for anything. That's right. I'm bringing in the A team. So brace yourselves. Get ready to learn. I'm Jan 11 Levin. I'm Steve Strogatz.

And this is... Quantum Magazine's podcast, The Joy of Why.

New episodes drop every other Thursday.

When you were a child, it seemed like an ingenious plan.

Splash hot water on your face and stagger into the kitchen with a dramatic moan.

It's the playbook from the movie Ferris Bueller's Day Off.

One touch of your flushed forehead would convince your parents to diagnose a fever and keep you home from school.

No matter how elaborately planned and performed,

these theatrics probably weren't as persuasive as you had hoped. But new research published last

summer in cell host and microbe suggests that long before birth, a similar tactic helps developing

humans and other mammals put on a more convincing

show. The study shows how the placenta, the embryonic organ that connects offspring and mother,

uses a molecular trick to feign illness. By pretending it's under viral attack, it keeps the immune

system running at a gentle,

steady pace to protect the enclosed fetus from viruses that slip past the mom's immune defenses.

...