bio

Immune tolerance

A body's ability to accept the presence of a foreign organism or tissue without mounting a destructive attack on it — while keeping its defenses against everything else intact. It is the first hurdle any endosymbiont must clear, because the immune system is built precisely to find and destroy that kind of intruder. Earth solves it several ways — the squid switches off a chemical defense, a mammalian pregnancy tolerates half-foreign tissue for months.