How helpful gut microbes send signals that they are friends, not foes

The finding in mice may help explain why a body’s immune system doesn’t kill beneficial bugs

bacteria

MICROBE MYSTERY  Segmented filamentous bacteria (green) hook into the gut walls (pink) of many animals, including mice, birds and humans. Why the immune system doesn’t attack these bacteria, as well as other beneficial gut microbes, has been a mystery.

I.I. Ivanov and D.R. Littman/Mucosal immunology 2010

Some gut bacteria really put the hooks into their host — but in a good way.