Work Together

Not all bacteria are killers. Gut bacteria help people use the food they eat to their advantage and studies show bacteria may even influence people's behavior. At Ars Technica, John Timmer says this creates a challenge for the immune system, which must learn to kill harmful bacteria while avoiding the helpful strains, though still keeping those good bugs under control. A study recently published in Science describes a way that the gut and the bacteria that live inside it cooperate to keep things under control, Timmer says. Cells in the gut can sense when the bacterial populations are starting to get out of control, and those cells produce a protein called RegIIIγ that kills some of the bugs off, the study says. This keeps the bacteria away from the small intestine, which in turn keeps the immune system calm. "The research started out with a fairly simple observation," Timmer says. "The small intestine, which is covered in tiny, finger-like projections, does not have a physical barrier to prevent bacteria from reaching it. But the bacteria don't manage to get in between the fingers; in fact, they're generally kept a safe distance away from the surface." When they looked at the innate immune system, the researchers found that it has receptors that recognize features common to all bacteria. When they knocked out the innate immune system in a mouse model, as well as the gene for RegIIIγ, the mice started to get bacterial growth near the surface of the intestine, Timmer says. However, RegIIIγ is only effective against gram-positive bacteria, and since the innate immune system keep many different kinds of bacteria under control, the team is continuing its work to look for other proteins that may perform a similar function to RegIIIγ, he adds.