As the immune system battles pneumonia, the outcome of that war may hinge on a microscopic arms race over iron.

Scientists say they have figured out how that race for iron actually increases the risk we face from one of our most dangerous microscopic foes, Klebsiella pneumoniae. They made the discovery in mice with pneumonia.

In a new paper in the journal mBio, researchers found the bacteria sends out tiny iron-scavenging molecules called siderophores, which attach to iron and steal it from us in order to grow and reproduce.

But the research found that K. pneumoniae actually uses its siderophores to help invade the rest of the body beyond their initial point of entry, and to bring on inflammation caused by our own immune system.