Surprise organ discovered in mice

After a century of scrutinizing the laboratory mouse, one might imagine that scientists would know the creature's body like the back of their own hands. Think again, because German researchers say they have discovered a whole new organ.

The discovery raises questions about some immunology studies in mice. Researchers interested in the immune system often slice out the main thymus of mice in order to study how this system works without it, and how T cells are produced in the gut and skin.

The presence of a second thymus suggests that many of these mice still had a working thymus in their necks, which could have confounded the results. These studies may need to be re-examined, Rodewald suggests: "Some people are not going to like this."