March, 2006

After years of study, the laboratory mouse can still surprise.

Hans-Reimer Rodewald at the University of Ulm, Germany, and his colleagues say they have discovered a new organ - a thymus the size of a pin-head - in the necks of mice. Previously, the mouse was thought to have just one
thymus, situated near the heart.

The thymus helps to supply the immune system with T cells, and this unexpected finding raises questions about studies that have used mice with the main thymus removed to investigate, for example, T-cell production in other organs, such as the gut and skin.