The existence of a second thymus in mice has been confirmed

German scientists have discovered a new organ in laboratory mice – a second thymus, located in the nape of the neck. This unexpected information has enriched existing knowledge of mouse anatomy, based on centuries of research, and could have significant implications for research on the immune system. Dr. Hans-Reimer Rodewald of the University of Ulm emphasizes that the presence of this organ could alter the results of previous experiments in which mice were exposed to various factors without taking the second thymus into account. This discovery opens up new avenues of research and raises questions about the thymus's role in the immune system.

After a century of observing laboratory mice, it might seem that scientists know the body of a living creature as well as the palms of their hands. Think again, because German scientists report they have discovered a new organ! As is common knowledge, mice possess a thymus, a pinkish-gray tissue that helps produce infection-fighting T cells of the immune system. This organ is the size of a pea and located in the chest, just above the heart. Now, Dr. Hans-Reimer Rodewald, of the University of Ulm in Germany, and his colleagues have announced the discovery of a smaller, second thymus, hidden in the necks of laboratory mice. " I couldn't believe it for a few months. '2006 wasn't the year I had envisioned for this change in anatomy ,'" Rodewald said.

This discovery raises new questions about immunology in mice. Researchers interested in the immune system often slice up the mouse thymus to test how the system works without it and to learn 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 functioning thymus located in their necks, which could have confounded the study results. It may be necessary to re-examine the mice. However, Rodewald said, some are reluctant to do so .

This discovery isn't as surprising as it might seem. Biologists already knew that other mammals, including some humans, have an extra thymus located in the neck. As early as the 1940s, it was suggested that five out of six human fetuses have a second thymus in the neck. Theories about a second thymus in mice emerged as early as the 1960s.