Mary E Brunkow, Fred Ramsdell, and Dr Shimon Sakaguchi won the Nobel Prize in medicine on Monday for their discoveries concerning peripheral immune tolerance. Brunkow, 64, is a senior program manager at the Institute for Systems Biology in Seattle. Ramsdell, 64, is a scientific adviser for Sonoma Biotherapeutics in San Francisco. Sakaguchi, 74, is a distinguished professor at the Immunology Frontier Research Centre at Osaka University in Japan.

The immune system has systems to detect and fight viruses. Key immune warriors, such as T cells, get trained on how to spot bad actors. If some instead go awry in a way that might trigger autoimmune diseases, they’re supposed to be eliminated in the thymus, a process called central tolerance. The Nobel winners unravelled an additional way the body keeps the system in check.