STOCKHOLM — Mary E. Brunkow, Fred Ramsdell and 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 Center at Osaka University in Japan.

The immune system has many overlapping systems to detect and fight bacteria, viruses and other bad actors. 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.

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