Mary E. Brunkow, Fred Ramsdell and Shimon Sakaguchi won the Nobel Prize in medicine on Monday for their discoveries concerning peripheral immune tolerance.

Brunkow is a senior program manager at the Institute for Systems Biology in Seattle. Ramsdell is a scientific adviser for Sonoma Biotherapeutics in San Francisco. Sakaguchi is a distinguished professor at the Immunology Frontier Research Center at Osaka University in Japan.

Thomas Perlmann, Secretary-General of the Nobel Committee, said he was only able to reach Sakaguchi by phone Monday morning. He left voicemails for Brunkow and Ramsdell.

Peripheral immune tolerance is one way the body helps keep the immune system from getting out of whack and attacking your own tissues instead of foreign invaders.

The award is the first of the 2025 Nobel Prize announcements and was announced by a panel at the Karolinska Institute in Stockholm.

Last year's prize was shared by Americans Victor Ambros and Gary Ruvkun for their discovery of microRNA, tiny bits of genetic material that serve as on and off switches inside cells that help control what the cells do and when they do it.

Nobel announcements continue with the physics prize on Tuesday, chemistry on Wednesday and literature on Thursday. The Nobel Peace Prize will be announced Friday and the Nobel Memorial Prize in economics Oct. 13.

The award ceremony will be held Dec. 10, the anniversary of the death of Alfred Nobel, who founded the prizes. Nobel was a wealthy Swedish industrialist and the inventor of dynamite. He died in 1896.

The trio will share the prize money of 11 million Swedish kronor (nearly $1.2 million).

AP Video shot by Kostya Manekov