A US-Japanese trio on Monday won the Nobel Prize in Medicine for research into how the immune system is kept in check by identifying its "security guards", the Nobel jury said.

The discoveries by Mary E. Brunkow and Fred Ramsdell of the United States and Japan's Shimon Sakaguchi have been decisive for understanding how the immune system functions and why we do not all develop serious autoimmune diseases.

Sakaguchi, a professor at the Immunology Frontier Research Centre in Osaka, told Swedish broadcaster Sveriges Radio: "It's an honour for me. I'm looking forward to visiting Stockholm in December" to receive the award in person.

The Nobel committee was however unable to reach the two US-based laureates to break the news to them in person.

"If you hear this, call me," the head of the Nob

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