Stockholm - Two Japanese researchers and an American were Thursday named winners of the 2009 Crafoord Prize for the discovery of two signal substances in the immune system that are linked to autoimmune diseases, the Royal Swedish Academy of Sciences said.

Tadamitsu Kishimoto, Toshio Hirano and Charles Dinarello were cited for "for their pioneering work to isolate interleukins, determine their properties and explore their role in the onset of inflammatory diseases."

The three jointly share the prize, worth 500,000 dollars.

During the 1970s and 1980s they isolated two signal substances - interleukins - in the immune system known as IL-1 and IL-6. The substances are released from white blood cells.

Millions of people suffer from rheumatoid arthritis, the most common form of polyarthritis, the academy said.

Other forms of polyarthritis include juvenile chronic arthritis, gout, psoriatic arthritis and Bechterew's disease.

Research has indicated that sufferers, both children and adults, often have too high concentrations of these substances in their bodies.

In a healthy immune system, IL-1 and IL-6 are important to mobilize protection against bacteria, viruses and other microbes. People with polyarthritis and other autoimmune diseases, such as type 2 diabetes, however have too high concentrations of IL-1 and IL-6, making the immune system run amok.

Special "smart" or targeted drugs can help prevent the immune system from breaking down cartilage and bone, the academy noted.

Kishimoto, 69, is with the Graduate School of Frontier Biosciences at Osaka University, Hirano, 61, is with Osaka University's Graduate School of Medicine, while Dinarello, 65, is attached to University of Colorado School of Medicine in Denver, US.

Swedish King Carl Gustaf was due to present the prizes on May 11 in Stockholm.

The prize was created in 1980 by industrialist Holger Crafoord and his wife Anna-Greta, and was first awarded in 1982 for discoveries in fields not covered by the Nobel Prizes in science.

The prize is awarded for research in the fields of astronomy and mathematics, geosciences, biosciences (especially ecology), and andolyarthritis (rheumatoid arthritis).

In 1964, Crafoord founded the medical company Gambro, where the artificial kidney was developed. (dpa)