Two studies discover new enzyme that acts as a sensor of innate immunity

Published on February 16, 2013 at 6:31 AM · No Comments

Two studies by researchers at UT Southwestern Medical Center could lead to new treatments for lupus and other autoimmune diseases and strengthen current therapies for viral, bacterial, and parasitic infections.

The studies identify a new enzyme that acts as a sensor of innate immunity - the body's first line of defense against invaders - and describe a novel cell signaling pathway. This pathway detects foreign DNA or even host DNA when it appears in a part of the cell where DNA should not be. In addition, the investigations show that the process enlists a naturally occurring compound in a class known to exist in bacteria but never before seen in humans or other multicellular organisms, said Dr. Zhijian "James" Chen.

Dr. Chen, professor of molecular biology and a Howard Hughes Medical Institute (HHMI) investigator at UTSW, is senior author of both studies available online and published in today's print edition of Science. Although the immune-boosting response of DNA has long been recognized, the mechanism underlying that response remained a mystery, he said.

"In his 1908 Nobel acceptance speech, Ilya Mechnikov noted that surgeons in Europe treated patients with nucleic acids - the building blocks of DNA - to boost their patients' immune responses. That observation came four decades before scientists showed that DNA was the carrier of genetic information," Dr. Chen said.

Dr. Chen credits a uniquely biochemical approach for solving the longstanding puzzle. The approach used classical protein purification combined with a modern technology called quantitative mass spectrometry to identify the mysterious compound at the heart of the discovered process.

Under normal conditions, DNA is contained within membrane-bound structures such as the nucleus and mitochondria that are suspended within the cell's soupy interior, called the cytoplasm, he said. DNA in the cytoplasm is a danger signal that triggers immune responses, including production of type-1 interferons (IFN).

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