Same Enzyme Repairs DNA, Repels Pathogens

An enzyme involved in genome defense has been shown to attack invading pathogens (W-M. Chu et al., "DNA-PKcs is required for activation of innate immunity by immunostimulatory DNA," Cell, 103:909-18, Dec. 8, 2000). Researchers already knew that DNA-dependent protein kinase (DNA-PK) in the nucleus repairs DNA double-stranded breaks created by radiation, but the role of DNA-PK in the cytoplasm was unknown. Testing DNA immunostimulatory (ISS) sequences in mice bred without DNA-PK, scientists at University of California, San Diego, discovered that the enzyme is the key to activating transcription factor NF-*B, leading to the activation of pathogen-attacking macrophages. Mice bred without the DNA-PK failed to mount an immune response against bacteria, viruses, and toxins. The scientists had theorized that the human body's innate immunity, the body's first-line defense system, must react like lower organisms such as bacteria to invading pathogens. But humans don't have...

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