Immune reaction to poison gas brings delayed effects.

In the weeks following their poisoning by carbon monoxide gas, some survivors develop concentration problems, personality changes, or sensory impairments. The causes of these neurological symptoms and their delayed onset have perplexed scientists.

Now, researchers at the University of Pennsylvania in Philadelphia have identified a potential explanation: a misguided immune response to a brain protein that's altered by exposure to the invisible, odorless gas. In the immediate aftermath of a poisoning, the right drug might blunt the immune response and prevent delayed symptoms, suggest Stephen R. Thom and his colleagues in an upcoming Proceedings of the National Academy of Sciences.

When the scientists exposed rats to the gas, an abundant brain protein called myelin basic protein underwent chemical changes. Unlike healthy rats, the poisoned ones later couldn't learn to navigate a maze.

The researchers determined that the protein alterations caused immune cells to flood the brain. The immune reaction continued for weeks, suggesting that it could explain the timing of the symptoms' onset.

The researchers also desensitized some rats to the problematic protein by inoculating them with it several times. Indeed, no unusual immune activity followed carbon monoxide exposure in those animals, which also had no trouble learning their way around the maze.