From Nature:
For some people, it just takes a taste of peanut to induce a sudden and possibly fatal allergic reaction. Now researchers have unpicked the mechanism behind this anaphylactic shock, and have managed to protect mice against the condition. Many allergic reactions settle down of their own accord, or respond to antihistamine treatment. Should severe anaphylactic shock kick in, however, the only effective treatment is a quick injection of adrenaline (epinephrine). “The adrenaline contracts blood vessels and increases heart rate, combating low blood pressure. But it doesn’t interfere with the mechanism of the anaphylactic shock.”
That mechanism, however, has been a bit of a mystery. An allergic reaction occurs when an allergen, such as a peanut protein, triggers the release of histamines and other molecules that cause swellings and pain. But the biochemical pathways that then lead to severe anaphylactic shock have been unknown. Previous research in mice, which have a similar immune system to humans, had hinted that extreme amounts of nitric oxide (NO) throughout the body might be responsible. So Brouckaert and colleagues took a closer look. They induced anaphylactic shock in mice in two ways: by injecting a molecule to deliberately lower blood pressure, and by creating an allergic reaction much like that experienced in humans.
By injecting nitric-oxide blockers into some of the mice before attempting to give them anaphylactic shock, the researchers were able to confirm that nitric oxide was indeed the culprit. But, they report in the Journal of Clinical Investigation, it was coming from an unexpected source.
More here.