Hydrogen peroxide, the colourless liquid often poured over cuts and scrapes, seems to marshal infection-fighting cells to wounded animal tissue, researchers have found.

Zebrafish are small, colourful fish that reproduce quickly and are often used as a laboratory model in medical research.

In Wednesday's online issue of the journal Nature, researchers in the U.S. said that within minutes of injuring the tail fins of zebrafish, hydrogen peroxide was released from the wound and entered the surrounding tissue.

Teams of white blood cells quickly responded to the chemical signal from the hydrogen peroxide and came to repair the damage.

"We've known for quite some time that when the body is wounded, white blood cells show up, and it's really a spectacular piece of biology because these cells detect the wound at some distance," said Timothy Mitchison, a professor of systems biology at Harvard Medical School.

"We do know something about what summons white blood cells to areas that are chronically inflamed, but in the case of an isolated physical wound, we haven't really known what the signal is."

Disease role

When the experiment was repeated in zebrafish without a working protein known to produce hydrogen peroxide in the human thyroid gland, hydrogen peroxide did not appear at the wound site and no white blood cells showed up.

This proves white blood cells need hydrogen peroxide to sense the wound and move toward it, said study co-author Philipp Niethammer, a postdoctoral researcher in Mitchison's lab.

In humans, hydrogen peroxide is produced mainly in the lungs, gut and thyroid gland. The researchers speculate that hydrogen peroxide might play a role in diseases that involve excess levels of white blood cells, such as asthma, chronic pulmonary obstruction and some inflammatory bowel diseases.

"Perhaps in conditions like asthma, the lung epithelia is producing too much hydrogen peroxide because it's chronically irritated, which, if our findings translate to humans, would explain inappropriate levels of white blood cells," said Mitchison, who plans to investigate the hypothesis.

The research was funded by the U.S. National Institutes of Health.