Hydrogen Peroxide Guides Immune Cells

When tissue is wounded by a cut, immune cells called leukocytes rush hundreds of micrometers to the injury to defend against opportunistic pathogens attempting to start an infection at the site. But how those immune cells find the wound has long kept scientists guessing. A research team led by Philipp Niethammer and Timothy J. Mitchison of Harvard Medical School proposes that a hydrogen peroxide concentration gradient guides immune cells to the wound—at least in the zebrafish they tested but perhaps in other animals, too (Nature, DOI: 10.1038/nature08119). The scientists found that three minutes after they cut zebrafish tail fins, a protein called dual oxidase creates a plume of H₂O₂. "This is the first observation, to our knowledge, of a tissue-scale H₂O₂ pattern, and the first evidence that H₂O₂ signals to leukocytes in tissues," the researchers write. They hypothesize that the H₂O₂ gradient system "evolved to have two useful roles in early responses to epithelial wounding: local killing of invading bacteria and rapid recruitment of phagocytic leukocytes from distant sites."