Peroxide perturbations

Injury triggers invasion of white blood cells into tissues. According to new results from Ji et al. (page 173), PECAM-1, an adhesion molecule on the endothelial cells (ECs) that line blood vessels, does double duty in this invasion process. Direct ligation of PECAM-1 is known to allow neutrophils to crawl between ECs. But, independent of this function in white cell invasion, PECAM-1 is now shown to activate an EC current that may prime cells by loosening their connections.

The messenger that triggers this current is the reactive oxygen species hydrogen peroxide (H₂O₂). Neutrophil-produced H₂O₂ signals increase the EC permeability by inducing cell depolarization and an increase in cytosolic Ca²⁺ concentration, but the mechanism behind these changes remained unknown.

Now, Ji et al. demonstrate...