H2O2: a chemoattractant?

H2O2 is a relatively stable, rapidly diffusing reactive oxygen species that has been recently implicated as a mediator of leukocyte recruitment to epithelial wounds and transformed cells in zebrafish. Whether H2O2 activates the innate immune response by acting as a bona fide chemoattractant, enhancing chemoattractant sensing, or triggering production of other chemoattractive ligands remains largely unclear. Here, we describe the basic experimental procedures required to study these questions. We present a detailed protocol of the zebrafish tail fin wounding assay and explain how to use it for analyzing leukocyte chemotaxis in vivo. We further outline a method for H2O2 measurement in live zebrafish larvae using the genetically encoded sensor HyPer on a wide-field and a spinning disk confocal microscope. These methods provide a basis for dissecting the role of H2O2 in leukocyte chemotaxis in a vertebrate animal.