Labeling cells with labeling antibodies and imaging with a fluorescent microscope is a staple technique in the Simon Lab. Our development of microfluidic flow chambers has allowed us to probe signaling pathways using fluorescent reporters in living neutrophils. In this technique, a neutrophil rolling on inflamed endothelial cells (or a substrate coated with similar adhesion molecules) is recorded in a rapid sequence of individual fluorescent images. For example, we have imaged the subcellular location of high affinity integrins in neutrophils migrating on endothelial cells, and found that the integrins redistribute on the cell surface following arrest, guiding the direction of migration.