A non-invasive imaging for the in vivo tracking of high-speed vesicle transport in mouse neutrophils

Neutrophils play an essential role in the innate immune response. To understand neutrophil activity, the development of a new technique to observe neutrophils in situ is required. Here, we report the development of a non-invasive technique for the in vivo imaging of neutrophils labeled with quantum dots, up to 100 mm below the skin surface of mice. Upon inflammation neutrophils began to extravasate from blood vessels and locomoted in interstitial space. Most intriguingly, the quantum dots were endocytosed into vesicles in the neutrophils, allowing us to track the vesicles at 12.5 msec/frame with 15-24 nm accuracy. The vesicles containing quantum dots moved as diffuse-and-go manner and were transported at higher speed than the in vitro velocity of a molecular motor such as kinesin or dynein. This is the first report in which non-invasive techniques have been used to visualize the internal dynamics of neutrophils.