Unhurried NK cells

Naive T cells race around lymph nodes in search of their specific antigens but, according to a study on page 619, natural killer (NK) cells are in less of a hurry. Bajénoff and colleagues provide the first glimpse of NK cells in live lymph nodes, revealing slow moving cells that form long-lasting contacts with dendritic cells (DCs).

In recent years, intravital imaging has shown that T cells dart rapidly around lymph nodes in search of their rare cognate antigens, making fleeting contacts with DCs as they go. An encounter with a cognate antigen delivers a stop signal that triggers stable T cell–DC interactions, during which the T cell presumably receives activating signals.

Bajénoff and colleagues used the same technology to show that NK cells move at a more leisurely pace than T...