NK cells maintain a motile behavior during priming in the LN. Ncr1^GFP/+ × CD11c-YFP mice were injected intravenously with poly I:C. At various time points, popliteal LNs were imaged by 2-photon microscopy. Mean velocities (A) and straightness indexes (B) were calculated for individual NK cells at various time points after poly I:C injection. Low straightness indexes indicate constrained trajectories. Mean values are shown as black bars. (C) Representative NK-cell trajectories corresponding to 5 minutes of imaging measured at the indicated time period after poly I:C injection. Results are from at least 5 representative videos obtained in 3 independent experiments. **P < .01 (Mann-Whitney test).