Interstitial movement of T cells within LNs. Purified WT EYFP⁺ T cells and EYFP⁺ T cells from Rac1^T, Rac2^−/−, or DKO mice were labeled with CFSE or CMTMR, mixed, and transferred into C57BL/6 recipient mice. Interstitial movement of labeled T cells within the popliteal LN was analyzed 15-72 hours later by multiphoton intravital video microscopy. All results are presented as a pair-wise comparison of WT with Rac1^T, Rac2^−/−, or DKO T cells. (A) Scatter plot of mean velocities of individual T cells. Red bar indicates the median of these velocities. (B) Graphs show the mean displacement of T cells as a function of √(time). The slope of this graph was used to determine the motility coefficient, a measure of the ability of a cell to move away from its starting position (Table 1).^6,30  (C) Turning angles of individual T cells measured as the change in direction of movement occurring between successive frames. (D) Top, a cumulative distribution plot of the meandering index (displacement/path length) of T cells of the indicated genotypes. Bottom, the median meandering index (± interquartile range). The meandering index is a measure of the straightness of track. WT v Rac1^T: 13 videos analyzed from 6 independent experiments; WT v Rac2^−/−: 14 videos analyzed from 9 independent experiments; WT v DKO: 7 videos analyzed from 4 independent experiments. *P < .001.