Rac1 and Rac2 are required for T-cell homing to T-cell areas of LN and spleen. (A, B) LN cells from mice of the indicated genotypes were mixed with LN cells from B6.SJL (Ly5.1⁺) mice at a 1:1 ratio and transferred intravenously into C57BL/6 recipient mice. Cells were harvested from the blood, PLN, MLN, and spleen either 1 hour (A) or 20 hours (B) after transfer. Graphs show mean ± SEM homing ratio of EYFP⁺ to Ly5.1⁺ T cells in the recovered cells normalized to the ratio of EYFP⁺ to Ly5.1⁺ T cells in the cells injected into the mice. Data in panel A are from 3 independent experiments (numbers of mice; PLN and spleen: WT, 18; DKO, 20; blood and MLN: WT, 6; DKO, 7). Data in panel B are from 6 independent experiments (numbers of mice: WT, 35; Rac1^T, 28; Rac2^−/−, 25; DKO, 27). *P < .05; **P < .01; ***P < .001. (C) CMTMR-labeled WT and CFSE-labeled DKO T cells were mixed (1:1 ratio), injected intravenously into C57BL/6 recipient mice (n = 3), and cells harvested from blood, spleen, and LNs 1 hour after transfer. Graph on left shows mean ± SEM homing ratio of DKO to WT T cells in the organs indicated, defined as the ratio of DKO to WT T cells in the recovered cells normalized to the same ratio in the injected cells. Images show immunofluorescence staining of section of spleen or LN from the recipient mice 1 hour after transfer with transferred WT and DKO T cells identified in red and green, respectively. Blue shows staining with anti-PNAd to identify HEV in LNs and anti-Madcam1 in spleen to identify the boundary between red and white pulp. Graph on right shows mean ± SEM ratio of DKO to WT T cells found either within or outside the HEV of LNs and in the red and white pulp of the spleen (15 different areas imaged/organ).