Tiam1 is required for homing and egress of T cells. (A) T-cell homing: CFDA-labeled WT and CMTMR-labeled Tiam1^−/− naive T cells were mixed and injected intravenously in a WT mouse. Mice were killed 2 hours after transfer and the percentage of labeled cells in different organs was determined. Results are expressed as a homing ratio, corresponding to the ratio between number of Tiam1^−/− and WT cells. Bars are means. All data points are depicted by a dot; P values between WT and Tiam1^−/− T cells are depicted for every organ tested. (B) Representative cryosection of a pLN after a homing experiment performed in panel A. Adoptively transferred WT T cells appear in green and Tiam1^−/− T cells, in red. HEVs (blue) are visualized using MECA-79 Ab. Scale bar represents 20 μm. (C-E) T-cell egress: mixed adoptively transferred CMFDA-labeled WT and CMTMR-labeled Tiam1^−/− T cells were allowed to home to pLNs for 24 hours. Homing was then blocked by Mel-14 Ab injection. Mice were killed 0, 12, and 24 hours after blocking of homing. The relative number of adoptively transferred cells present in pLNs was calculated by FACS analysis. (C) Ratio between the number of Tiam1^−/− and WT cells present in pLNs at different time points. Bars are means. All data points are depicted by a dot. Three independent experiments were performed; P values of 12- and 24-hour time points compared with 0 hours are depicted. (D) Kinetics of WT and Tiam1^−/− cell numbers present in pLNs during the egress assay. Results are expressed as a percentage of the initial population present at time point 0. Three independent experiments were performed. Values indicate mean ± SD; P values: comparison of the relative decrease of WT and Tiam1^−/− T-cell numbers at the same time point. (E) Representative cryosection of a pLN 24 hours after adoptive transfer of WT (green) and Tiam1^−/− T cells (red). HEVs (blue) are visualized using MECA-79 Ab.