Vav1^−/− T-cell motility is not susceptible to CD28-mediated regulation. (A) HY-specific CD4⁺ WT and Vav1^−/− T cells that had either undergone antibody-mediated CD28 ligation (30 minutes at 37°C, PKH26-labeled) or had been pretreated with an antibody isotype control (CFSE-labeled) were injected intravenously (10⁷/mouse) into syngeneic female recipients. The presence of fluorescently labeled cells in the indicated organs was assessed 24 hours later as described in the legend to Figure 2. The mean T-cell number plus or minus SEM observed in samples from at least 6 animals are shown (*P < .05, **P < .01). (B-C) HY-specific CD4⁺ WT and Vav1^−/− T cells that had undergone either antibody-mediated CD28 ligation (PKH26-labeled) or had been pretreated with an antibody isotype control (CFSE-labeled) were injected intravenously (10⁷/mouse) into male mice that had received an intraperitoneal injection of IFNγ 48 hours earlier. The presence of fluorescently labeled cells in the peritoneal membrane (B) and cavity (C) was assessed 24 hours later as described in the legend to Figure 3. The mean T-cell number plus or minus SEM observed in samples from at least 3 animals is shown in the right-hand side panels (*P < .05, **P < .01).