Activation of Bg1 CD8⁺ T cells in Tie2-LacZ mice. (A) A total of 1.5 × 10⁷ CFSE-labeled splenocytes (corresponding to 3 × 10⁶ CD8⁺ TCR-transgenic T cells) from Bg1 mice were adoptively transferred into C57BL/6 or Tie2-LacZ mice. Mice were killed on day 4 following transfer and cells from blood, spleen, and lymph nodes were analyzed by flow cytometry for CFSE dilution and CD44 up-regulation on CD8⁺ lymphocytes. Representative FACS plots from one representative of 2 independent experiments are shown. (B) Quantification of Bg1 T-cell proliferation. A total of 1.5 × 10⁷ CFSE-labeled Bg1 Thy1.1⁺ splenocytes were injected into C57BL/6 or naive Tie2-LacZ mice. Mice were killed on day 4 following transfer and cells from blood, spleen, and lymph nodes were analyzed by flow cytometry. Values represent mean percentage (± SEM, n = 7; pooled data from 2 independent experiments) of proliferating CD8⁺Thy1.1⁺ cells (*P < .05; **P < .005; ***P < .001).