CD4 T cells from TLR9 ligand–treated mice show a lower sensitivity to IR-induced apoptosis. (A) A schematic representation of the protocol used for the experiments described here. CD4 T cells were purified from CD45.1 BL/6 mice that were injected with TLR9 ligand (3 intraperitoneal injections of 50 μg/mL on days 1, 3, and 5) or from Thy1.1 (CD90.1) BL/6 mice injected with control ligand. T cells (4 × 10⁶) were mixed at a 1:1 ratio and intravenously injected into congenic CD90.2 CD45.2 BL/6 mice (n = 3). Twenty-four hours after adaptive transfer, mice underwent TBI (300 cGy) or not. (B) Ten days after TBI, the numbers of CD45.1 and CD90.1 cells were determined by flow cytometry by staining spleen cell suspensions with antibodies to CD4, CD45.1, or CD90.1. Data shown are the means (± SD); P values were determined by use of the Student t test; *P < .05; There was not a significant difference in T-cell numbers in non-IR hosts (P > .1).