Figure 1.

CD8⁺ immune T cells eliminate pre-existing cysts of Toxoplasma gondii through perforin-dependent cytotoxic activity. Severe combined immunodeficiency (SCID) mice were infected orally with 10 cysts of the ME49 strain of T. gondii and treated with sulfadiazine beginning at 10 days after infection to establish a chronic infection by forming cysts in their brains. A and B: CD8⁺ immune T cells (2.1 × 10⁶ cells) purified from the spleens of chronically infected wild-type (WT) or Prf1^−/− mice were injected intravenously from a tail vein, and 7 days later, amounts of mRNA for bradyzoite (cyst)-specific BAG1 and CST1 and tachyzoite-specific SAG1 (A) and CD3, a T-cell surface marker (B), were measured by real-time RT-PCR in the brains of the recipient animals. C: Amounts of mRNA for interferon (IFN)-γ and effector molecules [inducible nitric oxide synthase 2 (NOS2), immunity-related GTPases M3 (Irgm3), and guanylate-binding protein 1 (Gbp1)] of the IFN-γ–mediated protective immunity to prevent tachyzoite proliferation were also measured by real-time RT-PCR. P values were obtained using t-test, and corrected P values shown in the figure were calculated by multiplying the P values by the number of comparisons performed among three groups. D and E: Immunohistochemical detection of T cells in the parenchyma (D) and a perivascular area (E) of the brains of infected nude mice at 2 to 3 days after a systemic transfer of Prf1^−/− CD8⁺ immune T cells (4.2 × 10⁶ cells). The T cells (positive for CD3) were stained in red. Arrows indicate the representatives of the T cells. Data are expressed as means ± SEM in each group (A–C). ^∗P < 0.05, ^∗∗P < 0.01, and ^∗∗∗P < 0.001. Original magnification, ×200 (D and E).