Figure 6.

Prf1^−/− CD8⁺ T cells attach to cyst-containing cells but do not invade into or destroy cysts. Nude mice were infected with 20 cysts of the ME49 strain of Toxoplasma gondii and treated with sulfadiazine beginning at 9 days after infection to establish a chronic infection by forming cysts in their brains. CD8⁺ T cells (4.2 × 10⁶ cells) purified from the spleens of infected wild-type (WT) and Prf1^−/− mice were injected intravenously from a tail vein. At 2 to 3 days after the T-cell transfer, their brains were applied for immunohistochemical staining for T. gondii (brown), CD3 (red), and granzyme B (GzB; green). A: Left panel: Attachment of Prf1^−/− CD8⁺ T cells on a cyst-containing cell. Right panel: A cyst surrounded by the materials positive for granzyme B located outside of the cyst wall in the brain of the Prf1^−/− CD8⁺ T-cell recipient. B: A destroyed cyst associated with the granular structures positive for granzyme B in the brain of the WT CD8⁺ T-cell recipient. Original magnification, ×400 (A and B).