Blimp-1 is critical for limiting Th1-mediated inflammation and for IL-10 production in vivo. Wild-type (Prdm1^wt/wtCD4.Cre; WT) or conditional T cell–specific Prdm1-deficient (Prdm1^fl/flCD4.Cre; CKO) mice were infected with 10 cysts of T. gondii or left uninfected (naive). Animals were sacrificed at day 8 after infection for ex vivo analysis. (A) Survival rate of WT and CKO mice after infection. (B) Degree of hepatic inflammation scored by liver histology (left). ***, P = 0.0005. Representative histology staining (H&E staining) of WT and CKO liver sections (right; Bars, 100 µm). Black arrows indicate areas of cell infiltration and necrosis. (C) Abundance of T. gondii DNA in ileal biopsies of naive and infected WT or CKO mice. (D) Serum level of IL-12p70, IFN-γ, and TNF as determined by CBA. From left to right: ***, P = 0.0004; *, P = 0.042. (E) Relative amount of IFN-γ and TNF produced during ex vivo overnight liver organ cultures as determined by CBA. *, P = 0.04. (F) Frequency of CD154⁺ cells among CD4⁺ cells isolated from spleen (spl) or mesenteric lymph nodes (mln) after ex vivo antigen-specific restimulation with TLA measured by flow cytometry. *, P = 0.01. (G) Frequency of IL-10 and IFN-γ producers among CD4⁺CD154⁺ cells after TLA restimulation analyzed by intracellular staining and flow cytometry. *, P = 0.019. (H) Frequency of IL-10⁺ and IFN-γ⁺ cells among CD4⁺ cells isolated from liver, spleen, and mesenteric lymph node was determined by flow cytometry after ex vivo polyclonal restimulation with PMA/ionomycin. From left to right: **, P = 0.0025; **, P = 0.0022; ***, P = 0.0001. (I) Percentage of IL-10–producing cells among CD4⁺ IFN-γ producing (IFN-γ⁺) and nonproducing (IFN-γ⁻) cells after PMA/ionomycin restimulation as determined by flow cytometry. From left to right: **, P = 0.0012; **, P = 0.0042; ***, P = 0.0004; **, P = 0.0027; **, P = 0.0018; *, P = 0.015. (J) Frequency of IL-10⁺ cells among CD4⁺Foxp3⁺ cells isolated from spleen of infected mice after PMA/ionomycin restimulation as determined by flow cytometry. ***, P = 0.001. (K) Frequency of Foxp3⁺ cells among CD4⁺ spleen lymphocytes of infected animals measured ex vivo by flow cytometry. **, P = 0.0021. Data are summarized from two (A, B, D–I; n = 4/group) or three (C; n = 4–5/group) independent experiments, or are representative of two independent experiments (J, K; n = 4/group), respectively. Horizontal bars indicate mean.