Blockade of inhibitory receptors on disease-mediating T cells induces fatal HLH in Stx11^−/− mice. LCMV-infected Stx11^−/− mice were treated with blocking antibodies directed against PD-L1 and LAG-3 (bAB) or isotype control antibodies (iso) every third day from day 10 to day 22 after infection. (A) Body weight of either isotype (●) or blocking antibody–treated (▴) Stx11^−/− mice was followed (body weight by day 10 was adjusted to 100%). (B) Termination of the experiment due to animal guidelines is displayed as percentage of moribund mice in the 2 mouse groups. (C) Frequency and absolute numbers of GP33-tetramer–positive T cells in the 2 groups of antibody-treated Stx11^−/− mice at day 25 after infection. (D) Frequency and absolute numbers of IFN-γ–expressing CD8 T cells in isotype or blocking antibody–treated Stx11^−/− mice at day 25. Horizontal lines in graphs represent mean values. Data (mean ± SEM) are representative for 2 independent experiments with 3-5 mice per group. *P < .05 (Student unpaired t test). ***P < .001 (Student unpaired t test).