Excess IL-18 acts on expanding T cells to drive virus-induced hyperinflammation. (A) Mice were infected with LCMV-Arm and assessed for IL-18R1 expression on splenic CD8⁺ and CD4⁺ T cells. (B) Representative histograms of IL-18R1 expression on splenic NK, CD4⁺CD44⁺, and CD8⁺CD44⁺ T lymphocytes of uninfected mice of the indicated genotypes. (C) Mice of the indicated genotypes were infected with LCMV-Arm and assessed for weight loss, splenomegaly, anemia, and serum IFNg and IL-18. Dashed horizontal lines represent the median values of infected CD4Cre-Il18r1^fl/fl mice. Weight statistical significance compares Il18tg;CD4Cre-Il18r1^fl/fl; and Il18tg;CD4Cre⁺Il18r1^fl/fl mice. Data are representative of 2 independent experiments with a minimum of 3 mice per genotype. *Adjusted P < .05, **P < .01, ***P < .001, ***P < .0001 by unpaired t test on Day 8 values. Significance is only shown for comparisons where adjusted P < .05. Error bars represent SEM.