Interleukin-18 and cytotoxic impairment are independent and synergistic causes virus-induced hyperinflammation in mice

To determine the effects of excess IL-18 on virus-induced immunopathology, we infected Il18-transgenic (Il18tg) mice with Lymphocytic Choriomeningitis Virus (LCMV, Armstrong). LCMV infection is self-limited in wild-type (WT) mice, but Prf1-/- mice develop prolonged viremia and fatal HLH. LCMV-infected Il18-transgenic (Il18tg) mice developed cachexia and hyperinflammation comparable to Prf1-/- mice, albeit with minimal mortality. We use RNA-sequencing to identify differences in the transcriptome of GP33 - specific CD8 T cells from these mice in comparison to a wild type mouse under the same conditions. We saw expression of Ifng was elevated about 4-fold in both Prf1-/- and Il18tg mice. Genes specifically upregulated in Il18tg CD8 T-cells included Csf2, Il1rl1, and Il12rb2. We also saw differences between Prf1-/- and WT/Il18tg CD8 T-cells that included Klrg1 and transcripts associated with CD8 T-cell exhaustion, including the inhibitory receptors Lag3, Havcr2, and Tigit, and the transcription factors Tox and Prdm1. These data support that IL-18 as a potent, independent, and modifiable driver of life-threatening innate and adaptive hyperinflammation, and support the rationale for an IL-18-driven subclass of hyperinflammation. Overall design: FACS sorted GP33 Tetramer+ CD8 T lymphocytes from day 8 post LCMV-Armstrong infection in Prf1-/-, Il18tg, and C57BL/6 mice