IL-18 promotes pro-inflammatory cell death in cytotoxic T-cell responses

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Abstract Hyperinflammation is a life-threatening systemic inflammatory state that complicates 11% of all SIRS cases. Clinical observations have identified several genetic and/or acquired suseptibility factors. Though Perforin-deficiency is the best-studied mechanism of hyperinflammatory susceptibility, several genetic and biomarker discoveries support excess IL-18 is another. However, it remains unclear how IL-18 drives hyperinflammation. We hypothesized that excess IL-18 leads to excess IFN-y that operates, at least in part, at the critical point of T-cell activation known as the immunological synapse (IS). Methods. We observed the effects of IL-18 and IFN-y on three IS parameters: IS duration, cytokine production, and the mode of target cell death. We measured IS duration by live-cell microscopy, and measured cytokine levels in supernatants. We performed experiments in the presence of several cell death inhibitors. In vitro findings were further analyzed in Il18tg and Prf1-/- mice infected with LCMV. Results . Prf deficiency has been shown to increase IS duration and IFN-y production, however, excess IL-18 shortened IS duration but increased IFN-y production. Moreover, excess IL-18 or the use of BMDCs that were pre-exposed to high levels of IFN-y induced RIPK-1 dependent cell death. These data suggest that T-cell IFN-y, amplified by IL-18, acts on target BMDC to promote necroptosis. Correspondingly, in vivo Nec-1 (RIPK-1 inhibitor) dampened inflammation during LCMV infection.