The inflammasome next door: characterizing pyroptosis induction in HCV-infected and uninfected bystander cells in vitro

Despite the fact that hepatitis C virus (HCV) can be cured with direct-acting antivirals in >95% of infected individuals, many of these individuals still have evidence of ongoing inflammation and some even go on to develop liver disease in the absence of ongoing infection. Previous work has demonstrated HCV-induced pyroptosis in both infected Huh-7.5 cells and uninfected bystander cells <i>in vitro</i>. Pyroptosis is an important form of inflammatory cell death that has been implicated in the pathogenesis of various viral infections. In HCV-infected cells, it has been unclear which step of the virus life cycle actually triggered pyroptosis. Using various virus constructs, we show here that fully infectious HCV production is required to trigger pyroptosis in infected Huh-7.5 cells. However, in S29 cells, which are 1000-fold less permissive to HCV infection, and express functional RIG-I, viral RNA replication was sufficient to trigger pyroptosis. In order to further understand bystander pyroptosis, we also investigated whether immune cells were influenced or triggered to undergo bystander pyroptosis in the context of HCV. We found that THP-1 cells (monocyte-like cells) undergo pyroptosis when co-cultured with HCV-infected Huh-7.5 cells both in their monocyte state as well as when differentiated into macrophages although this was not the case for Jurkat or Ramos cells. Together, our results help elucidate the trigger for pyroptosis in HCV-infected hepatocyte-like cells and further our understanding of how pyroptosis of infected hepatocytes can influence other cell types, particularly those that are inflammatory in nature, which may contribute to the pathogenesis of HCV.