No IL-18BP? Avoid HAV

Fulminant viral hepatitis occurs in a very small number of infected individuals. Until now, the basis for this phenotype has remained unknown. In this issue of JEM, Belkaya et al. (https://doi.org/10.1084/jem.20190669) identify a deletion in the IL18BP gene in a severely affected child that results in excessive natural killer cell activation and uncontrolled killing of hepatocytes.