IL18 and macrophage activation syndrome: The CpG-induced mouse model of MAS has been well established as an appropriate model for ‘subclinical’ MAS, as it recapitulates a number of the pathologies associated with the disease and is worsened by removal of IL-18BP, i.e. the endogenous regulator of IL-18 signalling (Girard-Guyonvarc'h et al., 2018).