TLR9 and macrophage activation syndrome: We used a previously described murine model of MAS, in which repeated intraperitoneal administration of the CpG-oligonicleotide 1826 (ODN 1826, hereafter referred to as CpG), which acts as a TLR9 agonist, induces features of hyperinflammatory disease, similar to those observed in patients with MAS (Behrens et al., 2011).