In the current study, therefore, we investigated the miRNA alterations occurring during MAS using a well-characterized mouse model, in which unmethylated cytosine–guanine dinucleotide (CpG), a Toll-like receptor 9 (TLR-9) ligand, is repeatedly injected into C57BL/6 mice to induce MAS (14). This evidence concerns the gene TLR9 and macrophage activation syndrome.