Children who developed MAS showed increased ferritin, sCD163, IL-22, IL-18, IL-18 BP, MIG/CXCL9, IL-1β, IL-6, IL-8, IL-10, MCP-1/CCL2, MIP-1α, MIP-1β, TNF, IL-16, M-CSF, and SCF; decreased ADAMTS13 activity, whole blood ex vivo TNF response to endotoxin, and IFN-β (P-value < 0.05) (Fig. 2, Additional file 1: eTable 6, eFigure 4); and more Human Herpes Virus 6 DNAemias (P-value < 0.05) (Table 2). The gene discussed is CCL2; the disease is macrophage activation syndrome.