In the spectrum of MAS/HLH, due to genetic susceptibility, a trigger (infection, auto-immune disease, malignancy) results in excessive activation and expansion of monocytes and macrophages; with high levels of circulating cytokines (IFN-gamma/type II interferon-response); IL-2; IL-1, IL-6, IL-18 and TNF-alpha; and also cytokine inhibitors such as soluble TNF-receptors [10]. This evidence concerns the gene IL18 and infection.