Pathological features of HLH reveal abundant infiltration of immune cells, including CTLs and macrophages, along with oversecretion of pro-inflammatory cytokines such as interferon (IFN)-γ, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-10, and IL-18 (29, 30). This evidence concerns the gene IL18 and hemophagocytic syndrome.