Regardless of their underlying differences in pathogenesis, one of the features shared by primary and secondary HLH is the excessive production of pro-inflammatory cytokines with IFN-gamma, TNF, IL-1, IL-2, IL-6, IL-10, IL-12, IL-18 and granulocyte macrophage-colony stimulating factor (GM-CSF) representing some of the cytokines most notably elevated (13–16). This evidence concerns the gene IL2 and hemophagocytic syndrome.