The diagnosis of HLH hasevolved with the introduction, in particular, of new criteriadirectly related to the physiopathology, namely the increaseof the soluble receptor levels of interleukin-2 (IL-2), sCD25,reflection of the hyperactivation of the immunologicalsystem, and decreased cytotoxicity functions of innate immunity cells called Natural killer. Here, IL2 is linked to hemophagocytic syndrome.