The normal value of CD25 is 20%~40%, which is explained below in terms of definition and clinical use. CD25, also known as IL-2 receptor alpha chain, is mainly expressed on the surface of activated T cells, B cells, etc., and is also expressed in Treg cells.FOXP3, as a new member of the forkhead/winged helix family of transcription factors, is specifically expressed in Treg, and is closely related to the differentiation and immunosuppressive function of Treg. Cytokines such as IL-1 receptor antagonist factor, soluble sIL-2R (sCD25), IFN-γ and TNF were found to be increased during the active phase of phagocytic syndrome. Clinically increased soluble CD25 (IL-2 receptor) (≥2400 U/ml) is one of the diagnostic conditions for hemophagocytic syndrome. For specific knowledge consult a hematologist.