It revealed that the diagnostic values of the D-Dimer, IgA, and IgM levels and the CD3+, CD4+, CD8+, CD3-CD19+, and NK cell counts were all better than the plasma EBV DNA load and whole blood EBV DNA load, which suggests that the immune function changes after EBV infection are a main factor for the occurrence of EBV-HLH. This evidence concerns the gene CD19 and hemophagocytic syndrome.