IL18 and macrophage activation syndrome: Because Pearson correlation coefficient test indicated the positive correlation between serum KL-6 and IL-18 levels (r = 0.997, P <0.01) (Fig. 2b), we speculated that the leading cytokine may be IL-18 in sJIA-MAS, TNF-α in JSLE-MAS, and IL-6 in JDM-MAS, respectively.