IL18 and macrophage activation syndrome: The serum IL-18 levels in the AOSD MAS− group were significantly higher than those in the LAHS group (p<0.0001) and the non-LAHS group (p=0.00013), and similarly, the serum IL-18 levels in the AOSD MAS+ group were significantly higher than those in each subgroup of the adult HLH group (vs. LAHS, p=0.00010; vs. non-LAHS, p=0.00023).