IL-33 is a member of the IL-1 superfamily of cytokines, a determination based in part on the molecules β-trefoil structure, a conserved structure type described in other IL-1 cytokines, including IL-1α, IL-1β, IL-1Ra and IL-18.
IL-33 belongs to the IL-1 superfamily of cytokines, with its identity partly determined by the β-trefoil molecular structure, a conserved structural type present in other IL-1 cytokines including IL-1α, IL-1β, IL-1Ra and IL-18.