The IL-1 superfamily. The original members of the IL-1 superfamily were IL-1α, IL-1β and IL-1 receptor antagonist (IL-1Ra). IL-1F5, IL-1F6, IL-1F7, IL-1F8, IL-1F9, IL-1F10, IL-18 and IL-33 have been added to this family in recent years owing to their structural homology. NF-HEV, nuclear factor from high endothelial venules. Figure kindly provided by Dr John Sims (Amgen Inc., Thousand Oaks, CA, USA).