IL1R1 and cryopyrin-associated periodic syndrome: Rilonacept (Arcalyst®), a soluble decoy receptor composed of the extracellular domains of IL-1R1 and IL-1RAcP fused to a human IgG1 Fc domain, is an interleukin-1 blocker indicated for the treatment of CAPS, namely, Familial Cold Autoinflammatory Syndrome (FCAS) and Muckle–Wells Syndrome (MWS) in adults and in children at least 12 years old.