Anti-inflammatory antagonist of interleukin-1 family of proinflammatory cytokines such as interleukin-1beta/IL1B and interleukin-1alpha/IL1A. Protects from immune dysregulation and uncontrolled systemic inflammation triggered by IL1 for a range of innate stimulatory agents such as pathogens. Deficient mice still possess other negative regulators of IL1 activity and adapt to excessive IL1 via shedding of IL1R1. Belongs to the IL-1 family.