Intracellular IL-1 receptor antagonist type 1 inhibits IL-1-induced cytokine production in keratinocytes through binding to the third component of the COP9 signalosome.

The IL-1 receptor antagonist (IL-1Ra) exists in four isoforms, three of which lack signal peptides and are primarily intracellular proteins. The biologic roles of the intracellular isoforms of IL-1Ra have remained unknown. The objective of these studies was to determine whether the major intracellular isoform of IL-1Ra 18-kDa type 1 (icIL-1Ra1), mediated unique functions inside cells.