Human Interleukin 1 family member 7 (IL-1F7), also named FIL-1 zeta, IL-37, IL-1H4, IL-1HL and IL-1RP1, is an anti-inflammatory member of the IL-1 cytokine family. IL-1F7 shares approximately 21%, 24%, and 30% aa sequence identity with mature IL-1 alpha, IL-1 beta and IL-1ra, respectively. Mouse IL-1F7 has not been reported, but human IL-1F7 is active on mouse cells. Five isoforms (IL-1F7a through e) are generated through alternative exon usage and have distinct expression profiles (1‑5). Like IL-1 alpha, IL-1 beta and IL-18, all of the IL-1F7 variants lack a typical signal peptide. The longest IL-1F7 transcript is the basis for the product offered here. This product, also referred to as IL-1F7b, or IL-1F7 isoform 1, is normally generated from a 218 amino acid (aa) proprotein that consists of a 45 aa propeptide plus a 173 aa mature region that is cleaved by caspase-1 to generate the 32 kDa mature form (aa 46-218) (6). IL-1F7 is up-regulated by inflammatory stimuli in peripheral blood mononuclear cells (7). Experimental overexpression of IL-1F7b in vivo limits the inflammatory response and protects mice from colitis and LPS-induced shock (7, 8). Both unprocessed and mature IL-1F7b can form homodimers in solution (6, 7). Although IL-1F7b will bind to IL-18 R alpha with low affinity, this has no effect on IL‑18 receptor activity (4, 6, 9). Alternatively, IL-1F7b will also bind to IL-18 BP, generating a complex that interacts with IL-18R beta. This has the effect of attenuating IL‑18 activity via the IL-18 receptor (9). IL-1F7b can also function intracellularly. Following LPS-induced cleavage of its propeptide, IL-1F7b associates with Smad3 and translocates to the nucleus. This results in a reduction of pro-inflammatory cytokine secretion (10).