Recombinant Human IL-36Ra/IL-1F5 Protein

Human interleukin-36 receptor antagonist [IL-36Ra; previously IL-1F5 and also named FIL-1 delta (delta), IL‑1HY1, IL‑1H3, and IL-1L1] is a member of the IL‑1 family of proteins (1 ‑ 6). IL‑1 family members include IL-1 beta, IL-1 alpha, IL-1ra, IL‑18 and IL-1F5-F10 (7). All family members show a 12 beta-strand, beta-trefoil configuration, and all family members are believed to have arisen from a common ancestral gene that underwent multiple duplications (7). The human IL‑36Ra/IL‑1F5 gene is in closest proximity to the gene for IL-1ra and is likely a relatively recent duplication of the IL-1ra gene (2, 3). IL-36Ra/IL-1F5 is synthesized as a 155 amino acid (aa) protein that contains no signal sequence, no prosegment and no potential N-linked glycosylation site(s) (2 - 5). Nevertheless, it appears to be secreted as a 17 kDa monomer (5). There is an alternate start site that potentially gives rise to an alternate splice form (5). The translated product, however, has a premature stop codon, resulting in a truncated 16 aa peptide. Human to mouse, full length IL-1F5 has 90% aa identity. Within the family, IL-36Ra/IL-1F5 is 50% aa identical to IL-1ra, and 32%, 31%, 35%, 37%, 32% and 42% aa identical to IL-1 beta, IL-36 alpha/IL‑1F6, IL‑37/IL‑1F7, IL‑36 beta/IL‑1F8, IL‑36 gamma/IL‑1F9 and IL‑1F10, respectively. Cells reported to express
IL‑36Ra/IL‑1F5 include monocytes, B cells, dendritic cells/Langerhans cells, keratinocytes, and gastric fundus Parietal and Chief cells (1, 8). The receptor for
IL-36Ra/IL-1F5 has not been positively identified. Indirect evidence suggests it is IL-1 Rrp2 and/or IL-1 RAcP (9). In either case, activity association with receptor binding is also unclear. It was initially reported to be an antagonist of IL‑36 gamma/IL‑1F9 activity (4, 6). This would be consistent with its hypothesized relationship to
IL‑1ra. Studies, however, find IL-36Ra/IL-1F5 antagonist activity difficult to demonstrate (9).