Interleukin 1 receptor antagonist (IL-1Ra) is an acute-phase protein

J Clin Invest. 1997 Jun 15;99(12):2930-40. doi: 10.1172/JCI119488.


Interleukin 1 receptor antagonist (IL-1Ra) levels are elevated in the blood of patients with a variety of infectious, immune, or traumatic conditions. To examine whether IL1Ra is produced by liver cells with characteristics resembling an acute-phase protein, human primary hepatocytes isolated from liver biopsies and HepG2 hepatoma cells were stimulated with IL-1beta, IL-6, and TNFalpha. IL-1Ra was present in the supernatants of both cells, with production significantly enhanced by IL-1beta, and by the combination of IL-1beta and IL-6. The term IL-1Ra refers to two different proteins encoded by the same gene, but generated by alternative splicing of two different first exons. One isoform is secreted (17-kD sIL-1Ra), and the other isoform remains in the cytoplasm (18-kD icIL-1Ra). By Western blot analysis, the supernatants of human hepatoma (HepG2) cells contained only sIL-1Ra, whereas the lysates contained a novel smaller molecular mass isoform of 16 kD. RT-PCR and ribonuclease protection assay with RNA from HepG2 cells showed that only sIL-1Ra mRNA was expressed, and confirmed the inducing effect of IL-1beta and IL-6. Transfection studies were performed using constructs containing the promoters of either sIL-1Ra or icIL-1Ra coupled to the luciferase reporter gene. The sIL-1Ra promoter was active in HepG2 cells stimulated by IL-1beta and/or IL-6, whereas the icIL-1Ra promoter was inactive. Mutation of binding sites for transcription factors NF-kappaB and/or C/EBP within the proximal sIL-1Ra promoter led to significant decreases in response to IL-1beta and IL-6 in comparison to the wild-type promoter. Electromobility gel shift assays confirmed the presence of NF-kappaB and C/EBP binding sites within the sIL-1Ra promoter, and indicated a significant increase in the binding activities of nuclear proteins from HepG2 cells treated with IL-1beta and IL-6. In summary, sIL-1Ra, but not icIL-1Ra, is produced by hepatocytes, and is regulated by proinflammatory cytokines as an acute-phase protein. In addition, NF-kappaB and C/EBP family members are likely to play important roles in the full expression of IL-1Ra by hepatocytes during inflammatory conditions.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Acute-Phase Proteins*
  • Binding Sites
  • Carcinoma, Hepatocellular
  • Cells, Cultured
  • DNA / chemistry
  • DNA / metabolism
  • DNA-Binding Proteins / metabolism
  • Electrophoresis
  • Humans
  • Interleukin 1 Receptor Antagonist Protein
  • Interleukin-1 / pharmacology
  • Interleukin-6 / pharmacology
  • Liver / metabolism*
  • Liver Neoplasms
  • NF-kappa B / metabolism
  • Polymerase Chain Reaction
  • RNA, Messenger / analysis
  • Sialoglycoproteins / biosynthesis*
  • Sialoglycoproteins / genetics
  • Transfection
  • Tumor Cells, Cultured
  • Tumor Necrosis Factor-alpha / pharmacology


  • Acute-Phase Proteins
  • DNA-Binding Proteins
  • IL1RN protein, human
  • Interleukin 1 Receptor Antagonist Protein
  • Interleukin-1
  • Interleukin-6
  • NF-kappa B
  • RNA, Messenger
  • Sialoglycoproteins
  • Tumor Necrosis Factor-alpha
  • DNA