Administration of neutralizing antibody against rabbit IL-1 receptor antagonist exacerbates lipopolysaccharide-induced arthritis in rabbits

Inflamm Res. 1996 Sep;45(9):479-85. doi: 10.1007/BF02252320.


Endogenous IL-1 receptor antagonist (IL-1ra) may down-regulate part of IL-1 actions. We examined the participation of endogenous IL-1ra in the production of IL-1 beta in vitro. Macrophages cultured on adherent IgG produced a 100-fold molar excess of IL-1ra, compared with IL-1 beta. In the presence of a neutralizing monoclonal antibody (mAb) against rabbit IL-1ra, the production of antigenic IL-1 beta increased by 20-60%. Since the molar ratio of IL-1ra over IL-1 was 160- to 400-fold in synovial fluid (SF) of lipopolysaccharide (LPS)-induced arthritis, we examined the functional role of endogenous IL-1ra in the regulation of inflammatory responses. When measured in the presence of anti-IL-1ra mAb, masked IL-1 activity in SF became evident, with a 3- to 4-fold increment. The administration of anti-IL-1ra mAb with LPS into rabbit knee joints increased the IL-1 activity 4-fold and the production of antigenic IL-1 beta by 30-50%. The treatment also enhanced by 20-40% LPS-induced leukocyte infiltration and protein leakage. Therefore, endogenous IL-1ra apparently acts as a down-regulating factor for limiting deleterious effects of IL-1 by masking the biological activity and by inhibiting the production.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antibodies, Monoclonal / pharmacology*
  • Arthritis / etiology*
  • Female
  • Immunoglobulin Fab Fragments / pharmacology*
  • Interleukin 1 Receptor Antagonist Protein
  • Interleukin-1 / biosynthesis
  • Lipopolysaccharides / toxicity*
  • Macrophages / metabolism
  • Rabbits
  • Sialoglycoproteins / physiology*


  • Antibodies, Monoclonal
  • Immunoglobulin Fab Fragments
  • Interleukin 1 Receptor Antagonist Protein
  • Interleukin-1
  • Lipopolysaccharides
  • Sialoglycoproteins