Interleukin-18 enhances monocyte tumor necrosis factor alpha and interleukin-1beta production induced by direct contact with T lymphocytes: implications in rheumatoid arthritis

Arthritis Rheum. 2004 Feb;50(2):432-43. doi: 10.1002/art.20064.


Objective: At sites of inflammation, T cells exert pathologic effects through direct contact with monocyte/macrophages, inducing massive up-regulation of interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha). We examined the regulatory effects of IL-18 on monocyte activation by direct contact with T lymphocytes in rheumatoid arthritis (RA).

Methods: Activated T cells were isolated from RA synovial fluid. Resting T cells and monocytes were isolated from peripheral blood mononuclear cells. RA synovial T cells or phytohemagglutinin (PHA)-stimulated T cells were fixed by paraformaldehyde and then cocultured with monocytes at a ratio of 4:1. Levels of TNFalpha, IL-1beta, IL-10, and IL-18 were measured by enzyme-linked immunosorbent assay. Expression of adhesion molecules, IL-18 receptor, and TNF receptors was analyzed by flow cytometry. Expression of NF-kappaB p65, phosphorylated IkappaBalpha, and phosphatidylinositol 3-kinase (PI 3-kinase) p110 was analyzed by Western blotting.

Results: IL-18 dose-dependently enhanced the production of IL-1beta and TNFalpha, but not IL-10, by monocytes following contact with RA synovial T cells or PHA-prestimulated T cells. NF-kappaB inhibitors N-acetyl-L-cysteine and Bay 11-7085 and PI 3-kinase inhibitor LY294002 inhibited the enhancing effects of IL-18, but MAPK p38 inhibitor SB203580, ERK inhibitor PD98059, and JNK inhibitor SP600125 did not. Increased levels of NF-kappaB in the nucleus, phosphorylated IkappaB, and PI 3-kinase were confirmed in monocytes cocultured with PHA-prestimulated T cells, and the levels were further increased by stimulation with IL-18. Neutralizing antibody to IL-18 inhibited monocyte activation induced by direct contact with PHA-prestimulated T cells. Via cell-cell contact, PHA-prestimulated T cells increased autocrine production of IL-18 by monocytes, which was mediated by activation of the NF-kappaB and PI 3-kinase pathways, and up-regulated the expression of the IL-18 receptor in monocytes. IL-18 up-regulated the expression of the TNF receptors vascular cell adhesion molecule 1 (VCAM-1) and intercellular adhesion molecule 1 (ICAM-1) on monocytes. Blocking the binding of the TNF receptors VCAM-1 or ICAM-1 on monocytes to their ligands on stimulated T cells suppressed the IL-18-enhanced production of TNFalpha and IL-1beta in monocytes induced by contact with PHA-prestimulated T cells.

Conclusion: IL-18 augments monocyte activation induced by contact with activated T cells in RA synovitis, which is dependent on activation of the NF-kappaB and PI 3-kinase pathways. IL-18 up-regulates the expression of the TNF receptors VCAM-1 and ICAM-1 on monocytes, which mediate the enhancing effects of IL-18 on T cell-monocyte contact.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arthritis, Rheumatoid / immunology
  • Arthritis, Rheumatoid / metabolism*
  • Arthritis, Rheumatoid / pathology
  • Cells, Cultured
  • Coculture Techniques
  • Dose-Response Relationship, Drug
  • Enzyme Inhibitors / pharmacology
  • Humans
  • Interleukin-1 / metabolism*
  • Interleukin-18 / metabolism*
  • Interleukin-18 / pharmacology
  • Lymphocyte Activation
  • Monocytes / cytology
  • Monocytes / immunology
  • Monocytes / metabolism*
  • Signal Transduction / immunology
  • Synovial Fluid / cytology
  • Synovial Fluid / metabolism
  • T-Lymphocytes / cytology
  • T-Lymphocytes / immunology
  • T-Lymphocytes / metabolism*
  • Tumor Necrosis Factor-alpha / metabolism*


  • Enzyme Inhibitors
  • Interleukin-1
  • Interleukin-18
  • Tumor Necrosis Factor-alpha