Max Field

A proinflammatory role for IL-18 in rheumatoid arthritis

IL-18 is a novel cytokine with pleiotropic activities critical to the development of T-helper 1 (Th1) responses. We detected IL-18 mRNA and protein within rheumatoid arthritis (RA) synovial tissues in significantly higher levels than in osteoarthritis controls. Similarly, IL-18 receptor expression was detected on synovial lymphocytes and macrophages. Together with IL-12 or IL-15, IL-18 induced significant IFN-gamma production by synovial tissues in vitro. IL-18 independently promoted GM-CSF and nitric oxide production, and it induced significant TNF-alpha synthesis by CD14(+) macrophages in synovial cultures; the latter effect was potentiated by IL-12 or IL-15. TNF-alpha and IFN-gamma synthesis was suppressed by IL-10 and TGF-beta. IL-18 production in primary synovial cultures and purified synovial fibroblasts was, in turn, upregulated by TNF-alpha and IL-1beta, suggesting that monokine expression can feed back to promote Th1 cell development in synovial membrane. Finally, IL-18 administration to collagen/incomplete Freunds adjuvant-immunized DBA/1 mice facilitated the development of an erosive, inflammatory arthritis, suggesting that IL-18 can be proinflammatory in vivo. Together, these data indicate that synergistic combinations of IL-18, IL-12, and IL-15 may be of importance in sustaining both Th1 responses and monokine production in RA.

The role of interleukin-15 in T-cell migration and activation in rheumatoid arthritis.

Interleukin 15 (IL–15) is a novel cytokine with interleukin–2–like activity. It is also a potent T–lymphocyte chemoattractant. Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by the presence of activated T lymphocytes, macrophages and synoviocytes in the synovial membrane. The mechanisms of T–cell activation in RA are currently unclear. We report the presence of high concentrations of IL–15 in rheumatoid arthritis (RA) synovial fluid and have demonstrated its expression in the synovial membrane lining layer by immunohistochemistry. RA synovial fluids were found to contain chemotactic activity, which was attributable in part to the presence of IL–15. Moreover, in a murine model, injection of recombinant IL–15 was found to induce a local tissue inflammatory infiltrate consisting predominantly of T lymphocytes. Synovial fluid T lymphocytes proliferate in response to IL–15, demonstrating that continued responsiveness to IL–15 is a feature of T cells after entry into the synovial compartment. These data suggest that IL–15 can recruit and activate T lymphocytes into the synovial membrane, thereby contributing to RA pathogenesis.

A Proinflammatory Role of IL-18 in the Development of Spontaneous Autoimmune Disease

Serum from patients with systemic lupus erythematosus (SLE) contained significantly higher concentrations of IL-18 than normal individuals. MRL/lpr mice, which develop spontaneous lupus-like autoimmune disease, also had higher serum levels of IL-18 than wild-type MRL/++ mice. Daily injections of IL-18 or IL-18 plus IL-12 resulted in accelerated proteinuria, glomerulonephritis, vasculitis, and raised levels of proinflammatory cytokines in MRL/lpr mice. IL-18-treated MRL/lpr mice also developed a “butterfly” facial rash resembling clinical SLE. In contrast, MRL/lpr mice treated with IL-18 plus IL-12 did not develop a facial rash. The facial lesion in the IL-18-treated mice showed epidermal thickening with intense chronic inflammation accompanied by increased apoptosis, Ig deposition, and early systemic Th2 response compared with control or IL-12 plus IL-18-treated mice. These data therefore show that IL-18 is an important mediator of lupus-like disease and may thus be a novel target for therapeutic intervention of spontaneous autoimmune diseases.

Disease association of two distinct interleukin-18 promoter polymorphisms in Caucasian rheumatoid arthritis patients

Interleukin (IL)-18 is an important mediator of innate and adaptive immunity. We searched for an association of IL-18 promoter single-nucleotide polymorphisms (SNP) with rheumatoid arthritis (RA) in Caucasians. The entire study population was composed of two independent cohorts from Germany (n=200) and Scotland (n=410). Presence of IL-18 SNP at positions −607 and −137 was determined by allele-specific PCR in 327 RA patients and 283 healthy donors (HD). Diplotype distributions of both loci were in Hardy–Weinberg equilibrium (HWE) in the German and Scottish HD cohorts. In contrast, locus −607 was in HW disequilibrium in German, and locus −137 in Scottish RA patients. Diplotypic exact χ2 tests suggested that −607CC was overrepresented in German, and −137CC in Scottish RA patients, but conservative χ2 trend analyses could not prove any significant disease association of these single loci. SNP −607 and −137 were in strong linkage disequilibrium. The −607C*−137C haplotype was more prevalent in German RA (3.2 vs 1.2%) and in Scottish RA patients (4.1 vs 0.9%) than in the respective HD cohorts. These observations suggest that SNP of both positions contribute to the genetic background of RA pathogenesis.

A polymorphism within the Transforming Growth Factor β1 gene is associated with ankylosing spondylitis (AS).

Genetic factors that predispose individuals to ankylosing spondylitis (AS) are not fully understood. Axial and sacroiliac joint fibrosis are characteristic of AS and the presence of TGFβ1 mRNA in AS sacroiliac joints raised the possibility that this cytokine might be implicated in this fibrosis. We have therefore examined a group of HLA B27 positive AS patients to investigate whether they could be prone to fibrosis based on overproduction of TGFβ1.

Promoter polymorphisms in the IL-18 gene are associated with rheumatoid arthritis in two independent clinical cohorts

IL-18 in synovial tissues of patients with rheumatoid arthritis (RA) promotes local inflammation via effects on innate and adaptive immune responses. Promoter polymorphisms may modulate IL-18 expression. Using two independent clinical cohorts, we determined the frequency of single nucleotide polymorphisms (SNPs) in the IL-18 promoter for RA patients.