F.S. di Giovine

Tumour necrosis factor in synovial exudates.

The actions of tumour necrosis factor (TNF) include resorption of bone and cartilage, suggesting a potential role in the pathogenesis of arthritis. TNF activity was looked for in synovial fluids from 137 patients with different rheumatic diseases. Unfractionated samples were tested in the L929 bioassay. Significant TNF activity that was neutralised by monoclonal antibody to TNF alpha occurred in 13 (30%) of 44 samples. Raised TNF levels were not associated with any particular disease type or routine laboratory markers of inflammation but were related to disease duration in osteoarthritis. The finding of biologically active TNF in symptomatic joints of arthritic patients supports the idea that it may contribute to the pathogenesis of joint damage in chronic rheumatic diseases.

Urate crystals stimulate production of tumor necrosis factor alpha from human blood monocytes and synovial cells. Cytokine mRNA and protein kinetics, and cellular distribution.

Crystals of monosodium urate (MSU) provide a dose-dependent stimulus for the production by human blood monocytes of tumor necrosis factor (TNF), a cytokine with proinflammatory properties; TNF activity was inhibited selectively by monoclonal antibody to TNF alpha. Biologically active cell-associated TNF activity peaked at 3 h and was exceeded at 6 h by extracellular activity, which peaked at 12-18 h. Comparable kinetics were observed with immunoreactive TNF alpha. TNF alpha mRNA accumulation in monocytes stimulated with MSU crystals appeared as a single peak at 2-4 h, kinetics compatible with rapid production of a short half-life transcript. In contrast, crystals of calcium pyrophosphate or of hydroxyapatite did not stimulate significant production of TNF or of message. Fresh tophaceous material from a patient with gout contained significant levels of TNF alpha and cells cultured from the tophus produced TNF alpha in vitro. In rheumatoid synovial cells, spontaneous release of TNF alpha was increased by in vitro exposure to MSU crystals. Taken together with earlier work, these results support an expanded view of gouty inflammation in which the crystal-stimulated production of cytokines provides a crucial link between crystal deposition and many of the clinical and pathological facts of both acute and chronic gouty arthritis.

IL-1B and IL-1Ra gene polymorphisms and disease severity in rheumatoid arthritis: interaction with their plasma levels

The balance between interleukin-1 (IL-1) and its competitive antagonist IL-1 receptor antagonist (IL-1Ra) may contribute to the pathogenesis of rheumatoid arthritis (RA). We analysed the frequency of different alleles in the IL-1B gene (at −511 and at +3954) as well as in the IL-1Ra gene (at +2018) in an association study involving 297 RA patients and 112 healthy controls from the same geographic area. We tested associations with RA susceptibility or severity, and with circulating levels of IL-1Ra and IL-1β. Carriage of the rare IL-1B (+3954) allele 2 was increased in destructive arthritis (DRA) as compared to non-destructive arthritis (NDRA) (OR 1.7, 95% CI 1.1–2.8, 49.0% vs 35.9%) and controls (OR 1.7, 95% CI 1.1–2.8, 35.8%). Patients carrying this allele had a more destructive (Larsen wrist radiological index: mean ± s.e.m., 2.1 ± 0.2 vs 1.6 ± 0.1, P = 0.005; Steinbrocker functional index: 2.4 ± 0.1 vs 1.9 ± 0.1, P = 0.002) and active disease (Ritchie articular index: 8.1 ± 0.8 vs 5.3 ± 0.6, P = 0.002; erythrocyte sedimentation rate (ESR): 36.6 ± 2.9 mm/h vs 25.3 ± 1.8 mm/h, P = 0.002). This contribution was independent from that of HLA DR4/DR1 to severity. IL-1Ra plasma levels adjusted to ESR values were significantly lower in IL-1B2 (+3954) positive than negative RA patients (1.0 ± 0.1 vs 1.2 ± 0.1 ng/ml, P = 0.01). This IL-1B (+3954) gene polymorphism may be an important marker for the severity of joint destruction in RA and is associated with an imbalance in IL-1Ra production. As this genetic association was independent and additive to the risk of HLA DR4/DR1 status, it could be a useful addition to HLA-DR4/1 as a genetic prognostic marker early in the course of the disease.

Soluble CD8 in patients with rheumatic diseases

An ELISA was used to measure soluble CD8 (sCD8) in the sera and synovial fluids (SF) of patients with rheumatic diseases. Patients with rheumatoid arthritis (RA) had raised levels of sCD8 both in their sera and in their SF compared with patients with osteoarthritis and age‐matched healthy controls. In individual RA patients, serial serum sCD8 levels initially fell and then rose preceding clinical improvement. In four patients where serum sCD8 levels rose and clinical improvement occurred, subsequent spontaneous decreases of serum sCD8 level preceded increased clinical disease activity by up to 2 weeks. In general, RA SF mononuclear cells (SFMNC) spontaneously produced high levels of sCD8. In contrast, autologous peripheral blood MNC only produced comparable levels after mitogenic stimulation. Incubation of SFMNC with increasing concentrations of human recombinant tumour necrosis factor alpha resulted in a dose‐dependent potentiation of sCD8 release into the supernatant. There was an inverse relationship between the ability of SFMNC to release sCD8 and soluble interleukin‐2 receptor, indicating that the CD8+ T cell population may play an important immunoregulatory role in RA.

Functional correlates of the interleukin-1 receptor antagonist gene polymorphism in the colonic mucosa in ulcerative colitis

Association studies have identified the interleukin-1 receptor antagonist gene allele 2(IL-1RN*2) as a marker of susceptibility in ulcerative colitis (UC). This study investigated the significance of the IL-1RN genotype with respect to protein and mRNA expression in the colonic mucosa. Homogenates of rectal biopsies from 99 UC and 54 controls were assayed for cytokines IL-1ra, IL-1a and IL-1b using ELISA. IL1RN, IL1A and IL1B genotypes were determined using restriction-enzyme analysis. The ability of the two IL1RN alleles to generate steady-state mRNA accumulation was assessed in the colonic mucosa of seven heterozygous patients. Stepwise linear regression demonstrated that IL-1RN genotype (P=0.001), diagnosis (P<0.0001) and treatment (P<0.03) were independent factors associated with the IL-1ra protein level whilst IL1RN genotype (P=0.005) and macroscopic inflammatory grade (P<0.0001) were associated with the IL-1ra/ total IL-1 ratio. The IL1RN*2 correlated with reduced IL-1ra and IL-1ra/IL-1 ratio with a gene dosage effect. In heterozygous UC patients the ratio of allele 1 mRNA / allele 2 steady state mRNA was always greater than 1 (range: 1.2–3.1) (P=0.018). The IL-1RN*2 is associated with reduced levels of IL-1ra protein and IL-1RN mRNA in the colonic mucosa, providing a biologically plausible explanation for the observed association of the allele with the disease.

Evidence of a pharmacogenomic response to interleukin-l receptor antagonist in rheumatoid arthritis

Biological activity of the IL-1 system depends on the balance between two proinflammatory proteins (IL-1α and IL-1β) and the related anti-inflammatory protein, the IL-1 receptor antagonist (IL-1Ra). The genes for these proteins lie within 430 kb on human chromosome 2. Based on a clinical trial of human recombinant IL-1ra in rheumatoid arthritis, we tested whether IL-1 genotype might be related to the likelihood of response to anti-IL-1 therapy. A positive response was defined as a reduction of at least 50% in the number of swollen joints by week 24, following treatment with either 150 mg/day IL-1ra or placebo. The response rate to treatment, independent of genotype, was 48% (44/91). A highly significant association was found between carriage of the rarer allele at IL1A(+4845) and response to treatment (P=0.0009; OR=4.85 (1.85,12.70)). The response rate in patients carrying this allele was 63.4% compared with 26.3% in noncarriers. A weaker association was found for IL1B(+3954) (P=0.02). There was a highly significant interaction between treatment (150 mg/day or placebo) and the composite genotype across IL1A(+4845) and IL1B(+3954) (P=7.6 × 10−5). No associations with IL-1 genotypes were found in patients receiving placebo. Thus, a significant pharmacogenomic effect was found in the treatment of RA patients with recombinant IL-1ra.

Absence of correlations between indices of systemic inflammation and synovial fluid interleukin 1 (alpha and beta) in rheumatic diseases.

SummaryThere are two forms of the cytokine interleukin 1 (IL1), produced by two distinct genes encoding a neutral (IL1 beta) and an acidic (IL1 alpha) peptide. They have powerful pro-inflammatory, immunopotentiating, catabolic and arthritogenic properties in vivo and have been implicated in the pathogenesis of rheumatic diseases. In this study, using specific immunoassays, we have measured both IL1 alpha and IL1 beta levels in synovial fluids (SF) from a large number of patients with different rheumatic diseases. Biologically significant levels of both cytokines were found in SF from patients with different forms of arthritis, but no correlations were found with any of the measures of disease activity that we tested. We also describe the presence in joint exudates of biological inhibitor(s) that neutralize IL1-induced T-cell activation. This is the first report of IL1 alpha and IL1 beta measurements in the same synovial exudates and also of the comparison of local levels of these cytokines with conventional indices of systemic inflammation.

Kinetics of IL1 beta mRNA and protein accumulation in human mononuclear cells.

Interleukin 1 beta (IL1 beta) is an inducible polypeptide with many roles in host defence and homoeostasis. It has also been implicated as a mediator of infectious, inflammatory and autoimmune diseases, and the kinetics of its production are relevant to an understanding of the pathogenesis of these conditions. We report here the time-course of IL1 beta production in human adherent monocytes. Both IL1 beta protein and mRNA were measured following cell activation with bacterial endotoxin (lipopolysaccharide; LPS), and pro-inflammatory crystals of monosodium urate (MSU), which cause arthritis and kidney disease. We also tested other crystal types associated with arthritis, namely hydroxylapatite and calcium pyrophosphate dihydrate. IL1 was absent from unstimulated cells, but IL1 beta mRNA accumulated rapidly after LPS or MSU stimulation and was associated with the later appearance of intracellular IL1 beta protein which was subsequently released from the cells (60% at 9 h). The other crystals failed to induce significant IL1 production. Our findings support the view that production of IL1 beta in human mononuclear cells is based on rapid translation of an inducible pool of mRNA and that no pre-formed mRNA or intracellular protein exists in normal blood monocytes. Further, although IL1 beta is translated without a conventional leader sequence, it is translocated extracellularly with the kinetics of a secretory protein.