Is interleukin‐18 useful for monitoring rheumatoid arthritis?

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Abstract
Objective: Interleukin‐18 (IL‐18) is a proinflammatory regulator of immune responses. Its similarities to IL‐1β and ability to induce tumour necrosis factor‐α (TNF‐α) make it potentially important in the pathogenesis of rheumatoid arthritis (RA). Methods: The level of IL‐18 was assessed in matched pairs of blood and synovial fluid samples from 90 RA patients (47 erosive, 43 non‐erosive) by an enzyme‐linked immunosorbent assay (ELISA), and the results compared to 40 healthy controls. Results: In RA patients with erosive joint disease, the IL‐18 level was higher than that in non‐erosive RA [(median±QR) blood: 385±200 vs. 235±183 pg/mL, p = 0.02; synovial fluid: 392±392 vs. 224±324 pg/mL, p = 0.05]. IL‐18 levels in blood of RA patients were similar and closely related to the local, intra‐articular level (r = 0.96). The IL‐18 level was not related to other markers of inflammation, to the duration of RA, or to the treatment modality. The IL‐18 level in RA patients was similar to that of the controls (278±234 vs. 344±179 pg/mL, not significant). Conclusions: An increased IL‐18 level is associated with erosive joint disease, but the measurement of IL‐18 does not help to distinguish between RA patients and healthy controls.