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Published on: March 1, 2011
Transition of serum-free IL-18 levels in systemic juvenile idiopathic arthritis measured by a novel detection method
Yuki Miwa1, Norio Kawamoto2, Takao Miwa3
1Department of Pediatrics, Gifu University Graduate School of Medicine, Gifu, Japan.
Background:
Systemic juvenile idiopathic arthritis (sJIA) is a pediatric-onset autoinflammatory disease that may progress to fatal macrophage activation syndrome (MAS). Free interleukin-18 (IL-18), which is unbound to IL-18 binding protein (IL-18BP), may reflect its biological activity, but its accurate measurement remains challenging and its clinical usefulness in sJIA remains unclear.
Methods:
We generated a NanoLuc fused IL-18BP plasmid, expressed and highly purified the protein with the silkworm protein expression system, and used it to develop an Enzyme-Linked Immunosorbent Assay for measuring free IL-18 levels. Serum samples were collected longitudinally from 13 patients with sJIA and 11 healthy controls to evaluate free IL-18 levels and other biological markers. The ability to identify MAS was evaluated by a receiver operating characteristic analysis and compared by DeLong's test.
Results:
Purified NanoLuc-IL-18BP enabled the development of a straightforward ELISA for measuring free IL-18. Free IL-18 levels were elevated in 15% of patients during the active phase and in all patients during the MAS phase, and normalized in the inactive phase. Additionally, free IL-18 levels were significantly higher in the MAS phase than in the active phase. Free IL-18 showed the highest area under the curve and showed better performance to identify MAS than IL-6 and ferritin.
Conclusion:
We developed a novel ELISA for the convenient quantification of free IL-18 using IL-18BP that had been highly purified through NanoLuc technology. Free IL-18 levels may serve as a reliable biomarker for monitoring disease activity and predicting MAS when evaluated in conjunction with other cytokines and biological markers.
