Serum interleukin-1 receptor antagonist levels are a useful marker of disease activity and risk of relapse in large vessel vasculitis.

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OBJECTIVE: To examine whether serum interleukin-1β (IL-1β) or IL-1 receptor antagonist (IL-1Ra) levels are associated with disease activity or relapse risk in large vessel vasculitis (LVV), including giant cell arteritis (GCA) and Takayasu arteritis (TAK). METHODS: Twenty one patients with treatment-naive, active LVV (13 with GCA and 8 with TAK), and 14 healthy individuals were enrolled in the study. Serum levels of IL-1β, IL-1Ra, IL-2, IL-6, IL-12p40, IL-17, IL-23, IFN-γ, and TNF-α were measured. Association with C-reactive protein (CRP) levels, Indian Takayasu clinical activity score (ITAS-A), and relapse were analyzed. RESULTS: IL-1Ra levels were significantly higher in patients with with TAK (465.3 pg/mL) and GCA (384.9 pg/mL) compared to healthy individuals (170.4 pg/mL; p < 0.001). IL-6 levels were also elevated in LVV, while IL-1β and IFN-γ were increased only in GCA and IL-17 levels were increased only in TAK. IL-1Ra levels positively correlated with ITAS-A scores in TAK and with CRP levels in GCA. IL-6 correlated with CRP in both diseases; IL-1β and other cytokines showed no such association. During follow-up, six patients (five with GCA and one with TAK) experienced symptomatic relapse. In GCA, baseline IL-1Ra levels were significantly lower in those who relapsed compared to non-relapsed patients (270.8 vs. 616.4 pg/mL; p = 0.008). No significant difference in other cytokine levels were observed. Receiver operating characteristic analysis demonstrated that IL-1Ra levels >340.4 pg/mL could distinguish non-relapsed from relapsed cases (AUC = 0.95). CONCLUSION: Serum IL-1Ra levels correlate with CRP levels in GCA and ITAS-A scores in TAK and serve as a predictive biomarker for relapse.