A high interleukin 1 receptor antagonist/IL-1beta ratio occurs naturally in knee osteoarthritis

To assess the interleukin 1 receptor antagonist (IL-1Ra)/IL-1beta ratio in synovial fluid (SF) of patients with knee osteoarthritis (OA) or rheumatoid arthritis (RA) to determine a possible relation between cytokine level and disease activity.

IL-1beta and IL-1Ra concentrations were measured by ELISA in knee SF from patients with OA (n = 42) or RA (n = 11). For OA patients, pain and disability were assessed by a visual analog scale (VAS) and the Lequesne index. RA disease activity was assessed using the Disease Activity Score 28 Joint Count (DAS28).

Patients with OA showed lower median levels of IL-1beta and IL-1Ra in SF than patients with RA (p < 0.001) but a higher IL-1Ra/IL-1beta ratio: 1793 (584-6221) versus 773.5 (187.64-1570.5) (p = 0.05). For patients with OA, the IL-1Ra/IL-1beta ratio was not associated with pain or disability. For patients with RA, the IL-1Ra/IL-1beta ratio and IL-1Ra and IL-1beta levels were related to SF white blood cell count.

High endogenous IL-1Ra/IL-1beta ratio occurs in SF from knee OA and does not correlate with pain or Lequesne index. Our results suggest that intraarticular injection of IL-1Ra might be self-limited in patients with knee OA and a naturally high SF ratio.