ISSN: 2161-1149 (Printed)
Introduction: Expression of interleukin-1β (IL-1β) in the synovial fluid of patients with osteoarthritis has been confirmed. The overall effect of this cytokine can be described as a chondrocyte-dependent cartilage destructive potential. The interleukin-1β receptor antagonist (IL-1Ra) blocks the interaction between IL-1β and its receptor on the cell surface. Human chondrocytes and synoviocytes produce IL-1Ra in a response to stimulation by IL-1β and IL-6. The local production of IL-1Ra in the joint has a protective effect against the catabolic action of IL-1β.
Material and Methods: Synovial fluid and blood serum were obtained from 31 patients undergoing knee replacement surgery because of osteoarthritis. For comparison, samples were obtained from another 30 patients during diagnostic or therapeutic arthroscopy performed because of knee injury. The samples were analyzed for IL-1β and IL-1Ra using enzyme-linked immunosorbent assay. The U Mann-Whitney test and Spearman's test, as well as receiver operating characteristic (ROC) were used for statistical analysis.
Results: Statistical analysis showed that the concentration of IL-1Ra in serum was significantly higher in the osteoarthritis group compared to the injury group (p=0.0001), and there was a positive correlation of IL-1Ra concentration in the serum and in the synovial fluid (correlation coefficient R=0.41; significance p=0.02). In the osteoarthritis group there was a very high negative correlation between the intensity of pain and the concentration of IL-1Ra in the synovial fluid (correlation coefficient R=-0.75; significance p<0.000001). Furthermore very high negative correlation was observed between the intensity of pain and level of this cytokine in serum (R=0.86; p<0.000001). For the measurements of IL-1Ra in serum the sensitivity of this test was 71.0%, specificity 70.0%, positive prediction of a result was 71.0%, negative prediction 70.0%, and the area under the ROC curve was 0.792.
Conclusion: Late stage osteoarthritis is characterized by a systemic inflammatory reaction with high concentration of IL-1Ra in serum, which is positively correlated with its concentration in the synovial fluid. Pain in patients with late stage osteoarthritis may be reduced due to the high concentration of anti-inflammatory IL-1Ra both in the synovial fluid and in blood serum. The measurement of IL-1Ra in serum is a reliable immunoassay test that determines the status of osteoarthritis.