Synovial fluid interleukin-8 and neutrophil function in rheumatoid arthritis and seronegative polyarthritis.

The relationships between synovial fluid (SF) interleukin-8 (IL-8) and neutrophil turnover as measured by cytidine deaminase (CD), and SF metabolites were studied in 28 patients, 16 with rheumatoid arthritis (RA; median age and disease duration 62 and 14 yr, respectively) and 12 with seronegative polyarthritis (SNP; median age and disease duration 32 and 5 yr, respectively). Knee SF samples were aspirated using indwelling cannulae following a period of rest for 1 h. SF IL-8 levels (measured by an ELISA) were significantly elevated in RA compared to SNP (median 2.35 vs 0.22 ng/ml, P < 0.001), as were median levels of CD (55.8 vs 8.11 U/ml, P < 0.01), lactic acid (29.6 vs 16.6 mg/dl, P < 0.001), glucose (57.9 vs 84.5 mg/dl, P < 0.05) and the lactate to glucose ratio (0.85 vs 0.19, P < 0.001). Measures of disease activity, C-reactive protein, plasma viscosity and articular index were also elevated in RA compared to SNP (P < 0.05). SF IL-8 levels correlated strongly with CD, lactate, glucose and the lactate to glucose ratio when both disease groups were considered together (P < 0.001). These parameters also showed some association with the measures of disease activity (P < 0.05). All these associations were less marked when the individual disease groups were analysed separately. These results suggest that factors responsible for neutrophil accumulation and priming (probably IL-8) are present in SF, and these coincide with products of their activation (CD). The degree of neutrophil turnover is linked to the anaerobic metabolism of the synovial cavity.