Interrelationships between interleukin (IL)-1, IL-6 and IL-8 in synovial fluid of various arthropathies

High levels of many cytokines, including interleukin (IL)-1, IL-6 and IL-8, were found in various arthropathies suggesting that they play a role in the pathogenesis of disease, although their relationship with the type and activity of disease is still not clear. The synovial fluid (SF) of 24 patients with rheumatoid arthritis (RA), 19 with psoriatic arthritis (PA) and 33 with osteoarthritis (OA) was analyzed for IL-1 beta, IL-6 and IL-8. The highest concentration of the three cytokines was found in the SF of RA. IL-beta detectable levels (> or = 20 pg/ml) were observed in 8/24 (33.3%) patients with RA, in one patient with PA but in no patient with OA. IL-6 (mean +/- SD) (1610.37 +/- 1781.65 pg/ml) was higher in RA than in PA (672.47 +/- 867.40 pg/ml, p = 0.043) and OA (89.45 +/- 120.52 pg/ml, p = 0.0001). IL-8 (1042.72 +/- 698.64 pg/ml) was higher in RA than in PA (660.36 +/- 625.11 pg/ml, p = 0.03) and OA (89.9 +/- 45.88 pg/ml, p = 0.0001). A correlation between IL-1 beta, IL-6 and IL-8 was found in RA. In all patients a correlation between IL-6 and IL-8 levels was found; moreover, these two cytokines were associated with SF indices of inflammation, such as white blood cells (WBC) count and total protein (TP) concentration. Our findings suggest that these interrelationships play a role in the evolution of more severe erosive arthropathy such as RA.