Background Several investigations of synovial fluid (SF) and membrane derived T cells show a predominant Th1 response with high IFN-gamma production from rheumatoid arthritis (RA), and a predominant Th2 response with high IL-4 and IL-10 production in T cells from spondyloarthropathy (SpA) joints.

Objectives To investigate the concentrations of IFN-gamma, TNF-alpha, IL-4, IL-10, the Th1 propagating cytokines IL-12 and IL-18, and the monokine IL-1 in sera and synovial fluids from RA and SpA patients.

Methods Patients were selected according to the ACR classification criteria for RA (n = 13), and the ESSG classification criteria for SpA (n = 14). Cytokine concentrations were measured using commercial ELISA kits. Results are expressed as mean ± standard deviation, significance was calculated using the Mann-Whitney U-test for untailed groups. Sera from 8 healthy donors served as controls.

Results IFN-gamma concentrations were significantly lower (4,3 ± 2,6 pg/ml), but IL-18 (78,8 ± 29,3 pg/ml), TNF-alpha (105,4 ± 40,9 pg/ml), and IL-10 (100,1 ± 69,7 pg/ml) concentrations were significantly higher in RA than in SpA-SF (IFN-gamma 12,9 ± 10,4 pg/ml, p = 0,009, IL-18 55,1 ± 44,1 pg/ml, p = 0,038, TNF-alpha 74,1 ± 85,0 pg/ml, p = 0,044, IL-10 14,1 ± 19,9, p < 0,0001). IL-4 and IL-12 concentrations were rather low in RA- and SpA-SF. Serum concentrations of all investigated cytokines in RA and SpA differed – if at all -only marginally from the situation in healthy donors.

Conclusion Synovial fluid concentrations of the Th1 and Th2 cytokines in RA and SpA do not generally reflect the state of Th1/Th2 balance at the single cell level. There is strong evidence for substantially higher amounts of IL-10 in RA than SpA synovium, reflecting strong antiiflammatory processes are present in RA synovium. The observed Th1/Th2 balances in both investigated diseases are not explained by the corresponding IL-12 and IL-18 SF concentrations.