Lower level of synovial fluid interferon-γ in HLA-B27-positive than in HLA-B27-negative patients with Chlamydia trachomatis reactive arthritis

Objectives. To compare the synovial fluid (SF) concentrations of various cytokines in rheumatoid arthritis (RA) and in reactive arthritis, and to look for a correlation between cytokine levels and the presence of HLA-1327 antigen in reactive arthritis patients. Methods. Concentrations of interleukin (IL) 10, IL-12, IL-18, interferon gamma (IFN-gamma) and tumour necrosis factor alpha (TNF-alpha) were determined by commercially available enzyme-linked immunosorbent assays (ELISA) in the SF from 48 patients with reactive arthritis, 33 with RA and 13 with osteoarthritis (non-inflammatory controls). Results. The SF concentrations of IL-10 were significantly lower in patients with reactive arthritis (median 2.3 pg/ml) than in RA patients (median 14.6 pg/ml). The SF levels of IFN-gamma were not significantly different but the ratios of IFN-gamma to IL-10 were significantly higher in patients with reactive arthritis (median 9.2) than in RA patients (median 0.83). When the subset of patients with Chlamydia trrachomatis reactive arthritis was considered, the SF concentration of IFN-gamma was significantly lower in HLA-B27-positive (median 2.9 pg/ml) than in HLA-1327-negative patients (median 42.4 pg/ml). After 2 yr of follow-up, two HLA-1327-positive patients, who had low SF levels of IFN-gamma, had a chronic course of arthritis, whereas after 1 yr all HLA-B27-negative patients had complete resolution of arthritis. Conclusions. The lower IFN-gamma concentrations in HLA-1327-positive patients with C. trachomatis reactive arthritis could be related to the tendency of these patients to have more severe or chronic arthritis.