Serum and synovial cytokine profiles. (a) Serum cytokines in normal rats and in Chlamydia-induced arthritis alone or after prior exposure to mercuric chloride (HgCl2). After the onset of Chlamydia trachomatis-induced arthritis (CtIA), there was a significant increase in the serum levels of interferon-gamma (IFN-γ) (P < 0.005) and tumour necrosis factor-alpha (TNF-α) (P < 0.001). Prior HgCl2 exposure was associated with significant suppression of IFN-γ (P = 0.002) and TNF-α (P = 0.014) seen with CtIA. (b) Synovial cytokines in Chlamydia-induced arthritis alone or after prior exposure to HgCl2. HgCl2 exposure was accompanied by a decrease in local cytokine production for IFN-γ (P < 0.005), TNF-α (P < 0.05), and interleukin (IL)-1 (P < 0.05) compared with controls. No significant difference was observed for synovial IL-10 (n = 4 in each group).