Serum Interleukin-6 Level is a Sensitive Parameter of Disease Activity in Rheumatoid Arthritis.

In rheumatoid synovium, interleukin-6 (IL-6) is the most abundantly expressed cytokine. Therefore, we investigated whether serum IL-6 levels could be clinically useful parameters of disease activity in rheumatoid arthritis (RA). The serum IL-6 levels were measured by enzyme-linked immunosorbent assay. The IL-6 levels were significantly higher in sera from patients with RA (n = 108, 13.3 ± 14.0 pg/mL) than in those from the normal controls (n = 10,