High levels of interleukin-6 in rheumatoid arthritis joint fluids can stimulate local production of C-reactive protein resulting in elevated circulating levels.

• Locally produced IL-6 may stimulate CRP production in joints of anti-CCP2 positive RA patients. • This might partly explain circulating CRP levels. • Serum CRP levels might not only be a marker of systemic inflammation in RA. [ABSTRACT FROM AUTHOR]