Rheumatoid arthritis (RA) patients with low levels of anticollagen type II (CII) had a higher cellular reactivity to denatured CII compared with RA patients with high levels of anti-CII. Production of IFN-γ in RA patients with high serum levels of anti-CII antibodies (n = 19) or low anti-CII levels (n = 26) and healthy control individuals (n = 25) is shown. In (a), IFN-γ induction after stimulation with native or denatured CII is shown. In (b), the CII response has been expressed as a fraction of the purified protein derivative (PPD) response showing, on the y axis, the quotient between the CII-induced IFN-γ production and the PPD-induced IFN-γ production. Shaded boxes represent RA patients with high serum levels of anti-CII, striped boxes represent RA patients with low levels of anti-CII and open boxes represent healthy control individuals. The box plots show the median as a line and the 25th and 75th centiles limiting the box, with the 10th and 90th centiles indicated with bars.