Rheumatoid arthritis (RA) peripheral blood mononuclear cells (PBMCs) respond similarly to collagen type II (CII) as healthy control individual PBMCs, but they are hyporesponsive to other antigens. PBMCs from RA patients (n = 45) and healthy control individuals (n = 25) were stimulated with antigen for 7 days, and supernatants were analyzed by enzyme-linked immunosorbent assay (ELISA) for concentration of IFN-γ . The background IFN-γ production in wells without added antigen was subtracted in each case. (a) Levels of IFN-γ after stimulation with native or denatured CII, and (b) after stimulation with purified protein derivative (PPD) or killed influenza virus are shown. 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.