Diversity of citrullinated peptide-reactive IL-6 response among rheumatoid arthritis patients and healthy controls. (A) Peripheral blood mononuclear cells from 17 rheumatoid arthritis (RA) patients and six healthy controls were incubated with 0, 3 or 30 μg/ml citrullinated (cit) and native peptides as shown, and each individual's IL-6 response in supernatant was plotted. Disease duration and HLA type are indicated. (B) The frequency of RA patients with either recent-onset or longstanding disease with positive responses (> 2 standard deviations (SD) above the mean response towards the corresponding native peptide) for each peptide is shown. ACPA, anti-citrullinated peptide antibody.