Unstimulated cytokine secretion and net IL-6 secretion by peripheral blood mononuclear cells stimulated with peptides. (A) Peripheral blood mononuclear cells (PBMC) from 17 rheumatoid arthritis (RA) patients and six healthy controls were incubated in medium for 5 days and cytokines were assessed in supernatants by the BD Cytometric Bead Array. **P < 0.01, *P < 0.05 (Kruskal-Wallis test with post-hoc correction). (B) PBMC from 17 RA patients and six healthy controls were incubated with 0, 3 or 30 μg/ml citrullinated (cit) and native peptides as shown, and IL-6 was assessed in supernatants by the BD Cytometric Bead Array. Net cytokine secretion was calculated as the IL-6 concentration with peptide stimulation minus the IL-6 concentration without peptide stimulation. Each dot represents one individual. *P < 0.05, **P < 0.01 comparing IL-6 responses with citrullinated and native peptides (Mann-Whitney test).