HMGB1 in complex with LPS stimulates RASFs and OASFs to TNF, IL-6 and IL-8 production. Synovial fibroblasts were stimulated for nine hours with A) HMGB1, LPS or HMGB-LPS with the indicated concentrations. The addition of HMGB1-LPS complex to cells induced a 1 to 2 log-fold increased number of TNF producing cells recorded by Elispot. Individual results from RA (squares) and OA (dots) represent results from each donor; the horizontal line indicates the median values. Significant differences were evident between HMGB1-LPS complex stimulation compared to HMGB1 simulation alone. B) The ability of HMGB1-LPS complexes to induce an enhanced production of IL-10, IL-1β, IL-6 and IL-8 in RASFs and OASFs was analyzed by CBA after 24 hours stimulation. HMGB1-LPS complexes at indicated concentrations induced a significantly enhanced production of IL-6 and IL-8 compared to HMGB1 stimulation alone whereas no production of IL-10 or IL-1β could be detected. Pooled data from RAFSs and OASFs where the horizontal line indicates the median values. RASF n = 4, OASF n = 5. P-values were calculated using Kruskal-Wallis non-parametric ANOVA test. * (P < 0.05) ** (P < 0.01) *** (P < 0.001).