Shikonin, a major effective component in the Chinese herbal medicine Lithospermum erythrorhizon Sieb., exhibits an anti-inflammatory property towards rheumatoid arthritis (RA), but the potential mechanism is unclear. Our aim was to investigate the mechanism of shikonin on the lipopolysaccharide (LPS)-induced fibroblast-like synoviocyte (LiFLS) inflammation model. Fibroblast-like synoviocytes (FLSs) were treated with 200 mu g/ml of LPS for 24 h to establish the RA-like model, LiFLS. FLSs were pretreated with shikonin (0.1-1 mu M) for 30 min in the treatment groups. Quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assays were used to detect mRNA and protein levels of interleukin (IL)-10 and tumor necrosis factor (TNF)-alpha. Signal proteins involved in IL-10 production were analyzed by Western blotting. Shikonin significantly reversed the inhibitory effects of LPS on IL-10 expression in FLSs by inactivating the PKC-NF-kappa B pathway. In addition, shikonin inhibited LPS-induced TNF-alpha expression in FLSs, and this effect was markedly diminished by IL-10-neutralizing antibody. The IL-10-mediated suppression of TNF-alpha transcription was demonstrated by no response to the protein synthesis inhibitor cyclohexamide and no mRNA decay. Shikonin inhibits LPS-induced TNF-alpha production in FLSs through suppressing the PKC-NF-kappa B-dependent decrease in IL-10, and this study also highlights the potential application of shikonin in the treatment of RA.