Computer model of IL-6 dependent rheumatoid arthritis in F759 mice.

The IL-6 amplifier, which describes the simultaneous activation of STAT3 and NF-kB, in synovial fibroblasts causes the infiltration of immune cells into the joints of F759 mice. The result is a disease that resembles human rheumatoid arthritis. However, the kinetics and regulatory mechanisms of how augmented transcriptional activation by STAT3 and NF-kB leads to F759 arthritis is unknown. We here show that the STAT3-NF-κB complex is present in the cytoplasm and nucleus and accumulates around NFkB binding sites of the IL-6 promoter region and established a computer model that shows IL-6 and IL-17 signaling promotes the formation of the STAT3-NF-κB complex followed by its binding on promoter regions of NF-kB target genes to accelerate inflammatory responses, including the production of IL-6, epiregulin, and CCL2, phenotypes consistent with in vitro experiments. The binding also promoted cell growth in the synovium and the recruitment of Th17 cells and macrophages in the joints. Anti-IL-6 blocking antibody treatment inhibited inflammatory responses even at the late phase, but anti-IL-17 and anti-TNFα antibodies did not. However, anti-IL-17 antibody at the early phase showed inhibitory effects, suggesting that the IL-6 amplifier is dependent on IL-6 and IL-17 stimulation at the early phase, but only on IL-6 at the late phase. These findings demonstrate the molecular mechanism of F759 arthritis can be recapitulated in silico and identify a possible therapeutic strategy for IL-6 amplifier-dependent chronic inflammatory diseases.