Transforming Growth Factor-β1 and Laminin-111 Cooperate in the Regulation of Expression of Interleukin-6 and Interleukin-8 in Synovial Fibroblasts

In a recent study we showed that binding of synovial fibroblasts (SF) to laminin-111 (LM-111) in the presence of TGF-β1 induced a significant production of IL-16. Here we go on to investigate the regulation of IL-6 and IL-8 in SF by LM-111 and TGF-β1. Changes in steady state mRNA levels encoding the interleukins were investigated by quantitative RT-PCR. We screened for interleukin production by a multiplexed immunoarray and quantified it with ELISA. The biological activity of IL-6 and IL-8 was corroborated by B-lymphocyte proliferation and cell migration assays, respectively. Growth of SF on LM-111 in presence of TGF-β1 induced significant mRNA responses for IL-6 (mean 3.72-fold increase, ± 1.6, p<0.003) and IL-8 (mean 4.5-fold increase, ± 1.6, p<0.001). In the supernatants significantly elevated concentrations of IL-6 (mean 7.9 ± 5 ng/mL, p<0.005) and IL-8 (mean 73.0 ng/mL ± 51, p<0.05) were detected, and they were shown to be biologically active. Binding to LM-111 in the presence of TGF-β1 activates SF for expression of IL-6 and IL-8 and thus may contribute to synovial inflammation and to infiltration of leukocytes.