Interleukin-6 production by human liver (myo)fibroblasts in culture. Evidence for a regulatory role of LPS, IL-lβ and TNFα

Interleukin-6 is a major trigger forthe synthesis of acute phase proteins by liver parenchymal cells. Acute phase proteins may contribute to the regulation of liver fibrosis by inhibition of proteases (e.g. collagenase) and by binding of cytokines. Since liver (myo)fibroblasts play an important role in the production of extracellular matrix in fibrotic livers, a study was undertaken into whether these cells are able to synthesize interleukin-6, which would give them the opportunity to contribute to regulation of synthesis of acute phase proteins by neighbouring parenchymal cells.In the present study we investigated interleukin-6production by two cell types obtained from human liver tissue: human fat-storing cells obtained from 5–15% Percoll fractions, which transformed in culture into myofibroblasts co-expressing α-smooth muscle actin and vimentin (VA cells) and fibroblasts obtained from 30–40% Percoll fractions which express vimentin only (V vells). Interleukin-6 production was measured in culture media of these cells using an enzyme-linked immunosorbent assay after incubation with lipopolysaccharide, and mediators like interleukin-1β, tumor necrosis factor-a, transforming growth factor-β and interferon-gamma, known to be present in elevated concentrations in fibrotic livers.Unstimulated human liver (myo)fibroblasts produced considerable amounts of interleukin-6 (287 ng/mg cellular protein (VA cells), and 54 ng/mg cellular protein (V cells), within 48 h). Biological activity of these high concentrations of interleukin-6 measured in the enzyme-linked immuno-sorbent assay was confirmed in the B9-bioassay for interleukin-6 and by stimulation of α2-macroglobulin production in rat liver parenchymal cell cultures. Lipopolysaccharide, interleukin-1β and tumor necrosis factor-α were potent stimulators of basal interleukin-6 production by VA and V cells. 1 μg/ml lipopolysaccharide enhanced basal interleukin-6 production 3-fold within 48 h. 100 U/ml interleukin-1β and 1000 U/ml tumor necrosis factor-α each stimulated basal interleukin-6 production by VA cells 2–5 fold, whereas V cells were stimulated 10–25 fold. These effects were specific since the stimulation by lipopolysaccharide was completely inhibited by polymyxin B and the enhancing effects of interleukin-1β and tumor necrosis factor-α were neutralized by specific antibodies. Transforming growth factor-β and interferon gamma did not influence interleukin-6 synthesis by either cell type in culture.These results indicate that transformed fat-storing cells (VA cells) and fibroblasts (V cells) may function as a local source of interleukin-6 in the human liver. Since interleukin-6 plays a key role in the regulation of the production of acute phase proteins by liver parenchymal cells, we hypothesize that human liver (myo)fibroblasts may stimulate local production of acute phase proteins in the fibrotic liver, thus contributing to local regulation of inflammatory and fibrogenic reactions.