IL-17 and TNF-α co-operation contributes to the proinflammatory response of hepatic stellate cells

Hepatic stellate cells (HSCs) have a central role in liver inflammation and fibrosis by producing inflammatory and fibrotic mediators. Their activation is regulated through direct cell-cell interactions, but also through systemic and local effects of soluble factors such as cytokines. The effects of the proinflammatory cytokines interleukin (IL)-17 and tumor necrosis factor (TNF)-α and cell interactions with hepatocytes on HSC activation were assessed. Human HSC and HepaRG cells were exposed to IL-17 and/or TNF-α. IL-17 and TNF-α contribution from immune cells was determined in a co-culture model with phytohemagglutinin (PHA)-activated peripheral blood mononuclear cells (PBMC), HSC and/or hepatocytes. IL-17 enhanced TNF-α effects on the induction of IL-6, IL-1β, and the chemokine IL-8, chemokine (C-C motif) ligand 20 (CCL20) and monocyte chemoattractant protein-1 (MCP-1) expression/secretion in isolated HSC cultures. HSC-hepatocyte interactions did not enhance IL-6, IL-8 and CCL20 production compared to hepatocyte alone. However, HSC-hepatocyte interactions increased C-reactive protein expression. IL-17 and/or TNF-α had no direct profibrotic effects on collagen 1 α1, tissue inhibitor of matrix metalloproteinase (TIMP) and matrix metalloproteinase (MMP) 2 gene expression, whereas mRNA levels of MMP3, an enzyme involved in matrix destruction, were up-regulated in HSCs. The use of specific inhibitors of IL-17 and TNF-α indicated their contribution to the strong increase of IL-6 and IL-8 production induced by PBMC, HSC and/or hepatocyte interactions. As chronic liver inflammation leads to liver fibrosis, IL-17 and/or TNF-α neutralization can be of interest to control liver inflammation and therefore its effects on fibrosis.