Modification of chemokine pathways and immune cell infiltration as a novel therapeutic approach in liver inflammation and fibrosis

Despite increasing knowledge about molecular pathways in pathogenesis of chronic liver disease, selective therapeutic options are scarce, especially in advanced diseases characterized by scarring of the liver (termed fibrosis) or even complete cirrhosis. Sustained hepatic inflammation as a result to various types of injury (e.g., hepatitis C, nonalcoholic steatohepatitis) is generally accepted to represent the key prerequisite for fibrogenesis. Liver inflammation is characterized by an activation of distinct chemokine pathways in the liver and the circulation allowing distinct immune cell populations to enter the liver via sinusoids and postsinusoidal venules. Recent investigations have shed light on the intimate interactions between the fibrogenic hepatic stellate cell (HSC) and infiltrating immune cells, which fundamentally drive liver scarring. Experimental fibrosis and inflammation models have demonstrated that disruption of chemokine pathways such as CCL2 (MCP-1) or its receptor CCR2, CCL5 (RANTES) or CCR1 / CCR5 and others may efficiently prevent collagen deposition, by targeting monocytes and macrophages, T-cell populations or NKT cells. However, immigration of certain mononuclear cells may even be beneficial in the course of fibrosis. Infiltrating NK cells and monocyte-derived macrophage subsets can promote resolution of extracellular matrix. This emphasizes that hepatic fibrosis is not a unidirectional process, but can be reverted up to a certain point. The present review aims at summarizing the contribution of immune cell infiltration as well as related chemokine systems to experimental liver fibrosis and will discuss possible therapeutic applications in humans, with a special emphasis on the monocyte/macrophage lineage and their related chemokine pathways.