Up-regulated expression of fractalkine and its receptor CX3CR1 during liver injury in humans

Little is known about the role of fractalkine (CX3CL1) in the liver. The aim of this study was to investigate the expression patterns of fractalkine and its receptor CX3CR1 in normal human liver and in conditions of injury.Distribution and expression of fractalkine and its receptor were investigated using immunohistochemistry, in situ hybridization, flow cytometry and reverse transcriptase-polymerase chain reaction. In vitro experiments were conducted in HepG2 cells.Both fractalkine and CX3CR1 were up-regulated during chronic injury, in areas of portal and lobular inflammation. In severe acute hepatitis, fractalkine and CX3CR1 were expressed at high levels not only in areas of inflammation but also in regenerating epithelial cells within bile duct-like structures, which showed co-expression of fractalkine and cytokeratin-7 or CX3CR1. The human hepatocarcinoma cell line HepG2 expressed fractalkine at the gene and protein level, and HepG2-conditioned medium was chemotactic for cells overexpressing CX3CR1. Transcripts for CX3CR1 were detected in HepG2, and exposure of these cells to recombinant fractalkine induced cell migration.This study shows that the fractalkine system is up-regulated during liver damage, and suggests that fractalkine may play a role in the recruitment and adhesion of inflammatory cells and in the biology of liver epithelial cells.