Fractalkine, a CX3C-chemokine, functions predominantly as an adhesion molecule in monocytic cell line THP-1

A newly identified CX3C-chemokine, fractalkine, expressed on activated endo thelial cells plays an important role in leucocyte adhesion and migration. Co-immobilized fractalkine with fibronectin or intercellular adhesion molec ule-1 enhanced adhesion of THP-1 cells, which express the fractalkine recep tor (CX(3)CR1), compared with that observed for each alone. That adherence was fractalkine-dependent and was confirmed in blocking studies. However, s oluble fractalkine induced little chemotaxis in THP-1 cells in comparison t o monocyte chemotstatic protein-1 (MCP-1), which induced a strong chemotact ic response. Moreover, the membrane form of fractalkine expressed on ECV304 cells reduced MCP-1 mediated chemotaxis of THP-1 cells. These results indi cate that fractalkine may function as an adhesion molecule between monocyte s and endothelial cells rather than as a chemotactic factor.