Chemokine C-X3-C-Motif Ligand 1 (CX3CL1) also known as fractalkine is a large cytokine protein of 373 amino acids, it contains multiple domains and is the only known member of the CX3C chemokine family. Soluble CX3CL1 potently chemoattracts T cells and monocytes, while the cell-bound chemokine promotes strong adhesion of leukocytes to activated endothelial cells, where it is primarily expressed.Thus, chemotaxis assay used 24-well microchemotaxis system was undertaken to detect the chemotactic effect of CX3CL1 on the human monocytic cell line THP-1. Briefly, THP-1 cells were seeded into the upper chambers (150ul cell suspension,106 cells/ml in RPMI 1640 with FBS free) and CX3CL1 (0.1ng/ml, 0.01ng/ml ,0.001ng/ml, 0.0001 and 0.00001ng/ml diluted separately in serum free RPMI 1640 ) was added in lower chamber with a polycarbonate filter(8um pore size) used to separate the two compartments. After incubation at 37℃ with 5% CO2 for 1h, the filter was removed,then cells in low chamber were observed by inverted microscope at low magnification (×10) and the number of migrated cells were counted using Fluorescence Activating Cell Sorter. Result shows CX3CL1 is able to induce migration of THP-1 cells. The migrated THP-1 cells in low chamber at low magnification(×10) were shown in Figure 1. Statistical results of FACS were shown in Figure 2. The optimum chemotaxis of CX3CL1 occurs at 0.001-0.00001ng/ml.

Figure 2.The chemotactic effect of CX3CL1 on THP-1 cells