Chemotactic activity of F peptide for FPRL1/293 cells. Different concentrations of F peptide were placed in the lower wells of the chemotaxis chamber. FPRL1/293 cells were placed in the upper wells. After incubation for 5 hours at 37°C, the cells that migrated across the polycarbonate filter were counted and photographed. (A) Visualization (original magnification × 200) of FPRL1/293 cell migration in response to control medium (Medium; left panel) or F peptide (F pep; 5 × 10⁻⁵ M; right panel). Solid arrows in the figure denote cells migrated across the filters. An open arrow in the left panel indicates one of the micropores in the filter. (B) Fold increase (chemotaxis index) of FRPL1/293 cell migration in response to F peptide over control medium. (C) Lack of chemotactic activity of F peptide for 293 cells transfected to express CCR5 or CXCR4. MIP-1β and SDF-1 at 10 ng/mL were used as positive controls. *P < .01 compared with spontaneous migration.