Transfer of DN-Syk or Syk-siRNA results in the inhibition of phagocytosis. Macrophage-like differentiated Day3-HL60 cells were incubated with zymosan particles that were pretreated with PBS, serum, IgG-removed serum, serum containing compstatin (10 μM), or the control peptide to compstatin (10 μM) for 30 minutes at 37°C and then analyzed by flow cytometry to detect phagocytosis of fluorescent zymosan. (A) Representative histogram patterns of the treated cells by flow cytometry are shown. M2 region includes zymosan-positive cells. (B) The percentage of zymosan-positive cells (percentage of M2 region as shown in panel A) in parental HL60 cells incubated with zymosan particles that were pretreated with serum, IgG-removed serum, serum containing compstatin, or the control peptide to compstatin is presented. The mean values and SD of triplicate experiments are shown. The statistically significant difference was assessed by the Student t test; *P < .05. (C) The percentage of zymosan-positive cells (percentage of M2 region shown in panel A) in HL60 cells and primary monocytes is presented. Cells were treated with serum-opsonized or nonopsonized fluorescent zymosan for 10 minutes at 0°C or 37°C, washed with PBS, and further incubated for 10 minutes at 37°C. The mean values and SD of triplicate experiments are shown (left panel). Cell-surface expression of CR3 (integrin αMβ2) on macrophage-like differentiated Day3-HL60 cells and primary monocytes was analyzed by flow cytometry with anti-CR3 monoAb (thick line) or with control mouse IgG (thin line; right panel). (D) The percentage of zymosan-positive cells (percentage of M2 region shown in panel A) in HL60 cells and the mutant clones treated with serum-opsonized or nonopsonized fluorescent zymosan for 30 minutes at 37°C is presented. The mean values and SD of triplicate experiments are shown.