FIGURE 1.

Serum inhibits phagocytosis of non-opsonized beads by monocytes. Human monocytes (2 × 10⁶/ml) were labeled with APC-conjugated CD14 and incubated with 20 μm CytD for 20 min or with serum for 1 min before the addition of 1-μm YG beads. The fluorescence intensity of CD14⁺ monocytes was analyzed by time-resolved flow cytometry. a, a typical YG beads uptake curve shows complete inhibition of bead phagocytosis by freshly prepared human monocytes by 1% serum. The curve is representative of >10 human serum samples. b, shown is phagocytosis of YG beads by HEK-293 cells transfected with DsRed-tagged P2X7 constructs or DsRed-monomer-N1 vector (Mock) in the presence or absence of 2% serum pre-filtered through a 300-kDa ultrafiltration tube. Cells were gated on DsRed for analysis. c, uptake of YG beads opsonized by preincubation with 5% serum for 3 days at 4 °C is shown. 5% serum failed to inhibit uptake of serum-opsonized beads. d, serum pretreated with 1–10 mm TEPA showed little or no inhibition of YG bead uptake.