PHAGOCYTOSIS OF A FLUORESCENTLY LABELED PERFLUBRON EMULSION BY A HUMAN MONOCYTE CELL-LINE

We hypothesized that fluorocarbon-based lipid emulsions are phagocytos ed by monocytes and that many of the in vivo side effects related to t he infusion of these particulate emulsions are due to release of cytok ines by these monocytes. To clarify whether these emulsions are actual ly phagocytosed we attempted to measure by flow cytometry the apparent uptake of a fluorescently labeled high-concentration (90%, w/v) perfl ubron (perfluorooctyl bromide [PFOB]) emulsion by a differentiated hum an monocyte cell line. A fluorescent chromophore (Zynaxis Cell Science ) was used to label the egg yolk phospholipid in a perflubron emulsion . This phospholipid label was used to track the perflubron emulsion du ring overnight incubation with the human monocyte (THP-1) cell line wh ich had been differentiated, by exposure to PMA, into macrophage-like cells. Our results indicate that after 24 hours of incubation with the labeled perflubron emulsion, 64.9% (+/-11.0) of differentiated THP-1 cells had cell-associated emulsion (ingested and/or membrane bound) wh ereas 24.4 (+/-6.8%) of the control cells had cell-associated emulsion . We speculate that this technique may be a useful method to track the intravascular persistence and extravascular distribution of such emul sions, and that the degree of uptake of the emulsion by macrophages in this assay may correlate with its in vivo half life.