In vitro stimulation of phagocytosis in a macrophage cell line measured by a convenient radiolabeled latex bead assay.

Commercially available carboxylated latex beads were covalently labeled with ³H]-tyramine and used in a quantitative phagocytosis assay. Macrophage cells were incubated with ³H-beads, then treated with trypsin-Versene and washed through fetal calf serum to remove uningested beads. Uptake was linear with time (up to 6 hr) and cell number (up to 5 × 10⁵). PU5-1.8 and RAW264 macrophage tumor culture lines were more active than adherent cells from peptone- or oil-induced peritoneal exudates of mice, which were more active than normal peritoneal adherent cells. PU5-1.8 phagocytosis was especially resistant to inhibition by cytochalasin B, but cytochalasin A and iodoacetic acid were effective inhibitors. Treatment of PU5-1.8 cells with LPS or PPD in vitro stimulated latex ingestion; the presence of hydrocortisone blocked the increase but not baseline activity. The easy preparation and storage of labeled beads makes this convenient assay method particularly useful for comparison of the phagocytic activity of a number of cell populations.