Lipid composition alters phagocytosis of fluorescent latex beads

A new assay using fluoresbrite microspheres was developed to determine phagocytic rate in LM fibroblasts grown in a variety of culture conditions. Fluoresbrite beads of diameter 0.86 microns or greater were taken up by the cells at a linear rate for 60 min over a wide range of bead/cell ratios. Phagocytosis was measured as the difference in fluorescence of cells exposed to beads at 37 degrees C and at 4 degrees C, to correct for adsorbance of beads to the cells. Fluoresbrite bead phagocytosis was zero at zero time and was saturable. LM fibroblasts cultured in a serum-free, chemically-defined medium were supplemented with choline analogues or fatty acids to alter plasma membrane lipid composition. Choline analogue supplementation (N,N'-dimethylethanolamine, N-monomethylethanolamine, or ethanolamine) altered the plasma membrane phospholipid polar head group composition and dramatically decreased the phagocytic rate as compared with choline fed cells. Supplementation with polyunsaturated and monounsaturated fatty acids, but not saturated fatty acids, increased the phagocytic rate. The phagocytic rate was correlated with the plasma membrane phospholipid fatty acid index of unsaturation.