Functional Comparison Of Immunoglobulin G Versus Oxidized Low-Density Lipoprotien Phagocytic Receptors In Human U937 Macrophages

Phagocytic macrophages bind to solid oxidized low-density lipoprotein (oxLDL) deposited on the arterial intima, differentiate into foam cells and cause atherosclerosis - the largest cause of mortality in Canada. The mechanism of oxLDL internalization was examined in vitro using differentiated U937 cells exposed to latex microbeads coated with oxLDL or Immunoglobulin G (IgG). Bead internalization was quantified using immunofluorescent staining and laser confocal assays. IgG-mediated engulfment was more rapid than oxLDL-mediated engulfment indicating a qualitatively different internalization pathway. The filamentous actin inhibitors Cytochalasin D (10uM) and Latrunculin B (5uM) completely inhibited phagocytosis of both oxLDL-coated and IgG-coated beads. The Src and Spleen tyrosine kinase inhibitor 3,4-methylenedioxy-beta-nitrostyrene (20 uM), the phospholipase C inhibitor U73122 (5 uM), and the Janus kinase inhibitor AG 490 (25 uM) displayed significant inhibitory effects on the phagocytosis of both IgG and oxLDL microbeads. The specific isoforms of oxLDL and IgG receptor associated enzymes were determined by nano LC-ESI-MS/MS with an LTQ ion trap.