Internalization of phosphatidylserine by adherent and non-adherent rat mononuclear cells

Energy-dependent, protein-mediated incorporation of radiolabeled phosphatidylserine vesicles is observed in casein-elicited rat peritoneal cells. Cell fractionation and a comparison with other phospholipids demonstrate the selective interaction of phosphatidylserine with the mononuclear fraction of these cells. During 60 min of incubation, unchanged phosphatidylserine accumulates in the cells whereas lysophosphatidylserine is released in the medium. When adherence is used to fractionate the mononuclear cells, phosphatidylserine uptake is detected in the macrophage-enriched fraction (adherent cells) and in the lymphocyte-enriched fraction (non-adherent cells). Evidence of stereoselective uptake and of phosphatidylserine internalization in both cells is obtained by the use of phosphatidyl-D-serine and by digestion of the extracellular phospholipid with phospholipase A2. Only in lymphocytes is the uptake of phospholipid substantially inhibited by cytochalasin B, metabolic poisons and a low incubation temperature (17 degrees C). Phosphatidylserine deacylation-reacylation is instead detected in both cells. It is concluded that lymphocytes actively concur in the uptake of phosphatidylserine by rat mononuclear cells.