Lipids of alveolar macrophages, polymorphonuclear leukocytes, and their phagocytic vesicles

Abstract

Phagocytic vesicles were isolated from rabbit alveolar macrophages and guinea pig polymorphonuclear leukocytes that had ingested emulsified paraffin oil. Phospholipids and their fatty acids were determined in whole cells and in the phagocytic vesicle and pellet fractions separated from them. The cholesterol-to-phospholipid ratios in the vesicle fractions were distinctly higher than those of the respective whole cells or pellet fractions. The vesicle fractions also had higher phospholipid-to-protein ratios than did the whole cells. The phospholipids of the phagocytic vesicle fraction from macrophages contained relatively more sphingomyelin, lyso-(bis)phosphatidic acid, and phosphatidylserine and less lecithin, phosphatidylethanolamine, and phosphatidylinositol than did the whole cells or pellet fractions. The phospholipids of phagocytic vesicles from polymorphonuclear leukocytes contained significantly more phosphatidylinositol than did the pellet fractions. Lyso(bis)phosphatidic acid, which constituted 15% of the phospholipid in rabbit alveolar macrophages and 25% of that in their phagocytic vesicles, contained almost 60% oleic acid and 20% linoleic acid. This lipid was not detected in rabbit peritoneal macrophages or in rat alveolar macrophages.The polyunsaturated fatty acids of leukocyte phospholipids were chiefly linoleic, whereas in macrophages arachidonic accounted for almost 20% of the total fatty acids. The macrophages produced malondialdehyde when ingesting polystyrene beads or emulsified paraffin oil, from which it was inferred that peroxidation of endogenous lipid can occur during phagocytosis. Polymorphonuclear leukocytes in which less than 3% of phospholipid fatty acids were arachidonic did not produce malondialdehyde during phagocytosis of these inert particles, but did when ingesting an emulsion containing linolenate, thus providing evidence for peroxidation of ingested lipid. Isolated phagocytic vesicles from alveolar macrophages contained lipid peroxides and generated malondialdehyde when incubated with ADP, FeCl(3), and NADH.