COMPOSITION AND SYNTHESIS OF LIPIDS IN RESTING AND PHAGOCYTIZING LEUKOCYTES

The lipid content of rabbit polymorphonuclear leukocytes, obtained from peritoneal exudates, constituted 8.7 ± 2.9 per cent of the dry weight of these cells; 60 per cent of all lipids were phospholipids, 20 per cent triglycerides, and the remainder cholesterol and cholesterol esters and a small amount of non-esterified fatty acids (2 to 4 per cent). The composition of the fatty acids in leukocytes, as determined by gas-liquid chromatography, was slightly different from rabbit serum and red blood cells, but markedly different from the dietary fat. The synthesis, turnover, and composition of lipids in rabbit leukocytes at rest and during phagocytosis in vitro were compared. Lipid content and composition were not affected by the phagocytic process. However, active phagocytosis resulted in an increase in the rate of turnover of lipids. This stimulation of lipid metabolism was more marked in triglycerides and cholesterol esters than in phospholipids. It is suggested that the increased turnover of lipid during phagocytosis may reflect a general metabolic stimulation accompanying this process, rather than a specific synthesis of phospholipid for the production of new cell membrane.