Formation of lipid inclusions in normal human leukocytes

Normal peripheral blood leukocytes left standing at room temperature develop large inclusions which increase in number and size with time of incubation. The formation and nature of these inclusions were investigated. At 0 hour the structures were present in only 1% of the cells, whereas at 48 hr, they were in virtually all neutrophils and monocytes. Ultrastructurally, the globules measured 0.5-1.5 mu in diameter and they were usually not membrane bound. Histochemical analysis indicated that they were lipid in nature. The inclusions were separated on a sucrose density gradient and their isolation was confirmed by electron microscopy. Thin-layer chromatography of the isolated globules suggested that they consisted predominantly of triglycerides. Since it is known that the cells synthesize triglycerides at rest, it was postulated that the structures may represent the storage form for free fatty acids which may be utilized for membrane synthesis during phagocytosis.