INCREASED SATURATED TRIACYLGLYCEROL LEVELS IN PLASMA-MEMBRANES OF HUMAN NEUTROPHILS STIMULATED BY LIPOPOLYSACCHARIDE

Neutrophils isolated from patients with bacterial infections or stimul ated in vitro with lipopolysaccharide (LPS) produce a high resolution, lipid-dominated spectrum on H-1-NMR spectroscopy (May et al, 1993. J. Infect. Dis. 168: 386-392). We have investigated the origin of this l ipid signal using NMR and chemical analyses of both whole neutrophils and purified plasma membranes. Plasma membranes from neutrophils that had been stimulated with 50 mu g/ml LPS exhibited the high resolution H-1-NMR signal, and contained double the triacylglycerol (TAG) content of plasma membranes isolated from resting cells. Chemical analysis of the whole cells indicated that the TAG also increased at the cellular level (1.7-fold) after stimulation with LPS. Diradylglycerol increase d 2- to 3-fold in both whole cells and plasma membranes after stimulat ion, but was only a minor component compared with TAG. The plasma memb rane protein/phospholipid ratio increased 2.6-fold, whereas cholestero l (free and esterified) was unchanged. The membranes from LPS-stimulat ed neutrophils exhibited increased fluidity, as judged by increased me rocyanine 540 binding, consistent with a a-fold reduction in cholester ol/phospholipid ratio. LPS induced a shift in fatty acid content of wh ole cell polar lipids towards more oleic acid and less palmitic acid, whereas the neutral lipid fraction contained increased amounts of palm itic and stearic acids. The TAG fraction of plasma membrane lipids con tained increased amounts of palmitic acid when prepared from cells sti mulated with LPS. We conclude that the H-1-NMR signal in LPS-stimulate d neutrophils arises from increased amounts of plasma membrane TAG wit h an elevated content of palmitic acid.