Lipopolysaccharide-induced vacuoles in macrophages: Their origin is plasmamembrane-derived organelles and endoplasmic reticulum, but not lysosomes

Lipopolysaccharide (LPS) is one of the potent activators of macrophages. LP S was shown to induce cell spreading and large vacuoles in the cytoplasm of a macrophage-like cell line, JY3. These vacuoles were negative for acid ph osphatase histochemistry and did not take up Lucifer yellow added to the me dium. Latex beads were incorporated into cytoplasmic vesicles distinct from the vacuoles. These results indicated that the vacuoles are neither phagos omes nor lysosomes. DiIC(18)(3), a specific marker of endoplasmic reticulum (ER), stained the v acuoles intensely, and DiOC(6)(3) stained the vacuoles at a density similar to nuclear envelope, suggesting ER origin of their membrane. Glucose-6-pho sphatase, however, was not detected histochemically. Vacuoles were also stained with wheat germ agglutinin-horseradish peroxidas e (WGA-HRP) or WGA-biotin, suggesting that the vacuoles originated from pla sma membrane-endosome-trans Golgi network-secretory granule pathway. Golgi markers, TPPase or BODIPY-ceramide were not localized to the vacuolar membr ane. These results indicate that the vacuoles may have dual origins; ER and plas ma membrane-derived organelles.