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

Abstract

Lipopolysaccharide (LPS) is one of the potent activators of macrophages. LPS 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 phosphatase histochemistry and did not take up Lucifer yellow added to the medium. Latex beads were incorporated into cytoplasmic vesicles distinct from the vacuoles. These results indicated that the vacuoles are neither phagosomes nor lysosomes. DiIC18(3), a specific marker of endoplasmic reticulum (ER), stained the vacuoles intensely, and DiOC6(3) stained the vacuoles at a density similar to nuclear envelope, suggesting ER origin of their membrane. Glucose-6-phosphatase, however, was not detected histochemically. Vacuoles were also stained with wheat germ agglutinin-horseradish peroxidase (WGA-HRP) or WGA-biotin, suggesting that the vacuoles originated from plasma membrane-endosome-trans Golgi network-secretory granule pathway. Golgi markers, TPPase or BODIPY-ceramide were not localized to the vacuolar membrane. These results indicate that the vacuoles may have dual origins; ER and plasma membrane-derived organelles.