Endocytosis of lipopolysaccharide in mouse macrophages.

Lipopolysaccharide binding sites of mouse peritoneal macrophages were demonstrated by means of immunogold technique. Resident peritoneal macrophages identified by peroxidatic activity in the nuclear envelope and in the rough endoplasmic reticulum show moderate and constant specific binding of bacterial lipopolysaccharide from E. coli to cell surface structures. Labeling of peritoneal macrophages with LPS-gold particles (LPS-Au) at 4 degrees C followed by incubation of the cells at 37 degrees C permits the investigation of LPS endocytosis. After various incubation times LPS-Au was detected in different endocytic compartments. LPS was internalized via coated pits and coated and uncoated vesicles (5 min.). After 60 min, incubation time LPS-Au occurred in electron lucent endosomes, multivesicular bodies, tubulo-reticular structures and in lysosomes. Gold particles appeared mainly in lysosomes after a longer incubation time (240 min.). The results of LPS binding and internalization are in accordance with a postulated LPS-receptor binding.