The fate of injected human IgG in the mouse liver: Uptake, immunological inactivation, and lysosomal reactions.

1. Human IgG is stored in the form of remarkable droplets in the cytoplasm of mouse hepatocytes following intravenous injection. 2. The earliest protein uptake occurs within 1 minute after injection and droplets can be found up to 32 hours thereafter; 64 hours p.i. the foreign protein is no longer visible in hepatocytes. 3. Electron microscopy reveals that the uptake occurs by a process of "macropinocytosis". The resulting protein droplets fuse with primary lysosomes and are transformed into phagolysosomes. 4. At the same time as the phagolysosomes are formed the IgG-droplets loose their immunological activity--as early as 2 hours after injection.