Immunocytochemical localization of acid phosphatase in rat liver

Localization of acid phosphatase (ACPase) in rat liver was investigated by immunocytochemical techniques. Rat liver was fixed by perfusion and cut into thick tissue slices, which were embedded in Epon or Lowicryl K4M. For light microscopy (LM), semithin Epon sections were stained for the enzyme ACPase by an indirect immunoenzyme technique. For electron microscopy (EM), ultra-thin Lowicryl K4M sections were stained by a protein A-gold technique. By means of LM, granular reaction deposits were observed in hepatocytes and sinus-lining cells. Stained granules were present in the juxtanuclear cytoplasm, but they did not correspond to a typical staining pattern for the Golgi complex. EM revealed that gold particles indicating ACPase antigens were present on lysosomes and on some vesicles locating in the trans Golgi region. Endosomelike vesicles were strongly positive for the labeling. Golgi cisterna were mostly negative, but weak signals were noted in dilated sacules. The plasma membranes on the sinusoidal and bile canalicular sides were labeled by a few gold particles. The results indicate that ACPase is present in endosomes and in a restricted area of plasma membrane, as well as in the lysosomal system.