Acid-phosphatase activity of reticular cells and macrophages in the lymph node of the rat after ingestion of mast-cell granules.

Acid phosphatase (ACPase) was ultracytochemically demonstrated in the lymph-node sinus reticular cells and macrophages of rats. After the uptake of horseradish peroxidase (HRP), marked ACPase activities were seen in both reticular cells and macrophages, although only sparse ACPase activity was detected in the reticular cells of the control. After the injection of HRP into the footpad, the mast cells in the regional lymph node became degranulated, and the released granules were taken up by reticular cells and macrophages. In macrophages, these taken-up mast-cell granules exhibited ACPase reaction products, whereas none of the granules taken up by reticular cells showed ACPase activity. The heparin-protamine complex was also engulfed by reticular cells and macrophages, and ACPase activity was demonstrable in the complex taken up by both types of cell. It is probable that, as is the case in macrophages, reticular cells in the lymph-node sinuses take up and digest foreign substances through the formation of phagolysosomes, but they do not digest granules originating from the mast cells in the lymph node of the same animal.