Brain phagocytes: source of high acid phosphatase activity.

A stab wound was produced in the adult rat cerebral cortex, and the progress of enzyme cytochemistry of phagocytosis was studied over 450 days. Light- and electron-microscopic observations were made to establish the origin of high acid phosphatase activity commonly seen at the site of brain lesions. Cells with phagocytic potential became differentiated and activated by the presence of degenerating neurons. The Golgi-lysosomal system of the phagocytes became elaborated, as evidenced by thiamine pyrophosphatase and acid phosphatase activities, the synthesis of acid phosphatase was increased, and the enzyme then secreted into the digestive vacuoles containing dead cells to be digested. Progress of the digestive process resulted in the accumulation of large amounts of acid phosphatase reaction product within the digestive vacuoles. The results showed that the phagocytes were the only detectable source of increased acid phosphatase activity at the site of injury in the cerebral cortex. In contrast to the phagocytes, newly formed multi-nucleated giant cells exhibited weak acid phosphatase, and intense cytochrome oxidase activities, the difference between the two cells reflecting the functional characteristics of each.