Localisation of macrophage lysosomal enzyme in experimental toxoplasma retinitis

Rabbit retinal tissue experimentally infected with Toxoplasma gondii was processed for the lysosomal enzyme aryl sulphatase. Abundant lysosomal activity was found in lysosomal bodies of the infected macrophages. There appeared to be a lack of fusion of the lysosomal bodies with the phagosomes containing the organisms. Examination of the majority of macrophage vacuoles containing trophozoites failed to show consistently lead sulphide deposition for aryl sulphatase activity. By light microscopy 83% of 115 macrophage vacuoles containing the trophozoites of T. gondii showed an absence of lysosomal enzyme activity; 7% of the vacuole containing the trophozoites were found to contain lysosomal enzyme activity. In the remaining 10% of the vacuoles containing the trophozoites of T. gondii the presence or absence of lysosomal enzyme activity could not be determined with certainty. The frequent absence of lysosomal enzyme activity within the phagosomes containing T. gondii organisms may be related to the parasite's ability to multiply and encyst in an intracellular locus. The abundant lysosomal enzyme activity in the lysosomal bodies within the cytoplasm of the infected macrophages may contribute to the cellular destruction of surrounding tissues when infected macrophages burst open owing to proliferation of the trophozoites.