125I-labeled rat preputial gland beta-glucuronidase was shown by light and electron microscopic radioautography to accumulate within the parasitophorous vacuoles of in vitro derived bone marrow macrophages infected with Leishmania mexicana amazonensis. beta-glucuronidase uptake was mediated by the mannose receptor, since the penetration of the ligand was inhibited by mannan. Uptake was detected as soon as 4 h after incubation of infected cells with the ligand, and increased at 24 and 48 h. The label persisted in the vacuoles for at least 24 h after a 24-h pulse with the ligand, a finding compatible with the relatively long half-life of labeled beta-glucuronidase in normal macrophages. Parasitophorous vacuoles were also labeled in macrophages exposed to the ligand only before infection, indicating that secondary lysosomes containing the ligand fused with the parasitophorous vacuoles. Another mannosylated ligand, mannose-BSA, which, in contrast to beta-glucuronidase, is rapidly degraded in macrophage lysosomes, did not detectably accumulate in the vacuoles. The results support and extend information previously obtained with electron opaque tracers that emphasizes the phagolysosomal nature of Leishmania parasitophorous vacuoles. In addition, the results suggest that appropriate mannosylated molecules may be used as carriers for targeting of leishmanicidal drugs to the parasitophorous vacuoles of infected macrophages.

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