In vitro infection of murine macrophage by Leishmania brasiliensis. Mechanism of penetration.

The in vitro infection of peritoneal murine macrophages by a cultured pathogenic strain of Leishmania brasiliensis was studied. By phase contrast and light microscopy it could be observed that L. brasiliensis is rapidly endocytosed by the macrophages and localized in the cytoplasm in a vacuole inside which it multiplies. By phase contrast and electron microscopy it was observed that L. brasiliensis enters the macrophage by the anterior end through which it first attaches to the cell membrane. This penetration involves invagination of the cell membrane around the entering flagellum and parasite body. A mechanism of entry involving and active participation of the parasite membrane through receptor sites and membrane activity by the microfilament system is presented.