In vitro light and electron microscope studies on different virulent promastigotes ofLeishmania donovani in hamster peritoneal macrophages

Summary

Hamster peritoneal macrophages were infected with arivulent and virulent promastigotes of aL. donovani strain using various ratios (1∶1; 1∶10) of parasites and peritoneal cells. Light microscope studies have shown that there was a significant difference in the number of parasites taken up by phagocytic cells between the macrophage cultures infected with avirulent and virulent promastigotes at 4 h as well as during the following 14 days of infection. In both virulent groups the number of amastigotes were sharply increased. However, the surviving parasites were eliminated continuously when the macrophage cultures were infected with avirulent parasites. Electron microscope examinations of the different infected macrophage cultures did not show any difference in the localization of the surviving parasites. At one and 24 h post-infection, parasites have been observed in typical parasitophorous vacuoles. However, by day 4, 7, and 14 post-infections, the majority of intact parasites were surrounded by a four-laminar membrane without a space between parasite and vacuole membrane. Besides, some amastigotes were seen in large parasitophorous vacuoles. It seemed as if some of these amastigotes were trying to leave the parasitophorous vacuoles. In all cases acid phosphatase could be demonstrated in the parasitophorous vacoules and around the parasites indicating that the lysosomes of the host cell have been fused with the parasitophorous vacuole. It is indicated that the virulentLeishmania parasites are more resistant to the digestive system of the macrophages.