The interaction between XXXX and mammalian cells. I. Mechanism of entry and intracellular fate of the parasite.

@entity3251 @entity3204
Macrophage, fibroblast, and HeLa cell cultures have been infected with @entity3204 , and observations have been made on parasite entry and fate. A special procedure was devised for studying the entry of @entity3251 by electron microscopy. Toxoplasmas were centrifuged onto the cells in the cold; fixation 1-3 min after warming yielded specimens showing numerous examples of parasites in the process of entering cells. The mechanism of entry into macrophages, fibroblasts, and HeLa cells was in all cases by phagocytosis. Micropseudopods were extended by the cells to envelop the attached parasites in a typical phagocytic vacuole. Apparently the @entity3251 stimulated this response of HeLa cells and fibroblasts, cell types not usually phagocytic. No instance was seen of penetration of @entity3251 through the cell membrane, or of parasites located free in the cytoplasm. Essentially all of the @entity3251 that entered HeLa cells divided with a generation time of 9 hr; the parasites formed large rosettes situated in vacuoles, eventually leading to host cell rupture. Macrophages took in larger numbers of @entity3251 than did HeLa cells, but approximately half of the parasites inside of macrophages degenerated within a few hours. The surviving @entity3251 in macrophages divided every 8 hr, forming rosettes and eventually rupturing the cells.
