In vitro-model for Toxoplasma gondii invasion into neuroepithelial cells

In order to study the interactions of Toxoplasma gondii and neuroepithelial cells morphologically and biochemically we established an easy in vitro model, which simulates cellular contacts in congenital toxoplasmosis. Monolayer cultures of neuroepithelial cells from 13-14-day-old mouse embryos were prepared containing the typical ventricular cell types found in an embryonic brain, such as young neurons, macroglial and microglial cells. Ultrastructural investigations on cultures incubated for 1, 5 and 30 min or 1, 6, 12, 24 and 48 h with T. gondii indicated that all three cell types had been invaded by the parasites, multiplying in parasite vacuoles by means of endodyogeny. Microglial cells had already been penetrated by trophozoites within one minute and showed up to 3 or 5 parasite vacuoles per cell. Neurons and glial cells were invaded within 5 min and contained only one vacuole per host cell. All the parasite vacuoles were bounded by a membrane and bordered by the rough endoplasmic reticulum and mitochondria of the host cell after a few minutes. The vacuoles also contained some membranic tubuli. After 30 min some neuronal neurites were destroyed while the perikarya seemed to be unchanged. After 6 h the cytoplasm of the microglia lost more and more ribosomes and organelles. Neurons and glial cells showed no alterations. After 12h large areas of the vacuole membrane were folded up and lay curled up in the vacuoles. After 24 h incubation T. gondii had destroyed nearly all the microglial cells. The ultrastructure of neurons and glial cells now began to change in the same way as shown for microglial cells. The organelles and cellular membranes disintegrated and after 48 h incubation nearly all the cells in the neuroepithelial cell culture had fallen to pieces. For an identification of T. gondii in vitro by light microscopy or for the characterization of the cell surface we tried to label the parasites with 11 different FITC-stained lectins. None of the tested lectins bound to the parasites. We conclude that our in vitro-model for invasion of T. gondii in neuroepithelial cells opens an opportunity for studying the interaction of these cells or the pharmacological effects on this interaction under defined conditions.