Effects of neonatal spleen cell products on the multiplication of toxoplasma in rat peritoneal macrophages.

We studied the resistance of newborn rats to infection with T. gondii. Neonates of chronically infected rats were significantly more resistant to infection with Toxoplasma than were the newborn of normal, uninfected rats. Neonatal athymic rats (nu/nu) from immune mothers were susceptible to infection, whereas normal littermates (nu/+) were very resistant. Rat peritoneal macrophage monolayers did not exhibit enhanced toxoplasmacidal activity after the addition of immune serum to the culture medium. However, inhibition of Toxoplasma multiplication was observed when the parasites were exposed to immune serum just before the infection of macrophages. The effects of spleen cell products from neonates of chronically infected mothers on the multiplication of Toxoplasma in rat peritoneal macrophages were examined. A significant inhibition of Toxoplasma multiplication occurred in macrophages incubated with the supernatants of spleen cell cultures obtained from immune newborn rats, with added lysate antigen. The ability to be induced to make an inhibitory supernatant disappeared by the third week after birth. Also examined were supernatants of spleen cells sensitized in vitro by incubation with a Toxoplasma lysate antigen; when these were added to macrophage monolayers, inhibition of Toxoplasma multiplication was observed only if the antigen was accompanied by supernatant of immune spleen cells.