Effect of polyclonal antisera developed against dense granule-associated Neospora caninum proteins on cell invasion and development in vitro by N. caninum tachyzoites.

The effects of polyclonal antisera to 2 recombinant dense granule (DG) antigens of Neospora caninum on invasion and development by N. caninum tachyzoites in baby hamster kidney cell cultures were examined. In immunofluorescent antibody tests, the anti-DG sera, at dilutions of 1:100 to 1:500, reacted intensely with individual intracellular tachyzoites and groups of tachyzoites enclosed in parasitophorous vacuoles at 2 and 52 h p.i., respectively. Tachyzoites suspended in diluted anti-DG sera and inoculated immediately into the cell cultures invaded cells in significantly fewer numbers (53-68% fewer by 2 h p.i.) than tachyzoites suspended in similarly diluted normal rabbit serum. In contrast, tachyzoites suspended in anti-Eimeria tenella sporozoite serum invaded cells as efficiently as those suspended in normal rabbit serum. Addition of anti-DG sera at the time of inoculation of tachyzoites, or to the cell cultures after the parasites had entered cells, had little effect on either the percentage or rate of their subsequent development.