ANTIGEN-SPECIFIC CD8(-CELLS PROTECT AGAINST LETHAL TOXOPLASMOSIS IN MICE INFECTED WITH NEOSPORA-CANINUM() T)

Neospora caninum is a coccidial protozoan parasite that appears morpho logically indistinguishable from Toxoplasma gondii and that infects a large range of mammals. Both inbred and outbred strains of mice exhibi t a high degree of resistance to infection, with N, caninum. Three inb red strains of mice (A/J, BALB/c, and C57BL/6) that were infected intr aperitoneally with N. caninum were protected against a lethal challeng e from T.gondii. Vaccine-induced protection was Neospora dose dependen t. A rise in the CD8(+) T-cell population in mice that had been vaccin ated with N. caninum and challenged with T.gondii was observed. Adopti ve transfer of CD8(+) T-cell splenocytes from N. caninum-infected mice was protective against challenge with Toxoplasma. The CD8(+) T cells from Neospora-infected mice proliferate to both Neospora and Toxoplasm a antigens in vitro and secrete substantial quantities of gamma interf eron when pulsed with the parasite antigen, These observations demonst rate that N. caninum protects against lethal T. gondii infection by th e induction of CD8(+) T cells that are immunoreactive to both parasite s.