Cellular immune responses in cattle experimentally infected with Neospora caninum

Neospora caninum has recently been identified as an important cause of infe ctious abortion in cattle. The parasite is closely related to Toxoplasma go ndii, but the two species are antigenically distinct. To examine cell proli ferative responses and the induction of IFN-gamma in experimentally infecte d cattle, four 2-4 months old calves were subcutaneously inoculated with N. caninum tachyzoites. Peripheral blood mononuclear cells were collected reg ularly and stimulated in vitro with a come lysate of N. caninum or T. gondi i tachyzoites. Significant proliferative responses to N. caninum antigen we re recorded in all calves from days 4-6 postinoculation. This response was accompanied by production of high levels of IFN-gamma. Although the calves remained seronegative to T. gondii, while seroconverting to N. caninum, sti mulation with T. gondii lysate resulted in cell proliferation of a similar magnitude as that obtained using the N. caninum lysate. However the T. gond ii lysate appeared less effective than the N. caninum lysate to stimulate I FN-gamma production. Cells taken from uninfected control animals did not sh ow any significant proliferation to either N, caninum or T. gondii antigen and no IFN-gamma was produced These results suggest that the two parasites may possess cross-reacting T-cell epitopes, but that the T cells specific f or N, caninum may have a different functional capacity. This highlights the need to investigate the antigen specificity and cytokine profile of T cell s from infected animals to help understand their role in immunity to N. can inum.