Neospora caninum: a cause of immune-mediated failure of pregnancy?

Resistance to many intracellular protozoan parasites is dependent on T helper cell 1 cytokine responses. This has important repercussions for pregnant females because strong T helper cell 1 cytokine responses are incompatible with successful pregnancy. Thus, there are two possible consequences of infection with protozoans such as Leishmania major, Plasmodium falciparum and Toxoplasma gondii during pregnancy: (1) pregnancy is compromised; or (2) resistance to the parasite is compromised. The apicomplexan Neospora caninum is a parasite renowned for its association with abortion in cattle. Furthermore, a major route of transmission for this parasite is congenital. The evidence for the hypothesis that T helper cell 1 cytokines play a role in these events is reviewed here. Apicomplexan parasites like Neospora caninum, Toxoplasma gondii and Plasmodium spaceies have long been recognised to have adverse effects on pregnancy but could it be that the immune response rather than the parasites per se is to blame?