Protection against abortion linked to gamma interferon production in pregnant dairy cows naturally infected with Neospora caninum

Abstract: Many immunological aspects of pregnancy, such as the role played by gamma interferon (IFN-γ) in abortion, are not well understood. Neospora caninum is an intracellular protozoan considered to be among the main causes of abortion in cattle worldwide. The present study analyzes the interaction between IFN-γ production and N. caninum infection in naturally infected pregnant cows. Data were obtained from 126 pregnant cows: 86 seropositive and 40 seronegative for the parasite. Pregnancy diagnosis and blood sample collection were performed on days 40, 90, 120, 150, 180 and 210 post-insemination or until the time of abortion detection. Plasma was tested for antibodies against N. caninum and IFN-γ. Interferon-gamma was detected at some point along the pregnancy in 16 (19%) of the 86 Neospora-seropositive cows yet was undetectable in the 40 seronegative animals. Of the 126 pregnancies examined, 22 (17.5%) ended in abortion. Abortion occurred in 24.4% of seropositive cows (21/86) and in 2.5% of seronegative animals (1/40). Significant (P <0.0001) interaction was observed between Neospora-seropositivity and IFN-γ production. Based on the odds ratio, the risk of abortion was 15.6 times higher in seropositive cows not producing IFN-γ than in seronegative animals, whereas neosporosis had no effect in seropositive cows with IFN-γ production. A significant (P =0.001) negative effect of IFN-γ production on the Neospora titer was furthermore observed in the 65 non-aborting seropositive animals. These results indicate that IFN-γ production affords protection against abortion in Neospora-infected cows and also point to a reduced humoral immune response to N. caninum during gestation in cows producing IFN-γ. [Copyright &y& Elsevier]