Gamma interferon production correlates negatively with plasma levels of pregnancy-associated glycoprotein-1 (PAG-1) during gestation in dairy cows naturally infected with Neospora caninum

Abstract

Gamma interferon (IFN-γ) production has been ascribed a role in protecting cows infected with Neospora caninum against abortion. The present study analyzes the interaction between IFN-γ production and levels of plasma pregnancy-associated glycoprotein-1 (PAG-1), as a marker of placental/fetal well-being, throughout gestation in naturally Neospora-infected dairy cows. Data were obtained from 88 pregnant cows from two herds: 62 seropositive and 26 seronegative for the parasite. Blood sample collection was performed on days 40, 90, 120, 150, 180 and 210 of gestation. Plasma was tested for antibodies against N. caninum, PAG-1 and IFN-γ. Twenty five (28.4%) pregnancies were recorded after AI using Holstein-Friesian semen (19 in seronegative and 6 in seropositive animals), and 63 (71.6%) after AI using Limousin semen (7 in seronegative and 56 in seropositive animals). Gamma interferon was detected in the plasma of 14 (22.6%) of the 62 Neospora-seropositive cows and could not be detected in any of the 26 seronegative animals. All 14 cows producing IFN-γ became pregnant by using Limousin semen. Our GLM repeated measures showed no effect of herd, lactation number, milk production at the time of pregnancy diagnosis and Neospora-seropositivity on plasma PAG-1 concentrations. Significant positive effects of both the day of gestation (P<0.0001) and interaction between day of gestation and breed of sire (P = 0.001) on PAG-1 values were registered. Cows carrying twins had higher (P = 0.002) PAG-1 concentrations throughout gestation than cows carrying singletons. Interactions between breed of sire and Neospora-seropositivity (P<0.0001), and between IFN-γ production and Neospora-seropositivity (P = 0.04) were also detected. Thus, Neospora-seronegative cows inseminated with Limousin and Neospora-seropositive cows with no IFN-γ production, exhibited higher PAG-1 concentrations throughout gestation than seropositive cows inseminated with Limousin semen and producing IFN-γ, respectively. Our data indicate that production of IFN-γ correlates negatively and, the production of antibodies against N. caninum is uncorrelated with plasma PAG-1 concentrations during gestation in Neospora-infected dairy cows. Our results also suggest that augmented Th1 cell-mediated immunity is related to a lower risk of abortion and therefore higher resistance to the parasite in cows inseminated with Limousin versus Holstein-Friesian semen