Abstract
The immune responses of pregnant cattle and their foetuses were examined following inoculation on day 70 of gestation either intravenously (iv) (group 1) or subcutaneously (sc) (group 2) with live NC1 strain tachyzoites or with Vero cells (control) (group 3). Peripheral blood mononuclear cell (PBMC) responses to Neospora antigen and foetal viability were assessed throughout the experiment. Two animals from each group were sacrificed at 14, 28, 42 and 56 days post inoculation (pi). At post mortem, maternal lymph nodes, spleen and PBMC and when possible foetal spleen, thymus and PBMC samples were collected for analysis. Inoculation with NC1 (iv and sc) lead to foetal deaths in all group 1 dams (6/6) and in 3/6 group 2 dams from day 28pi; statistically significant (p ≤ 0.05) increases in cell-mediated immune (CMI) responses including antigen-specific cell proliferation and IFN-γ production as well as increased levels of IL-4, IL-10 and IL-12 were observed in challenged dams compared to the group 3 animals. Lymph node samples from the group 2 animals carrying live foetuses showed greater levels of cellular proliferation as well as significantly (p ≤ 0.05) higher levels of IFN-γ compared to the dams in group 2 carrying dead foetuses. Foetal spleen, thymus and PBMC samples demonstrated cellular proliferation as well as IFN-γ, IL-4, IL-10 and IL-12 production following mitogenic stimulation with Con A from day 14pi (day 84 gestation) onwards. This study shows that the generation of robust peripheral and local maternal CMI responses (lymphoproliferation, IFN-γ) may inhibit the vertical transmission of the parasite.
Highlights
The protozoan parasite Neospora caninum is a major cause of abortion and reproductive failure in cattle worldwide
Experimental infections of pregnant cattle have shown that foetal death may occur when dams were challenged with N. caninum tachyzoites at day 70 of gestation [10,11], while a challenge administered around mid gestation resulted in the vertical transmission of the parasite, but no foetal death [12,13]
The maternal serology and histopathology data from this experiment is described in Macaldowie et al, (2004) Neospora caninum parasites were only demonstrated in placental and foetal tissues from challenged animals carrying dead foetuses and they were associated with lesions [11]
Summary
The protozoan parasite Neospora caninum is a major cause of abortion and reproductive failure in cattle worldwide. Experimental infections of pregnant cattle have shown that foetal death may occur when dams were challenged with N. caninum tachyzoites at day 70 of gestation [10,11], while a challenge administered around mid gestation resulted in the vertical transmission of the parasite, but no foetal death [12,13]. These observations would suggest that the timing of a parasitaemia during pregnancy is critical in the clinical outcome and will likely be influenced by both the maternal and foetal immune responses to the parasite. Work carried out by Williams et al (2000); Collantes-Fernandez et al, (2006) and Rosbottom et al, (2007) [10,14,15] would support this conclusion
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