Cantón, G.J., Katzer, F., Maley, S.W., Bartley, P.M., Benavides, J., Palarea Albaladejo, J., Pang, Y.P., Smith, S., Rocchi, M.S., Buxton, D.A., Inglis, N.F. and Chianini, F.
||Despite Neospora caninum being a major cause of bovine abortion worldwide, its pathogenesis is not completely understood. N. caninum stimulates host cell-mediated immune responses, which may be responsible for placental damage leading to abortion. The aim of our studies was to characterise placental immune responses following experimental infection in different stages of pregnancy. Cows were infected with the Nc-1 isolate in early, mid and late gestation and culled at different time points post inoculation. Placentomes were examined by immunohistochemistry using antibodies against macrophages, T cells, NK and B cells. Inflammation at early gestation was generally moderate to severe, whereas it was mild to moderate at mid gestation and minimal to mild at late gestation. Cellular infiltrates were mainly characterised by the presence of CD3+, CD4+ and γδ T-cells. Macrophages were detected in increasing numbers during later time-points after infection. The distribution of the cellular subsets observed in the three studies was similar. However, cellular infiltrates were more severe following infection during the first trimester in comparison to the second and third trimester, particularly in the placentas carrying non-viable foetuses. This distinctive cellular immune response may explain the milder clinical outcome observed when animals are infected at mid or late gestation.