Abstract
Despite Neospora caninum being a major cause of bovine abortion worldwide, its pathogenesis is not completely understood. Neospora infection stimulates host cell-mediated immune responses, which may be responsible for the placental damage leading to abortion. The aim of the current study was to characterize the placental immune response following an experimental inoculation of pregnant cattle with N. caninum tachyzoites at day 210 of gestation. Cows were culled at 14, 28, 42 and 56 days post inoculation (dpi). Placentomes were examined by immunohistochemistry using antibodies against macrophages, T-cell subsets (CD4, CD8 and γδ), NK cells and B cells. Macrophages were detected mainly at 14 days post inoculation. Inflammation was generally mild and mainly characterized by CD3+, CD4+ and γδ T-cells; whereas CD8+ and NK cells were less numerous. The immune cell repertoire observed in this study was similar to those seen in pregnant cattle challenged with N. caninum at early gestation. However, cellular infiltrates were less severe than those seen during first trimester Neospora infections. This may explain the milder clinical outcome observed when animals are infected late in gestation.
Highlights
The coccidian parasite Neospora caninum is recognized as a major cause of abortion in cattle [1,2] and has a facultative heteroxenous life cycle involving a definitive canid host [3,4,5] and a wide range of intermediate hosts, of which cattle are the most economically important [6,7]
Infection due to neosporosis may occur postnatally following ingestion of oocysts shed in the faeces of infected canids potentially leading to exogenous transplacental transmission [8,9] or through recrudescence of a previous infection leading to endogenous transplacental transmission of the parasite from mother to foetus via the placenta [10,11,12]
The aim of the present study was to characterise the phenotype of the cellular immune infiltrate in the placenta of cattle experimentally inoculated with live N. caninum (Nc-1 strain) tachyzoites on day 210 of gestation
Summary
The coccidian parasite Neospora caninum is recognized as a major cause of abortion in cattle [1,2] and has a facultative heteroxenous life cycle involving a definitive canid host (dogs, coyotes, dingoes) [3,4,5] and a wide range of intermediate hosts, of which cattle are the most economically important [6,7]. Neospora is an abortifacient in cattle since the brain and heart lesions usually observed in infected foetuses may be severe enough to cause mortality [14,15,16] and the infection-associated placental damage can disrupt the vascular supply of nutrients leading to foetal death [17,18]. In some instances, relatively small numbers of parasites, whilst producing mild lesions, may cause a shift from a beneficial T helper 2 (Th2) response towards a more harmful Th1 response during pregnancy, thereby inducing abortion [19,20]
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