Crosstalk between Neospora caninum and the bovine host at the maternal-foetal interface determines the outcome of infection

Abstract

Neospora caninum is an apicomplexan cyst-forming parasite that is considered one of the main causes of abortion. The pathogenic mechanisms associated with parasite virulence at the maternal-foetal interface that are responsible for the outcome of infection are largely unknown. Here, utilizing placentomes from cattle experimentally infected with high-virulence (Nc-Spain7) and low-virulence (Nc-Spain1H) isolates, we studied key elements of the innate and adaptive immune responses, as well as components of the extracellular matrix (ECM), at 10 and 20 days post-infection (dpi). The low-virulence isolate elicited a robust immune response characterized by upregulation of genes involved in pathogen recognition, chemokines and pro-inflammatory cytokines, crucial for its adequate control. In addition, Nc-Spain1H triggered the expression of anti-inflammatory cytokines and other mechanisms implicated in the maintenance of ECM integrity to ensure foetal survival. In contrast, local immune responses were initially (10 dpi) impaired by Nc-Spain7, allowing parasite multiplication. Subsequently (20 dpi), a predominantly pro-inflammatory Th1-based response and an increase in leucocyte infiltration were observed. Moreover, Nc-Spain7-infected placentomes from animals carrying non-viable foetuses exhibited higher expression of the IL-8, TNF-α, iNOS and SERP-1 genes and lower expression of the metalloproteases and their inhibitors than Nc-Spain7-infected placentomes from animals carrying viable foetuses. In addition, profound placental damage characterized by an alteration in the ECM organization in necrotic foci, which could contribute to foetal death, was found. Two different host-parasite interaction patterns were observed at the bovine placenta as representative examples of different evolutionary strategies used by this parasite for transmission to offspring.

Proteomic Characterization of Host-Pathogen Interactions during Bovine Trophoblast Cell Line Infection by Neospora caninum

“…The greater similarity of proteome profiles between Nc-Spain7-infected cells and uninfected cells could indicate a greater host response against the low-virulence isolate, which could slow parasite multiplication and dissemination. Similar results have been found in transcriptomic analyses of infected trophoblast [5] and macrophage [21] cells and in analyses of gene expression of placentomes from an experimental infection in bovines, which could suggest a higher capacity of high-virulence isolates to restrain the host response at early stages of infection [22].…”

Modeling the Ruminant Placenta-Pathogen Interactions in Apicomplexan Parasites: Current and Future Perspectives

“…Consequently, different research groups have developed alternative simplified cell culture models based on the two major populations of the mature placenta: trophoblast and caruncular cells. These systems have provided useful information on the behavior of specific cell subsets when challenged with N. caninum or T. gondii , but offering a partial vision of the cellular processes that take place in the placenta, as they fail to mimic its complex structure ( 16 , 56 , 57 ). The use of in vitro models is mainly constrained by the lack of stimulation and activity of the immune cells resident or attracted to the placenta, the omission of host's ability to compensate for stress conditions, and the absence of the ECM, which is not only responsible for placental remodeling and function, but is also involved in the pathogenesis of some diseases, including toxoplasmosis ( 16 , 58 , 59 ).…”

“…These systems have provided useful information on the behavior of specific cell subsets when challenged with N. caninum or T. gondii , but offering a partial vision of the cellular processes that take place in the placenta, as they fail to mimic its complex structure ( 16 , 56 , 57 ). The use of in vitro models is mainly constrained by the lack of stimulation and activity of the immune cells resident or attracted to the placenta, the omission of host's ability to compensate for stress conditions, and the absence of the ECM, which is not only responsible for placental remodeling and function, but is also involved in the pathogenesis of some diseases, including toxoplasmosis ( 16 , 58 , 59 ). In this sense, and considering that explant cultures are able to retain the placental architecture and the dynamic relationship between fetal and maternal tissues, the use of ex vivo approaches seems an appealing alternative to deepen in the study of host-parasite relationships as they offer a mid-point between in vivo and classical in vitro systems ( 60 ).…”

“…Regarding the parameters that can be measured for studying parasite-placental interactions, these have been traditionally restricted to parasite detection and/or description of lesions in the placenta. Recent works have deepened in such interactions by investigating local immune responses in placentomes to elucidate its role in the clinical outcome of the disease, or in the control of parasite transmission ( 16 , 53 ). However, current trends of research are moving forward the implementation of “omics” techniques (i.e., transcriptomics, proteomics, etc.)…”

“…When the immune response was determined in placentomes from aborted dams or dams carrying non-viable fetuses at the euthanasia, Th2 and Treg cytokines were down-regulated ( 71 ). Recently, cytokines expression pattern in Nc-Spain7 infected animals at mid-gestation, carrying non-viable fetuses and euthanized at 20 dpi, showed an up-regulation of IL-8, iNOS, and TNF-α, previously associated with placental inflammation, luteolysis and abortion ( 16 ). Other studies have described a reduced expression of SERPINA14 (linked to maternal immunosuppression during pregnancy) in aborting dams, and a negative relationship with IFN-γ expression in cotyledon samples ( 94 ).…”