Immune response profile of caruncular and trophoblast cell lines infected by high- (Nc-Spain7) and low-virulence (Nc-Spain1H) isolates of Neospora caninum

Abstract

Background Bovine neosporosis, one of the main causes of reproductive failure in cattle worldwide, poses a challenge for the immune system of pregnant cows. Changes in the Th-1/Th-2 balance in the placenta during gestation have been associated with abortion. Cotyledon and caruncle cell layers form the maternal-foetal interface in the placenta and are able to recognize and induce immune responses against Neospora caninum among other pathogens. The objective of the present work was to elucidate the immunomodulation produced by high- (Nc-Spain7) and low-virulence (Nc-Spain1H) isolates of N. caninum in bovine trophoblast (F3) and caruncular cells (BCEC-1) at early and late points after infection. Variations in the mRNA expression levels of toll-like receptor-2 (TLR-2), Th1 and Th2 cytokines (IL-4, IL-10, IL-8, IL-6, IL-12p40, IL-17, IFN-γ, TGF-β1, TNF-α), and endothelial adhesion molecules (ICAM-1 and VCAM-1) were investigated by RT-qPCR, and protein variations in culture supernatants were investigated by ELISA. Results A similar pattern of modulation was found in both cell lines. The most upregulated cytokines in infected cells were pro-inflammatory TNF-α ( P < 0.05–0.0001) and IL-8 ( P < 0.05–0.001) whereas regulatory IL-6 ( P < 0.05–0.001) and TGF-β1 ( P < 0.05–0.001) were downregulated in both cell lines. The measurement of secreted IL-6, IL-8 and TNF-α confirmed the mRNA expression level results. Differences between isolates were found in the mRNA expression levels of TLR-2 ( P < 0.05) in both cell lines and in the mRNA expression levels ( P < 0.05) and protein secretion of TNF-α ( P < 0.05), which were higher in the trophoblast cell line (F3) infected with the low-virulence isolate Nc-Spain1H. Conclusions Neospora caninum infection is shown to favor a pro-inflammatory response in placental target cells in vitro. In addition, significant immunomodulation differences were observed between high- and low-virulence isolates, which would partially explain the differences in virulence. Electronic supplementary material The online version of this article (10.1186/s13071-019-3466-z) contains supplementary material, which is available to authorized users.

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

“…This result is quite remarkable, since pro-inflammatory cytokines have been implicated in host defence during N. caninum infection [1-3, 15, 16], and they lead to enhanced control of Nc-Spain1H growth and dissemination. In addition, in previous in vitro studies, we showed stronger stimulation of the immune response in bovine macrophages [12] and trophoblast cells [9,11] infected by Nc-Spain1H than in those infected by Nc-Spain7. How placental tissues can recognize and mount an appropriate immune response against this isolate is a fascinating question whose answer remains unknown.…”

“…Previously, we used in vitro and in vivo models to characterize two N. caninum isolates with marked differences in virulence: Nc-Spain7 and Nc-Spain1H, previously classified as high-and lowvirulence isolates, respectively [6][7][8]. Specifically, in bovine trophobast cells [9][10][11] and macrophages [12], Nc-Spain7 showed an increased infection and proliferation rates, whereas Nc-Spain1H displayed a reduced proliferation associated to a higher stimulation of immune responses. However, in vitro models cannot mimic the complex architecture of the bovine placenta, as they lack the microenvironmental influences and the host ability to compensate for stress conditions.…”

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

“…The results showed certain immune responses of trophoblast cells to infection. However, perhaps due to a lack of stimulation of other immune cells or even due to the limitations of the analysis technique, we were not able to find key elements such as cytokines widely studied by other authors in placental cells [6,[36][37][38]. No clear differences were found between isolates, corroborating the results previously found by gene expression analyses in the same model of N. caninum [6].…”

“…Trophoblast cells are a recognized component of the immune system and are capable of responding to pathogens [32,33]. Recently, it has been shown by quantitative PCR analyses that trophoblast cells are able to respond to Neospora infection with a pro-inflammatory cytokine expression profile [6]. In the present study, none of these immune-related proteins were identified.…”

“…Using this model, we have previously shown that N. caninum infection modulates the transcriptome of host cells, especially in pathways such as extracellular matrix organization and cholesterol metabolism, favouring a pro-inflammatory response. In addition, some differences in parasite-trophoblast interactions between isolates have been described [5,6]. Parasite intraspecific variation in virulence has been widely demonstrated, and isolates have been characterized with low (e.g., Nc-Spain1H), moderate (e.g., Nc-1) and high virulence (e.g., Nc-Liv, Nc-Spain7) according to their capacity to produce foetal death after infection of dams during pregnancy [7][8][9][10][11].…”