Systemic and local immune responses in sheep after Neospora caninum experimental infection at early, mid and late gestation

No Evidence of Neutrophil Response Modulation in Goats after Immunization against Paratuberculosis with a Heat-Inactivated Vaccine

Neutrophils are believed to play a role in the initial stages of paratuberculosis, and it has recently been demonstrated that vaccination can modulate their function via priming or through epigenetic and metabolic reprogramming (training). Modulation of the neutrophil response against Mycobacterium avium subspecies paratuberculosis (Map) through vaccination has been demonstrated in a rabbit model but not in ruminants. Therefore, in the present work, the effect of vaccination on the response of caprine neutrophils against Map was studied. Neutrophils were isolated from non-vaccinated (n = 7) and Gudair®-vaccinated goat kids (n = 7), before vaccination and 30 days post-vaccination. Then, several neutrophil functions were quantified ex vivo: cell-free and anchored neutrophil extracellular trap (NET) release, phagocytosis, and the differential expression of several cytokines and TLR2. The induction of cell-free NETosis and TLR2 expression by Map is reported for the first time. However, vaccination showed no significant effect on any of the functions studied. This suggests that the protection conferred by Gudair® vaccination is based on mechanisms that are independent of the neutrophil function modulation. Further research into the impact of alternative vaccination strategies or the paratuberculosis infection stage on ruminant neutrophil function could provide valuable insights into its role in paratuberculosis.

Ovine placental explants: A new ex vivo model to study host‒pathogen interactions in reproductive pathogens

Reproductive failure is one of the main performance constraints in ruminant livestock. Transmissible agents such as Toxoplasma gondii and Neospora caninum are commonly involved in the occurrence of abortion in ruminants, but little is known about the mechanisms involved. While in vivo models are optimal for the study of abortion pathogenesis, they have a high economic cost and come with ethical concerns. Unfortunately, alternative in vitro models fail to replicate the complex in vivo placental structure. To overcome the limitations of currently available models, we developed an ex vivo model based on the cultivation of fresh and cryopreserved sheep placental explants, enabling the biobanking of tissues. Reproducible and simple markers of tissue integrity (histology, RNA concentrations), viability (resazurin reduction), and functionality (synthesis of steroid hormones) were also investigated, allowing a clear quality assessment of the model. This work shows that, similar to fresh explants, tissues cryopreserved in ethylene glycol using slow freezing rates maintain not only their structure and function but also their receptivity to T. gondii and N. caninum infection. In addition, the findings demonstrate that explant lifespan is mainly limited by the culture method, with protocols requiring improvements to extend it beyond 2 days. These findings suggest that cryopreserved tissues can be exploited to study the initial host‒pathogen interactions taking place in the placenta, thus deepening the knowledge of the specific mechanisms that trigger reproductive failure in sheep. Importantly, this work paves the way for the development of similar models in related species and contributes to the reduction of experimental animal use in the future.

Evaluation of the innate immune response of caprine neutrophils against Mycobacterium avium subspecies paratuberculosis in vitro

Neutrophils constitute an essential component of the innate immune response, readily killing most bacteria through phagocytosis, degranulation, and the release of neutrophil extracellular traps (NETs) among other mechanisms. These cells play an unclear role in mycobacterial infections such as Mycobacterium avium subspecies paratuberculosis (Map), the etiological agent of paratuberculosis, and its response is particularly understudied in ruminants. Herein, a wide set of techniques were adapted, or newly developed, to study the in vitro response of caprine neutrophils after Map infection. Immunofluorescence was used to demonstrate, simultaneously, chemotaxis, phagocytosis, degranulation, and NETs. The quantification of neutrophil phagocytic activity against Map at a 1:10 multiplicity of infection (MOI), through flow cytometry, showed values that varied from 4.54 to 5.63% of phagocyting neutrophils. By immunofluorescence, a 73.3 ± 14.5% of the fields showed NETs, and the mean release of DNA, attributable to NETosis, calculated through a fluorometric method, was 16.2 ± 3.5%. In addition, the RNA expression of TGF-β, TNF and IL-1β cytokines, measured through reverse transcription qPCR, was significantly higher in the two latter. Overall, neutrophil response was proportional to the number of bacteria. This work confirms that the simultaneous study of several neutrophil mechanisms, and the combination of different methodologies, are essential to reach a comprehensive understanding of neutrophil response against pathogens, demonstrates that, in vitro, caprine neutrophils display a strong innate response against Map, using their entire repertoire of effector functions, and sets the basis for further in vitro and in vivo studies on the role of neutrophils in paratuberculosis.

A preliminary study on placental damage associated to experimental neosporosis in BALB/c mice

Neospora caninum is a protozoan parasite which can infect a range of animals, including dogs, cattle, and sheep. Bovine neosporosis, which mainly causes abortion in cattle, results in substantial economic losses worldwide. To study the effects of N. caninum infection on the placenta, a pregnant mouse model for N. caninum infection was established. The litter size (8.6 ± 1.5) and the number of live pups (6.4 ± 1.8) of infected dams were significantly lower compared with those of non-infected dams. Trophoblast cell shrinkage and a large number of apoptosomes were detected in the placentas of the infected group. The parasite load in the placental tissue was significantly higher with time after infection. Likewise, apoptosis of placental trophoblast cells significantly increased with time after infection. Among the 66 apoptotic genes detected in this study, eight genes, including Bcl-2, were significantly differentially expressed by about > tenfold in infected and uninfected mice. The expression of BAX and tumor necrosis factor-alpha (TNF-α) was upregulated in the placental cells of the infected mice, whereas the expression of BCL-2 was downregulated. Enzyme-linked immunosorbent assays (ELISAs) showed that apoptotic protease caspase-3 level was significantly increased in placental cell suspension, and insulin-like growth factor (IGF)-2 level was significantly reduced. Acetylcholine (ACH) and placental prolactin (PL) levels were initially decreased but eventually increased. In summary, infection of mice with N. caninum caused apoptotic damage to the placental tissues, cells, and genes and affected the normal physiological functions of placenta, which may largely explain the adverse pregnancy outcomes caused by N. caninum infection in mice.

Bovine Enteroids as an In Vitro Model for Infection with Bovine Coronavirus

Bovine coronavirus (BCoV) is one of the major viral pathogens of cattle, responsible for economic losses and causing a substantial impact on animal welfare. Several in vitro 2D models have been used to investigate BCoV infection and its pathogenesis. However, 3D enteroids are likely to be a better model with which to investigate host–pathogen interactions. This study established bovine enteroids as an in vitro replication system for BCoV, and we compared the expression of selected genes during the BCoV infection of the enteroids with the expression previously described in HCT-8 cells. The enteroids were successfully established from bovine ileum and permissive to BCoV, as shown by a seven-fold increase in viral RNA after 72 h. Immunostaining of differentiation markers showed a mixed population of differentiated cells. Gene expression ratios at 72 h showed that pro-inflammatory responses such as IL-8 and IL-1A remained unchanged in response to BCoV infection. Expression of other immune genes, including CXCL-3, MMP13, and TNF-α, was significantly downregulated. This study shows that the bovine enteroids had a differentiated cell population and were permissive to BCoV. Further studies are necessary for a comparative analysis to determine whether enteroids are suitable in vitro models to study host responses during BCoV infection.

Experimental infection with Neospora caninum in Texel ewes at different stages of gestation

In this study Texel sheep, at different stages of pregnancy, were experimentally infected with Neospora caninum. Eleven ewes, seronegative for N. caninum and Toxoplasma gondii, were inoculated 30 days before breeding (Group A), or at 65, 100, and 120 days of gestation (Groups B, C, and D). The group E (control) was inoculated with PBS. Blood samples were collected at -2, 2, 5, and 7 days post-infection (dpi), and weekly up to 42 dpi, for hematology, parasitemia (PCR), and serology (RIFI) assessments. Blood and tissue samples were collected from the lambs for molecular and histological analyses. All animals in Groups B, C, and D were seroconverted, whilst those in groups A and E remained seronegative. Parasitic DNA was detected in the blood of two ewes (groups B and D) and a lamb (group D), and in the brain of a lamb (group B). The parasitemia-positive ewe in group B delivered a weak and seropositive lamb, and had parasitic DNA in its placenta. These results confirm the vertical transmission of N. caninum in ewes inoculated at the beginning and end of pregnancy. The absence of abortions and other clinical signs suggest that Texel sheep may potentially have resistance to N. caninum.

Ovine Neosporosis: The Current Global Situation

Simple Summary

This review summarizes the current global situation of Neospora caninum infection in sheep by referring to all of the available descriptions of natural ovine neosporosis to date, focusing on epidemiology, clinical signs, lesions, and diagnosis. The data suggest that ovine neosporosis is more prevalent than currently thought, that it has increased in the last few decades, and that it should now be considered in the differential diagnosis when investigating abortion in sheep.

Abstract

In the past 20 years, Neospora caninum infection in sheep has been reported in at least 31 countries worldwide from all sheep-rearing continents (Europe, Asia, the Americas, Africa, and Oceania), and its role as an abortifacient agent is becoming more evident. Most studies of ovine neosporosis have focused on its epidemiology, based primarily on serological analysis, with only a few studies investigating the actual presence of the parasite by PCR and/or IHC. Individual seroprevalence rates were highly variable between countries, and even between regions within the same country, ranging from 0.0% to 67.4% positive. Furthermore, most of the studies were not directly comparable due to differences in experimental designs, sample sizes, husbandry systems, ecological factors, and serological tests (e.g., IFAT, ELISA, MAT, Western blot). The latter, along with the scarcity of studies on the relevance of N. caninum as an abortifacient agent, may bias the perception of the importance of this disease. This review summarizes the situation of N. caninum infection in sheep using all available published studies describing natural ovine neosporosis. The epidemiology shows that ovine neosporosis is found worldwide, and it poses a relevant risk to the sustainability of sheep flocks.

Congenital Transmission of Apicomplexan Parasites: A Review

Apicomplexans are a group of pathogenic protists that cause various diseases in humans and animals that cause economic losses worldwide. These unicellular eukaryotes are characterized by having a complex life cycle and the ability to evade the immune system of their host organism. Infections caused by some of these parasites affect millions of pregnant women worldwide, leading to various adverse maternal and fetal/placental effects. Unfortunately, the exact pathogenesis of congenital apicomplexan diseases is far from being understood, including the mechanisms of how they cross the placental barrier. In this review, we highlight important aspects of the diseases caused by species of Plasmodium, Babesia, Toxoplasma, and Neospora, their infection during pregnancy, emphasizing the possible role played by the placenta in the host-pathogen interaction.

Early response of monocyte-derived macrophages from vaccinated and non-vaccinated goats against in vitro infection with Mycobacterium avium subsp. paratuberculosis

Paratuberculosis is a disease of ruminants caused by Mycobacterium avium subsp. paratuberculosis (Map). Vaccination is the most cost-effective control method. However, despite the fact that macrophages are the main target cells for this pathogen, the precise mechanisms behind the response of the macrophage to Map infection and how it is modified by vaccination are yet poorly understood. The aim of this study was to investigate the effect of Silirum^® vaccination in the early immune response of caprine monocyte-derived macrophages (CaMØs). Peripheral blood mononuclear cells (PBMCs) were obtained from vaccinated and non-vaccinated goats, cultured in vitro until differentiation to macrophages and infected with Map. After a 24 h incubation, Map viability and DNA were assessed in culture by viable colony count and real time quantitative polymerase chain reaction (qPCR). In addition, Map phagocytosis and expression of IL-10, IL-12, IFN-γ, TNF-α, IL-17A, IL-1β, iNOS, IL-6 and MIP-1β were also evaluated through immunofluorescence labelling and reverse transcriptase qPCR (RT-qPCR), respectively. A significant reduction of Map viability was observed in both supernatants (P < 0.05) and CaMØs (P < 0.001) from the vaccinated group. Similarly, the percentage of infected CaMØs and the number of internalized Map by CaMØs (P < 0.0001) was higher in the vaccinated group. Finally, iNOS (P < 0.01) and IL-10 were significantly up-regulated in CaMØs from vaccinated goats, whereas only MIP-1β was up-regulated in non-vaccinated animals (P < 0.05). These results show that vaccination modifies the immune response of CaMØs, suggesting that the phagocytosis and microbiocidal activity of macrophages against Map is enhanced after vaccination.

Transplacental transmission of Neospora caninum to lambs in successive pregnancies of naturally infected sheep in Southern Brazil

This study aims to report the detection of N. caninum DNA in a newborn lamb (1) with neurological signs and congenital neosporosis and in a stillborn lamb (2), both born from the same ewe in a herd of Southern Brazil. The lambs were born during different pregnancies of a Suffolk ewe seropositive to N. caninum and seronegative to T. gondii. Histopathological lesions were observed only in the central nervous system of the lambs. The newborn lamb (1) showed mild and focal gliosis in the frontal lobe. In the hippocampal region of the stillborn lamb (2), lymphoplasmacytic perivascular cuffs and N. caninum cysts were observed in the cytoplasm of neurons and confirmed by IHC. PCR was performed using brain samples to detect the protozoa N. caninum and Toxoplasma gondii. The infection with N. caninum was confirmed in the newborn lamb (1) by PCR and in the stillborn lamb (2) by histopathology, immunohistochemistry, and PCR tests.

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

Neospora caninum and Toxoplasma gondii are one of the main concerns of the livestock sector as they cause important economic losses in ruminants due to the reproductive failure. It is well-known that the interaction of these parasites with the placenta determines the course of infection, leading to fetal death or parasite transmission to the offspring. However, to advance the development of effective vaccines and treatments, there are still important gaps on knowledge on the placental host-parasite interactions that need to be addressed. Ruminant animal models are still an indispensable tool for providing a global view of the pathogenesis, lesions, and immune responses, but their utilization embraces important economic and ethics restrictions. Alternative in vitro systems based on caruncular and trophoblast cells, the key cellular components of placentomes, have emerged in the last years, but their use can only offer a partial view of the processes triggered after infection as they cannot mimic the complex placental architecture and neglect the activity of resident immune cells. These drawbacks could be solved using placental explants, broadly employed in human medicine, and able to preserve its cellular architecture and function. Despite the availability of such materials is constrained by their short shelf-life, the development of adequate cryopreservation protocols could expand their use for research purposes. Herein, we review and discuss existing (and potential) in vivo, in vitro, and ex vivo ruminant placental models that have proven useful to unravel the pathogenic mechanisms and the host immune responses responsible for fetal death (or protection) caused by neosporosis and toxoplasmosis.

Maternal immune response in the placenta of sheep during recrudescence of natural congenital infection of Neospora caninum

In order to gain further insight into the pathogenesis and transmission of ovine neosporosis, the serological response of 13 naturally infected pregnant sheep was monitored. All sheep were euthanized upon the detection of a sharp increase in the level of specific antibodies against N. caninum in order to study the maternal immune response after the recrudescence of a chronic infection. Ten sheep were euthanized between 84 and 118 days of gestation, whereas the three remaining and three control not infected, pregnant sheep were euthanized at 135 days of gestation after no sharp increase in antibodies was detected. Vertical transmission was confirmed in 11 sheep by detection of N. caninum-DNA in at least one fetus, confirming recrudescence. Not all of fetuses showed pathologic microscopic lesions, however, multifocal non-purulent encephalitis was the main finding. Furthermore, nine out of the 11 vertical transmission positive sheep had lesions in placentomes (mainly multifocal necrotic foci), and the parasite was detected in eight out of 11 placentas by PCR and/or immunohistochemestry. The placentomes from sheep that suffered recrudescence showed an increased number of T lymphocytes CD3+ (CD4/CD8 < 1) and macrophages (MHC-II+), assessed by immunohistochemestry, together with an up-regulation of IFN-γ, IL-10, IL-4, TNFα, IL-2 and IL-18. IL-17 was only upregulated in the three infected sheep that did not have a sharp increase in antibody levels. In the sheep that showed fetal death at the time of euthanasia (n = 3) the placental microscopic lesions were more severe, the inflammatory infiltrate was higher, and the upregulation of cytokines was greater than in those sheep carrying viable fetuses. This study suggests that, similarly to bovine neosporosis, the time of gestation when recrudescence occurs determines the viability of the fetuses and, thus, seems to be related to the severity of lesions and immune response in the placenta. These results suggest that there might be a correlation, either as cause or as a consequence, between protection against vertical transmission of the parasite and a milder maternal serological response together with a high level of transcription of IL-17 in the placenta.

Attempts to induce tolerance to Trichostrongylus colubriformis infection in sheep

BACKGROUND AND OBJECTIVES

The possibility of manipulating the immune response in lambs to the gastrointestinal nematode Trichostrongylus colubriformis to reduce production losses associated with infection was investigated. In a series of four experiments, attempts to immunize sheep via the mucosal route to modify the immune response and induce mucosal tolerance are outlined. Initially, a proof of concept study was conducted with lambs being injected with multiple doses of a somatic T colubriformis antigen without an adjuvant in the rectal submucosa and subsequently challenged with T colubriformis L3 larvae. This was followed by a dose-response study comparing different antigen doses to identify the optimum dose of the nematode antigen for successful induction of mucosal tolerance. The final two studies were conducted to determine the larval stage specificity of the parasite antigen and the most suitable site of delivery required to stimulate mucosal tolerance.

METHODS

In the proof of concept study, lambs either received repeated injections in the rectal submucosa at 3 × weekly intervals with 15 µg of L3, 11 µg of L4 and 21 µg of immature adult (L5) somatic T colubriformis antigens (ANT) or not (INF) prior to infection with T colubriformis. In the dose-rate study, antigen dose rates of 100%, 50%, 10%, 1% or 0% of the antigen concentration used in the proof of concept study were compared while the larval stage study compared antigen from either L3, L4, L5 stages or combination of all (COMB) and the route of administration study compared antigen delivery into either the rectal submucosa (RE) or sub-cutaneous injection (SC).

RESULTS

During infection, lamb growth was improved by antigen treatment between days 21 and 42 in the proof of concept study (P = .009), for groups 10%, 50% and 100% in the dose-rate study (P < .05 for all) and in RE in the route of administration study with no improvement observed in the larval stage study. No differences in faecal egg counts were observed (P > .05 for all). Parasite-specific IgA and IgE showed a dose-response (the dose-rate study), were not affected by larval stage (the larval stage study) and were greater in RE than SC (the route of administration study). IL-4 production following lymphocyte stimulation was greatest in COMB (the larval stage study) and RE (the route of administration study).

CONCLUSIONS

Although antigen treatment improved performance, this was inconsistent and appeared to stimulate immunity rather than induce tolerance. Combined larval stages were more efficient than individual stages, and intra-rectal administration was more effective than sub-cutaneous.

Research into Neospora caninum-What Have We Learnt in the Last Thirty Years?

BACKGROUND

Neospora caninum has been recognised world-wide, first as a disease of dogs, then as an important cause of abortions in cattle for the past thirty years. Over that time period, there have been improvements in the diagnosis of infection and abortion, new tests have been developed and validated, and it is timely to review progress to date.

METHODS

Bibliometric methods were used to identify major trends and research topics present in the published literature on N. caninum. The tools used were SWIFT-Review, VOSviewer and SciMAT, along with the published papers found in the MEDLINE, Dimensions and Web of Science databases. A systematic review of the published Neospora literature (n = 2933) was also carried out via MEDLINE and systematically appraised for publications relevant to the pathogenesis, pathology and diagnosis of Neospora abortions.

RESULTS

A total of 92 publications were included in the final analysis and grouped into four main time periods. In these four different time periods, the main research themes were "dogs", "abortion", "seroprevalence" and "infection". Diagnostics, including PCR, dominated the first two time periods, with an increased focus on transmission and abortions, and its risk factors in cattle.

CONCLUSIONS

Longitudinal analyses indicated that the main themes were consistently investigated over the last 30 years through a wide range of studies, with evolving emphasis initially on dogs and diagnostic test development, followed by application to cattle, the identification of the risk factors leading to abortion, and in the latter time periods, an understanding of the immunity and a search for vaccines.

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

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.

Effects of challenge dose and inoculation route of the virulent Neospora caninum Nc-Spain7 isolate in pregnant cattle at mid-gestation

Parameters such as pathogen dose and inoculation route are paramount in animal models when studying disease pathogenesis. Here, clinical findings, including foetal mortality, parasite transmission rates and lesion severity, and immune responses were evaluated in Asturiana pregnant heifers at day 110 of gestation challenged with a virulent (Nc-Spain7) Neospora caninum isolate. Four different doses of parasite tachyzoites were inoculated intravenously (IV1, 10⁷ parasites, n = 6; IV2, 10⁵, n = 6; IV3, 10³, n = 6; and IV4, 10², n = 5), and the subcutaneous (SC) inoculation route was also assessed for the dose of 10⁵ tachyzoites (SC, n = 6). In addition, a control group (n = 4 pregnant heifers) was evaluated. Foetal death was observed in all infected groups from 25 to 62 days post-infection, varying with the dose (IV1:4/6, IV2:3/6; IV4:2/5, IV3:1/6), and was three times less frequently associated with the SC route than IV inoculation (1/6 vs. 3/6). A dose-dependent effect for parasite loads in placental and foetal brain tissues was also detected. After SC challenge, a reduced number of tachyzoites were able to reach foetal brain tissues, and no lesions were observed. In calves, specific IgG responses in precolostral sera were mainly associated with high-dose groups (IV1 [100.0%] and IV2 [66.7%]), and cerebral parasite DNA detection was scarce (3/18). In dams, IFN-γ production and the dynamics of anti-N. caninum IgG antibodies varied with the dose, and the cell-mediated immune response was also found to be route-dependent. Our results confirm the influence of parasite dose and inoculation route on the outcome and dynamics of bovine neosporosis at mid-gestation.

Peripheral and placental immune responses in sheep after experimental infection with Toxoplasma gondii at the three terms of gestation

Although it is known that gestation could influence the clinical course of ovine toxoplasmosis, the precise effect of the term of gestation when sheep are infected are yet mostly unknown. The aim of this study was to evaluate the peripheral and placental immune responses developed in pregnant sheep after experimental infection with Toxoplasma gondii at different times of gestation. Thirty-six pregnant sheep were allocated in different groups, orally inoculated with sporulated oocysts of T. gondii at early, mid and late gestation and culled within 30 days post-infection. The peripheral humoral and cytokine responses were evaluated, as well as the transcription of cytokines at the placenta. Serological analysis revealed that, regardless the term of gestation when infected, specific IgG against T. gondii were detected from day 8 post-infection and there was an early peripheral release of IFN-γ at the first week post-infection followed by a short peak of IL10 and TNF-α at the second week post-infection. There were no significant differences in this response between infected groups. At the placenta, a similar increase in transcription of IFN-γ, and TNF-α was found at the three terms of gestation, while IL-4 increased mainly at the first and second terms and IL-10 transcription was higher at the last term. While these findings show that both Th1 and Th2 cytokines play a key role in the pathogenesis of ovine toxoplasmosis and that placental and peripheral immune responses do not closely correlate, there seems to be no clear modulation of these responses along the gestation.

A model for chronic bovine besnoitiosis: Parasite stage and inoculation route are key factors

In this work, an experimental model for chronic besnoitiosis in bovine was developed and characterized. Using a previously established calf model, two new variables (parasite stage and inoculation route) were combined and used. Twelve Holstein Friesian 3-month-old male calves were randomly divided into four groups of three animals each. Bradyzoites were obtained from a chronically infected bull and used for inoculation via three different inoculation routes. Three groups were inoculated with 10⁶ bradyzoites by intravenous (G1), subcutaneous (G2) and intradermal (G3) routes, and a non-infected control group (G4) was inoculated with PBS. The trial lasted for 90 days and included daily clinical monitoring as well as weekly skin biopsies and blood sampling. Sera were obtained to analyse both cellular and humoral responses. Once the calves were euthanized, tissues from the skin, eyes, respiratory and reproductive tracts, among others, were collected to study presence of the parasite. Clinically, the infection was classified as mild to moderate for the acute stage since all infected calves showed lymphadenopathy from four days post-infection (pi) and fever from one week pi until 24 days pi. However, the most relevant results were achieved during the chronic stage that was classified as moderate to severe. In fact, pathognomonic conjunctival cysts were observed in all infected calves from 40 days pi onwards and were more abundant in G3. Moreover, one calf from this group developed skin lesions (49 days pi). The microscopic tissue cysts and Besnoitia DNA were detected primarily in skin, reproductive tract and respiratory tissue samples, and parasite load was higher in G3. In conclusion, the parasite stage (bradyzoite) and the inoculation route are key factors that influence the outcome of an infection. In particular, the intradermal route led to more severe clinical signs of the chronic phase in the inoculated calves.

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

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.

Promising Plant-Derived Adjuvants in the Development of Coccidial Vaccines

Coccidial parasites cause medical and veterinary diseases worldwide, frequently leading to severe illness and important economic losses. At present, drugs, chemotherapeutics and prophylactic vaccines are still missing for most of the coccidial infections. Moreover, the development and administration of drugs and chemotherapeutics against these diseases would not be adequate in livestock, since they may generate unacceptable residues in milk and meat that would avoid their commercialization. In this scenario, prophylactic vaccines emerge as the most suitable approach. Subunit vaccines have proven to be biologically safe and economically viable, allowing researchers to choose among the best antigens against each pathogen. However, they are generally poorly immunogenic and require the addition of adjuvant compounds to the vaccine formulation. During the last decades, research involving plant immunomodulatory compounds has become an important field of study based on their potential pharmaceutical applications. Some plant molecules such as saponins, polysaccharides, lectins and heat shock proteins are being explored as candidates for adjuvant/carriers formulations. Moreover, plant-derived immune stimulatory compounds open the possibility to attain the main goal in adjuvant research: a safe and non-toxic adjuvant capable of strongly boosting and directing immune responses that could be incorporated into different vaccine formulations, including mucosal vaccines. Here, we review the immunomodulatory properties of several plant molecules and discuss their application and future perspective as adjuvants in the development of vaccines against coccidial infections.

Immunization with a cocktail of antigens fused with OprI reduces Neospora caninum vertical transmission and postnatal mortality in mice

OprI is an outer membrane lipoprotein from Pseudomonas aeruginosa, and when fused to a recombinant antigen, will exert adjuvant properties by engaging Toll-like receptor 2, leading to dendritic cell activation. Previous studies have shown that the Neospora caninum (Nc) antigens NcPDI, NcROP2 and NcROP40 are implicated in host cell interactions and are promising vaccine candidates. In two independent experiments, the efficacy of a polyvalent vaccine formulation composed of OprI-NcPDI, OprI-NcROP2 and OprI-NcROP40 (collectively named O-Ags) was assessed in non-pregnant and pregnant Balb/c mouse models challenged with tachyzoites of the high-virulence isolate Nc-Spain7. Parameters that were investigated were clinical signs, fertility, parasite burden in adult mice, humoral and cellular immune responses at different time-points prior to and after challenge infection, vertical transmission and post-natal survival of offspring mice, all to explore potential correlations with efficacy. Vaccination of mice with O-Ags induced a mixed Th1/Th2 immune response in adult mice and led to significantly increased protection against cerebral infection. Vaccination with O-Ags also resulted in reduced vertical transmission, and postnatal disease in offspring was significantly inhibited at a rate not observed in mice infected with a high-virulence isolate to date. However, O-Ags mixed with TLR ligands targeting TLR3 and TLR7, which are known to induce clear Th1-biased responses, or vaccination with OprI fused to the non-N. caninum antigen ovalbumin (OprI-OVA) did not confer protection.

Antibody and cytokine response to Cystoisospora suis infections in immune-competent young pigs

Background

To date, investigations on the immune response to Cystoisospora suis infections focused on suckling piglets, the age group clinically most affected. Actively immunizing piglets is unfeasible due to their immature immune system and the typically early infection in the first days after birth. Therefore, understanding and possibly enhancing the immune response of immune-competent animals is the prerequisite to develop a passive immunization strategy for piglets which currently rely on very limited treatment options.

Methods

To investigate antibody and cytokine responses of immune-competent animals and the impact of the oral immunization protocol on their immune response, growers with unknown previous exposure to C. suis (10–11 weeks-old) were infected one or three times with different doses (600 and 6000 or 200 and 2000, respectively) of C. suis oocysts, and compared to uninfected controls. Oocyst excretion was evaluated, and blood and intestinal mucus antibody titers were determined by IFAT. Systemic production of Th1, Th2, inflammatory and regulatory cytokines was determined in different immune compartments at mRNA and (after stimulation with a recombinant merozoite-protein) at protein level by PCR and multiplex fluorescent immunoassay, respectively.

Results

Infection generated significantly increased serum IgA and IgG levels against C. suis sporozoites and merozoites, irrespective of infection mode, with IgG against merozoites showing the strongest increase. No clinical signs and only occasional excretion were observed. The systemic cytokine response to C. suis was only weak. Nonetheless, in white blood cells, IL-4, IL-6 and IL-10 mRNA-levels significantly increased after infection, whereas IFN-ɣ, IL-2 and TGF-β expression tended to decrease. In mesenteric lymph nodes (MLN), IL-10 and TNF-α levels were elevated while splenic cytokine expression was unaltered upon infection. Stimulated MLN-derived lymphocytes from infected pigs produced slightly more IL-12 and less IFN-α than controls.

Conclusions

An infection and a subsequent systemic immune response can be induced in immune-competent animals by all evaluated infection models and growers can be used as models to mimic sow immunizations. The immune response to C. suis, although mild and with considerable variation in cytokine expression, was characterized by a Th2-associated and regulatory cytokine profile and antibody production. However, none of the parameters clearly stood out as a potential marker associated with protection. Antibody titers were significantly positively related with oocyst excretion and might thus serve as correlates for parasite replication or severity of infection.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2974-6) contains supplementary material, which is available to authorized users.

Influence of dose and route of administration on the outcome of infection with the virulent Neospora caninum isolate Nc-Spain7 in pregnant sheep at mid-gestation

Experimental infections in pregnant sheep have been focused on studying the effect of the time of challenge on the outcome of N. caninum infection, whereas the impact of the dose and route of challenge has not been studied in depth. Therefore, clinical outcome, immune responses, parasite detection and burden, and lesion severity in placental tissues and foetal brains were investigated in 90-day-pregnant sheep inoculated intravenously with 10⁵ (G1), 10⁴ (G2), 10³ (G3), or 10² (G4) tachyzoites or subcutaneously with 10⁴ (G5) tachyzoites of the virulent Nc-Spain7 isolate and an uninfected group (G6). Comparing challenge doses, G1 was the only group that had 100% abortion. Likewise, IFNγ levels in G1 increased earlier than those in other intravenously infected groups, and IgG levels on day 21 post-infection (pi) were higher in G1 than those in other intravenously infected groups. Concerning vertical transmission, G1 shows a higher parasite burden in the foetal brain than did G2 and G3. Comparing routes of administration, no differences in foetal survival rate or parasite load in the foetal brain were found. Although G2 had higher IFNγ levels than G5 on day 10 pi, no differences were found in humoral immune responses. Because the outcome after intravenous infection with 10⁵ tachyzoites was similar to that observed after intravenous infection with 10⁶ tachyzoites used in a previous work (100% abortion and vertical transmission), we conclude that it may be reasonable to use 10⁵ tachyzoites administered by the intravenous route in further experiments when assessing drugs or vaccine candidates.

Early feed restriction of lambs modifies ileal epimural microbiota and affects immunity parameters during the fattening period

Bacteria firmly attached to the gastrointestinal epithelium during the pre-weaning phase may show a significant impact on nutrient processing, immunity parameters, health and feed efficiency of lambs during post-weaning phases. Thus, the aim of this study was to describe the differences in the ileal epimural microbiota (e.g. total bacteria, Prevotella spp., Bifidobacterium spp. and Lactobacillus spp.) of fattening lambs promoted by early feed restriction during the suckling phase trying to elucidate some of the underlying mechanisms behind changes in feed efficiency during the fattening period. A total of 24 Merino lambs (average BW 4.81±0.256 kg) were used, 12 of them (ad libitum, ADL) kept permanently in individual pens with their mothers, whereas the other 12 lambs were separated from their dams for 9 h each day to be exposed to milk restriction (RES). After weaning (BW=15 kg) all the animals were penned individually, offered the same complete pelleted diet (35 g/kg BW per day) and slaughtered at a BW of 27 kg. During the fattening period, reduced gain : feed ratio (0.320 v. 0.261, P<0.001) was observed for the RES group. Moreover, increments of Prevotella spp. were detected in the ileal epimural microbiota of RES lambs (P<0.05). There were also higher numbers of infiltrated lymphocytes (T and B cells) in the ileal lamina propria (P<0.05), a higher M-cell labelling intensity in ileal Peyer's patches domes (P<0.05) and a trend towards a thickening of the submucosa layer when compared with the ADL group (P=0.057). Some other immunological parameters, such as an increased immunoglobulin A (IgA) production (pg IgA/µg total protein) and increments in CD45+ cells were also observed in the ileum of RES group (P<0.05), whereas transforming growth factor β and toll-like receptor gene expression was reduced (P<0.05). In conclusion, early feed restriction during the suckling phase promoted changes in ileal epimural microbiota and several immunity parameters that could be related to differences in feed efficiency traits during the fattening period of Merino lambs.

Genetic correlations between endo-parasite phenotypes and economically important traits in dairy and beef cattle

Parasitic diseases have economic consequences in cattle production systems. Although breeding for parasite resistance can complement current control practices to reduce the prevalence globally, there is little knowledge of the implications of such a strategy on other performance traits. Records on individual animal antibody responses to Fasciola hepatica, Ostertagia ostertagi, and Neospora caninum were available from cows in 68 dairy herds (study herds); national abattoir data on F. hepatica-damaged livers were also available from dairy and beef cattle. After data edits, 9,271 dairy cows remained in the study herd dataset, whereas 19,542 dairy cows and 68,048 young dairy and beef animals had a record for the presence or absence of F. hepatica-damaged liver in the national dataset. Milk, reproductive, and carcass phenotypes were also available for a proportion of these animals as well as their contemporaries. Linear mixed models were used to estimate variance components of antibody responses to the three parasites; covariance components were estimated between the parasite phenotypes and economically important traits. Heritability of antibody responses to the different parasites, when treated as a continuous trait, ranged from 0.07 (O. ostertagi) to 0.13 (F. hepatica), whereas the coefficient of genetic variation ranged from 4% (O. ostertagi) to 20% (F. hepatica). The antibody response to N. caninum was genetically correlated with the antibody response to both F. hepatica (-0.29) and O. ostertagi (-0.67); a moderately positive genetic correlation existed between the antibody response to F. hepatica and O. ostertagi (0.66). Genetic correlations between the parasite phenotypes and the milk production traits were all close to zero (-0.14 to 0.10), as were the genetic correlations between F. hepatica-damaged livers and the carcass traits of carcass weight, conformation, and fat score evaluated in cows and young animals (0.00 to 0.16). The genetic correlation between F. hepatica-damaged livers in cows and milk somatic cell score was 0.32 (SE = 0.20). Antibody responses to F. hepatica and O. ostertagi had favorable genetic correlations with fertility traits, but conversely, antibody response to N. caninum and F. hepatica-damaged livers were unfavorably genetically correlated with fertility. This study provides the necessary information to undertake national multitrait genetic evaluations for parasite phenotypes.

Safety and efficacy of the bumped kinase inhibitor BKI-1553 in pregnant sheep experimentally infected with Neospora caninum tachyzoites

Neospora caninum is one of the main causes of abortion in cattle, and recent studies have highlighted its relevance as an abortifacient in small ruminants. Vaccines or drugs for the control of neosporosis are lacking. Bumped kinase inhibitors (BKIs), which are ATP-competitive inhibitors of calcium dependent protein kinase 1 (CDPK1), were shown to be highly efficacious against several apicomplexan parasites in vitro and in laboratory animal models. We here present the pharmacokinetics, safety and efficacy of BKI-1553 in pregnant ewes and foetuses using a pregnant sheep model of N. caninum infection. BKI-1553 showed exposure in pregnant ewes with trough concentrations of approximately 4 μM, and of 1  μM in foetuses. Subcutaneous BKI-1553 administration increased rectal temperatures shortly after treatment, and resulted in dermal nodules triggering a slight monocytosis after repeated doses at short intervals. BKI-1553 treatment decreased fever in infected pregnant ewes already after two applications, resulted in a 37–50% reduction in foetal mortality, and modulated immune responses; IFNγ levels were increased early after infection and IgG levels were reduced subsequently. N. caninum was abundantly found in placental tissues; however, parasite detection in foetal brain tissue decreased from 94% in the infected/untreated group to 69–71% in the treated groups. In summary, BKI-1553 confers partial protection against abortion in a ruminant experimental model of N. caninum infection during pregnancy. In addition, reduced parasite detection, parasite load and lesions in foetal brains were observed.

•

BKI-1553 showed excellent exposure in pregnant ewes and foetuses.

•

BKI-1553 confers partial protection against abortion in N. caninum infected ewes.

•

Treatment reduces parasite detection, parasite load and lesions in foetal brains.

Innate immune transcriptomic evaluation of PBMC isolated from sheep after infection with E. ruminantium Welgevonden strain

Heartwater is a tick-borne non-infectious fatal disease of wild and domestic ruminants caused by the bacterium Ehrlichia ruminantium, transmitted by Amblyomma ticks. Although there is evidence that interferon-gamma (IFN-γ) controls E. ruminantium growth and that cellular immune responses could be protective, an effective recombinant vaccine for this disease is lacking. An overall analysis of which immune pathways are up- or down-regulated in sheep peripheral blood mononuclear cells is expected to lead to a better understanding of the global immune response of sheep to E. ruminantium infection. Therefore, a systems biology oriented approach following the infection with E. ruminantium was investigated from peripheral blood mononuclear cells to aid recombinant vaccine development. In this study, heartwater naïve sheep were infected and challenged by allowing E. ruminantium infected ticks to feed on them. After primary infection, all the animals were treated with antibiotic during the resulting febrile response. Blood was collected daily for E. ruminantium detection by qPCR (pCS20 assay). The pCS20 assay only detected the pathogen in the blood one day prior to and during the febrile stage of infection confirming infection of the sheep. IFN-γ real-time PCR indicated that this cytokine was expressed at specific time points: post infection, during the febrile stage of the disease and after challenge. These were used as a guide to select samples for transcriptome sequencing. This paper focuses on transcripts that are associated with innate activating pathways that were identified to be up- and down-regulated after primary infection and the subsequent challenge. These included the CD14 monocyte marker, toll-like receptor (TLR), nod-like receptor, chemokine, cytosolic and cytokine-cytokine interaction receptor pathways. In particular, TLR4, TLR9 and CD14 were activated together with DNA detection pathways, suggesting that vaccine formulations may be improved if CpG motifs and lipopolysaccharides are included. This data indicates that innate immune activation, perhaps by using adjuvants, should be an important component for consideration during future heartwater recombinant vaccine development.

Peripheral and placental immune responses in goats after primoinfection with Neospora caninum at early, mid and late gestation

Neospora caninum can cause reproductive failure in goats. However, the pathogenesis of neosporosis in this domestic species remains largely unknown. We recently demonstrated that the outcome of experimental infection by N. caninum in pregnant goats is highly dependent on the time of gestation, during which infection occurs. In the present study, we examined the peripheral and placental immune responses in these groups of goats infected with 10⁶ tachyzoites of the Nc-Spain7 isolate at early (G1, at day 40 of gestation, dg), mid (G2, 90 dg) and late (G3, 120 dg) gestation, together with a group of non-infected goats as a control group (G4). Seroconversion was observed as early as day 10 post-infection (pi) in all goats from G1 that aborted earlier (10-11 pi). The remaining infected goats had seroconverted by day 14 pi. Similar IFN-γ kinetic profiles were found in sera from goats in G1 and G2 with a significant increase in the IFN-γ levels on days 7 and 10 pi. This increase was not observed in G3. A similar pattern of placental cytokine expression was found in all infected groups. IFN-γ and IL-4 showed the highest increase, followed by a weaker up-regulation in TNF-α and IL-10. The lowest up-regulation was observed for IL-12 expression. In summary, this study provides information regarding the dynamics of immune responses and their relationship with the outcome of N. caninum infection in goats during gestation.

Molecular analyses on Neospora caninum-triggered NETosis in the caprine system

Neospora caninum is an obligate intracellular protozoan parasite causing serious reproductive disorders in large and small ruminants worldwide. Polymorphonuclear neutrophils (PMN) react against multiple invading pathogens through different mechanisms including the release of neutrophil extracellular traps (NETs). Here, in vitro interactions of caprine PMN and N. caninum tachyzoites were studied. Scanning electron microscopic- and immunofluorescence-analyses demonstrated that caprine PMN undergo NETosis upon contact with tachyzoites of N. caninum, extruding filaments that entrap parasites. Detailed co-localization studies of N. caninum tachyzoite-induced NETs revealed the presence of PMN-derived DNA being decorated with histones (H1, H2A/H2B, H3,H4) and neutrophil elastase (NE) corroborating the molecular characteristics of classical mammalian NETs. As a new result for parasite-induced NETosis, we identified pentraxin and cathepsin B in N. caninum-triggered NETs. Nonetheless, functional inhibition assays revealed that during caprine NET formation triggered by N. caninum different molecular signaling pathways are induced, when compared to other apicomplexan parasites or host species. As such, N. caninum-induced NETosis appears to be influenced by MPO but independent of NADPH oxidase, SOCE, ERK1/2 and p38 MAPK activities. Furthermore, the inhibition of PMN autophagy via blockage of the PI3K-mediated signaling pathway failed to influence tachyzoite-induced NETosis. Since N. caninum-tachyzoites induced caprine NETosis, this effector mechanism should be considered as an early host immune response during acute caprine neosporosis.

Bovine Polymorphonuclear Neutrophils Cast Neutrophil Extracellular Traps against the Abortive Parasite Neospora caninum

Neospora caninum represents a relevant apicomplexan parasite causing severe reproductive disorders in cattle worldwide. Neutrophil extracellular trap (NET) generation was recently described as an efficient defense mechanism of polymorphonuclear neutrophils (PMN) acting against different parasites. In vitro interactions of bovine PMN with N. caninum were analyzed at different ratios and time spans. Extracellular DNA staining was used to illustrate the typical molecules of NETs [i.e., histones (H3), neutrophil elastase (NE), myeloperoxidase (MPO), pentraxin] via antibody-based immunofluorescence analyses. Functional inhibitor treatments were applied to reveal the role of several enzymes [NADPH oxidase (NOX), NE, MPO, PAD4], ATP-dependent P2Y2 receptor, store-operated Ca⁺⁺entry (SOCE), CD11b receptor, ERK1/2- and p38 MAPK-mediated signaling pathway in tachyzoite-triggered NETosis. N. caninum tachyzoites triggered NETosis in a time- and dose-dependent manner. Scanning electron microscopy analyses revealed NET structures being released by bovine PMN and entrapping tachyzoites. N. caninum-induced NET formation was found not to be NOX-, NE-, MPO-, PAD4-, ERK1/2-, and p38 MAP kinase-dependent process since inhibition of these enzymes led to a slight decrease of NET formation. CD11b was also identified as a neutrophil receptor being involved in NETosis. Furthermore, N. caninum-triggered NETosis depends on Ca⁺⁺ influx as well as neutrophil metabolism since both the inhibition of SOCE and of P2Y2-mediated ATP uptake diminished NET formation. Host cell invasion assays indicated that PMN-derived NETosis hampered tachyzoites from active host cell invasion, thereby inhibiting further intracellular replication. NET formation represents an early and effective mechanism of response of the innate immune system, which might reduce initial infection rates during the acute phase of cattle neosporosis.

Incidence and vertical transmission rate of Neospora caninum in sheep

The infection by Neospora caninum in sheep can lead to abortion and the birth of weak and debilitated lambs. The aim of this study was to assess the incidence of natural infection by Neospora caninum and the vertical transmission rate among sheep. A flock of 50 sheep was monitored for serum antibody titres against N. caninum and seroconversion over a period of six months using an indirect ELISA technique. The offspring of the herd was also investigated regarding anti-N. caninum antibodies to determine the vertical transmission rate through the indirect immunofluorescence technique. The initial and final prevalences of infection by N. caninum were 26.0% (13/50) and 72.0% (36/50), respectively, and the incidence of infection by N. caninum in the present study was 62.2% (23/37). The vertical transmission rate found was 15.4% (2/13). A high incidence of infection by N. caninum in sheep was observed, and this is the first report assessing the incidence of N. caninum among naturally infected sheep.