Prevention of vertical transmission of Neospora caninum in BALB/c mice by recombinant vaccinia virus carrying NcSRS2 gene

Immunogenicity, safety and dual DIVA-like character of a recombinant candidate vaccine against neosporosis in cattle

Neosporosis is the major infectious cause of abortion and reproductive losses in cattle worldwide; however, there are no available vaccines or drugs to control this disease. Recently, a dual (positive and negative) DIVA-like (Differentiation of Infected from Vaccinated Animals) vaccine was evaluated in a pregnant mouse model of neosporosis, showing promising immunogenic and protective results. The current report aimed to study the safety, the dose-dependent immunogenicity and the dual DIVA-like character of a recombinant subunit vaccine composed of the major surface antigen from Neospora caninum (rNcSAG1) and the carrier/adjuvant Heat shock protein 81.2 from Arabidopsis thaliana (rAtHsp81.2) in cattle. Healthy heifers were separated and assigned to experimental groups A-F and subcutaneously immunized with 2 doses of vaccine formulations 30 days apart as follows: A (n = 4): 50 μg rNcSAG1 + 150 μg rAtHsp81.2; B (n = 4): 200 μg rNcSAG1 + 600 μg rAtHsp81.2; C (n = 4): 500 μg rNcSAG1 + 1,500 μg rAtHsp81.2; D (n = 3): 150 μg rAtHsp81.2; E (n = 3):1,500 μg rAtHsp81.2, and F (n = 3) 2 ml of sterile PBS. The immunization of heifers with the different vaccine or adjuvant doses (groups A-E) was demonstrated to be safe and did not modify the mean value of the evaluated serum biomarkers of metabolic function (GOT/ASP, GPT/ALT, UREA, Glucose and total proteins). The kinetics and magnitude of the immune responses were dose-dependent. The higher dose of the vaccine formulation (group C) stimulated a broad and potent humoral and cellular immune response, characterized by an IgG1/IgG2 isotype profile and IFN-γ secretion. In addition, this was the first time that dual DIVA-like character of a vaccine against neosporosis was demonstrated, allowing us to differentiate vaccinated from infected heifers by two different DIVA compliant test approaches. These results encourage us to evaluate its protective efficacy in infected pregnant cattle in the future.

Working towards the development of vaccines and chemotherapeutics against neosporosis-With all of its ups and downs-Looking ahead

Neospora caninum is an apicomplexan and obligatory intracellular parasite, which is the leading cause of reproductive failure in cattle and affects other farm and domestic animals, but also induces neuromuscular disease in dogs of all ages. In cattle, neosporosis is an important health problem, and has a considerable economic impact. To date there is no protective vaccine or chemotherapeutic treatment on the market. Immuno-prophylaxis has long been considered as the best control measure. Proteins involved in host cell interaction and invasion, as well as antigens mediating inflammatory responses have been the most frequently assessed vaccine targets. However, despite considerable efforts no effective vaccine has been introduced to the market to date. The development of effective compounds to limit the effects of vertical transmission of N. caninum tachyzoites has emerged as an alternative or addition to vaccination, provided suitable targets and safe and efficacious drugs can be identified. Additionally, the combination of both treatment strategies might be interesting to further increase protectivity against N. caninum infections and to decrease the duration of treatment and the risk of potential drug resistance. Well-established and standardized animal infection models are key factors for the evaluation of promising vaccine and compound candidates. The vast majority of experimental animal experiments concerning neosporosis have been performed in mice, although in recent years the numbers of experimental studies in cattle and sheep have increased. In this review, we discuss the recent findings concerning the progress in drug and vaccine development against N. caninum infections in mice and ruminants.

Neospora caninum surface antigen 1 is a major determinant of the pathogenesis of neosporosis in nonpregnant and pregnant mice

Introduction

NcSAG1 is one of most widely investigated antigens of Neospora caninum in various research fields. Such studies demonstrated the proficiency of NcSAG1 in the regulatory process of parasite adhesion and invasion of host cells. Accordingly, the contribution of NcSAG1 to the pathogenesis of neosporosis can undoubtedly be extrapolated, but direct evidence is lacking. Herein, we provide the first successful attempt at the gene disruption of NcSAG1 and novel data on the invasion and virulence potentials of N. caninum in vitro and in vivo.

Methods

The disruption of the NcSAG1 gene was applied using the CRISPR/Cas9 system and confirmed by PCR, western blot and indirect fluorescent antibody tests as NcSAG1 knockout parasites (NcSAG1KO). Then, we investigated the role of NcSAG1 in the growth kinetics of the parasite in vitro.

Results and discussion

The deletion of the NcSAG1 gene significantly decreased the infection rate and reduced the egress rate of the parasite. An in vivo study using nonpregnant female and male BALB/c mice revealed a significantly higher survival rate and lower body weight change in the group infected with the NcSAG1KO parasite than in the parental strain (Nc-1)-infected group. Regarding the vertical transmission model of BALB/c mice, the absence of the NcSAG1 gene significantly enhanced the survival of pups and greatly lowered the parasite burden in the brains of pups. In conclusion, our study suggested NcSAG1 as a key molecule in the pathogenesis of N. caninum.

Towards the First Multiepitope Vaccine Candidate against Neospora caninum in Mouse Model: Immunoinformatic Standpoint

Neospora caninum is an economically significant parasite among livestock, particularly in dairy cattle herds, causing storm abortions. Vaccination seems necessary to limit the infection and its harsh consequences. This is the first steps towards developing a multiepitope vaccine candidate against N. caninum using in silico approaches. High-ranked mouse MHC-binding and shared linear B-cell epitopes from six proteins (SRS2, MIC3, MIC6, GRA1, IMP-1, and profilin) as well as IFN-γ-inducing epitopes (from SAG1) were predicted, screened, and connected together through appropriate linkers. Finally, RS-09 protein (TLR4 agonist) and histidine tag were added to N- and C-terminal of the vaccine sequence, yielding 486 residues in length. Physicochemical properties showed a stable (instability index: 27.23), highly soluble, antigenic (VaxiJen score: 0.9554), and nonallergenic candidate. Secondary structure of the multiepitope protein included 58.85% random coil, 20.99% extended strand, and 20.16% alpha helix. Also, the tertiary structure was predicted, and further analyses validated a stable interaction between the vaccine model and mouse TLR4 (binding score: -1261.6). Virtual simulation of immune profile demonstrated potently stimulated humoral (IgG+IgM) and cell-mediated (IFN-γ) responses upon multiepitope vaccine injection. Altogether, a potentially immunogenic vaccine candidate was developed using several N. caninum proteins, with the capability to elicit IFN-γ upsurge and other components of cellular immunity, and can be used in prophylactic purposes against neosporosis.

Determination of B and T Cell Epitopes in Neospora caninum Immune Mapped Protein-1 (IMP-1): Implications in Vaccine Design against Neosporosis

Prevention of neosporosis is advantageous for cattle health and productivity. Previously, several vaccine candidates were nominated for vaccination against Neospora caninum. This study was premised on in silico evaluation of N. caninum IMP-1 in order to determine its physicochemical features and immunogenic epitopes. We employed a wide array of network-based tools for the prediction of antigenicity, allergenicity, solubility, posttranslational modification (PTM) sites, physicochemical properties, transmembrane domains and signal peptide, secondary and tertiary structures, and intrinsically disordered regions. Also, prediction and screening of potential continuous B cell peptides and those epitopes having stringent affinity to couple with mouse major histocompatibility complex (MHC) and cytotoxic T lymphocyte (CTL) receptors were accomplished. The protein had 393 residues with a molecular weight of 42.71 kDa, representing aliphatic index of 85.83 (thermotolerant) and GRAVY score of -0.447 (hydrophilic). There were 47 PTM sites without a signal peptide in the sequence. Secondary structure comprised mostly of extended strand and helices, followed by coils. The Ramachandran plot of the refined model showed 90.1%, 9.9%, 0.0%, and 0.0% residues in the favored, additional allowed, generously allowed, and disallowed regions, correspondingly. Additionally, various potential B cell (linear and conformational), CTL, and MHC binding epitopes were predicted for N. caninum IMP-1. The findings of the present study could be further directed for next-generation vaccine design against neosporosis.

Neospora caninum SRS2 Protein: Essential Vaccination Targets and Biochemical Features for Next-Generation Vaccine Design

Vaccination is a standout preventive measure to combat neosporosis among cattle herds. The present in silico study was done to evaluate the physicochemical properties and potent immunogenic epitopes of N. caninum SRS2 protein as a possible vaccine candidate. Web-based tools were used to predict physicochemical properties, antigenicity, allergenicity, solubility, posttranslational modification (PTM) sites, transmembrane domains and signal peptide, and secondary and tertiary structures as well as intrinsically disordered regions, followed by identification and screening of potential linear and conformational B-cell epitopes and those peptides having affinity to bind mouse major histocompatibility complex (MHC) and cytotoxic T lymphocyte (CTL). The protein had 401 residues with a molecular weight of 42 kDa, representing aliphatic index of 69.35 (thermotolerant) and GRAVY score of -0.294 (hydrophilic). There were 53 PTM sites without a signal peptide in the sequence. Secondary structure comprised mostly by extended strand, followed by helices and coils. The Ramachandran plot of the refined model showed 90.2%, 8.8%, 0.5%, and 0.5% residues in the favored, additional allowed, generously allowed, and disallowed regions, correspondingly. Additionally, various potential B-cell (linear and conformational), CTL, and MHC-binding epitopes were predicted for N. caninum SRS2. These epitopes could be further utilized in the multiepitope vaccine constructs directed against neosporosis.

Role of dense granule antigen 7 in vertical transmission of Neospora caninum in C57BL/6 mice infected during early pregnancy

Neosporosis is a parasitic disease affecting the health of dogs and cattle worldwide. It is caused by Neospora caninum, an obligate intracellular apicomplexan parasite. Dogs are its definitive host, it mostly infects livestock animals, especially cattle that acts as intermediate host. It is necessary to have well-established models of abortion and vertical transmission in experimental animals, in order to determine basic control measures for the N. caninum infection. We evaluated the role of N. caninum dense granule antigen 7 (NcGRA7) in the vertical transmission of N. caninum using the C57BL/6 pregnant mouse model. We inoculated mice on day 3.5 of pregnancy with parental Nc-1 or NcGRA7-deficient parasites (NcGRA7KO). Post-mortem analyses were performed on day 30 after birth and the surviving pups were kept until day 30 postpartum. The number of parasites in the brain tissues of offspring from NcGRA7KO-infected dams was significantly lower than that of the Nc-1-infected dams under two infection doses (1 × 10⁶ and 1 × 10⁵ tachyzoites/mouse). The vertical transmission rates in the NcGRA7KO-infected group were significantly lower than those of the Nc1-infected group. To understand the mechanism by which the lack of NcGRA7 decreases the vertical transmission, pregnant mice were sacrificed on day 13.5 of pregnancy (10 days after infection), although parasite DNA was detected in the placentas, no significant difference was found between the two parasite lines. Histopathological analysis revealed a greater inflammatory response in the placentas from NcGRA7KO-infected dams than in those from the parental strain. This finding correlates with upregulated chemokine mRNA expression for CCL2, CCL8, and CXCL9 in the placentas from the NcGRA7KO-infected mice. In conclusion, these results suggest that loss of NcGRA7 triggers an inflammatory response in the placenta, resulting in decreased vertical transmission of N. caninum.

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.

Neospora caninum glycosylphosphatidylinositols used as adjuvants modulate cellular immune responses induced in vitro by a nanoparticle-based vaccine

Neospora caninum causes abortion in ruminants, leading to important economic losses and no efficient treatment or vaccine against neosporosis is available. Considering the complexity of the strategies developed by intracellular apicomplexan parasites to escape immune system, future vaccine formulations should associate the largest panel of antigens and adjuvants able to better stimulate immune responses than natural infection. A mucosal vaccine, constituted of di-palmitoyl phosphatidyl glycerol-loaded nanoparticles (DGNP) and total extract (TE) of soluble antigens of Toxoplasma gondii, has demonstrated its efficacy, decreasing drastically the parasite burden. Here, DGNP were loaded with N. caninum TE and glycosylphosphatidylinositol (GPI) of N. caninum as Toll-like receptor (TLR) adjuvant able to induce specific cellular and humoral immune responses. Activation of TLR2 and TLR4 signalling pathway in HEK reporter cells induced by GPI was abrogated after its incorporation into DGNP. However, in murine bone marrow-derived dendritic cells, an adjuvant effect of GPI was observed with higher levels of interleukin (IL)-1β, reduced levels of IL-6, IL-12p40 and IL-10, and decreased expression of major histocompatibility complex (MHC) molecules. GPI also modulated the responses of bovine peripheral blood mononuclear cells, by increasing the production of IFN-γ and by decreasing the expression of MHC molecules. Altogether, these results suggest that GPI delivered by the DGNP might modulate cell responses through the activation of an intracellular pathway of signalisation in a TLR-independent manner. In vivo experiments are needed to confirm the potent adjuvant properties of N. caninum GPI in a vaccine strategy against neosporosis.

Vaccination with Neospora GRA6 Interrupts the Vertical Transmission and Partially Protects Dams and Offspring against Neospora caninum Infection in Mice

Vaccination is the mainstay of preventative measures for numerous infectious diseases. Neospora caninum infection induces storms of abortion in pregnant cows and ewes, resulting in drastic economic losses because of fetal losses and culling of the dams. Herein, we evaluated the potential of recombinant protein of N. caninum dense granule protein 6 fused with glutathione-S-transferase (NcGRA6+GST) as a vaccine candidate against neosporosis in a pregnant mouse model. The protective efficacy was investigated by subcutaneous inoculation of BALB/c mice with recombinant NcGRA6+GST (25 pmol), and GST alone (25 pmol) or phosphate-buffered saline (PBS) as the controls. This study revealed the partial ability of NcGRA6+GST to protect the dams and offspring from N. caninum infection during the critical period of pregnancy. This ability was revealed by higher survival rate and lower parasite burden in brains of offspring of the NcGRA6+GST-immunized group in comparison with the control groups. In addition, mouse dams from NcGRA6+GST-immunized groups exhibited lower clinical score and minimum alteration in body weight in comparison with PBS or GST groups after challenge with N. caninum tachyzoites. Taken together, our results suggest the efficacy of recombinant NcGRA6 for interrupting the vertical transmission of N. caninum in mice by reducing the severity of infections in dams and offspring.

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.

The potential of a DIVA-like recombinant vaccine composed by rNcSAG1 and rAtHsp81.2 against vertical transmission in a mouse model of congenital neosporosis

Neospora caninum is the etiological agent of neosporosis, a worldwide infectious disease recognized as the major cause of abortions and reproductive failures in livestock, responsible for significant economic losses in cattle industries. Currently, there are not cost-effective control options for this pathology, and the development of a vaccine involving new and integrated approaches is highly recommended. In this study, we evaluated the immunogenic and protective efficacy, as well as the potential DIVA (Differentiation of Infected from Vaccinated Animals) character of a recombinant subunit vaccine composed by the major surface antigen from N. caninum (NcSAG1) and the carrier/adjuvant heat shock protein 81.2 from Arabidopsis thaliana (AtHsp81.2) in a mouse model of congenital neosporosis. BALB/c female mice were intraperitoneal (i.p.) immunized with a mixture of equimolar quantities of rNcSAG1 and rAtHSP81.2 or each protein alone (rNcSAG1 or rAtHsp81.2). The vaccine containing a mixture of rNcSAG1 and rAtHsp81.2 significantly enhanced the production of specific anti-rNcSAG1 total IgG (tIgG), IgG1 and IgG2a antibodies in immunized mice when compared to control groups (non-vaccinated and rAtHsp81.2 immunized mice) as well as to the group of mice immunized only with the antigen (rNcSAG1). In addition, partial protection against vertical transmission and improvement of the offspring survival time was observed in this group. On the other hand, rAtHsp81.2 induced the production of specific anti-rAtHsp81.2 tIgG, allowing us to differentiate vaccinated from infected mice. Despite further experiments have to be made in cattle to test the capability of this vaccine formulation to differentiate vaccinated from infected animals in the field, our results suggest that the formulation composed by rNcSAG1 and rAtHsp81.2 could serve as a basis for the development of a new vaccine approach against bovine neosporosis.

Neospora GRA6 possesses immune-stimulating activity and confers efficient protection against Neospora caninum infection in mice

Vaccination has the potential to be the most cost-effective control measure for reducing the economic burden of neosporosis in cattle. In this study, the immune-stimulatory effect of recombinant Neospora caninum dense granule protein 6 (NcGRA6) was confirmed via its triggering of IL-12p40 production in murine macrophages. BALB/c mice were immunized with recombinant NcGRA6 fused with glutathione S-transferase (GST) protein with or without oligomannose-coated-liposomes (OMLs) as the potential adjuvant. Specific IgG1 antibody production was observed from 21 and 35 days after the first immunization in NcGRA6+GST- and NcGRA6+GST-OML-immunized mice, respectively. However, specific IgG2a was detected 1 week after the infection, and IgG2a levels of the NcGRA6+GST- group were higher than those of the NcGRA6+GST-OML-group. Moreover, spleen cell proliferation with concomitant interferon-gamma production was detected in mice immunized with NcGRA6+GST, indicating that a significant cellular immune response was induced. Mouse survival rates against N. caninum challenge infection were 91.7% for NcGRA6+GST and 83.3% for NcGRA6+GST-OML, which were significantly higher than those of control groups (GST-OML: 25%, phosphate-buffered saline: 16.7%). This indicates that naked NcGRA6+GST induced protective immunity. Thus, our findings highlight the immune-stimulating potential of NcGRA6 and the ability to induce protective immunity against N. caninum infection in mice.

Towards a preventive strategy for neosporosis: challenges and future perspectives for vaccine development against infection with Neospora caninum

Neosporosis is caused by the intracellular protozoan parasite Neospora caninum. This major disease-causing pathogen is responsible for inducing abortion in cattle, and these adverse events occur sporadically all over the world, including Japan. Currently, there are no vaccines on the market against infection with N. caninum. Because live and attenuated vaccines against N. caninum have had safety and effectiveness issues, development of a next-generation vaccine is urgently required. To develop a vaccine against neosporosis, my laboratory has been focused on the following: 1) understanding the host immune responses against Neospora infection, 2) identifying vaccine antigens and 3) developing an effective antigen-delivery system. The research strategy taken in my laboratory will have strong potential to progress current understanding of the pathogenesis of N. caninum infection and promote development of a novel subunit vaccine based on the specific vaccine antigen with an antigen-delivery system for controlling neosporosis.

Constitutive expression and characterization of a surface SRS (NcSRS67) protein of Neospora caninum with no orthologue in Toxoplasma gondii

Neospora caninum is a parasite of the Apicomplexa phylum responsible for abortion and losses of fertility in cattle. As part of its intracellular cycle, the first interaction of the parasite with the target cell is performed with the surface proteins known as the SRS superfamily (Surface Antigen Glycoprotein - Related Sequences). SAG related or SRS proteins have been a target of intense research due to its immunodominant pattern, exhibiting potential as diagnostic and/or vaccine candidates. The aim of this study was the cloning, expression and characterization of the gene NcSRS67 of N. caninum using a novel designed plasmid. The coding sequence of NcSRS67 (without the signal peptide and the GPI anchor) was cloned and expressed constitutively instead of the ccdB system of pCR-Blunt II-TOPO. The protein was purified in a nickel sepharose column and identified by mass spectrometry (MS/MS). The constitutive expression did not affect the final bacterial growth, with a similar OD 600nm compared to the non-transformed strains. The recombinant NcSRS67 was over expressed and the native form was detected by the anti-rNcSRS67 serum on 1D western blot as a single band of approximately 38kDa as predicted. On an in vitro assay, the inhibitory effect of the polyclonal antiserum anti-rNcSRS67 was nearly 20% on adhesion/invasion of host cells. The NcSRS67 native protein was localised on part of the surface of N. caninum tachyzoite when compared to the nucleus by confocal immunofluorescence.

Oligomannose-coated liposome-entrapped dense granule protein 7 induces protective immune response to Neospora caninum in cattle

Neospora caninum is an intracellular protozoan parasite that causes abortion in cows. Vaccination is an important strategy for control of neosporosis, and a safe and effective vaccine suitable for cattle is required. Dense granule protein 7 of N. caninum (NcGRA7) is a secretory protein with high antigenicity in hosts. We demonstrated previously that NcGRA7 entrapped in liposomes coated with mannotriose (M3-NcGRA7) could induce a parasite-specific T-helper type 1 immune response and produce humoral antibodies that resulted in increased offspring survival and decreased infection in the brains of mice dams. In the present study, the efficacy of M3-NcGRA7 as a vaccine candidate against N. caninum has been evaluated in cattle (n=12). Cattle were immunized with M3-NcGRA7 containing 50 μg (n=4) or 200 μg NcGRA7 (n=4) subcutaneously twice with a 4-week interval and all cattle including the non-immunized controls (n=4) were inoculated with 10(7) tachyzoites of Nc-1 strain 27 days after the second immunization and euthanized at 85-87 days post infection (dpi). In immunized cattle, NcGRA7-specific antibody production and IFN-γ production in PBMC was induced before challenge. At 3 dpi, body temperature and concentration of serum IFN-γ tended to be higher in control cattle than in the immunized cattle. Furthermore, the parasite load in the brain significantly decreased in cattle immunized with 50 μg M3-NcGRA7 compared with controls. These results suggest that M3-NcGRA7 can induce protective immune responses to N. caninum tachyzoites in cattle, which could lead to practical application of safe and effective subunit vaccines.

Generation and immunity testing of a recombinant adenovirus expressing NcSRS2-NcGRA7 fusion protein of bovine Neospora caninum

Neospora caninum is the etiologic agent of bovine neosporosis, which affects the reproductive performance of cattle worldwide. The transmembrane protein, NcSRS2, and dense-granule protein, NcGRA7, were identified as protective antigens based on their ability to induce significant protective immune responses in murine neosporosis models. In the current study, NcSRS2 and NcGRA7 genes were spliced by overlap-extension PCR in a recombinant adenovirus termed Ad5-NcSRS2-NcGRA 7, expressing the NcSRS2-NcGRA7 gene, and the efficacy was evaluated in mice. The results showed that the titer of the recombinant adenovirus was 10(9)TCID50/ml. Three weeks post-boost immunization (w.p.b.i.), the IgG antibody titer in sera was as high as 1:4,096. IFN-γ and IL-4 levels were significantly different from the control group (P<0.01). This research established a solid foundation for the development of a recombinant adenovirus vaccine against bovine N. caninum.

Tissue distribution of Neospora caninum in experimentally infected cattle

Histopathology and quantitative PCR (qPCR) were used to determine the tissue distribution of Neospora caninum in calves at 80 days postinfection. Our findings revealed that the most appropriate brain areas for researching N. caninum pathogenesis were the amygdala and hippocampus for qPCR and the corpus striatum and diencephalon for histopathology.

Adjuvant and immunostimulatory effects of a D-galactose-binding lectin from Synadenium carinatum latex (ScLL) in the mouse model of vaccination against neosporosis

Vaccination is an important control measure for neosporosis that is caused by a coccidian parasite, Neospora caninum, leading to abortion and reproductive disorders in cattle and serious economic impacts worldwide. A D-galactose-binding lectin from Synadenium carinatum latex (ScLL) was recently described by our group with potential immunostimulatory and adjuvant effects in the leishmaniasis model. In this study, we evaluated the adjuvant effect of ScLL in immunization of mice against neosporosis. First, we investigated in vitro cytokine production by dendritic cells stimulated with Neospora lysate antigen (NLA), ScLL or both. Each treatment induced TNF-α, IL-6, IL-10 and IL-12 production in a dose-dependent manner, with synergistic effect of NLA plus ScLL. Next, four groups of C57BL/6 mice were immunized with NLA + ScLL, NLA, ScLL or PBS. The kinetics of antibody response showed a predominance of IgG and IgG1 for NLA + ScLL group, whereas IgG2a response was similar between NLA + ScLL and NLA groups. Ex vivo cytokine production by mouse spleen cells showed the highest IFN-γ/IL-10 ratio in the presence of NLA stimulation for mice immunized with NLA + ScLL and the lowest for those immunized with ScLL alone. After parasite challenge, mice immunized with NLA + ScLL or ScLL alone presented higher survival rates (70-80%) and lower brain parasite burden as compared to PBS group, but with no significant changes in morbidity and inflammation scores. In conclusion, ScLL combined with NLA was able to change the cytokine profile induced by the antigen or lectin alone for a Th1-biased immune response, resulting in high protection of mice challenged with the parasite, but with low degree of inflammation. Both features may be important to prevent congenital neosporosis, since protection and low inflammatory response are necessary events to guide towards a successful pregnancy.

A review of the infection, genetics, and evolution of Neospora caninum: from the past to the present

This paper is a review of current knowledge on Neospora caninum in the context of other apicomplexan parasites and with an emphasis on: life cycle, disease, epidemiology, immunity, control and treatment, evolution, genomes, and biological databases and web resources. N. caninum is an obligate, intracellular, coccidian, protozoan parasite of the phylum Apicomplexa. Infection can cause the clinical disease neosporosis, which most notably is associated with abortion in cattle. These abortions are a major root cause of economic loss to both the dairy and beef industries worldwide. N. caninum has been detected in every country in which a study has been specifically conducted to detect this parasite in cattle. The major mode of transmission in cattle is transplacental (or vertical) transmission and several elements of the N. caninum life cycle are yet to be studied in detail. The outcome of an infection is inextricably linked to the precise timing of the infection coupled with the status of the immune system of the dam and foetus. There is no community consensus as to whether it is the dam's pro-inflammatory cytotoxic response to tachyzoites that kills the foetus or the tachyzoites themselves. From economic analysis the most cost-effective approach to control neosporosis is a vaccine. The perfect vaccine would protect against both infection and the clinical disease, and this implies a vaccine is needed that can induce a non-foetopathic cell mediated immunity response. Researchers are beginning to capitalise on the vast potential of -omics data (e.g. genomes, transcriptomes, and proteomes) to further our understanding of pathogens but especially to identify vaccine and drug targets. The recent publication of a genome for N. caninum offers vast opportunities in these areas.

Development of a diagnostic method for neosporosis in cattle using recombinant Neospora caninum proteins

Background

Neosporosis is an infectious disease primarily of cattle and dogs, caused by intracellular parasite, Neospora caninum. Neosporosis appears to be a major cause of abortion in dairy cattle worldwide and causes to huge economic loss to dairy industry.

Results

Recombinant surface associated antigen 1 (NcSAG1), NcSAG1 related sequence 2 (NcSRS2) and the dense granule antigen 2 (NcGRA2) of N. caninum were expressed either in silkworm or in Escherichia coli and purified. The purified recombinant proteins bound to the N. caninum-specific antibodies in serum samples from infected cattle as revealed by an enzyme-linked immunosorbent assay (ELISA). By co-immobilizing these recombinant proteins, a novel indirect ELISA was developed for detection of neosporosis. With the use of 32 serum samples, comprising 12 positive serum samples and 20 negative serum samples, the sensitivity and specificity of the assay were found to be 91.7 and 100%, respectively. Seventy-two serum samples from dairy farms were also tested and one was diagnosed with neosporasis with both this method and a commercial assay.

Conclusions

A diagnostic method employing recombinant proteins of N. caninum was developed. The method showed high sensitivity and specificity. Diagnostic test with field serum samples suggested its applicability to the practical diagnosis of neosporosis.

Identification and characterization of a novel Neospora caninum immune mapped protein 1

Immune mapped protein 1 (IMP1) is a newly discovered protein in Eimeria maxima. It is recognized as a potential vaccine candidate against E. maxima and a highly conserved protein in apicomplexan parasites. Although the Neospora caninum IMP1 (NcIMP1) orthologue of E. maxima IMP1 was predicted in the N. caninum genome, it was still not identified and characterized. In this study, cDNA sequence encoding NcIMP1 was cloned by RT-PCR from RNA isolated from Nc1 tachyzoites. NcIMP1 was encoded by an open reading frame of 1182 bp, which encoded a protein of 393 amino acids with a predicted molecular weight of 42·9 kDa. Sequence analysis showed that there was neither a signal peptide nor a transmembrane region present in the NcIMP1 amino acid sequence. However, several kinds of functional protein motifs, including an N-myristoylation site and a palmitoylation site were predicted. Recombinant NcIMP1 (rNcIMP1) was expressed in Escherichia coli and then purified rNcIMP1 was used to prepare specific antisera in mice. Mouse polyclonal antibodies raised against the rNcIMP1 recognized an approximate 43 kDa native IMP1 protein. Immunofluorescence analysis showed that NcIMP1 was localized on the membrane of N. caninum tachyzoites. The N-myristoylation site and the palmitoylation site were found to contribute to the localization of NcIMP1. Furthermore, the rNcIMP1-specific antibodies could inhibit cell invasion by N. caninum tachyzoites in vitro. All the results indicate that NcIMP1 is likely to be a membrane protein of N. caninum and may be involved in parasite invasion.

ArtinM, a D-mannose-binding lectin from Artocarpus integrifolia, plays a potent adjuvant and immunostimulatory role in immunization against Neospora caninum

ArtinM and Jacalin (JAC) are lectins from the jackfruit (Artocarpus integrifolia) that have important role in modulation of immune responses to pathogens. Neospora caninum is an Apicomplexa parasite that causes neuromuscular disease in dogs and reproductive disorders in cattle, with economic impact on the livestock industry. Hence, we evaluated the adjuvant effect of ArtinM and JAC in immunization of mice against neosporosis. Six C57BL/6 mouse groups were subcutaneously immunized three times at 2-week intervals with Neospora lysate antigen (NLA) associated with lectins (NLA+ArtinM and NLA+JAC), NLA, ArtinM and JAC alone, and PBS (infection control). Animals were challenged with lethal dose of Nc-1 isolate and evaluated for morbidity, mortality, specific antibody response, cytokine production by spleen cells, brain parasite burden and inflammation. Our results demonstrated that ArtinM was able to increase NLA immunogenicity, inducing the highest levels of specific total IgG and IgG2a/IgG1 ratio, ex vivo Th1 cytokine production, increased survival, the lowest brain parasite burden, along with the highest inflammation scores. In contrast, NLA+JAC immunized group showed intermediate survival, the highest brain parasite burden and the lowest inflammation scores. In conclusion, ArtinM presents stronger immunostimulatory and adjuvant effect than Jacalin in immunization of mice against neosporosis, by inducing a protective Th1-biased pro-inflammatory immune response and higher protection after parasite challenge.

Vaccines against a Major Cause of Abortion in Cattle, Neospora caninum Infection

Simple Summary

We review the efforts to develop a vaccine against neosporosis, caused by the apicomplexan parasite Neospora caninum. Vertical transmission is the main mode of infection, and can lead to stillbirth, abortion, or birth of weak calves. We provide information on the biology of Neospora caninum and on the disease caused by this parasite, and summarize the current understanding on how the host deals with infection. We review studies on live- and subunit-vaccines, and demonstrate advantages and setbacks in the use of small laboratory animal models in investigations on a disease with high relevance in cattle.

Abstract

Neosporosis, caused by the apicomplexan parasite Neospora caninum, represents one of the economically most important causes of abortion in cattle. During pregnancy, the parasite infects the placental tissue and the fetus, which can lead to stillbirth, abortion, or birth of weak calves. Alternatively, calves are born without clinical symptoms, but they can carry over the parasite to the next generation. In addition, N. caninum causes neuromuscular disease in dogs. The economic importance of neosporosis has prompted researchers to invest in the development of measures to prevent infection of cattle by vaccination. A good vaccine must stimulate protective cellular immune responses as well as antibody responses at mucosal sites and, systemically, must activate T-helper cells to produce relevant cytokines, and must elicit specific antibodies that aid in limiting parasite proliferation, e.g., by interference with host cell invasion, activation of complement, and/or opsonization of parasites to have them killed by macrophages. Different types of vaccines have been investigated, either in bovines or in the mouse model. These include live vaccines such as naturally less virulent isolates of N. caninum, attenuated strains generated by irradiation or chemical means, or genetically modified transgenic strains. Live vaccines were shown to be very effective; however, there are serious disadvantages in terms of safety, costs of production, and stability of the final product. Subunit vaccines have been intensively studied, as they would have clear advantages such as reduced costs in production, processing and storage, increased stability and shelf life. The parasite antigens involved in adhesion and invasion of host cells, such as surface constituents, microneme-, rhoptry- and dense granule-components represent interesting targets. Subunit vaccines have been applied as bacterially expressed recombinant antigens or as DNA vaccines. Besides monovalent vaccines also polyvalent combinations of different antigens have been used, providing increased protection. Vaccines have been combined with immunostimulating carriers and, more recently, chimeric vaccines, incorporating immuno-relevant domains of several antigens into a single protein, have been developed.

Comparative efficacy of immunization with inactivated whole tachyzoites versus a tachyzoite-bradyzoite mixture against neosporosis in mice

The worldwide economic impact ofNeospora caninuminfection has caused the development of effective vaccines to become one of the main goals in the field of neosporosis research. In this study, the protection conferred by antigens from inactivated whole tachyzoites (TZ) and a tachyzoite-bradyzoite mixture (TZ-BZ) ofN. caninum(Nc-Spain7 isolate) incorporated into a water-in-oil emulsion (W/O) and aluminium hydroxide-ginseng extract (Al/G) was evaluated in mouse models of congenital and cerebralN. caninuminfection. Immunization with TZ-BZ induced congenital and cerebral neosporosis exacerbation that was mainly characterized by reduced neonatal median survival time and increased parasite presence in adult mouse brains. The immune response of mice immunized with TZ-BZ was characterized by an increase in IFN-γexpression prior to challenge and an increase in IL-4 expression accompanied with significantly higher levels of antibodies against 2 recombinant bradyzoite-specific proteins (rNcSAG4 and rNcBSR4) after challenge. Immunization with TZ in W/O significantly reduced neonatal mortality, vertical transmission as well as parasite presence in adult mouse brains and induced a strong humoral immune response. The current study demonstrates the critical role of stage-specific antigens and adjuvants on the development of effective inactivated vaccines for the prevention ofN. caninuminfection.

Transgenic Neospora caninum strains constitutively expressing the bradyzoite NcSAG4 protein proved to be safe and conferred significant levels of protection against vertical transmission when used as live vaccines in mice

At present, there is no effective treatment or vaccine to prevent vertical transmission or abortion associated with Neospora caninum infection in cattle. Different vaccine formulations have been assayed, and live vaccines have shown the most promising results in terms of protection. Previously, transgenic N. caninum tachyzoites expressing the bradyzoite stage-specific NcSAG4 antigen in a constitutive manner (Nc-1 SAG4(c)) were obtained and showed a reduced persistence of parasite in inoculated mice. Thus, the present study evaluates the Nc-1 SAG4(c)1.1 and Nc-1 SAG4(c)2.1 transgenic strains and the Nc-1 wild-type (WT) strain to determine their protective efficacy against vertical transmission and cerebral neosporosis in mice. Consequently, dams were immunized twice with 5 × 10(5) tachyzoites of each strain and challenged with 2 × 10(6) tachyzoites of a heterologous and virulent isolate at 7-10 days of gestation. The Nc-1 SAG4(c)1.1 strain offered less protection than the other transgenic strain (Nc-1 SAG4(c)2.1) or their ancestor (Nc-1 WT). Indeed, 40%, 7% and 5.6% of the postnatal deaths corresponded to pups from dams vaccinated with Nc-1 SAG4(c)1.1, Nc-1 SAG4(c)2.1 and Nc-1 (WT) strains, respectively. In comparison, the non-immunized challenge group had a 100% mortality rate. In addition, mice were protected against congenital transmission; vertical transmission rates were 45%, 11.1% and 10.8% in the Nc-1 SAG4(c)1.1, Nc-1 SAG4(c)2.1 and Nc-1 WT immunized groups, respectively, vs. 94.9% in the non-vaccinated infected group. However, this protection against the postnatal mortality and the vertical transmission was not associated with a consistent Th1 or Th2-type immune response. Nonetheless, the Nc-1 SAG4(c)2.1 strain appears to be the best candidate for use as a live vaccine, as evidenced by results demonstrating its high levels of protection against vertical transmission and its lower persistence in mice, making this transgenic strain safer than Nc-1 WT.

RecNcMIC3-1-R is a microneme- and rhoptry-based chimeric antigen that protects against acute neosporosis and limits cerebral parasite load in the mouse model for Neospora caninum infection

In order to achieve host cell entry, the apicomplexan parasite Neospora caninum relies on the contents of distinct organelles, named micronemes, rhoptries and dense granules, which are secreted at defined timepoints during and after host cell entry. It was shown previously that a vaccine composed of a mixture of three recombinant antigens, corresponding to the two microneme antigens NcMIC1 and NcMIC3 and the rhoptry protein NcROP2, prevented disease and limited cerebral infection and transplacental transmission in mice. In this study, we selected predicted immunogenic domains of each of these proteins and created four different chimeric antigens, with the respective domains incorporated into these chimers in different orders. Following vaccination, mice were challenged intraperitoneally with 2 × 10(6)N. caninum tachzyoites and were then carefully monitored for clinical symptoms during 4 weeks post-infection. Of the four chimeric antigens, only recNcMIC3-1-R provided complete protection against disease with 100% survivors, compared to 40-80% of survivors in the other groups. Serology did not show any clear differences in total IgG, IgG1 and IgG2a levels between the different treatment groups. Vaccination with all four chimeric variants generated an IL-4 biased cytokine expression, which then shifted to an IFN-γ-dominated response following experimental infection. Sera of recNcMIC3-1-R vaccinated mice reacted with each individual recombinant antigen, as well as with three distinct bands in Neospora extracts with similar Mr as NcMIC1, NcMIC3 and NcROP2, and exhibited distinct apical labeling in tachyzoites. These results suggest that recNcMIC3-1-R is an interesting chimeric vaccine candidate and should be followed up in subsequent studies in a fetal infection model.

Immunization of female BALB/c mice with Neospora cyclophilin and/or NcSRS2 elicits specific antibody response and prevents against challenge infection by Neospora caninum

Neospora caninum is the causal agent of bovine neosporosis which results in high levels of abortion. The present study determined the protective efficacy of two Neospora antigens--Neospora cyclophilin (NcCyP) and NcSRS2. The ability of native NcCyP to upregulate mouse IFN-γ was also confirmed in this study. Recombinant NcCyP or NcSRS2 were tested either alone or in combination and formulated with adjuvant ImmuMax-SR and CpG. Female BALB/c mice (n=15) of 10-12 weeks of age were immunized s.c. twice over a 2-week interval with vaccines containing either NcCyP (20 μg/dose) alone, NcSRS2 (20 μg/dose) alone, NcCyP plus NcSRS2, or non-recombinant bacterial antigen (NR) in 2 separate trials. All mice were challenge-infected 3 weeks following the booster immunization and necropsied 3 weeks after the challenge infection. Brain and serum were collected and Nc-specific DNA sequence in brain tissue and antibodies in serum were analyzed by PCR or ELISA/Western blotting. Results showed that mice vaccinated with rNcCyP, rNcSRS2, or both rNcCyP and rNcSRS2 responded with high levels of NcCyP or NcSRS2 specific antibodies. Overall, mice received vaccines formulated with either rNcCyP or rNcCyP and rNcSRS2 had a higher (p<0.01) percent protection when compared to the mock- or non-vaccinated mice. The group immunized with rNcSRS2 alone exhibited slightly lower levels of protection, which was higher (p<0.05) than that of the non-vaccinated group but did not differ (p=0.06) from that of the mock-vaccinated group. The results of the present study indicate that NcCyP is a highly efficacious vaccine candidate which may be useful in protection against Neospora infection.

Neospora caninum: cloning and expression of a gene coding for cytokine-inducing profilin

Profilins are actin-binding proteins that in Toxoplasma gondii stimulate innate immunity in mice by binding Toll-like receptors (TLR) on dendritic cells (DC) leading to release of inflammatory cytokines, primarily IL-12 and IFN-gamma. The purpose of the present study was to characterize Neospora caninum profilin, termed NcProfilin. Recombinant NcProfilin was purified by affinity chromatography, and used to prepare specific antisera to allow characterization of native NcProfilin antigen in N. caninum tachyzoites. By immunoblotting, recombinant NcProfilin is 22kDa, and is similar in size to the respective 22kDa native protein. Immunofluorescence and immunoelectron microscopy localized native NcProfilin to the apical end of N. caninum tachyzoites. Incubation of recombinant NcProfilin with spleen cells from BALB/c mice induced release of IFN-gamma. Also, injection of BALB/c mice with purified rNcProfilin elicited a strong IFN-gamma and IL-12 responses at 6 and 24h after injection indicating that NcProfilin may be an important protein in regulation of cytokine responses to N. caninum.

Failure of a vaccine using immunogenic recombinant proteins rNcSAG4 and rNcGRA7 against neosporosis in mice

The development of an effective vaccine against Neospora caninum infection in cattle is an important issue due to the significant economic impact of this parasitic disease worldwide. In this work, the immune response, safety and efficacy of different vaccine formulations using the N. caninum recombinant proteins rNcSAG4 (the first bradyzoite-specific protein assayed as a vaccine) and rNcGRA7 were evaluated in mouse models. The survival curves of pups from all vaccinated groups showed a slight delay in time to death compared to control groups; this difference was statistically significant for rNcSAG4+adjuvant group. Immune response of mice vaccinated with rNcSAG4 was characterized by reduced specific IgG and cytokine levels with an equilibrated IFN-gamma/IL-10 balance. Regarding mice vaccinated with rNcGRA7, a very strong humoral and cellular immune response was generated characterized by a hyper-production of IFN-gamma. This response was not accompanied by significant protection. Vaccination with a mixture of both recombinant proteins reduced infection in lung and brain during acute and chronic infection, respectively, although it was not statistically significant. In summary, no significant protection was obtained with these vaccine formulations in the present mouse models. However, the study reveals some positive results on immune response and efficacy for both recombinant proteins; these results are being discussed in order to suggest new approaches with new chronic infection mouse models and adjuvants.

Indoleamine 2,3-dioxygenase is involved in defense against Neospora caninum in human and bovine cells

Neospora caninum is an apicomplexan parasite closely related to Toxoplasma gondii. In nature this parasite is found especially in dogs and cattle, but it may also infect other livestock. The growth of N. caninum, which is an obligate intracellular parasite, is controlled mainly by the cell-mediated immune response. During infection the cytokine gamma interferon (IFN-gamma) plays a prominent role in regulating the growth of N. caninum in natural and experimental disease. The present study showed that induction of the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO) is responsible for the inhibition of parasite growth that is mediated by IFN-gamma-activated bovine fibroblasts and endothelial cells. This antiparasite effect could be abrogated by addition of tryptophan, as well as by the IDO-specific inhibitor 1-L-methyltryptophan. In conclusion, our data show that human and bovine cells use the same effector mechanism to control the growth of N. caninum.

Neospora caninum--how close are we to development of an efficacious vaccine that prevents abortion in cattle?

Neospora caninum is a protozoan parasite that causes abortion in cattle around the world. Although the clinical signs of disease in both dogs and cattle have now been recognised for over 20years, treatment and control options are still limited, despite the availability of a commercial vaccine in some countries of the world. The case for an efficacious vaccine has not been convincingly waged by farmers, veterinarians and other members of the agricultural and rural communities. In recent times, however, economic modelling has been used to estimate the industry losses due to Neospora-associated abortion, providing, in turn, the business case for forms of control for this parasite, including the development of vaccines. In this review, we document progress in all areas of the vaccine development pipeline, including live, killed and recombinant forms and the animal models available for vaccine evaluation. In addition, we summarise the main outcomes on the economics of Neospora control and suggest that the current boom in the global dairy industry increases the specific need for a vaccine against N. caninum-associated abortion.

Vaccination with recombinant NcROP2 combined with recombinant NcMIC1 and NcMIC3 reduces cerebral infection and vertical transmission in mice experimentally infected with Neospora caninum tachyzoites

We investigated the protective potential of recombinant his-tagged antigens recNcMIC1, recNcMIC3 and recNcROP2, applied either as single vaccines or as vaccine combinations, in BALB/c mouse models for cerebral and fetal infection. Subsequently, mice were mated and challenged by i.p. inoculation of 2 x 10(6)Neospora caninum tachyzoites at day 7 of pregnancy. The mortality and morbidity of adult mice (non-pregnant and dams) and of the newborn pups was studied for a period of 40 days following birth. Vaccination of non-pregnant mice with recNcROP2 or combinations of recNcROP2 with recNcMIC antigens significantly reduced the numbers of mice suffering from clinical signs, and morbidity was completely prevented with the combination of all three antigens. Of the dams, the groups receiving either recNcROP2 alone or the combination of all three antigens did not exhibit any morbidity, the groups receiving ROP2 mixed with either MIC1 or MIC3 exhibited reduced numbers of deaths, and in the infection control group and the adjuvant group 50% and 43% of mice, respectively, succumbed to disease. For pups, the highest survival rates were noted for the groups receiving recNcROP2 (50%) and recNcROP2/NcMIC1/NcMIC3 (35%), while in the infection- and adjuvant- control groups all pups died, the latest at days 25 and 30, respectively. Quantification of parasite DNA by N. caninum-specific real-time PCR revealed consistently lower parasite burdens in brain tissue of pups from vaccinated groups compared with the controls. However, dense granule antigen 2 (GRA2) real-time reverse transcriptase-PCR on brain tissue of surviving pups (applied here to detect viable parasites) demonstrated that only the pups from the group vaccinated with all three antigens in combination appeared free of viable tachyzoites, while in all other groups viable parasites were still present. Serological analysis of humoral (total IgG, IgG1 and IgG2a) and serum cytokine (IL-4 and IFN-gamma) responses showed that this effect was associated with a Th-2-biased immune response, with a clearly elevated IL-4/IFN-gamma ratio in the mice receiving all three antigens in combination. In conclusion, a mixture of recombinant antigens representing important secretory micronemal and rhoptry proteins leads to a significant protection against vertical transmission of N. caninum in mice.

Immunization with oligomannose-coated liposome-entrapped dense granule protein 7 protects dams and offspring from Neospora caninum infection in mice

The present study demonstrates that the subcutaneous administration of Neospora caninum dense granule protein 7 (NcGRA7) entrapped in liposomes coated with mannotriose strongly induces the parasite-specific T-helper type 1 immune response and humoral antibody in mice. Although anti-NcGRA7 immunoglobulin G1 antibody production was induced in mice injected with NcGRA7 alone, the dams and offspring were never protected from N. caninum infection. The immunization of mice with liposome-entrapped NcGRA7 before pregnancy resulted in increased offspring survival and decreased the infection rates in the brains of dams after parasite infection at 6 to 9 days of gestation. In conclusion, oligomannose-coated liposome-entrapped NcGRA7 can be used as a new type of effective vaccine to control neosporosis.

CpG-ODN combined with Neospora caninum lysate, but not with excreted-secreted antigen, enhances protection against infection in mice

CpG oligodeoxynucleotides (ODN) have shown to be potent immunoadjuvants for several pathogens, but there is limited information concerning their use in immunization protocols against neosporosis. This study aimed to evaluate the potential of CpG-ODN combined with Neospora lysate antigen (NLA) or excreted-secreted antigen (NcESA) to induce protective immune response against Neospora caninum infection in mice. C57BL/6 mice were vaccinated subcutaneously three times at 2-week intervals with NLA, NLA+CpG, NcESA, NcESA+CpG, CpG (adjuvant control) or PBS (infection control). Serological assays showed an increased specific IgG2a response in animals immunized with either antigen plus adjuvant and elevated levels of the IgG1 isotype in those vaccinated with antigens alone. Splenocyte proliferative responses upon antigen stimulation were higher in groups immunized with NLA or NcESA combined with CpG, showing increased IL-12 levels. Also, mice vaccinated with NcESA or NcESA+CpG demonstrated higher IFN-gamma levels and IFN-gamma/IL-10 ratio. After lethal challenge, mice immunized with NLA+CpG or NLA had lower morbidity score and body weight changes in comparison to other groups, and animals did not succumb during acute infection. In contrast, NcESA+CpG or NcESA groups exhibited the highest morbidity scores, body weight impairment and mortality rates, associated with greatest brain parasite burden and inflammation. In conclusion, CpG-ODN was able to induce a Th1-type humoral immune response with predominant IgG2a levels for either NLA or NcESA, but resulting in an effective Th1-driven cellular immune response and total protection only when combined with NLA. Vaccination with NcESA alone or combined with CpG resulted in a strong cellular immune response associated with high levels of IFN-gamma and inflammation, rendering mice more susceptible to parasite challenge.

Effects of a transferring antibody against Neospora caninum infection in a murine model

We investigated the roles of a transferring antibody against Neospora caninum infection based on a murine model using recombinant vaccinia virus carrying NcSRS2 gene. Higher levels of anti-NcSRS2 antibody were detected in surviving offspring from vaccinated dams than controls while the transferring anti-NcSAG1 antibody was detected in the surviving offspring from unvaccinated dams. After mating, the female mice with transferring antibody against N. caninum were challenged with the parasites in mid-gestation. The transferring antibodies disappeared during pregnancy upon parasite infection. There was no significant difference on the parasite burden in dams and the survival rates of their offspring. Here, we have shown that N. caninum-specific transferring antibody does not control parasite infection in mice.

Vaccination of mice with recombinant NcROP2 antigen reduces mortality and cerebral infection in mice infected with Neospora caninum tachyzoites

Rhoptry antigens are involved in a variety of cellular functions related to host cell invasion, formation of the parasitophorous vacuole and parasite-host cell interplay. The cDNA sequence of one of these antigens, NcROP2 was identified from Neospora caninum expressed sequence tags (ESTs), amplified by reverse transcription-PCR, expressed in Escherichia coli as a (His)(6)-tagged recombinant protein (recNcROP2) and purified over Ni(2+)-affinity chromatography. Both recNcROP2 and antibodies directed against recNcROP2 had a negative impact on N. caninum tachyzoite host cell invasion in vitro, indicating that this protein participates in the host cell entry process. Subsequently, the protective efficacy of NcROP2 as a potential vaccine candidate was evaluated in a C57BL/6 mouse cerebral disease model. Mice were vaccinated three times at 2-week intervals with recNcROP2 emulsified either in Freund's incomplete adjuvants (FIA) or saponin, and control groups were treated with adjuvants alone (adjuvants control) or PBS (infection control). Subsequently, mice were challenged with 2x10(6)N. caninum tachyzoites. Nine mice, all belonging to the infection control or adjuvants control groups, exhibited clinical signs of cerebral neosporosis and succumbed to infection, whilst no clinical signs were noted for recNcROP2-vaccinated mice. For all other animals, the experiment was terminated 35 days p.i. Cerebral parasite burdens were assessed by quantitative PCR in all mice, and were revealed to be significantly reduced in the recNcROP2-vaccinated mice. ELISA of sera revealed IgG1 to be elevated in recNcROP2-saponin vaccinated mice, whilst IgG2a was higher in recNcROP2-FIA vaccinated animals. This shows that, depending on the adjuvants used, vaccination with NcROP2 induces a protective Th-1- or Th-2-biased immune response against experimental N. caninum infection.

Bovine immune response to inoculation with Neospora caninum surface antigen SRS2 lipopeptides mimics immune response to infection with live parasites

Infection of cattle with Neospora caninum protozoa, the causative agent of bovine protozoal abortion, results in robust cellular and humoral immune responses, particularly CD4(+) T-lymphocyte activation and gamma interferon (IFN-gamma) secretion. In the present study, N. caninum SRS2 (NcSRS2) T-lymphocyte-epitope-bearing subunits were incorporated into DNA and peptide preparations to assess CD4(+) cell proliferation and IFN-gamma T-lymphocyte-secretion immune responses in cattle with predetermined major histocompatibility complex (MHC) genotypes. In order to optimize dendritic-cell processing, NcSRS2 DNA vaccine was delivered with granulocyte macrophage-colony-stimulating factor and Flt3 ligand adjuvant. The synthesized NcSRS2 peptides were coupled with a palmitic acid molecule (lipopeptide) and delivered with Freund's adjuvant. Cattle vaccinated with NcSRS2 DNA vaccine alone did not induce T-lymphocyte activation or IFN-gamma secretion, whereas subsequent booster inoculation with NcSRS2-lipopeptides induced robust NcSRS2-specific immune responses. Compared to the response in control animals, NcSRS2-lipopeptide-immunized cattle had significantly increased NcSRS2-specific T-lymphocyte proliferation, numbers of IFN-gamma-secreting peripheral blood mononuclear cells, and immunoglobulin G1 (IgG1) and IgG2a antibody levels. The findings show that N. caninum NcSRS2 subunits bearing T-lymphocyte epitopes induced cell-mediated immune responses similar to the protective immune responses previously described against live parasite infection, namely T-lymphocyte activation and IFN-gamma secretion. The findings support the investigation of NcSRS2 immunogens for protection against N. caninum-induced fetal infection and abortion in cattle.

Prevention of vertical transmission of Neospora caninum in C57BL/6 mice vaccinated with Brucella abortus strain RB51 expressing N. caninum protective antigens

Bovine abortions caused by the apicomplexan parasite Neospora caninum have been responsible for severe economic losses to the cattle industry. Infected cows either experience abortion or transmit the parasite transplacentally at a rate of up to 95%. Neospora caninum vaccines that can prevent vertical transmission and ensure disruption in the life cycle of the parasite greatly aid in the management of neosporosis in the cattle industry. Brucella abortus strain RB51, a commercially available vaccine for bovine brucellosis, can also be used as a vector to express plasmid-encoded proteins from other pathogens. Neospora caninum protective antigens MIC1, MIC3, GRA2, GRA6 and SRS2 were expressed in strain RB51. Female C57BL/6 mice were vaccinated with a recombinant strain RB51 expressing N. caninum antigen or irradiated tachyzoites, boosted 4 weeks later and then bred. Antigen-specific IgG, IFN-gamma and IL-10 were detected in vaccinated pregnant mice. Vaccinated mice were challenged with 5 x 10(6)N. caninum tachyzoites between days 11-13 of pregnancy. Brain tissue was collected from pups 3 weeks after birth and examined for the presence of N. caninum by real-time PCR. The RB51-MIC3, RB51-GRA6, irradiated tachyzoite vaccine, pooled strain RB51-Neospora vaccine, RB51-MIC1 and RB51-SRS2 vaccines elicited approximately 6-38% protection against vertical transmission. However, the differences in parasite burden in brain tissue of pups from the control and vaccinated groups were highly significant for all groups. Thus, B. abortus strain RB51 expressing the specific N. caninum antigens induced substantial protection against vertical transmission of N. caninum in mice.

Reduced cerebral infection of Neospora caninum in BALB/c mice vaccinated with recombinant Brucella abortus RB51 strains expressing N. caninum SRS2 and GRA7 proteins

Neospora caninum, an obligate intracellular protozoan parasite, is the causative agent of bovine neosporosis, an important disease affecting the reproductive performance of cattle worldwide. Currently there is no effective vaccine available to prevent N. caninum infection in cattle. In this study, we examined the feasibility of developing a live, recombinant N. caninum vaccine using Brucella abortus vaccine strain RB51 as the expression and delivery vector. We generated two recombinant RB51 strains each expressing SRS2 (RB51/SRS2) or GRA7 (RB51/GRA7) antigens of N. caninum. BALB/c mice immunized by single intraperitoneal inoculation of the recombinant RB51 strains developed IgG antibodies specific to the respective N. caninum antigen. In vitro stimulation of splenocytes from the vaccinated mice with specific antigen resulted in the production of interferon-gamma, but not IL-5 or IL-10, suggesting the development of a Th1 type immune response. Upon challenge with N. caninum tachyzoites, mice vaccinated with strain RB51/SRS2, but not RB51/GRA7, showed significant resistance to cerebral infection when compared to the RB51 vaccinated mice, as determined by the tissue parasite load using a real-time quantitative TaqMan assay. Interestingly, mice vaccinated with either strain RB51 or RB51/GRA7 also contained significantly lower parasite burden in their brains compared to those inoculated with saline. Mice vaccinated with strain RB51/SRS2 or RB51/GRA7 were protected to the same extent as the strain RB51 vaccinated mice against challenge with B. abortus virulent strain 2308. These results suggest that a recombinant RB51 strain expressing an appropriate protective antigen(s), such as SRS2 of N. caninum, can confer protection against both neosporosis and brucellosis.

Comparative host–parasite relationships in ovine toxoplasmosis and bovine neosporosis and strategies for vaccination

Toxoplasma gondii and Neospora caninum are important causes of reproductive loss in ruminant species worldwide. Both parasites cause disease during pregnancy that may result in foetal death or birth of live congenitally infected offspring. T. gondii is also an important human pathogen with the main risk groups including pregnant women and immuno-compromised individuals, although clinical disease has also been observed in outbreaks among immuno-competent people. While the two parasites are closely related there are distinct differences between the two in their interactions with different host species and subsequent clinical outcome. This paper discusses the respective host-parasite relationships in ovine toxoplasmosis and bovine neosporosis and how the immune response may be host-protective, parasite-protective or contribute to disease pathogenesis, and how this knowledge may help in the development of more effective and targeted vaccination strategies.

Prevention of lethal experimental infection of C57BL/6 mice by vaccination with Brucella abortus strain RB51 expressing Neospora caninum antigens

Bovine abortions caused by the intracellular protozoal parasite Neospora caninum are a major concern to cattle industries worldwide. A strong Th1 immune response is required for protection against N. caninum. Brucella abortus strain RB51 is currently used as a live, attenuated vaccine against bovine brucellosis. Strain RB51 can also be used as an expression vector for heterologous protein expression. In this study, putative protective antigens of N. caninum MIC1, MIC3, GRA2, GRA6 and SRS2, were expressed individually in B. abortus strain RB51. The ability of each of the recombinant RB51 strains to induce N. caninum-specific immunity was assessed in C57BL/6 mice. Mice were immunised by two i.p. inoculations, 4 weeks apart. Five weeks after the second immunisation, spleen cells from the vaccinated mice secreted high levels of IFN-gamma and IL-10 upon in vitro stimulation with N. caninum whole cell lysate antigens. N. caninum-specific antibodies of both IgG1 and IgG2a subtypes were detected in the serum of the vaccinated mice. Mice in the vaccinated and control groups were challenged with 2 x 10(7)N. caninum tachyzoites i.p. and observed for 28 days after vaccination. All unvaccinated control mice died within 7 days. Mice in the MIC1 and GRA6 vaccine groups were completely protected while the mice in the SRS2, GRA2 and MIC3 vaccinated groups were partially protected and experienced 10-50% mortality. The non-recombinant RB51 vector control group experienced an average protection of 69%. These results suggest that expression of protective antigens of N. caninum in B. abortus strain RB51 is a novel approach towards the development of a multivalent vaccine against brucellosis and neosporosis.

Immunogenicity and protective effect against murine cerebral neosporosis of recombinant NcSRS2 in different iscom formulations

Recombinant NcSRS2, a major immunodominant surface antigen of the intracellular protozoan parasite Neospora caninum, was used as a model antigen to compare the immunogenicity of iscoms prepared according to three different methods. Two NcSRS2 fusion proteins were used, one that was biotinylated upon expression in Escherichia coli and linked to Ni2+-loaded iscom matrix (iscom without any protein) via a hexahistidyl (His6)-tagged streptavidin fusion protein, and another that contained both a His6-tag and streptavidin (His6-SA-SRS2') and was coupled to either Ni2+-loaded or biotinylated matrix. While all three iscom preparations induced N. caninum specific antibodies at similar levels, His6-SA-SRS2' coupled to biotinylated matrix generated the strongest cellular responses measured as in vitro proliferation and production of interferon-gamma and interleukin-4 after antigen stimulation of spleen cells. However, the relationship between the levels of these cytokines as well as between IgG1 and IgG2a titres in serum induced by the three iscom preparations were similar, indicating that the balance between Th1 and Th2 responses did not differ. After challenge infection, mice immunised with His6-SA-SRS2' coupled to biotinylated matrix had significantly lower amounts of parasite DNA in their brains compared to the other immunised groups. Possible reasons for the performance of the different iscom formulations are discussed.

Optimization of the use of C57BL/6 mice as a laboratory animal model for Neospora caninum vaccine studies

The development and testing of vaccines for Neospora caninum in mice require challenge studies to demonstrate a reduction in clinical signs or prevention of vertical transmission of the parasite after vaccination. Genetic susceptibility to N. caninum varies with the strain of mice. In this study, C57BL/6 mice were evaluated as a model for Neospora vaccine studies. A lethal challenge model was developed and the LD(50) was determined to be 1.5 x 10(7)N. caninum tachyzoites/mouse, delivered intraperitoneally. Brain lesions encountered in sections from sub-lethally challenged mice were scored on the basis of severity and total number of lesions to develop a histopathological scoring system for vaccine efficacy. A vertical transmission model for N. caninum vaccine studies was developed by studying mice that were infected either 2 weeks prior to mating or between days 12 and 14 of pregnancy. It was found that infection prior to mating reduced the average number of pups per litter. DNA extracted from fetal tissue was examined by a N. caninum specific polymerase chain reaction (PCR). The rate of vertical transmission was 0, 100 and 90.5% for the uninfected controls, mice infected during pregnancy and mice infected before mating, respectively. This study demonstrates that the C57BL/6 strain of mice is a good model for N. caninum vaccine studies because it is possible to establish a clear-cut lethal challenge model in C57BL/6 mice and they transmit the disease to their offspring efficiently.