Dense-granule protein NcGRA7, a new marker for the serodiagnosis of Neospora caninum infection in aborting cows

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.

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.

The Utility of Serological Analysis for Neospora caninum Infection in Dairy Cattle Farms Management: Serological Investigation and Evaluation of the Effects on Reproductive and Productive Performances in Two Study Herds in Northern Italy

Simple Summary

Among infectious agents triggering reproductive disorders in cattle, Neospora caninum, an obligate intracellular protozoan parasite, is a major cause of abortion in cows worldwide. A serosurvey was designed in two cattle herds, both located in northern Italy and with similar reproductive management features, recruited as a case study. The clinical outcome and the effects on herd performances were evaluated in association with the seropositivity to N. caninum. This study showed that the integration of serological analysis results for N. caninum, the reproductive and productive parameters, and the information on herd performances, could give indications for the application of control strategies.

Abstract

Neospora caninum is recognized as a major cause of abortion in cattle, determining economic losses, particularly in dairy industries. To evaluate the impact of neosporosis on herd efficiency, and to understand how the serological analysis for N. caninum is explicative of the farm picture, an epidemiological study was designed in two dairy farms recruited as a case study. Blood samples were collected from 540 animals, including cows and heifers over 12 months, and analyzed by an indirect immunofluorescent antibody test with subsequent antibody titration. Overall, 94 animals (17.4%) were identified as positive to N. caninum antibodies (15.5% and 18.5% in Farm 1 and Farm 2), with differences between the farms concerning the antibody titers (Chi-square, p-value = 0.04), particularly in cows (Chi-square, p-value = 0.018). Consequently, a different pattern of abortion episodes was depicted in the two investigated farms. Considering reproductive and productive performances, the number of inseminations necessary to make an animal pregnant was higher in seropositive cows (2.4 and 2.9 in Farm 1 and 2, respectively) than in seronegative ones (2.1 and 2.4 in Farm 1 and 2, respectively). Similarly, particularly in Farm 1, the number of days in milk of not-pregnant cows was higher in seropositive (167.7) than seronegative animals (133.4). Moreover, although the association between N. caninum infection and milk production is still unclear, both the daily milk production and the 305-mature equivalent milk yield were lower in seropositive (31.02 and 11,838.94) than seronegative cows (33.59 and 12,274.88) in Farm 1; an opposite pattern was otherwise depicted in Farm 2. The study showed that even if N. caninum circulated equally in the two herds, the dynamics of the parasite infection and its outcome may be different, also depending on the specific situation of the farm. In this way, the integration of serological analysis for N. caninum, the reproductive and productive parameters, and the information on herd performances, could give specific indications for the application of control strategies.

Immune Protective Evaluation Elicited by DNA Vaccination With Neospora caninum Dense Granules Proteins in Mice

Neospora caninum, an obligate intracellular protozoan, is the major cause for neosporosis and brings serious economic losses to cattle breeding industries worldwide. After invasion, dense granules proteins are abundantly secreted and being important components of parasitophorous vacuole and intravacuolar network where N. caninum survives and replicates. The aim of the present study was to evaluate the protective immunity induced by DNA vaccines with genes encoding dense granules proteins 1 (GRA1), GRA4, GRA9, GRA14, GRA17, and GRA23 against N. caninum tachyzoites in BALB/C mice. Eukaryotic expressing plasmids of pcNcGRAs were constructed and the mice were intramuscularly immunized with pcNcGRAs followed by challenging infection with lethal doses of N. caninum. Immune responses were evaluated through monitoring the levels of serum antibodies, measurement of lymphocyte proliferation, and secretion of cytokines. Immune protection assays were carried out through monitoring survival time, body weight, and parasite burden in the brains. Results showed that all the pcNcGRA DNA vaccines could trigger remarkably specific humoral and cellular responses, with higher levels of IgG and IgG2a antibodies as well as obviously increased secretion of Th1-type IFN-γ cytokines. The immune protective efficacy revealed that pcNcGRA4, pcNcGRA14, and pcNcGRA17 DNA vaccines could individually increase the survival rate to 50, 37.5, and 25% in comparison with 0% in the control group; prolong the survival time more than 20.88 ± 11.12, 18.88 ± 10.83, and 16.63 ± 10.66 days compared with the control group of 4 ± 1.31 days; and decrease parasite burden in the brains to 297.63 ± 83.77, 471.5 ± 110.74, and 592.13 ± 102.2 parasites/100 ng comparing with 1221.36 ± 269.59 parasites/100 ng in the control group. These findings indicated that NcGRA4, NcGRA14, and NcGRA17 are potential vaccine candidates; NcGRA4 displayed better performance in immune protective efficacy and could be further combined with other advantageous antigens applied to the development of safe and effective DNA vaccines against N. caninum.

Function of Neospora caninum dense granule protein 7 in innate immunity in mice

The intracellular parasite Neospora caninum can parasitize all nucleated cells of the host. Dense granule proteins (GRAs) secreted by dense granules are an important material involved in the formation of parasitophorous vacuoles (PVs), which facilitate parasite survival and replication in host cells. Due to the secretory and immune properties of NcGRA7, it is considered to be a promising serodiagnosis marker and an effective neosporosis vaccine candidate. However, the intracellular regulatory mechanisms involved in NcGRA7-induced host responses have rarely been examined. Here, we used the CRISPR/Cas9 genome editing system to obtain a NcGRA7 knockout strain (ΔNcGRA7) and a NcGRA7 complementary strain (iΔNcGRA7) to study their function. We found that ΔNcGRA7 exhibited slower growth in vitro and weakened virulence in mice compared with Nc1 and iΔNcGRA7. All parasite strains can stimulate host immune cells to produce IFN-γ, and the amount of IFN-γ production stimulated by Nc1 was significantly higher than that stimulated by ΔNcGRA7. The transcription levels of the cellular immune factors GBP1, GBP2, IRGa6, and IRGb6 were significantly higher after stimulation with ΔNcGRA7 parasites than after stimulation with Nc1. Furthermore, ΔNcGRA7 infection resulted in greater IRGa6 recruitment to the PVM than Nc1 infection. ΔNcGRA7 parasites were more easily cleared by macrophages than Nc1 parasites. Collectively, these results showed that NcGRA7 plays an important role in regulating the immune factors of mice and the aggregation of IRGa6 at the PVM, which affects the pathogenicity of N. caninum.

Urological detection of specific antibodies against Neospora caninum infection in mice: A prospect for novel diagnostic approach of Neospora

The intracellular protozoan parasite Neospora caninum is incriminated to induce drastic economic losses in both livestock and pet animal industries. Neosporosis is primarily characterized by abortion in cattle and paralytic symptoms in dogs. Because there are no effective treatments or vaccines, diagnosis is critical for Neospora control. Thus, diversification of laboratory tests and specimens used for diagnosis of N. caninum is an essential scientific endeavor to judge and select the most appropriate diagnostic tool. Herein, we provide the first evidence for the utility of urine samples for demonstration of specific antibodies against N. caninum employing an experimentally infected murine model. Specific antibodies to recombinant N. caninum dense granule 7, surface antigen 1, and lysate antigen were assayed using different antibodies-based ELISAs. Urine based IgG ELISA efficiently discriminated between infected mice (acute or chronic infection), and those of non-infected mice. This effect was also noticed for IgG1 and IgG2a suggesting the utility of urine for assessment of T-helper 2- and T-helper 1-mediated immunities, respectively. In addition, reactivity of specific antibody in urine was also confirmed against parasites when indirect fluorescent antibody test was employed. Usefulness of urine as an additional clinical sample for Neospora diagnosis was confirmed via comparison with the relevant control non-infected and infected mouse sera as reference samples. Because of minimum invasiveness and ease of urine collection, this approach might offer new diagnostic opportunities for N. caninum either for the field or research purposes. However, further studies are required to extrapolate this preliminary study and results in the animal species of interest particularly in dogs.

Evaluation of Neospora caninum serodiagnostic antigens for bovine neosporosis

Abortion and reproductive failure caused by Neospora caninum infection has a dramatic negative economic impact on the cattle industry. To date, no definitive serodiagnostic tool for assessing N. caninum abortion has been reported. In this study, we evaluated the diagnostic performance of numerous N. caninum antigens in relation to abortion in cattle. Five recombinant proteins with potential as diagnostic antigens (NcGRA6, NcGRA7, NcGRA14, NcCyP, and NcSAG1) were compared by indirect enzyme-linked immunosorbent assay (iELISA) using sera from mice and cattle experimentally infected with N. caninum. The best-performing three antigens (NcSAG1, NcGRA7, and NcGRA6) were evaluated by IgG-iELISAs to assess their utility in diagnosing Neospora abortion using sera from confirmed N. caninum-aborted dams based on immunohistochemical assays (IHC). Additionally, all samples were tested using a commercial N. caninum antibody competitive ELISA (cELISA). The iELISAs against both NcSAG1 and NcGRA7 could efficiently distinguish IHC positive and negative samples compared with iELISAs against NcGRA6 and the cELISA. Furthermore, antibody levels against NcSAG1 and NcGRA7 were significantly higher in aborting cows comparing with infected but non-aborted dams in a herd experiencing a Neospora abortion outbreak. Tracking the dynamics of antibody levels during pregnancy revealed a marked increase in NcSAG1- and NcGRA7-specific antibodies at the last trimester of pregnancy. In contrast, no marked differences in antibody levels against either antigen were noted in neurologically symptomatic calves compared with non-symptomatic infected calves. Our data suggests NcSAG1 and NcGRA7 as indicators for Neospora abortion.

A time-resolved fluorescence immunoassay for the detection of anti-Neospora caninum antibodies in sheep

Neospora caninum is a protozoan parasite (Phylum Apicomplexa) that has been recently suggested as a relevant cause of reproductive disorders in small ruminants. The aim of the present study is to develop and validate a new serological test based on time resolved fluorescency using N. caninum GRA7 recombinant antigen (GRA7-TRFIA) for the detection of N. caninum antibodies in sheep. A total of 346 serum samples (208 from experimentally infected sheep, 117 from a dairy farm with a previous history of Neospora-associated abortion, and 21 negative sera) were used. The validation of the new assay was performed by the evaluation of assay precision, analytical sensitivity (Se), accuracy and cross reactivity. In the experimentally infected sheep, antibody kinetics was compared between GRA7-TRFIA and an in house N. caninum tachyzoite soluble extract-based ELISA (NcSALUVET ELISA) by Wilcoxon matched-pairs signed rank test. The cut-off and diagnostic Se and specificity (Sp) of GRA7-TRFIA was estimated by ROC analysis with field samples. In addition, concordance and correlation between GRA7-TRFIA and a commercial ELISA and NcSALUVET ELISA were assessed by kappa value and Spearman correlation coefficient, respectively. Overall, GRA7-TRFIA showed an adequate precision, analytical Se and accuracy to detect anti-N. caninum antibodies in ovine serum, and no cross reactivity with the closely related protozoan Toxoplasma gondii. In naturally infected sheep, 100% Se and 95.35% Sp were obtained for a cut-off point of 62.68 Units of Fluorometry for N. caninum (UFN). Moreover, GRA7-TRFIA allowed earlier detection of N. caninum infection than NcSALUVET ELISA in experimentally infected sheep.

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.

Identification of the antigenic region of Neospora caninum dense granule protein 7 using ELISA

Dense granule protein 7 (NcGRA7) is a potent diagnostic antigen of Neospora caninum. Some studies have reported on the difficult expression, low yield, and variable degree of solubility of recombinant NcGRA7. We aimed to unravel the possible causes for these issues and tested NcGRA7 antigenicity in enzyme linked immunosorbent assays (ELISAs). The NcGRA7 coding sequence (217 amino acids) was split into five amino acid regions: NcGRA7m (27-217), NcGRA7m3 (27-160), NcGRA7m4 (27-135), NcGRA7m5 (161-190), and NcGRA7m6 (188-217). Three fragments, NcGRA7m, NcGRA7m3 and NcGRA7m4, exhibited high antigenic properties when tested against experimentally-infected mice and dog sera by ELISA. High levels of IgG2 antibodies against NcGRA7m3 were observed in field dog sera. In experimentally and naturally-infected cattle, the N. caninum-specific sera only reacted with NcGRA7m, indicating that this antigenic region differs among the three animal species. This study presents valuable information about the antigenic properties and topology of NcGRA7, and highlights its suitability for diagnostic purposes.

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.

Immunization with inactivated antigens of Neospora caninum induces toll-like receptors 3, 7, 8 and 9 in maternal-fetal interface of infected pregnant heifers

Neospora caninum is an obligate parasite and a major cause of abortion in cattle. Pregnancy failures appear to be associated with weak innate defences on the maternal-fetal interface during infection with N. caninum. Herein, we studied the gene expression of Toll-like receptors (TLRs) in pregnant heifers immunized with different vaccine formulations against N. caninum before mating and then challenged the heifers with live N. caninum on day 70 of gestation. TLR7 and TLR8 expression was upregulated in the placental caruncle of infected-pregnant heifers previously exposed to live N. caninum as immunogen. However, TLR7 and 8 expression in both placenta and caruncle as well as, TLR3 and 9 expression in caruncle were upregulated when heifers were previously immunized with inactivated soluble whole antigens and recombinant NcSAG1, NcHSP20 and NcGRA7 proteins. All dams were carrying viable fetuses when they were culled at day 104 of gestation. Upregulation of TLR7 and IFNγ expression was detected in fetal spleen when their mothers where previously vaccinated with soluble antigens and recombinant NcSAG1, NcHSP20 and NcGRA7 proteins. These studies demonstrate that soluble or recombinant NcSAG1, NcHSP20 and NcGRA7 antigens induce key TLRs expression at the maternal-fetal interface, probably triggering damaging inflammatory cellular immune responses associated with abortion. Previous infection with N. caninum seems to attenuate the innate immune response at the maternal-fetal interface, which could favour pregnancy maintenance and perpetuation of the disease. This finding represents novel information on how N. caninum vaccination and infection modulate TLRs expression at the placenta and fetal spleen, the possible role in the pregnancy outcomes and transplacental transmission of the protozoa.

Importance of serological cross-reactivity among Toxoplasma gondii, Hammondia spp., Neospora spp., Sarcocystis spp. and Besnoitia besnoiti

Toxoplasma gondii, Neospora spp., Sarcocystis spp., Hammondia spp. and Besnoitia besnoiti are genetically related cyst-forming coccidia. Serology is frequently used for the identification of T. gondii, Neospora spp. and B. besnoiti-exposed individuals. Serologic cross-reactions occur in different tests among animals infected with T. gondii and H. hammondi, as well as among animals infected by T. gondii and N. caninum. Infections caused by N. caninum and N. hughesi are almost indistinguishable by serology. Neospora caninum, B. besnoiti and Sarcocystis spp. infections in cattle show some degree of serologic cross-reactivity. Antibody cross-reactivity between Neospora spp. and H. heydorni-infected animals is suspected, but not proven to occur. We review serologic cross-reactivity among animals and/or humans infected with T. gondii, Neospora spp., Sarcocystis spp., Hammondia spp. and B. besnoiti. Emphasis is laid upon antigens and serological methods for N. caninum diagnosis which were tested for cross-reactivity with related protozoa. Species-specific antigens, as well as stage-specific proteins have been identified in some of these parasites and have promising use for diagnosis and epidemiological surveys.

Neospora caninum tachyzoite immunome study reveals differences among three biologically different isolates

Pathogenesis of bovine neosporosis is determined by different host- and parasite-dependent factors, including isolate virulence. A previous study identified that several Neospora caninum tachyzoite proteins were more abundant in virulent isolates, Nc-Liv and Nc-Spain7, compared with the low-virulent isolate Nc-Spain1H. Herein, we explored differences in the immunomes of these three isolates. Protein extracts from the Nc-Liv, Nc-Spain1H and Nc-Spain7 isolates were analysed in a 3×3 design by 2-DE immunoblot using sera from experimentally infected mice with these same three isolates. All isolates displayed a highly similar antigenic pattern when they were assessed using the same serum. Most of the reactive spots were located in the acidic region (pH 3-7) and grouped in 3 antigenic areas (250-70, 45-37 and 35-15 KDa). Differences found in the immunome depended on the sera used, regardless of the extract employed. In this sense, sera from Nc-Liv and Nc-Spain7 infected mice recognized the highest number of antigens, followed by Nc-Spain1H infected mice sera. In fact, 4 proteins identified by MS were not consistently detected in each isolate extract by sera from low-virulent Nc-Spain1H-infected mice: serine-threonine phosphatase 2C and superoxide dismutase (related to metabolism), gliding associated protein GAP45 (related to tachyzoites invasion), and NcGRA1 (located on dense granules). Similarly, 4 non-identified spots and another 2 spots chains located in 45-37 kDa area were not detected by this pooled sera. Variations between virulent Nc-Spain7 and Nc-Liv were limited to the absence of recognition by sera from Nc-Spain7-infected mice of GAP45 and the spot chains located in the 45-37 kDa area. These results suggest that variations in the immunome profiles rely on the immune response induced by each isolate and that these differentially recognized antigens could be investigated as putative virulence markers of neosporosis.

Evaluation of Neospora caninum truncated dense granule protein 2 for serodiagnosis by enzyme-linked immunosorbent assay in dogs

Neosporosis is an infectious disease caused by Neospora caninum, and it primarily affects cattle and dogs. An infection by N. caninum causes fetal abortion and neonatal mortality. Previous proteomics and immunoscreening analyses revealed that N. caninum dense granule antigen 2 (NcGRA2) has potential for serodiagnosis of N. caninum. Consequently, we expressed the truncated NcGRA2 (NcGRA2t), which lacks a signal peptide. We compared the serodiagnostic performances of recombinant NcGRA2t with that of truncated surface antigen 1 of N. caninum (NcSAG1t). Specificity testing using sera from mice infected with Toxoplasma gondii indicated that the NcGRA2t recombinant protein does not cross-react with T. gondii. In addition, we detected anti-NcGRA2t antibody at the acute stage in experimentally infected dogs, while detecting anti-NcSAG1t antibody during both the acute and chronic stages. Our results suggest that the levels of anti-NcGRA2 antibody reflect parasite activation in dogs. In conclusion, antibodies against NcGRA2t and NcSAG1t are suitable indicators to distinguish the acute and chronic stages of N. caninum infection.

Markers related to the diagnosis and to the risk of abortion in bovine neosporosis

Bovine neosporosis has emerged as a main cause of abortion in cattle worldwide. An important question to understand the disease is why not all infected cows abort. In the present review we summarize the knowledge on markers related to the diagnosis and more importantly to the risk of abortion in the infected cow. Markers considered herein include those based on specific antibodies, antibody titers and antibody subtypes, cellular immunological markers, hormones and other proteins related to gestation. The identification of parasite molecules that are specifically identified in the aborting cows might help to understand the mechanism of parasite-associated abortion and control the disease.

Development of an Indirect ELISA Using Different Fragments of Recombinant Ncgra7 for Detection of Neospora caninum Infection in Cattle and Water Buffalo

BACKGROUND

Dense granules are immunodominant proteins for the standardization of immunodiagnostic procedures to detect neosporosis. In the presented study different fragment of a dense-granule protein was evaluated for serodiagnosis of Neospora caninum in cattle and water buffalo.

METHODS

NcGRA7, from N. caninum tachyzoites was amplified. PCR product and pMAL-c2X plasmid were digested with EcoR1 restriction enzyme and expressed in Escherichia coli to evaluate its competence for detection of anti- N. caninum antibodies with ELISA in comparison with commercial IDEXX ELISA. Furthermore, 230 sera of presumably healthy cattle and water buffaloes (108 cattle and 122 water buffaloes) were analyzed by both tests to determine the agreement of these two procedures.

RESULTS

Sensitivities and specificities of NcGRA7-based ELISA were 94.64% and 90.38% respectively using sera of cattle, but were 98.57% and 86.54% in the case of buffaloes respectively. A good correlation between the results of IDEXX ELISA and ELISA based on recombinant NcGRA7 for detecting N. caninum antibodies was appeared. Analyzing by Mc Nemar's showed that NcGRA7-based ELISA has acceptable capability to differentiate the positive results in comparison with IDEXX ELISA.

CONCLUSION

NcGRA7-based ELISA considering utilized new fragment of genomic DNA is a good tool for serodiagnosis of anti- N. caninum antibodies for screening and epidemiological purposes on cattle herd and water buffaloes as well.

A Neospora caninum vaccine using recombinant proteins fails to prevent foetal infection in pregnant cattle after experimental intravenous challenge

The aim of the present study was to evaluate the immunogenicity and protective efficacy of rNcSAG1, rNcHSP20 and rNcGRA7 recombinant proteins formulated with immune stimulating complexes (ISCOMs) in pregnant heifers against vertical transmission of Neospora caninum. Twelve pregnant heifers were divided into 3 groups of 4 heifers each, receiving different formulations before mating. Immunogens were administered twice subcutaneously: group A animals were inoculated with three recombinant proteins (rNcSAG1, rNcHSP20, rNcGRA7) formulated with ISCOMs; group B animals received ISCOM-MATRIX (without antigen) and group C received sterile phosphate-buffered saline (PBS) only. The recombinant proteins were expressed in Escherichia coli and purified nickel resin. All groups were intravenously challenged with the NC-1 strain of N. caninum at Day 70 of gestation and dams slaughtered at week 17 of the experiment. Heifers from group A developed specific antibodies against rNcSAG1, rNcHSP20 and rNcGRA7 prior to the challenge. Following immunization, an statistically significant increase of antibodies against rNcSAG1 and rNcHSP20 in all animals of group A was detected compared to animals in groups B and C at weeks 5, 13 and 16 (P<0.001). Levels of antibodies against rNcGRA7 were statistical higher in group A animals when compared with groups B and C at weeks 5 and 16 (P>0.001). There were no differences in IFN-γ production among the experimental groups at any time point (P>0.05). Transplacental transmission was determined in all foetuses of groups A, B and C by Western blot, immunohistochemistry and nested PCR. This work showed that rNcSAG1, rNcHSP20 and rNcGRA7 proteins while immunogenic in cattle failed to prevent the foetal infection in pregnant cattle challenged at Day 70 of gestation.

Cloning and expression of Neospora caninum dense-granule 7 in E. coli

Neospora caninum is an obligate intracellular protozoan which induces abortion, still birth and neuromuscular disorders in cattle and is an important problem in dairy and beef industry worldwide. The dense granule protein 7 (GRA7) of N. caninum is an immune-dominant protein shared by both tachyzoite and bradyzoites. This study was conducted to produce recombinant GRA7 of N. caninum using a plasmid with high level of expression of this protein in E. coli. For this purpose, a segment of N. caninum DNA corresponding to GRA7 was amplified using PCR. After sequencing, this fragment was cloned into expression vector pMAL-c2X under the control of the lac promoter. Expression of this plasmid in E. coli strain TG1 was identified by western blotting. In this study, pMAL-c2X had a strong promoter to produce high level expression of NcGRA7. This result revealed that this recombinant protein with pMAL-c2X vector may be suitable for developing of diagnostic procedures.

Development and Standardization of Dot - ELISA for Detection of Neospora caninum Antibodies in Cattle and Comparison with Standard Indirect ELISA and Direct Agglutination Test (DAT)

BACKGROUND

Neospora caninum is a protozoan parasite from phylum apicomplexa and an important agent causing abortion in cattle which produce notable economic loss all around the world.

METHODS

Dot-Elisa was set up performing checker board procedure and then 178 sera of cattle examined with commercial indirect ELISA and direct agglutination test (DAT) were also evaluated by dot-ELISA afterwards.

RESULTS

Kappa statistical analysis revealed that Dot-ELISA has good agreements with ELISA as well as the DAT and also, Mc Nemar's analyzing showed that this procedure has acceptable ability to discriminate positive results. Relative sensitivity and specificity of Dot-ELISA were respectively 92.63% and 89.16% and 93.4% and 90.8% in comparison with ELISA and DAT.

CONCLUSION

Since the dot-ELISA is easy, inexpensive and not needed high experience to interpret the results, it is superior to ELISA and DAT when we aim to screen the cattle on the farm and slaughterhouses or when the laboratory equipment is not available.

Identification of a highly antigenic region of subtilisin-like serine protease 1 for serodiagnosis of Neospora caninum infection

Neospora caninum is an apicomplexan parasite that causes abortion in cattle; hence, accurate diagnosis of this pathogen is important to the cattle farming industry. Our previous proteomics and immunoscreening analyses revealed that the N. caninum subtilisin-like serine protease 1 (NcSUB1) has potential as a serodiagnostic tool for Neospora. Consequently, we expressed two fragments containing five NcSUB1 tandem repeat copies covering amino acids (aa) 524 to 843 (NcSUB1t) and 555 to 679 (NcSUB1tr) to identify the antigenic regions. The serodiagnostic performances of NcSUB1t and NcSUB1tr were compared with that of N54, which contains a single copy of the repeats (aa 649 to 784), and with the truncated NcSAG1 (NcSAG1t), which lacks a signal peptide and C-terminal hydrophobic regions, as a positive reference. Serum samples from N. caninum experimentally infected cattle and mice and cattle from a farm with confirmed cases of Neospora abortion were tested by enzyme-linked immunosorbent assay (ELISA) with the four antigens. In the N. caninum experimentally infected cattle, the highest IgG1 antibody titers were detected against NcSUB1t, while specific IgG1 antibodies were detectable from 16 days postinfection (dpi), with levels peaking at 36 dpi for all of the antigens. On the other hand, the levels of anti-NcSUB1 IgG2 antibodies were lower than those of anti-SAG1t IgG2 antibodies. The ELISA with NcSUB1t and NcSUB1tr had good sensitivity (94.59 to 95.95%) and specificity (80 to 100%) with bovine serum field samples compared to NcSAG1t and showed no cross-reactions with sera from Toxoplasma gondii experimentally infected mice. Moreover, IgG antibodies against NcSUB1t were detected during parturition in the NcSAG1t antibody-positive cattle, and NcSUB1t-specific antibody transfer was observed from a mother to her calf. Our results show that the NcSUB1 tandem repeat is potentially useful for serodiagnosis of N. caninum.

Prevalence and dynamics of antibodies against NcSAG1 and NcGRA7 antigens of Neospora caninum in cattle during the gestation period

Bovine abortion caused by the Apicomplexan parasite Neospora caninum is a major economic problem in the livestock industry worldwide. Our study measured the prevalence and temporal changes in levels of antibodies specific for two N. caninum derived antigens, NcSAG1 and NcGRA7, to determine an appropriate strategy for serodiagnosis. Using an enzyme-linked immunosorbent assay (ELISA), blood samples showed that 71 cows out of 129 were positive for anti-NcSAG1 antibodies and that only nine cows were positive for anti-NcGRA7 antibodies. By longitudinal sampling, it was revealed that positive and negative antibody conversion occurred frequently for anti-NcGRA7, but that anti-NcSAG1 antibodies persisted for a long-term. These results indicate the usefulness of measuring anti-NcSAG1 antibody levels for the detection of chronically infected cows. Twelve cows showed positive seroconversion during pregnancy, nine of which showed seropositivity for anti-NcGRA7 antibody at the sixth and/or seventh month of pregnancy; serum samples were not obtained from the remaining three cows during this period. Therefore, the optimal time for detection of anti-NcGRA7 antibodies appears to be between the fifth and eighth month of pregnancy.

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.

ELISAs based on rNcGRA7 and rNcSAG1 antigens as an indicator of Neospora caninum activation

Bovine abortion caused by the Apicomplexa parasite Neospora caninum is a major economical problem in the livestock industry worldwide. However, the relationship between N. caninum infection and abortion is still unknown. Our study aimed to elucidate the relationship between parasite-specific antibody responses, parasite stages and abortion. In experimentally infected cattle, anti-NcGRA7 IgG1 antibody was predominantly detected during the acute infection stage, while the production of anti-NcSAG1 IgG1 antibody was observed during both acute and chronic stages. Furthermore, levels of anti-NcGRA7 IgG2 antibody were lower than those of anti-NcSAG1 IgG2 antibody. When tested on cattle with Neospora-associated abortion, positive rates of the anti-NcGRA7 IgG2 antibody were significantly lower than those of the anti-NcSAG1 antibody, although there was no difference in IgG1 antibody-positive rates between the two antigens. In addition, anti-NcGRA7 IgG2 antibodies were not detected in cattle for more than 30days after abortion. Our results suggested that anti-NcGRA7 and anti-NcSAG1 antibodies are suitable indicators for the activation stage of N. caninum infection and broad detection of the infection, respectively. In conclusion, the use of recombinant NcGRA7 and NcSAG1-based ELISAs will be useful for evaluating the abortion risk associated with N. caninum infection.

Enzyme-linked immunosorbent assays based on Neospora caninum dense granule protein 7 and profilin for estimating the stage of neosporosis

Neospora caninum is an intracellular protozoan parasite that causes bovine and canine neosporosis, characterized by fetal abortion and neonatal mortality and by neuromuscular paralysis, respectively. Although many diagnostic methods to detect parasite-specific antibodies or parasite DNA have been reported, to date no effective serodiagnostic techniques for estimating pathological status have been described. Our study aimed to elucidate the relationship between the parasite-specific antibody response, parasite activation, and neurological symptoms caused by N. caninum infection by using a recombinant antigen-based enzyme-linked immunosorbent assay. Among experimentally infected mice, anti-N. caninum profilin (NcPF) antibody was only detected in neurologically symptomatic animals. Parasite numbers within the brains of the symptomatic mice were significantly higher than those in asymptomatic animals. In addition, anti-NcPF and anti-NcGRA7 antibodies were mainly detected at the acute stage in experimentally infected dogs, while anti-NcSAG1 antibody was produced during both acute and chronic stages. Furthermore, among anti-NcSAG1 antibody-positive clinical dogs, the positive rates of anti-NcGRA7 and anti-NcPF antibodies in the neurologically symptomatic dogs were significantly higher than those in the non-neurologically symptomatic animals. Our results suggested that the levels of anti-NcGRA7 and anti-NcPF antibodies reflect parasite activation and neurological symptoms in dogs. In conclusion, antibodies against NcGRA7 and NcPF may have potential as suitable indicators for estimating the pathological status of neosporosis.

Immunological characterization of Neospora caninum cyclophilin

Neospora caninum is an intracellular parasite that poses a unique ability to infect a variety of cell types by causing host cell migration. Although previous studies demonstrated that parasite-derived proteins could trigger host cell migration, the related molecules have yet to be determined. Our study aimed to investigate the relationship between Neospora-derived molecules and host cell migration using recombinant protein of N. caninum cyclophilin (NcCyp). Indirect fluorescent antibody test revealed that NcCyp was expressed in the tachyzoite cytosol. Furthermore, NcCyp release from extracellular parasites was detected by sandwich enzyme-linked immunosorbent assay in a time-dependent manner. Recombinant NcCyp caused the cysteine-cysteine chemokine receptor 5-dependent migration of murine and bovine cells. Furthermore, immunohistochemistry indicated that NcCyp was consistently detected in tachyzoites distributed within or around the brain lesions. In conclusion, N. caninum-derived cyclophilin appears to contribute to host cell migration, thereby maintaining parasite/host interactions.

Identification of the cross-reactive and species-specific antigens between Neospora caninum and Toxoplasma gondii tachyzoites by a proteomics approach

The characterization of the cross-reactive and species-specific antigens of Neospora caninum and Toxoplasma gondii is important in the exploration to determine the common mechanisms of parasite-host interaction and to improve the serological diagnosis; it is also useful for the selection of the cross-reactive antigens that could be used in the development of vaccines or drugs for controlling the diseases caused by these two parasites. In this study, cross-reactive and species-specific antigens between N. caninum and T. gondii tachyzoites were comprehensively investigated using a proteomics approach with the application of two-dimensional gel electrophoresis, immunoblot analysis, matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF-MS), and MALDI-TOF/TOF-MS analysis. Immunoblotting and mass spectrometry analysis revealed that at least 42 individual protein spots of N. caninum were reacted with the anti-N. caninum serum, among which at least 18 protein spots were cross-reacted with the anti-T. gondii serum. Moreover, at least 31 protein spots of T. gondii were reacted with the anti-T. gondii serum, among which at least 19 protein spots were cross-reacted with the anti-N. caninum serum. Furthermore, some new specific proteins were also identified in the N. caninum protein profile by searching Toxoplasma sequences or sequences from other organisms. This study substantiates the usefulness of proteomics in the immunoscreening of the cross-reactive or species-specific antigens of both parasites. In addition, the present study showed that there was significant homology in the antigenic proteome profiles between the two parasites. These observations have implications for the design of multicomponent common vaccines against both parasite infections.

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.

Stage-specific expression of Nc SAG4 as a marker of chronic Neospora caninum infection in a mouse model

Neospora caninum infection persists throughout the life of its intermediate host due to the conversion of tachyzoites to slowly dividing bradyzoites that encyst in the brain. This event results in persistent N. caninum infection in bovine herds and partially explains the poor efficacy of many chemotherapeutic agents and vaccine formulations. Thus, there is a need for greater understanding of the tachyzoite-to-bradyzoite conversion mechanisms. Here we studied for the first time the transcription kinetics of the N. caninum bradyzoite-specific gene NcSAG4 in brain samples from chronically infected mice by means of real-time RT-PCR. NcSAG4-messenger RNA (mRNA) levels increased significantly during the chronic phase but followed 2 different expression patterns depending on the isolate used for murine inoculation. NcSAG4-mRNA levels in brains from Nc-1-inoculated mice peaked during late chronic infection (on day 64 post-infection, p.i.), whereas those from Nc-Liv-inoculated mice peaked earlier during the chronic infection (on day 32 p.i.). This difference could be a reflection of the different abilities of these isolates to replicate and form cysts in parasitized brains. These results are consistent with our observations of anti-rNcSAG4 antibody production; low levels were present at seroconversion and slowly increased during the chronic phase. In contrast, NcSAG1 transcription levels, which mark the tachyzoite stage, were maintained without variation in both groups of mice. This suggests the presence of a significant amount of tachyzoites or intermediate zoites expressing NcSAG1 in the brain, even during the late chronic infection.

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.

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.