Characterization of Neospora caninum surface protein NcSRS2 based on baculovirus expression system and its application for serodiagnosis of Neospora infection

Neospora caninum truncated recombinant proteins formulated with liposomes and CpG-ODNs triggered a humoral immune response in cattle after immunisation and challenge

Abortions caused by Neospora caninum are a serious problem in cattle production and require effective immunoprophylaxis. The objective of this work was to assess the humoral immune response to four recombinant (r) N. caninum antigens in cattle after immunisation and challenge. MIC1 and MIC3 proteins from the micronemes, SRS2 from the surface of tachyzoites, and GRA7 from the dense granules were expressed as truncated recombinant proteins in Escherichia coli. Cationic liposomes (Lip) and CpG oligodeoxynucleotides (CpG-ODNs) were used as adjuvant. Steers were assigned to three groups of six steers each and were inoculated twice subcutaneously, 21 days apart. The rP + Lip + CpG-ODN group received the truncated recombinant proteins rMIC1, rMIC3, rSRS2 and rGRA7 formulated with the adjuvant; the Lip + CpG-ODN group received the adjuvant alone; and the PBS group received sterile phosphate-buffered saline. All steers were subcutaneously challenged with the NC-1 strain of N. caninum 35 days after the second dose of immunisation. Steers from the rP + Lip + CpG-ODN group developed specific IgG, IgG1 and IgG2 against the four recombinant proteins after immunisation. After challenge, IgG against rMIC1 and rMIC3 was detected in rP + Lip + CpG-ODN group and against rSRS2 and rGRA7 in all groups. IgG1 and IgG2 against the four recombinant proteins remained high after challenge in the rP + Lip + CpG-ODN group. Indirect ELISA detected anti-N. caninum antibodies after challenge in all groups, with the highest level of antibodies being detected in the rP + Lip + CpG-ODN group. The recombinant vaccine formulated with rMIC1, rMIC3, rSRS2 and rGRA7 using Lip + CpG-ODN as adjuvant was immunogenic in cattle and the humoral immune response after challenge was enhanced in vaccinated cattle.

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.

Serology-Based Diagnostics for the Control of Bovine Neosporosis

The protozoan Neospora caninum is a primary infectious cause of abortion in cattle that causes significant economic losses worldwide. Because effective vaccines and licensed pharmacological treatments are currently unavailable, control measures rely on biosecurity and management practice. Serological diagnosis plays a crucial role in the identification of infected animals and several tests have been developed. However, owing to the particular dynamics of the host-parasite interaction and to the characteristics of the currently used diagnostic tools, a proportion of infected cattle may not be reliably identified, and can potentially undermine efforts towards the control of bovine neosporosis. Current diagnostic methods for N. caninum infection in cattle and the advances necessary to support effective control strategies are discussed.

Use of ELISA based on NcSRS2 of Neospora caninumexpressed in Pichia pastoris for diagnosing neosporosis in sheep and dogs

Neosporosis is a disease caused by the protozoon Neospora caninum that leads to significant economic losses in many countries. In the present study, we report on use of the recombinant protein NcSRS2 of N. caninum expressed in Pichia pastoris in an indirect immunoenzymatic assay (ELISA) for diagnosing neosporosis infection in sheep and dogs. We observed that the ELISA test yielded specificity of 94.5% and sensitivity of 100% for sheep and specificity of 93.3% and sensitivity of 100% for dogs. We observed that the sensitivity was higher than shown by the indirect fluorescent antibody test, and this was confirmed by means of Western blot. The results from this study suggest that the recombinant protein expressed in P. pastoris is a suitable antigen for use in immunodiagnosis to detect N. caninum in two important species exposed to this parasitosis.

Seroprevalence of Neospora caninum infection in dairy cows in Northern provinces, Thailand

Neospora caninum, an obligate intracellular protozoan parasite, is the causative agent of neosporosis, recognized as a major cause of bovine abortion around the world. Thailand is a developing agricultural country located in Southeast Asia. Livestock developments particularly in dairy cows of this country have been hampered by low productivity including milk and slow growth rate due to the impact of many pathogens including N. caninum. Currently, there is no effective method for control of neosporosis since there is less information regarding current status of infections. The objective of this study was to investigate the seroprevalence of neosporosis in dairy cows of the northern part of Thailand. During 2006-2007, the sera of 642 cows from 42 small farm holders with the top three highest consensus of dairy farms in the northern provinces, such as Chiang Rai, Chiang Mai and Lumpang were collected and performed tests. Antibodies to N. caninum were assayed by enzyme-linked immunosorbent assay (ELISA) with recombinant N. caninum surface antigen 1 (NcSAG1) and indirect fluorescent antibody test (IFAT). The overall prevalence of N. caninum infection in this study was 46.9% (301/642) by ELISA and 34.3% (220/642) by IFAT.

Expression of Neospora caninum NcSRS2 surface protein in Pichia pastoris and its application for serodiagnosis of Neospora infection

Neospora caninum is considerd a major cause of abortion in cattle worldwide. The antigenic domain of NcSRS2 in N. caninum is an important surface antigen present in the membrane of this parasite. In the present study, the Pichia pastoris expression system proved to be a useful tool for the production of recombinant protein. The truncated NcSRS2 gene (by removal of the N-terminal hydrophobic sequence), was cloned in the vector pPICZalphaB, and integrated on the genome of the methylotrophic yeast P. pastoris. Subsequently, the NcSRS2 protein was expressed, purified, and characterized using naturally infected cattle sera and Mab 6xhistag. The recombinant protein NcSRS2 was present in the supernatant of the culture, where later it was concentrated and purified using ammonium sulfate (∼100 mg/ml). An indirect immunoenzymatic assay (ELISA) was performed using cattle sera from endemic N. caninum area.

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.

Neospora caninum surface antigen (p40) is a potential diagnostic marker for cattle neosporosis

Neospora caninum is an intracellular protozoan that infects domestic and wild canids as well as many warm-blooded animals as shown by the isolation of viable parasites. The effectiveness of diagnostic tests for detecting specific antibodies against N. caninum is hampered by potential cross-reaction with other Coccidia. So, there is currently an urgent need for a sensitive and specific diagnostic assay for detecting N. caninum in animals. The N. caninum 40-kD surface antigen (p40), similar to NcSAG1 and NcSRS2, was shown to belong to surface antigen super family and thus represents an excellent marker for the diagnosis of neosporosis. In order to test the hypothesis, recombinant Ncp40 (rNcp40) was expressed in Escherichia coli, and an indirect ELISA test was developed using recombinant NCp40 antigen for N. caninum serodiagnosis. The antigen used in this study did not have cross-reactivity with anti-Toxoplasma gondii serum. Anti-p40 antibodies were detected by ELISA in the sera of Yellow cattle and were compared with (IFAT). Optimal sensitivity and specificity (98.2 and 98.6 %) were identified by IFAT. Additionally, 37 positive sera of T. gondii were detected and there was no significant difference with the negative serum of N. caninum. The rNcp40 ELISA developed here provides a specific and sensitive assay for detecting neosporosis in cattle.

Cloning, Nucleotide Sequencing and Bioinformatics Study of NcSRS2 Gene, an Immunogen from Iranian Isolate of Neospora caninum

BACKGROUND

Neosporosis is caused by an obligate intracellular parasitic protozoa Neospora caninum which infect variety of hosts. NcSRS2 is an immuno-dominant antigen of N. caninum which is considered as one of the most promising targets for a recombinant or DNA vaccine against neosporosis. As no study has been carried out to identify the molecular structure of N. caninum in Iran, as first step, we prepared a scheme to identify this gene in this parasite in Iran.

METHODS

Tachyzoite total RNA was extracted and cDNA was synthesized and NcSRS2 gene was amplified using cDNA as template. Then the PCR product was cloned into pTZ57R/T vector and transformed into E. coli (DH5α strain). Finally, the recombinant plasmid was extracted from transformed E. coli and sequenced. Bioinformatics analysis also carried out.

RESULTS

The PCR product of NcSRS2 gene was sequenced and recorded in GenBank. The deduced amino acid sequence of NcSRS2 in current study was compared with other N. caninum NcSRS2 and showed some identities and differences.

CONCLUSION

NcSRS2 gene of N. caninum successfully cloned in pTZ57R/T. Recombinant plasmid was confirmed by sequencing, colony PCR and enzymatic digestion. It is ready to express recombinant protein for further studies.

Optimization of expression conditions for production of anti-colorectal cancer monoclonal antibody CO17-1A in baculovirus-insect cell system

The baculovirus-insect cell system is considered a feasible expression system for recombinant glycoprotein production due to its several advantages, including high capacity, flexibility, and glycosylation capability. However, accurate titering of the recombinant baculovirus is required to ensure high expression in insect cells using a commercial and expensive immunoassay titer kit in which the envelope glycoprotein of the Autographa californica multiple nucleopolyhedrovirus (AcMNPV)-type baculovirus is detected by anti-envelope glycoprotein antibody and a secondary antibody conjugated to horseradish peroxidase (HRP). In this study, conditions for the expression of the CO17-1A immunotherapeutic monoclonal antibody (MAb) against colorectal cancer cells in a baculovirus system were optimized without using a commercial titering kit. Several variables were investigated to optimize antibody expression in a baculovirus-insect cell system, including baculovirus passage, volume of the infecting baculovirus inoculum (100, 200, 400, and 800 μL), and the harvest time of insect cells or cell supernatants after virus infection (24, 48, and 72 h). Two different pFastBac vectors carrying the CO17-1A MAb genes with or without the KDEL endoplasmic reticulum (ER) retention motif (Lys-Asp-Glu-Leu) fused to the HC (MAb CO17-1A K and MAb CO17-1A, respectively) were constructed and used to generate baculoviruses. Immunoblot analysis was conducted to confirm expression of MAb CO17-1A K and MAb CO17-1A in baculovirus-infected insect cells. Densitometry analysis of the protein bands was used to quantify the relative expression under different conditions. The highest expression was observed in lysed cells infected with 400 μL of passage 3 baculovirus (P(3) BV) carrying the gene encoding the CO17-1A MAb without KDEL at 72 h after virus infection. These results suggest that the infection conditions, the number of virus passages, baculovirus inoculum volume, and the harvest time can be modified to optimize MAb expression without using a BaculoELISA titer kit in a baculovirus-insect cell system.

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.

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.

Evaluation of a SRS2 Sandwich Commercial Enzyme-Linked Immunosorbent Assay for the Detection of Anti-Neospora Caninum Antibodies in Bovine and Canine Sera

Neospora caninum is a parasite responsible for abortion in cows and neuromuscular disease in dogs. Serology is the most widely used technique to evaluate the prevalenceof N. caninum in different host populations. A sandwich enzyme-linked immunosorbent assay (ELISA) based on the use of an anti-SRS2 monoclonal antibody was evaluated against the indirect fluorescent antibody test for 100 canine sera and against a well-characterized ELISA for 102 bovine sera. In cattle sera, the relative sensitivity and relative specificity were 100%. In dog sera, the relative specificity and relative sensitivity were 94% and 86%, respectively. The kappa value was 1 for bovine sera and 0.77 for canine sera. The seroprevalence was 3.9% in bovine sera and 21–23% in canine sera. The SRS2 sandwich ELISA was considered a valuable tool in both species.

First identification of Neospora caninum infection in aborted bovine foetuses in China

The first identification of Neospora caninum infection in the tissues of aborted bovine foetuses in China is reported. Aborted foetuses were collected from 16 dams, and 12 of the dams had high serum antibody titres to N. caninum determined using an ELISA test kit. The Nc-5 gene of N. caninum was amplified from DNA samples extracted from brains of four aborted foetuses using a Neospora-specific PCR assay, confirming N. caninum infection in the aborted foetuses. Histology and immunohistochemistry showed thick-walled (3 microm) tissue cyst in 25 microm diameter in the brain of one foetus. Non-suppurative encephalomyelitis, focal haemorrhage, hepatic lesions consisted of lymphocyte infiltration and haemorrhage were also found in the heart and lung of the foetus. Thus, we have confirmed for the first time the infection of N. caninum in aborted foetuses of cattle in the People's Republic of China.

The NcGRA7 gene encodes the immunodominant 17 kDa antigen of Neospora caninum

A Neospora caninum 17-19 kDa antigenic protein fraction (p17) in one-dimensional polyacrylamide gel electrophoresis (SDS-PAGE) is the immunodominant antigen recognized by sera from bovines naturally infected by N. caninum. To identify the proteins making up the p17 fraction, we screened a new N. caninum tachyzoite cDNA library with an affinity-purified antibody against p17 (APA17). We isolated several cDNA clones with 100% sequence identity to the NcGRA7 gene. This previously described gene encodes a dense granule protein with an apparent molecular mass of 33 kDa. A second line of evidence emerged through a combined proteomic approach associating two-dimensional PAGE (2D-PAGE) to Western blotting and to mass spectrometry to characterize the p17 fraction. Two acidic immunodominant but minority protein spots were recognized by APA17 and by bovine sera. These antigens of 17 and 33 kDa are respectively composed of 4 and 2 isoforms. Furthermore, p17 isolation by 2D-PAGE and peptide sequencing by tandem mass spectrometry yielded a partial sequence of 17 amino acids, which allowed the putative amino terminal region of the NcGRA7 protein to be identified unambiguously. The NcGRA7 protein, without the putative signal peptide at the NH2-terminus, was cloned and expressed in Escherichia coli and when the purified recombinant protein (rNcGRA7) was analysed by SDS-PAGE and mass spectrometry, 2 bands of 24 and 33 kDa were resolved and identified as NcGRA7. These results demonstrate that the immunodominant 17 kDa antigen of N. caninum is encoded by the NcGRA7 gene.

Diagnosis of bovine neosporosis

The protozoan parasite Neospora caninum is a major cause of abortion in cattle. The diagnosis of neosporosis-associated mortality and abortion in cattle is difficult. In the present paper we review histologic, serologic, immunohistochemical, and molecular methods for dignosis of bovine neosporosis. Although not a routine method of diagnosis, methods to isolate viable N. caninum from bovine tissues are also reviewed.

Enzyme-linked immunosorbent assays for detection of equine antibodies specific to Sarcocystis neurona surface antigens

Sarcocystis neurona is the primary causative agent of equine protozoal myeloencephalitis (EPM), a common neurologic disease of horses in the Americas. We have developed a set of enzyme-linked immunosorbent assays (ELISAs) based on the four major surface antigens of S. neurona (SnSAGs) to analyze the equine antibody response to S. neurona. The SnSAG ELISAs were optimized and standardized with a sample set of 36 equine sera that had been characterized by Western blotting against total S. neurona parasite antigen, the current gold standard for S. neurona serology. The recombinant SnSAG2 (rSnSAG2) ELISA showed the highest sensitivity and specificity at 95.5% and 92.9%, respectively. In contrast, only 68.2% sensitivity and 71.4% specificity were achieved with the rSnSAG1 ELISA, indicating that this antigen may not be a reliable serological marker for analyzing antibodies against S. neurona in horses. Importantly, the ELISA antigens did not show cross-reactivity with antisera to Sarcocystis fayeri or Neospora hughesi, two other equine parasites. The accuracy and reliability exhibited by the SnSAG ELISAs suggest that these assays will be valuable tools for examining the equine immune response against S. neurona infection, which may help in understanding the pathobiology of this accidental parasite-host interaction. Moreover, with modification and further investigation, the SnSAG ELISAs have potential for use as immunodiagnostic tests to aid in the identification of horses affected by EPM.

Development of rapid immunochromatographic test with recombinant NcSAG1 for detection of antibodies to Neospora caninum in cattle

An immunochromatographic test (ICT) with recombinant surface antigen 1 of Neospora caninum (NcSAG1) was developed for the rapid detection of antibodies to N. caninum in cattle. The ICT was used to clearly discriminate between immunofluorescent-antibody test (IFAT)-positive bovine sera and IFAT-negative bovine sera. Serum samples collected from cattle in Yanbian, China, were examined by the ICT. Of the 96 serum samples, 23 (24.0%) were positive by the ICT, and 19 (19.8%) samples were positive by a previously developed enzyme-linked immunosorbent assay (ELISA). Eighteen of 19 ELISA-positive samples were positive according to the ICT. A good agreement was found between the results of the ICT and the ELISA. The results presented here suggest that the ICT with recombinant truncated NcSAG1 fused to glutathione S-transferase is a useful and reliable method for the detection of antibodies to N. caninum in cattle.

Comparison of proteome and antigenic proteome between two Neospora caninum isolates

This study was conducted to explore the relationship between two isolates of Neospora caninum (N. caninum) (KBA-2 and VMDL-1) using proteomics. To achieve the goal, proteins of N. caninum tachyzoite lysates of KBA-2 and VMDL-1 were separated by two-dimensional gel electrophoresis (2-DE), stained with silver-nitrate and analyzed using matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) to compare protein profiles. In addition, proteins separated by 2-DE were transferred to membranes, probed with bovine anti-N. caninum KBA-2 immunoglobulin G, and reactive proteins were visualized and compared between the two isolates. Most spots on 2-DE profiles and antigenic spots on 2-DE immunoblot profiles were located at similar locations in terms of isoelectric point and molecular weight. Proteins common to both isolates included the following: heat shock protein 70, subtilisin-like serine protease, nucleoside triphosphatase, heat shock protein 60, pyruvate kinase, tubulin alpha, tubulin beta, enolase, putative protein disulfide isomerase, actin, fructase-1,6-bisphosphatase, putative ribosomal protein S2, microneme protein Nc-P38, lactate dihydrogenase, fructose-1,6-bisphosphatase aldolase, serine threonine phosphatase 2C, 14-3-3 protein homologue, N. caninum dense granule-1 and NcGRA2. As a consequence, even though N. caninum KBA-2 and VMDL-1 isolates were isolated from geographically distinct locations there were significant homology in the proteome and antigenic proteome profiles. In addition, proteomic approach was verified as a useful tool for understanding of host immune response against different isolates of protozoa.

HPLC purification of recombinant NcGRA6 antigen improves enzyme-linked immunosorbent assay for serodiagnosis of bovine neosporosis

The gene for a dense granule protein (NcGRA6) of Neospora caninum was expressed in Escherichia coli as a His-tag fusion protein and purified by NiNTA affinity chromatography. In a preliminary study, high binding of antibodies from N. caninum-negative cows was observed in enzyme-linked immunosorbent assay (ELISA) using NiNTA-purified NcGRA6. Analysis of NiNTA eluates revealed a significant number of E. coli proteins that co-purified with recombinant NcGRA6. In an attempt to improve the relative sensitivity and specificity of the NcGRA6-based ELISA, the rNcGRA6 eluates were subjected to a secondary purification using reverse phase-high performance liquid chromatography (RP-HPLC). Analysis of RP-HPLC eluates by SDS-PAGE/silver staining revealed the purification of recombinant NcGRA6 from contaminating E. coli proteins. ELISAs using the RP-HPLC purified NcGRA6 (dELISA) or singly purified NcGRA6 (sELISA) for identifying seropositive and seronegative cows in a beef herd experiencing an epidemic outbreak of neosporosis were compared to standard assays based on native tachyzoite protein-immunofluorescence antibody test, immunoblot assay, and ISCOM-ELISA. The relative sensitivity, specificity, and kappa value of the NcGRA6d-ELISA were greatly improved over the NcGRA6s-ELISA when compared to the three native antigen immunoassays. These results indicate that removal of contaminating E. coli proteins improves the performance of recombinant NcGRA6 ELISA in diagnosing bovine neosporosis, and may have applicability to the use of recombinant proteins in diagnosing other infectious agents.

Identification of antigenic proteins from Neospora caninum recognized by bovine immunoglobulins M, E, A and G using immunoproteomics

Antigenic proteins of Neospora caninum (N. caninum) against bovine immunoglobulins M, E, A, and G were investigated by using immunoproteomics. Proteins of N. caninum (KBA-2) tachyzoite lysates separated by two-dimensional gel electrophoresis were transferred to polyvinylidene difluoride (PVDF) membranes, probed with different bovine immunoglobulin class and classified. Antigenic spots recognized were also identified by matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS) analysis. 132, 84, 4, and 40 antigenic protein spots were recognized on N. caninum immunoblot profiles against bovine IgM, IgE, IgA, and IgG, respectively. Of these protein spots, the antigenic proteins recognized by either IgM, IgE, and IgG, or IgM and IgG were HSP70, pyruvate kinase, actin, NCDG-1, tubulin alpha-chain, and putative ribosomal protein S2. On the other hand, IgM, IgE, and IgA reacted with NTPase, HSP60, tubulin beta-chain, putative protein disulfide isomerase, enolase, lactate dehydrogenase, serine-threonine phosphatase, 14-3-3 protein homologue, and GRA2 protein. Most of the antigenic proteins identified were associated with the process of invasion, proliferation, and egression of apicomplexans. In our study, HSP70, actin, NTPase, HSP60, pyruvate kinase, enolase, putative ribosomal protein S2, NCDG-1, and GRA2 proteins were found to be immunodominant proteins, which may contribute to the development of diagnostic markers and vaccine.

Detection of Antibodies to Neospora caninum in Cattle by Enzyme-Linked Immunosorbent Assay with Truncated NcSRS2 Expressed in Escherichia coli

The surface antigen 1-related sequence 2 of Neospora caninum (NcSRS2) is considered as an immunodominant antigen. In this study, the gene encoding truncated NcSRS2 (NcSRS2t) lacking an N-terminal signal peptide and C-terminal hydrophobic regions was expressed in Escherichia coli, and its diagnostic potential in an enzyme-linked immunosorbent assay (ELISA) was evaluated. ELISA could discriminate clearly between known N. caninum-positive and -negative sera from cattle. Field serum samples collected from cattle in Brazil were examined for the diagnosis of N. caninum infection using ELISA. Of the 197 samples analyzed, 64 (32.5%) samples were positive for antibodies to N. caninum. Of the 64 ELISA-positive samples, 58 (90.6%) were confirmed as positive by Western blot analysis with whole-parasite antigens. These results suggest that ELISA with recombinant NcSRS2t is an effective method for diagnosis of N. caninum infection in cattle.

Antigenic evaluation of a recombinant baculovirus-expressed Sarcocystis neurona SAG1 antigen

Sarcocystis neurona is the primary parasite associated with equine protozoal myeloencephalitis (EPM). This is a commonly diagnosed neurological disorder in the Americas that infects the central nervous system of horses. Current serologic assays utilize culture-derived parasites as antigen. This method requires large numbers of parasites to be grown in culture, which is labor intensive and time consuming. Also, a culture-derived whole-parasite preparation contains conserved antigens that could cross-react with antibodies against other Sarcocystis species and members of Sarcocystidae such as Neospora spp., Hammondia spp., and Toxoplasma gondii. Therefore, there is a need to develop an improved method for the detection of S. neurona-specific antibodies. The sera of infected horses react strongly to surface antigen 1 (SnSAG1), an approximately 29-kDa protein, in immunoblot analysis, suggesting that it is an immunodominant antigen. The SnSAG1 gene of S. neurona was cloned, and recombinant S. neurona SAG1 protein (rSnSAG1-Bac) was expressed with the use of a baculovirus system. By immunoblot analysis, the rSnSAG1-Bac antigen detected antibodies to S. neurona from naturally infected and experimentally inoculated equids, cats, rabbit, mice, and skunk. This is the first report of a baculovirus-expressed recombinant S. neurona antigen being used to detect anti-S. neurona antibodies in a variety of host species.

Serodiagnosis of Neospora caninum infection in cattle by enzyme-linked immunosorbent assay with recombinant truncated NcSAG1

Neospora caninum is a veterinary medically important pathogen capable of causing abortion in cattle and neuromuscular paralysis in dogs. The surface antigen 1 of N. caninum (NcSAG1) is an important candidate for the development of a diagnostic reagent for neosporosis. In order to establish an effective diagnostic method, the gene encoding truncated NcSAG1 (NcSAG1t) lacking a signal peptide and C-terminal hydrophobic regions was cloned and expressed in Escherichia coli as a fusion protein with glutathione S-transferase (GST). The purified GST-NcSAG1t was tested in an enzyme-linked immunosorbent assay (ELISA) for the detection of N. caninum antibodies in cattle. The ELISA with GST-NcSAG1t clearly differentiated between immunofluorescent antibody test (IFAT)-positive and -negative sera from cattle. In addition, the ELISA detected no cross-reactivity with sera from mice experimentally infected with the closely related parasite Toxoplasma gondii. Field serum samples collected from cattle in Brazil were examined for the diagnosis of neosporosis by using the ELISA. Of the 197 samples analyzed, 66 (33.5%) samples were positive for antibodies to N. caninum. Of the 66 ELISA-positive samples, 60 (90%) samples were confirmed as positive by Western blot analysis with whole parasite antigens. These results suggest that the recombinant NcSAG1t could be a reliable reagent for use as an antigen in ELISA for the serodiagnosis of N. caninum infection in cattle.

Neospora caninum antigens recognized by mouse IgG at different stages of infection including recrudescence

Western blotting was performed to analyze Neospora caninum tachyzoite antigens recognized by mouse IgG at different stages of infection including recrudescence. At the early stage of infection, a 36-38 kDa antigen was clearly recognized by the mouse antisera. After day 48 postinoculation, the signal of the 36-38 kDa antigen gradually weakened. Meanwhile, a 43 kDa antigen was intensely and continuously recognized from 48 to 125 days postinoculation. This 43 kDa antigen was clearly detectable with the antisera from the mice under immunosuppression. Sera from naturally infected cattle strongly reacted with the 43 kDa antigen. Therefore, the 43 kDa antigen may be useful for immunological reactions to detect infected animals except in the early stage of the infection.

Neospora caninum NcSRS2 is a transmembrane protein that contains a glycosylphosphatidylinositol anchor in insect cells

We investigated the terminal location of NcSRS2, a surface antigen of Neospora caninum that has potential use for diagnosis, and demonstrated its importance as a vaccine component against neosporosis, in an insect-baculovirus expression system. To examine the role of the hydrophobic C-terminal tail in NcSRS2, four types of recombinant baculoviruses were constructed. Immunoblotting and N-terminal amino acid analysis revealed cleavage of a 6 kDa of the N-terminal signal peptide in the mature NcSRS2 protein. The recombinant NcSRS2 (rNcSRS2) lacking 25, and 62 amino acids from the termination codon were detected in supernatants from recombinant virus-infected cells, but not in recombinants with truncated 147 amino acids from the termination codon, and intact NcSRS2 gene (401 amino acids). By flow cytometric and confocal laser scanning microscopic analyses, the truncation of the hydrophobic C-terminal tail in NcSRS2 was shown to result in the reduction of protein expression on the cell surface relative to intact rNcSRS2. Except for the recombinant lacking the 147 C-terminal residues, three other rNcSRS2 were detected in the supernatants after treatment with phosphatidylinositol-specific phospholipase C. Our results demonstrate that the N. caninum NcSRS2 is a transmembrane protein that contains a glycosylphosphatidylinositol-anchor molecule in insect cells, and that the hydrophobic C-terminal domain is an essential component for GPI-membrane attachment. We have likewise shown the usefulness of the insect-recombinant baculovirus system in the expression of rNcSRS2.