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

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.

Unfolded protein response is involved in resistance to Neospora caninum infection via IRE1α-XBP1s-NOD2 Axis

Neospora caninum, an intracellular protozoan parasite, causes neosporosis resulting in major losses in the livestock industry worldwide. However, no effective drugs or vaccines have been developed to control neosporosis. An in-depth study on the immune response against N. caninum could help to search for effective approaches to prevent and treat neosporosis. The host unfolded protein response (UPR) functions as a double-edged sword in several protozoan parasite infections, either to initiate immune responses or to help parasite survival. In this study, the roles of the UPR in N. caninum infection in vitro and in vivo were explored, and the mechanism of the UPR in resistance to N. caninum infection was analyzed. The results revealed that N. caninum triggered the UPR in mouse macrophages, such as the activation of the IRE1 and PERK branches, but not the ATF6 branch. Inhibition of the IRE1α-XBP1s branch increased the N. caninum number both in vitro and in vivo, while inhibition of the PERK branch did not affect the parasite number. Furthermore, inhibition of the IRE1α-XBP1s branch reduced the production of cytokines by inhibiting NOD2 signalling and its downstream NF-κB and MAPK pathways. Taken together, the results of this study suggest that the UPR is involved in the resistance of N. caninum infection via the IRE1α-XBP1s branch by regulating NOD2 and its downstream NF-κB and MAPK pathways to induce the production of inflammatory cytokines, which provides a new perspective for the research and development of anti-N. caninum drugs.

Host defense against Neospora caninum infection via IL-12p40 production through TLR2/TLR3-AKT-ERK signaling pathway in C57BL/6 mice

Neospora caninum is an intracellular parasite which can cause neosporosis and significant economic losses in both dairy and beef industries worldwide. A better understanding of the immune response by host cells against N. caninum could help to design better strategies for the prevention and treatment of neosporosis. Although previous studies have shown TLR2/TLR3 were involved in controlling N. caninum infection in mice, the precise mechanisms of the AKT and MAPK pathways controlled by TLR2/TLR3 to regulate N. caninum-induced IL-12p40 production and the role of TLR2/TLR3 in anti-N. caninum infection in bovine macrophages remain unclear. In the present study, TLR2^-/- mice displayed more parasite burden and lower level of IL-12p40 production compared to TLR3^-/- mice. N. caninum could activate AKT and ERK signaling pathways in WT mouse macrophages, which were inhibited in TLR2^-/- and TLR3^-/- mouse macrophages. In N. caninum-infected WT mouse macrophages, AKT inhibitor or AKT siRNA could decrease the phosphorylation of ERK. AKT or ERK inhibitors reduced the production of IL-12p40 and increased the number of parasites. The productions of ROS, NO, and GBP2 were significantly reduced in TLR2^-/- and TLR3^-/- mouse macrophages. Supplementation of rIL-12p40 inhibited N. caninum proliferation and rescued the productions of IFN-γ, NO, and GBP2 in WT, TLR2^-/-, and TLR3^-/- mouse macrophages. In bovine macrophages, the expressions of TLR2, TLR3, and IL-12p40 mRNA were significantly enhanced by N. caninum, and N. caninum proliferation was inhibited by TLR2/TLR3 agonists. Taken together, the proliferation of N. caninum in mouse macrophages was controlled by the TLR2/TLR3-AKT-ERK signal pathway via increased IL-12p40 production, which in turn lead to the productions of NO, GBP2, and IFN-γ during N. caninum infection. And in bovine macrophages, TLR2 and TLR3 contributed to inhibiting N. caninum proliferation via increased IL-12p40 production.

Vaccination with Neospora caninum-cyclophilin and -profilin confers partial protection against experimental neosporosis-induced abortion in sheep

The purpose of this study was to evaluate the protective efficacy of a vaccine consisting of recombinant Neospora caninum-cyclophilin (NcCyP) and -profilin (NcPro) in sheep. At 42 d and 21 d prior to mating, adult Dorset ewes were immunized with the rNcCyP-rNcPro vaccine (Group 1) or co-purifying non-recombinant (NR) control vaccine (Group 2). At 90 days post-mating, all immunized ewes and were challenged by intravenous injection with 10⁶Nesopora caninum Illinois tachyzoites (NcTZ). Significant protection (P < 0.05) was observed in Group 1 with 9 out of 13 ewes giving birth to live-born lambs (69.2%), whereas all Group 2 ewes aborted (6/6). Neospora caninum was detected by PCR in both fetal and placental tissues from all Group 2 aborting ewes and in the placental tissues of Group 1 aborting ewes. In contrast, tissues and placentas of Group 1 live-born lambs were Neospora DNA-negative. Immunoreactive Neospora antigens were demonstrated in placentas associated with abortions, but not in tissues of aborted fetuses or those of the live-born lambs and their associated placentas. Anti-NcCyP and anti-NcPro titers were high in sera from Group 1 ewes and were further boosted by challenge infection, resulting in long-lasting (≥14.5 mos.) elevated titers. Lambs born to Group 1 ewes also had high NcCyP and NcPro titers in pre-colostrum sera. Immunofluorescence staining (IFA) of NcTZ with Group 1 post-immunization sera revealed both surface and internal TZ staining, a pattern consistent with that observed with rabbit sera to rNcCyP or rNcPro. Infection of NR-vaccinated ewes produced high but transient anti-NcCyP and anti-NcPro Ab titers. The results indicate that the NcCyP-NcPro vaccine elicited strong anti-N. caninum responses and conferred significant protection against abortion and transplacental transmission of N. caninum TZ in sheep.

Immediate Interferon Gamma Induction Determines Murine Host Compatibility Differences between Toxoplasma gondii and Neospora caninum

Rodents are critical for the transmission of Toxoplasma gondii to the definitive feline host via predation, and this relationship has been extensively studied as a model for immune responses to parasites. Neospora caninum is a closely related coccidian parasite of ruminants and canines but is not naturally transmitted by rodents. We compared mouse innate immune responses to N. caninum and T. gondii and found marked differences in cytokine levels and parasite growth kinetics during the first 24 h postinfection (hpi). N. caninum-infected mice produced significantly higher levels of interleukin-12 (IL-12) and interferon gamma (IFN-γ) by as early as 4 hpi, but the level of IFN-γ was significantly lower or undetectable in T. gondii-infected mice during the first 24 hpi. "Immediate" IFN-γ and IL-12p40 production was not detected in MyD88-/- mice. However, unlike IL-12p40-/- and IFN-γ-/- mice, MyD88-/- mice survived N. caninum infections at the dose used in this study. Serial measures of parasite burden showed that MyD88-/- mice were more susceptible to N. caninum infections than wild-type (WT) mice, and control of parasite burdens correlated with a pulse of serum IFN-γ at 3 to 4 days postinfection in the absence of detectable IL-12. Immediate IFN-γ was partially dependent on the T. gondii mouse profilin receptor Toll-like receptor 11 (TLR11), but the ectopic expression of N. caninum profilin in T. gondii had no impact on early IFN-γ production or parasite proliferation. Our data indicate that T. gondii is capable of evading host detection during the first hours after infection, while N. caninum is not, and this is likely due to the early MyD88-dependent recognition of ligands other than profilin.

Secretory Nanoparticles of Neospora caninum Profilin-Fused with the Transmembrane Domain of GP64 from Silkworm Hemolymph

Neosporosis, which is caused by Neospora caninum, is a well-known disease in the veterinary field. Infections in pregnant cattle lead to abortion via transplacental (congenitally from mother to fetus) transmission. In this study, a N. caninum profilin (NcPROF), was expressed in silkworm larvae by recombinant Bombyx mori nucleopolyhedrovirus (BmNPV) bacmid and was purified from the hemolymph. Three NcPROF constructs were investigated, native NcPROF fused with an N-terminal PA tag (PA-NcPROF), PA-NcPROF fused with the signal sequence of bombyxin from B. mori (bx-PA-NcPROF), and bx-PA-NcPROF with additional C-terminal transmembrane and cytoplasmic domains of GP64 from BmNPV (bx-PA-NcPROF-GP64TM). All recombinant proteins were observed extra- and intracellularly in cultured Bm5 cells and silkworm larvae. The bx-PA-NcPROF-GP64TM was partly abnormally secreted, even though it has the transmembrane domain, and only it was pelleted by ultracentrifugation, but PA-NcPROF and bx-PA-NcPROF were not. Additionally, bx-PA-NcPROF-GP64TM was successfully purified from silkworm hemolymph by anti-PA agarose beads while PA-NcPROF and bx-PA-NcPROF were not. The purified bx-PA-NcPROF-GP64TM protein bound to its receptor, mouse Toll-like receptor 11 (TLR-11), and formed unique nanoparticles. These results suggest that profilin fused with GP64TM was secreted as a nanoparticle with binding affinity to its receptor and this nanoparticle formation is advantageous for the development of vaccines to N. caninum.

In vitro cellular responses to Neospora caninum glycosylphosphatidylinositols depend on the host origin of antigen presenting cells

Neosporosis due to Neospora caninum causes abortions in farm animals such as cattle. No treatment and vaccine exist to fight this disease, responsible for considerable economic losses. It is thus important to better understand the immune responses occurring during the pathogenesis to control them in a global strategy against the parasite. In this context, we studied the roles of N. caninum glycosylphosphatidylinositols (GPIs), glycolipids defined as toxins in the related parasite Plasmodium falciparum. We demonstrated for the first time that GPIs could be excreted in the supernatant of N. caninum culture and trigger cell signalling through the Toll-like receptors 2 and 4. In addition, antibodies specific to N. caninum GPIs were detected in the serum of infected mice. As shown for other protozoan diseases, they could play a role in neutralizing GPIs. N. caninum GPIs were able to induce the production of tumour necrosis factor-α, interleukin(IL)-1β and IL-12 cytokines by murine macrophages and dendritic cells. Furthermore, GPIs significantly reduced expression of major histocompatibility complex (MHC) molecules of class I on murine dendritic cells. In contrast to murine cells, bovine blood mononuclear cells produced increased levels of IFN-γ and IL-10, but reduced levels of IL-12p40 in response to GPIs. On these bovine cells, GPI had the tendency to up-regulate MHC class I, but to down-regulate MHC class II. Altogether, these results suggest that N. caninum GPIs might differentially participate in the responses of antigen presenting cells induced by the whole parasite in mouse models of neosporosis and in the natural cattle host.

14-3-3 Protein of Neospora caninum Modulates Host Cell Innate Immunity Through the Activation of MAPK and NF-κB Pathways

Neospora caninum is an obligate intracellular apicomplexan parasite, the etiologic agent of neosporosis, and a major cause of reproductive loss in cattle. There is still a lack of effective prevention and treatment measures. The 14-3-3 protein is a widely expressed acidic protein that spontaneously forms dimers within apicomplexan parasites. This protein has been isolated and sequenced in many parasites; however, there are few reports about the N. caninum 14-3-3 protein. Here, we successfully expressed and purified a recombinant fusion protein of Nc14-3-3 (rNc14-3-3) and prepared a polyclonal antibody. Immunofluorescence and immunogold electron microscopy studies of tachyzoites or N. caninum-infected cells suggested that 14-3-3 was localized in the cytosol and the membrane. Western blotting analysis indicated that rNc14-3-3 could be recognized by N. caninum-infected mouse sera, suggesting that 14-3-3 may be an infection-associated antigen that is involved in the host immune response. We demonstrated that rNc14-3-3 induced cytokine expression by activating the MAPK and AKT signaling pathways, and inhibitors of p38, ERK, JNK, and AKT could significantly decrease the production of IL-6, IL-12p40, and TNF-α. In addition, phosphorylated nuclear factor-κB (NF-κB/p65) was observed in wild-type peritoneal macrophages (PMs) treated with rNc14-3-3, and the protein level of NF-κB/p65 was reduced in the cytoplasm but increased correspondingly in the nucleus after 2 h of treatment. These results were also observed in deficient in TLR2^-/- PMs. Taken together, our results indicated that the N. caninum 14-3-3 protein can induce effective immune responses and stimulate cytokine expression by activating the MAPK, AKT, and NF-κB signaling pathways but did not dependent TLR2, suggesting that Nc14-3-3 is a novel vaccine candidate against neosporosis.

Neospora caninum Dense Granule Protein 7 Regulates the Pathogenesis of Neosporosis by Modulating Host Immune Response

Neospora caninum is a protozoan parasite closely related to Toxoplasma gondii Neosporosis caused by N. caninum is considered one of the main causes of abortion in cattle and nervous-system dysfunction in dogs, and identification of the virulence factors of this parasite is important for the development of control measures. Here, we used a luciferase reporter assay to screen the dense granule proteins genes of N. caninum, and we found that NcGRA6, NcGRA7, and NcGRA14 are involved in the activation of the NF-κB, calcium/calcineurin, and cAMP/PKA signals. To analyze the functions of these proteins and Neospora cyclophilin, we successfully knocked out their genes in the Nc1 strain using plasmids containing the CRISPR/Cas9 components. Among the deficient lines, the NcGRA7-deficient parasites showed reduced virulence in mice. An RNA sequencing analysis of infected macrophage cultures showed that NcGRA7 mainly regulates the host cytokine and chemokine production. The levels of gamma interferon in the ascites fluid, CXCL10 expression in the peritoneal cells, and CCL2 expression in the spleen were lower 5 days after infection with the NcGRA7-deficient parasite than after infection with the parental strain. The parasite burden and the degree of necrosis in the brains of mice infected with the NcGRA7-deficient parasite were also lower than in those of the parental strain. Collectively, our data suggest that both the NcGRA7-dependent activation of the inflammatory response and the parasite burden are important in Neospora virulence.IMPORTANCENeospora caninum invades and replicates in a broad range of host species and cells within those hosts. The effector proteins exported by Neospora induce its pathogenesis by modulating the host immunity. We show that most of the transcriptomic effects in N. caninum-infected cells depend upon the activity of NcGRA7. A deficiency in NcGRA7 reduced the virulence of the parasite in mice. This study demonstrates the importance of NcGRA7 in the pathogenesis of neosporosis.

Extracellular Vesicles Secreted by Neospora caninum Are Recognized by Toll-Like Receptor 2 and Modulate Host Cell Innate Immunity Through the MAPK Signaling Pathway

Neospora caninum is an obligate intracellular parasite, which causes significant economic losses in the cattle industry. However, the immune mechanism of the parasite–host interaction is not yet fully understood. Extracellular vesicles (EVs) have emerged as a ubiquitous mechanism by which almost all cells, especially immune and tumor cells, participate in intercellular communications. Although studies have indicated that EVs secreted by Toxoplasma gondii or Trypanosoma brucei promote exchanges of biological molecules important for the host–parasite interplay, however, EVs and their biological activities in N. caninum is not clear. Here, we used multiple methods, including electron microscopy, nanoparticle tracking analysis, RT-PCR, immunofluorescence, western blot, proteomics, and cytokine analyses, to examine the properties of N. caninum EVs. We found that N. caninum produced EVs that are similar to mammalian exosomes, which generally range from 30 to 150 nm in diameter. It was shown that N. caninum EVs could remarkably increase the production of pro-inflammatory cytokines IL-12p40, TNF-α, IL-1β, IL-6, and IFN-γ by wild-type (WT) mouse bone marrow-derived macrophages (BMDMs) whereas the secretion of IL-12p40, TNF-α, and IFN-γ was very strongly downregulated in TLR2^−/− mouse BMDMs. The levels of IL-6 were not affected, but the secretion of IL-10 was upregulated. We found that the phosphorylation levels of P38, ERK, and JNK were significantly reduced in the TLR2^−/− cells compared with those in WT mouse BMDMs and that treatment with chemical inhibiters of P38, ERK, and JNK resulted in upregulation of IL-6, IL-12p40, and IL-10 production. Together, these results demonstrated that N. caninum EVs could be rapidly internalized to deliver proteins to the host cells and modulate the host cell immune responses through MAPK signaling pathway in a TLR2-dependent manner. Our study is the first to reveal potential roles for N. caninum EVs in host communication and immune response in parasite–host interactions.

Apicomplexan profilins in vaccine development applied to bovine neosporosis

Neospora caninum, an intracellular protozoan parasite from the phylum Apicomplexa, is the etiologic agent of neosporosis, a disease considered as a major cause of reproductive loss in cattle and neuromuscular disease in dogs. Bovine neosporosis has a great economic impact in both meat and dairy industries, related to abortion, premature culling and reduced milk yields. Although many efforts have been made to restrain bovine neosporosis, there are still no efficacious control methods. Many vaccine-development studies focused in the apicomplexan proteins involved in the adhesion and invasion of the host cell. Among these proteins, profilins have recently emerged as potential vaccine antigens or even adjuvant candidates for several diseases caused by apicomplexan parasites. Profilins bind Toll-like receptors 11 and 12 initiating MyD88 signaling, that triggers IL-12 and IFN-γ production, which may promote protection against infection. Here we summarized the state-of-the-art of novel vaccine development based on apicomplexan profilins applied as antigens or adjuvants, and delved into recent advances on N. caninum vaccines using profilin in the mouse model and in cattle.

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.

Neospora caninum Activates p38 MAPK as an Evasion Mechanism against Innate Immunity

Due to the high prevalence and economic impact of neosporosis, the development of safe and effective vaccines and therapies against this parasite has been a priority in the field and is crucial to limit horizontal and vertical transmission in natural hosts. Limited data is available regarding factors that regulate the immune response against this parasite and such knowledge is essential in order to understand Neospora caninum induced pathogenesis. Mitogen-activated protein kinases (MAPKs) govern diverse cellular processes, including growth, differentiation, apoptosis, and immune-mediated responses. In that sense, our goal was to understand the role of MAPKs during the infection by N. caninum. We found that p38 phosphorylation was quickly triggered in macrophages stimulated by live tachyzoites and antigen extracts, while its chemical inhibition resulted in upregulation of IL-12p40 production and augmented B7/MHC expression. In vivo blockade of p38 resulted in an amplified production of cytokines, which preceded a reduction in latent parasite burden and enhanced survival against the infection. Additionally, the experiments indicate that the p38 activation is induced by a mechanism that depends on GPCR, PI3K and AKT signaling pathways, and that the phenomena here observed is distinct that those induced by Toxoplasma gondii’s GRA24 protein. Altogether, these results showed that N. caninum manipulates p38 phosphorylation in its favor, in order to downregulate the host’s innate immune responses. Additionally, those results infer that active interference in this signaling pathway may be useful for the development of a new therapeutic strategy against neosporosis.

Immunization with Neospora caninum profilin induces limited protection and a regulatory T-cell response in mice

Profilins are actin-binding proteins that regulate the polymerization of actin filaments. In apicomplexan parasites, they are essential for invasion. Profilins also trigger the immune response of the host by activating TLRs on dendritic cells (DCs), inducing the production of pro-inflammatory cytokines. In this study we characterized for the first time the immune response and protection elicited by a vaccine based on Neospora caninum profilin in mice. Groups of eight BALB/c mice received either two doses of a recombinant N. caninum profilin expressed in Escherichia coli. (rNcPRO) or PBS, both formulated with an aqueous soy-based adjuvant enriched in TLR-agonists. Specific anti-profilin antibodies were detected in rNcPRO-vaccinated animals, mainly IgM and IgG3, which were consumed after infection. Splenocytes from rNcPRO-immunized animals proliferated after an in vitro stimulation with rNcPRO before and after challenge. An impairment of the cellular response was observed in NcPRO vaccinated and infected mice following an in vitro stimulation with native antigens of N. caninum, related to an increase in the percentage of CD4+CD25+FoxP3+. Two out of five rNcPRO-vaccinated challenged mice were protected; they were negative for parasite DNA in the brain and showed no histopathological lesions, which were found in all PBS-vaccinated animals. As a whole, our results provide evidence of a regulatory response elicited by immunization with rNcPRO, and suggest a role of profilin in the modulation and/or evasion of immune responses against N. caninum.

Macrophage depletion prior to Neospora caninum infection results in severe neosporosis in mice

We observed that murine macrophages showed greater activation and increased interleukin 6 (IL-6), IL-12p40, and interferon gamma (IFN-γ) production during Neospora caninum infection. Many macrophages migrated to the site of infection. Furthermore, macrophage-depleted mice exhibited increased sensitivity to N. caninum infection. This study indicates that macrophages are required for achieving protective immunity against N. caninum.

Characterization of Neospora caninum macrophage migration inhibitory factor

The present study is the first characterization of Neospora caninum macrophage migration inhibitory factor (NcMIF). BLAST-N analysis of NcMIF revealed high similarity (87%) to the Toxoplasma gondii MIF. NcMIF was cloned and expressed in Escherichia coli in 3 forms, NcMIF (mature protein), NcMIFm (mutation of proline-2 to glycine), and NcMIFhis (addition of a polyhistidine tag at the N-terminus). None of these recombinant NcMIFs (rNcMIF) had tautomerase, oxidoreductase, or immunologic regulatory activities. rNcMIF was unable to compete with recombinant human MIF for a MIF receptor (CD74), suggesting that NcMIF does not bind to this MIF receptor. The glycine substitution for proline-2 of NcMIF resulted in increased retention time on SEC-HPLC and decreased formation of dimers and trimers. The addition of N-terminal HIS-tag led to increased formation of trimers. Immunofluorescence staining demonstrated that NcMIF was localized to the apical end of N. caninum tachyzoites. Immunoelectron microscopy further revealed that NcMIF was present in the micronemes, rhoptries, dense granules, and nuclei. NcMIF was abundant in the tachyzoite lysate and present in excretory and secretory antigen (ESAg) preparations. Total and secretory NcMIF was more abundant in a non-pathologic clone, Ncts-8, than in the wild type isolate (NC1). Furthermore, NcMIF release by the both isolates was increased in the presence of calcium ionophore. This differential production of NcMIF by the pathologic and non-pathologic isolates of N. caninum may suggest a critical role of this molecule in the infectious pathogenesis of this parasite.

Immune response and immunopathology during toxoplasmosis

Toxoplasma gondii is a protozoan parasite of medical and veterinary significance that is able to infect any warm-blooded vertebrate host. In addition to its importance to public health, several inherent features of the biology of T. gondii have made it an important model organism to study host-pathogen interactions. One factor is the genetic tractability of the parasite, which allows studies on the microbial factors that affect virulence and allows the development of tools that facilitate immune studies. Additionally, mice are natural hosts for T. gondii, and the availability of numerous reagents to study the murine immune system makes this an ideal experimental system to understand the functions of cytokines and effector mechanisms involved in immunity to intracellular microorganisms. In this article, we will review current knowledge of the innate and adaptive immune responses required for resistance to toxoplasmosis, the events that lead to the development of immunopathology, and the natural regulatory mechanisms that limit excessive inflammation during this 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.