Monoclonal antibodies preventing invasion of Neospora caninum tachyzoites into host cells

Toxoplasma gondii infection in Amami spiny rat on Amami-Oshima Island, Japan

The Amami spiny rat (Tokudaia osimensis) is an endangered rodent species that is endemic to the forests of Amami-Oshima Island, Kagoshima, Japan. In July 2018, a deceased adult male Amami spiny rat was found on the Yuwandake Mountain Trail on the south-central coast of Amami-Oshima Island. Histopathological observations revealed protozoan infections in the liver, lungs, and heart. Nested or semi-nested PCRs targeting the B1, SAG3, GRA6, and ROP18 genes successfully detected the genomic DNA of Toxoplasma gondii in the formalin-fixed and paraffin-embedded specimen. Sequence analyses of the SAG3, GRA6, and ROP18 genes suggested that the strain detected in the study specimen was related to the type II strain of T. gondii. This is the first confirmed case of T. gondii infection in an Amami spiny rat.

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A deceased Amami spiny rat was diagnosed with disseminated toxoplasmosis.

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We present the first case report of T. gondii infection in the Amami spiny rat.

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Feral cat populations require control to avoid the spread of T. gondii infection.

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.

Discovering a vaccine against neosporosis using computers: is it feasible?

A vaccine is urgently needed to prevent cattle neosporosis. This infectious disease is caused by the parasite Neospora caninum, a complex biological system with multifaceted life cycles. An in silico vaccine discovery approach attempts to transform digital abstractions of this system into adequate knowledge to predict candidates. Researchers need current information to implement such an approach, such as understanding evasion mechanisms of the immune system, type of immune response to elicit, availability of data and prediction programs, and statistical models to analyze predictions. Taken together, an in silico approach involves assembly of an intricate jigsaw of interdisciplinary and interdependent knowledge. In this review, we focus on the approach influencing vaccine development against Neospora caninum, which can be generalized to other pathogenic apicomplexans.

Protective effect of intranasal immunization with Neospora caninum membrane antigens against murine neosporosis established through the gastrointestinal tract

Neospora caninum is an Apicomplexa parasite that in the last two decades was acknowledged as the main pathogenic agent responsible for economic losses in the cattle industry. In the present study, the effectiveness of intranasal immunization with N. caninum membrane antigens plus CpG adjuvant was assessed in a murine model of intragastrically established neosporosis. Immunized mice presented a lower parasitic burden in the brain on infection with 5 × 10(7) tachyzoites, showing that significant protection was achieved by this immunization strategy. Intestinal IgA antibodies raised by immunization markedly agglutinated live N. caninum tachyzoites whereas previous opsonization with IgG antibodies purified from immunized mice sera reduced parasite survival within macrophage cells. Although an IgG1 : IgG2a ratio < 1 was detected in the immunized mice before and after infection, indicative of a predominant T helper type 1 immune response, no increased production of interferon-γ was detected in the spleen or mesenteric lymph nodes of the immunized mice. Altogether, these results show that mucosal immunization with N. caninum membrane proteins plus CpG adjuvant protect against intragastrically established neosporosis and indicate that parasite-specific mucosal and circulating antibodies have a protective role against this parasitic infection.

Gene cloning and characterization of the protein encoded by the Neospora caninum bradyzoite-specific antigen gene BAG1

Neospora caninum is an Apicomplexan parasite that causes repeated abortion and stillbirth in cattle. The aim of this study was to clone the gene encoding the N. caninum orthologue (NcBAG1) of the Toxoplasma gondii bradyzoite-specific protein TgBAG1 and characterize its expression pattern in the parasite. Isolation of the full-length 684-bp gene revealed that it shared 78.3% sequence similarity with TgBAG1. NcBAG1 encodes a predicted protein of 227 amino acids with 80.3% similarity to TgBAG1. A putative signal peptide sequence and an invariant GVL motif characteristic of small heat-shock proteins were identified in the predicted N. caninum amino acid sequence. We expressed the NcBAG1 gene as a recombinant glutathione S-transferase fusion protein (rNcBAG1) in Escherichia coli and used the purified 60 kDa protein to obtain a monoclonal antibody (Mab). rNcBAG1 reacted to Mabs specific for NcBAG1 and TgBAG1. No reaction between the NcBAG1 Mab and N. caninum tachyzoites was observed. Although the predicted molecular mass of NcBAG1 is 25 kDa, Western blot analysis of parasite lysates using the NcBAG1 Mab revealed a cross-reactive protein of approximately 30 kDa. Additionally, immunofluorescence assays using the tachyzoite-specific Mab for NcSAG1 and the bradyzoite-specific Mab for TgBAG1 or NcSAG4 revealed NcBAG1-specific expression in bradyzoites in cultures exposed to sodium nitroprusside, a reagent that increases the frequency of bradyzoites. Interestingly, the NcBAG1 protein was identified in the cytoplasm of the bradyzoite-stage parasites. This preliminary analysis of the NcBAG1 gene will assist investigations into the role of this protein in N. caninum .

Detection of Nesopora caninum-specific DNA from cerebrospinal fluid by polymerase chain reaction in a dog with confirmed neosporosis

A one-month male Greyhound dog presented with a swinging gait of the hindlimbs, and later developed muscular atrophy of the femoral region and hyperextension of hindlimbs. The dog had positive serum IFAT titers to Neospora caninum, but a negative titer in the cerebrospinal fluid (CSF). N. caninum-specific DNA was amplified from the CSF using a semi-nested polymerase chain reaction assay. Clusters of protozoa in biopsied muscle fibers were subsequently confirmed as N. caninum tachyzoites by immunohistochemical examination. Early recognition and treatment are necessary for effective recovery of clinical canine neosporosis, but antemortem diagnosis is difficult. We suggest that the detection of parasite deoxyribonucleic acid in the CSF is a useful antemortem diagnostic method in facilitating treatment of this disease.

Current and emerging approaches to studying invasion in apicomplexan parasites

In this chapter, we outline the tools and techniques available to study the process of host cell invasion by apicomplexan parasites and we provide specific examples of how these methods have been used to further our understanding of apicomplexan invasive mechanisms. Throughout the chapter we focus our discussion on Toxoplasmagondii, because T. gondii is the most experimentally accessible model organism for studying apicomplexan invasion (discussed further in the section, "Toxoplasma as a Model Apicomplexan") and more is known about invasion in T. gondii than in any other apicomplexan.

Cellular and immunological basis of the host-parasite relationship during infection with Neospora caninum

Neospora caninum is an apicomplexan parasite that is closely related to Toxoplasma gondii, the causative agent of toxoplasmosis in humans and domestic animals. However, in contrast to T. gondii, N. caninum represents a major cause of abortion in cattle, pointing towards distinct differences in the biology of these two species. There are 3 distinct key features that represent potential targets for prevention of infection or intervention against disease caused by N. caninum. Firstly, tachyzoites are capable of infecting a large variety of host cells in vitro and in vivo. Secondly, the parasite exploits its ability to respond to alterations in living conditions by converting into another stage (tachyzoite-to-bradyzoite or vice versa). Thirdly, by analogy with T. gondii, this parasite has evolved mechanisms that modulate its host cells according to its own requirements, and these must, especially in the case of the bradyzoite stage, involve mechanisms that ensure long-term survival of not only the parasite but also of the host cell. In order to elucidate the molecular and cellular bases of these important features of N. caninum, cell culture-based approaches and laboratory animal models are being exploited. In this review, we will summarize the current achievements related to host cell and parasite cell biology, and will discuss potential applications for prevention of infection and/or disease by reviewing corresponding work performed in murine laboratory infection models and in cattle.

Neospora caninum and neosporosis — recent achievements in host and parasite cell biology and treatment

Neospora caninum is an apicomplexan parasite, which owes its importance to the fact that it represents the major infectious cause of bovine abortion worldwide. Its life cycle is comprised of three distinct stages: Tachyzoites, representing the proliferative and disease-causing stage, bradyzoites, representing a slowly replicating, tissue cyst-forming stage, and sporozoites, which represent the end product of a sexual process taking place within the intestinal tissue of the final canine host. Tachyzoites are capable of infecting a large variety of host cells in vitro and in vivo, while bradyzoites have been found mainly within the central nervous system. In order to survive, proliferate, and proceed in its life cycle, N. caninum has evolved some amazing features. First, the parasite profits immensely from its ability to interact with, and invade, a large number of host cell types. Secondly, N. caninum exploits its capability to respond to alterations in living conditions by converting into another stage (tachyzoite-to-bradyzoite or vice versa). Thirdly, this parasite has evolved mechanisms that modulate its host cells according to its own requirements, and these must, especially in the case of the bradyzoite stage, involve mechanisms that ensure long term survival of not only the parasite but also of the host cell. These three key events (host cell invasion — stage conversion — host cell modulation) represent potential targets for intervention. In order to elucidate the molecular and cellular bases of these important features of N. caninum, cell culture-based approaches and laboratory animal models are extensively exploited. In this review, we will summarize the present knowledge and achievements related to host cell and parasite cell biology.

Neospora caninum: antibodies directed against tachyzoite surface protein NcSRS2 inhibit parasite attachment and invasion of placental trophoblasts in vitro

Polyclonal and monoclonal antibodies to native Neospora caninum tachyzoite surface protein NcSRS2 were generated and tested in vitro for their ability to neutralize tachyzoite attachment to and invasion of host cells. Host cells included Vero cells and a newly cloned, immortalized ovine trophoblast cell line obtained from primary cultures of ovine placenta. The ovine trophoblasts had morphology consistent with fetal trophoblasts and expressed mRNA for interferon-tau, a marker for trophoblasts. Native NcSRS2 was used to immunize mice to obtain monospecific anti-NcSRS2 polyclonal serum and anti-NcSRS2 monoclonal antibodies. Compared to irrelevant antibodies, monospecific anti-NcSRS2 serum and two anti-NcSRS2 monoclonal antibodies, 100.2.4.4 and 119.4.9.10, significantly blocked invasion of tachyzoites into both trophoblasts and Vero cells. Parasite attachment, assessed by IFA, was significantly reduced by anti-NcSRS2 mAb 100.2.4.4 and monospecific serum. The findings provide rationale to investigate a role for antibodies to NcSRS2 in prevention of N. caninum transplacental transmission in vivo.