• Parasites, Hosts and Diseases
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• v.56 no.5
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• pp.429-435
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• 2018

Toxoplasma gondii is a ubiquitous protozoan parasite responsible for causing toxoplasmosis. Preventive measures for toxoplasmosis are currently lacking and as such, development of novel vaccines are of urgent need. In this study, we generated 2 virus-like particles (VLPs) vaccines expressing T. gondii rhoptry protein 4 (ROP4) or rhoptry protein 18 (ROP18) using influenza matrix protein (M1) as a core protein. Mice were intranasally immunized with VLPs vaccines and after the last immunization, mice were challenged with ME49 cysts. Protective efficacy was assessed and compared by determining serum antibody responses, body weight changes and the reduction of cyst counts in the brain. ROP18 VLPs-immunized mice induced greater levels of IgG and IgA antibody responses than those immunized with ROP4 VLPs. ROP18 VLPs immunization significantly reduced body weight loss and the number of brain cysts in mice compared to ROP4 VLPs post-challenge. These results indicate that T. gondii ROP18 VLPs elicited better protective efficacy than ROP4 VLPs, providing important insight into vaccine design strategy.

• Parasites, Hosts and Diseases
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• v.44 no.3
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• pp.251-254
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• 2006

Monoclonal antibody (mAb) Tg786 against Toxoplasma gondii has been found to detect a 42-kDa rhoptry protein (ROP6) which showed protease activity and host cell binding characteristics after secretion. Using the mAb, a colony containing a 3'-UTR was probed in a T. gondii cDNA expression library. A full length cDNA sequence of the rhoptry protein was completed after 5'-RACE, which consisted of 1,908 bp with a 1,443 bp ORF. The deduced amino acid sequence of ROP6 consisted of a polypeptide of 480 amino acids without significant homology to any other known proteins. This sequence contains an amino terminal stop transfer sequence downstream of a short neutral sequence, hydrophilic middle sequence, and hydrophobic carboxy terminus. It is suggested that the ROP6 is inserted into the rhoptry membrane with both N- and C-termini.

• Parasites, Hosts and Diseases
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• v.57 no.5
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• pp.543-547
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• 2019

Toxoplasma gondii can infect humans worldwide, causing serious diseases in pregnant women and immunocompromised individuals. T. gondii rhoptry protein 13 (ROP13) is known as one of the key proteins involved in host cell invasion. In this study, we generated virus-like particles (VLPs) vaccine expressing T. gondii rhoptry ROP13 and investigated VLPs vaccine efficacy in mice. Mice immunized with ROP13 VLPs vaccine elicited significantly higher levels of T. gondii-specific IgG, IgG1, IgG2a, and IgA antibody responses following boost immunization and challenge infection, whereas antibody inductions were insignificant upon prime immunization. Differing immunization routes resulted in differing antibody induction, as intranasal immunization (IN) induced greater antibody responses than intramuscular immunization (IM) after boost and challenge infection. IN immunization induced significantly higher levels of IgG and IgA antibody responses from feces, antibody-secreting cells (ASCs), $CD4^+$ T, $CD8^+$ T cells and germinal center B cell responses in the spleen compared to IM immunization. Compared to IM immunization, IN immunization resulted in significantly reduced cyst counts in the brain as well as lesser body weight loss, which contributed to better protection. All of the mice immunized through either route survived, whereas all na?ve control mice perished. These results indicate that the ROP13 VLPs vaccine could be a potential vaccine candidate against T. gondii infection.

• Parasites, Hosts and Diseases
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• v.60 no.6
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• pp.393-400
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• 2022

Human infection with simian malaria Plasmodium knowlesi is a cause for concern in Southeast Asian countries, especially in Malaysia. A previous study on Peninsular Malaysia P. knowlesi rhoptry associated protein-1 (PkRAP1) gene has discovered the existence of dimorphism. In this study, genetic analysis of PkRAP1 in a larger number of P. knowlesi samples from Malaysian Borneo was conducted. The PkRAP1 of these P. knowlesi isolates was PCR-amplified and sequenced. The newly obtained PkRAP1 gene sequences (n=34) were combined with those from the previous study (n=26) and analysed for polymorphism and natural selection. Sequence analysis revealed a higher genetic diversity of PkRAP1 compared to the previous study. Exon II of the gene had higher diversity (π=0.0172) than exon I (π=0.0128). The diversity of the total coding region (π=0.0167) was much higher than those of RAP1 orthologues such as PfRAP-1 (π=0.0041) and PvRAP1 (π=0.00088). Z-test results indicated that the gene was under purifying selection. Phylogenetic tree and haplotype network showed distinct clustering of Peninsular Malaysia and Malaysian Borneo PkRAP1 haplotypes. This geographical-based clustering of PkRAP1 haplotypes provides further evidence of the dimorphism of the gene and possible existence of 2 distinct P. knowlesi lineages in Malaysia.

• Korean Journal of Veterinary Research
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• v.31 no.1
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• pp.89-97
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• 1991

For the ultrastructural observation on Babesia gibsoni(B gibsoni), the protozoa were challenged experimentally to splectomized dog. To examine the ultrastructure of the B gibsoni in the erythrocyte, the infected erythrocytes were collected at the cephalic or jugular vein of the dog. The results obtained by TEM(transmission electron microscopy) were as follows; 1. The sizes of protozoa in erythrocytes are $0.92{\pm}0.36{\mu}m{\times}0.67{\pm}0.21{\mu}m$, the sizes of nucleus of the protozoa are $0.55{\pm}0.24{\mu}m{\times}0.38{\pm}0.26{\mu}m$, and sizes of rhoptries in plasma of the protozoa are $0.33{\pm}0.05{\mu}m{\times}0.25{\pm}0.07{\mu}m$, respectively. 2. The tropozoite membrane in the erythrocyte was one, and it's nuclear membrane was made up of double. But the protozoa of initial stage in infected erythrocyte had double clear mambranes, and distinguished from plasma membrane of red blood cell. 3. The mitochondrialike structures covered with two membranes were observed in the protozoa. 4. Mitochondria and vesicles of the reticulocyte were observed near protozoa in the erythrocyte. 5. There are rhoptry, coiled structure and single nucleous in the merozoite. 6. The shape of rhoptry was round or ovoid form and in occasionally, the content of rhoptry was lost partially. 7. There was able to observe the dividing process of the protozoa. 8. Maurer's cleft-like structure was observed.

• Parasites, Hosts and Diseases
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• v.37 no.3
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• pp.157-162
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• 1999

Serum from mouse orally ingested with tissue cyst forming stain (Me49) of Toxoplasma gondii was assayed by Western blot and immunofluorescene assay (IFA) to establish early responses in antigenicity of the parasite in mouse model of foodborne toxoplasmosis. Sera were collected weekly to blot the RH antigen transferred onto nitrocellulose paper after being separated by 12% SDS-PAGE. With the second week serum, 34 kDa protein (p34) was detected uniquely, and all antigens of T.gondii were detected with the sera from 3 or 4 weeks. p34 was not a member of the major surface membrane proteins and confirmed to be localized in the rhoptry by IFA. It was secreted into parasitophorous vacuolar membrane (PVM) during the entry into host cells. 10.3% of sera detected p34, while all the ELISA positive sera detected the band. It has diagnostic usefulness of presumed T.gondii infection. We suggest the name of the p34 protein as ROP9.

• Bulletin of the Korean Chemical Society
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• v.35 no.10
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• pp.3071-3076
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• 2014

Proteomic analyses of the excretory/secretory proteins from the RH strain of Toxoplasma gondii have been performed to understand their functions in the host-parasite interaction. A total of 34 proteins were identified from LC/MS/MS analysis and their abundance was estimated by spectral counting methods. Among them, 8 species of micronemal proteins (MICs), 2 species of rhoptry proteins (ROPs), and 6 species of dense granular proteins (GRAs) were confirmed. Besides these, 18 species of protein were newly identified, and their cellular functions were estimated from sequence analysis. The three most abundant of the 34 identified extractor/secretory proteins-GRA1, GRA7 and GRA2-were confirmed to be highly expressed in T. gondii using the spectral count method. This phenomenon is another demonstration of the importance of GRA proteins for the penetration and survival of T. gondii.

• Parasites, Hosts and Diseases
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• v.59 no.6
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• pp.565-572
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• 2021

Toxoplasma gondii ME49 infections are typically diagnosed by serological tests. However, serological diagnosis of RH strain-induced toxoplasmosis remains unknown. In order to develop seradiagnosis of above 2 kinds of infections, we generated recombinant virus-like particles (VLPs) displaying the T. gondii rhoptry protein 4 (ROP4) and evaluated their potential in T. gondii ME49 or RH strain infection diagnostics. Mice were orally infected with either the tachyzoites of T. gondii (RH) or cysts of T. gondii (ME49) at various dosages, and sera were collected at regular intervals. ELISA-based serological tests were performed to assess IgG, IgM, and IgA antibody responses against ROP4 VLP antigen and tissue lysate antigen (TLA). Compared to TLA, IgG, IgM, and IgA levels to ROP4 VLP antigen were significantly higher in the sera of T. gondii RH-infected mice 1 and 2 week post-infection (PI). T. gondii-specific IgG antibody was detected at 1, 2, 4, and 8 week PI in the T. gondii ME49-infected mice with infection dose-dependent manner. These results indicated that the ROP4 VLP antigen was highly sensitive antigens detecting T. gondii RH and ME49 antibodies at an early stage.

• Parasites, Hosts and Diseases
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• v.55 no.2
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• pp.143-148
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• 2017

Toxoplasma gondii infections occur throughout the world, and efforts are needed to develop various vaccine candidates expressing recombinant protein antigens. In this study, influenza matrix protein (M1) virus-like particles (VLPs) consisting of T. gondii rhoptry antigen 4 (ROP4 protein) were generated using baculovirus (rBV) expression system. Recombinant ROP4 protein with influenza M1 were cloned and expressed in rBV. SF9 insect cells were coinfected with recombinant rBVs expressing T. gondii ROP4 and influenza M1. As the results, influenza M1 VLPs showed spherical shapes, and T. gondii ROP4 protein exhibited as spikes on VLP surface under transmission electron microscopy (TEM). The M1 VLPs resemble virions in morphology and size. We found that M1 VLPs reacted with antibody from T. gondii-infected mice by western blot and ELISA. This study demonstrated that T. gondii ROP4 protein can be expressed on the surface of influenza M1 VLPs and the M1 VLPs containing T. gondii ROP4 reacted with T. gondii-infected sera, indicating the possibility that M1 VLPs could be used as a coating antigen for diagnostic and/or vaccine candidate against T. gondii infection.

• Genomics & Informatics
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• v.14 no.2
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• pp.53-61
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• 2016

Toxoplasma gondii is an intracellular Apicomplexan parasite and a causative agent of toxoplasmosis in human. It causes encephalitis, uveitis, chorioretinitis, and congenital infection. T. gondii invades the host cell by forming a moving junction (MJ) complex. This complex formation is initiated by intermolecular interactions between the two secretory parasitic proteins-namely, apical membrane antigen 1 (AMA1) and rhoptry neck protein 2 (RON2) and is critically essential for the host invasion process. By this study, we propose two potential leads, NSC95522 and NSC179676 that can efficiently target the AMA1 hydrophobic cleft, which is a hotspot for targeting MJ complex formation. The proposed leads are the result of an exhaustive conformational search-based virtual screen with multilevel precision scoring of the docking affinities. These two compounds surpassed all the precision levels of docking and also the stringent post docking and cumulative molecular dynamics evaluations. Moreover, the backbone flexibility of hotspot residues in the hydrophobic cleft, which has been previously reported to be essential for accommodative binding of RON2 to AMA1, was also highly perturbed by these compounds. Furthermore, binding free energy calculations of these two compounds also revealed a significant affinity to AMA1. Machine learning approaches also predicted these two compounds to possess more relevant activities. Hence, these two leads, NSC95522 and NSC179676, may prove to be potential inhibitors targeting AMA1-RON2 complex formation towards combating toxoplasmosis.