Localization of surface antigens on Theileria sergenti merozoite by monoclonal antibodies

Emergence of new genotype and diversity of Theileria orientalis parasites from bovines in India

Bovine theileriosis is a serious threat to livestock worldwide. Uncertainty around species prevalence, antigenic diversity and genotypes of strains make it difficult to assess the impact of this parasite and to provide necessary treatment. We aimed to characterize genotypic diversity, phylogeny and prevalence of Theileria orientalis parasites from the states of Telangana and Andhra Pradesh, India by collecting bovine blood samples from the major districts of the two states. Bioinformatic analysis identified antigenic diversity among the prevalent parasite strains using major piroplasm surface protein (MPSP) gene. Our study revealed a prevalence rate of 4.8% (n=41/862) of T. orientalis parasites in bovine animals and a new genotype of T. orientalis parasite which was not previously reported in India. The emergence of these new genotypes could be an explanation for the frequent outbreaks of bovine theileriosis. Further, whole genome sequencing of T. orientalis strains will help to elucidate the genetic factors relevant for transmissibility and virulence as well as vaccine and new drug development.

The taxonomy of the bovine Theileria spp

The classification of the benign species of Theileria of cattle is very confusing Representatives of this group of parasites appear worldwide, and are known as T. sergenti in Japan, T. buffeli in Australia and T. orientalis elsewhere. Consequently, these parasites are frequently referred to as the T. sergenti/buffeli/orientalis group. Kozo Fujisaki, Shin-ichiro Kawazu and Tsugihiko Kamio here argue that the Australian T. buffeli and British T. orientalis belong to one and the same species, and that the Japanese T. sergenti is a separate species.

Epitope-Mapping of antigen-specific T lymphocyte in cattle immunized with recombinant major piroplasm surface protein of Theileria sergenti

The cellular immune responses against major piroplasm surface protein (MPSP) of Theileria sergenti were characterized. Three cattle were immunized with recombinant MPSP (C type) encapsulated by mannan-coated liposome. The proliferative responses of peripheral blood mononuclear cells (PBMC) against MPSP were detected in all immunized animals. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed that T cell lines derived from each animal expressed relatively high levels of interferon (IFN)-gamma mRNA, low levels of interleukin (IL)-2, IL-10, and tumor necrosis factor (TNF)-alpha mRNAs, but no detectable level of IL-4 mRNA. From the results of T cell epitope-mapping, T-cell lines from two animals responded to DTSKFTPTVAHRLKHAEDLF (residues 61 to 80), while other animal responded to GTGKVYDFVGNFKVTKVKFE (residues 141 to 160). The MPSP-type specific response of a T-cell line was observed in the latter region of MPSP. These data suggest that immunization with cocktail vaccine consisting of different types of MPSP may be necessary in the field trial.

Expression of major piroplasm protein (p33) of Theileria sergenti (Korean isolate) and its immunogenicity in guinea pigs

To investigate the development of a subunit vaccine against theileriosis in cattle, the DNA fragments encoding piroplasm surface protein (p33) of Theileria sergenti of a Korean isolate were expressed in baculoviruses. The expressed p33 was characterized by indirect fluorescent antibody (IFA) and western blotting analysis. The expression of p33 was mainly detected on the surface of infected Sf21 cells by IFA. The immunoblotting analysis revealed the presence of a same molecular weight protein band of p33. The antigenicity of expressed polypeptide was further examined through the inoculation of a guinea pig. The sera of guinea pigs immunized with p33 expressed cell lysate showed similar fluorescent antibody patterns and reacted with the same molecular weight protein of T. sergenti in immunoblotting analysis, thus indicating that this protein can be a promising candidate for a subunit vaccine in the future.

Molecular cloning and characterisation of 23-kDa piroplasm surface proteins of Theileria sergenti and Theileria buffeli

The cDNA encoding a 23-kDa piroplasm membrane protein (p23) of Theileria sergenti Chitose (C)-type was isolated and its nucleotide sequence was determined. The gene encodes a polypeptide of 223 aa with a 28 residue N-terminal signal sequence and a hydrophobic, valine-rich, C-terminal transmembrane domain, as deduced from its nucleotide sequence. Southern blot hybridisation analysis proved that p23 gene was a single copy gene and had allelic forms of the gene in the parasite population. By PCR, the open reading frames of T. sergenti Ikeda (I)-type and Theileria buffeli (B)-type p23 were amplified from genomic DNA and their nucleotide sequences were also determined. Comparison of C-type sequence with that of I-type and B-type revealed 90.5% and 93.5% sequence similarity, respectively, at the aa level. These results suggest that a conserved molecule in these benign Theileria spp. could be a candidate antigen for the development of an anti-piroplasm vaccine.

Expression of a major piroplasm surface protein of Theileria sergenti in sporozoite stage

A 32 kilodalton major piroplasm surface protein (MPSP) is expressed abundantly on the surface of intraerythrocytic piroplasms of Theileria sergenti and is considered to be a candidate antigen for vaccine development against piroplasmosis. In this study, transcripts of MPSP gene were detected in an expression cDNA library prepared from T. sergenti-infected tick salivary glands. Expression of MPSP in the sporozoite stage was also confirmed by immunoblot analysis. Its expression at the sporozoite and intraerythrocytic stages gives scope for possible induction of protective immunity being targeted at both stages by immunization with recombinant MPSP.

Differentiation and quantification of Theileria sergenti piroplasm types using type-specific monoclonal antibodies

Antigenic properties of two representative allelic products of the major piroplasm surface protein (MPSP) of Theileria sergenti were studied. Sera from cattle infected with either of Ikeda and Chitose types of the parasite reacted strongly with homologous but weakly with heterologous recombinant antigens in immunoblotting. Monoclonal antibodies (MoAbs) produced against the both allelic products of MPSP parasites reacted only to the immunizing antigen. These results suggested that crossreactivity between two allelic products is very low inspite of relatively high homology in their amino acid sequences. Double staining of parasitized erythrocyte smear using type-specific MoAbs by an indirect immunofluorescent assay revealed that the set of MoAbs was useful for quantitative and differential detection of each type of parasite in mixed population.

Control of Theileria sergenti infection by vaccination

Bovine piroplasmosis caused by Theileria sergenti is a major cause of economic loss in grazing cattle in Japan. Infected calves show chronic anaemia with intraerythrocytic piroplasms and occasionally die in severe cases. We found that parasite stocks and isolates consist of genetically and antigenically mixed populations. To differentiate parasite populations bearing 3 allelic forms of p32/34, an immunodominant piroplasm surface protein, 3 sets of oligonucleotide primers were designed to amplify either of 3 alleles by polymerase chain reaction (PCR). By using this allele-specific PCR, we found that the majority of T. sergenti-infected calves in Japan harbored mixed parasite populations bearing C and I type parasites. To control Theileria infection, we produced 2 vaccine candidates: recombinant baculovirus p32 and synthetic peptide containing Lys-Glu-Lys (KEK) motif. Immunization with either recombinant p32 or synthetic peptide containing KEK sequences with Freund's complete adjuvant resulted in low parasitemia and reduced the clinical symptoms compared to control calves. Interestingly, the parasite with the p32 allelic form corresponding to the one used as the immunogen was suppressed.

[Cloning and sequencing of p33 in a Korean isolate of Theileria sergenti]

The gene encoding the 33 kDa piroplasm surface protein of Theileria sergenti isolated in Korea was cloned and the nucleotide sequence was determined by dideoxy chain termination method. The cloned gene corresponds to 869 bp encoding an open reading frame 283 amino acids. Comparison of the sequence between Korean and Japanese isolates showed 99.4% homology rate in the nucleotide sequence and 98.9% homology rate in the amino acid sequence.

Population dynamics of Theileria sergenti in persistently infected cattle and vector ticks analysed by a polymerase chain reaction

Theileria sergenti Shintoku stock consists of 2 parasite populations bearing 2 allelic forms of p33/32, an immunodominant piroplasm surface protein. Parasite population changes during parasite passages among cattle and tick vectors, and during persistent infection in individual calves were analysed by using allele-specific polymerase chain reaction (PCR). The parasite DNAs were prepared from piroplasms from calves which had been infected with Shintoku stock by inoculation of sporozoite stabilates or parasitized erythrocytes, and from sporozoite stabilates which had been prepared from Shintoku stock-infected ticks. Changes in a dominant parasite population were demonstrated during transmission from calves to vector ticks and from infected ticks to calves. Parasite population changes were also apparent during persistent infection in cattle over several months, and this change is thought to occur under host immune pressure. The results of this study indicate that expression of diverse forms of p33/32 may play a role in parasite persistence within mammalian hosts and its transmission from tick vector.

Antigenic alteration in major piroplasm surface proteins of Theileria sergenti during infection

Theileria sergenti piroplasms were purified from different parasitemia peaks of cattle infected with parasitized erythrocytes or sporozoites during persistent infection. Their reactivities with monoclonal antibodies 13F5 and C9, which recognize 23 kDa and 32 kDa piroplasm surface proteins, respectively, were analyzed. Antigenic differences were observed among parasites from different parasitemia peaks during persistent infection when cattle were infected with sporozoites. Results of two-dimensional polyacrylamide gel electrophoresis showed that the 23 and 32 kDa proteins were expressed in all samples tested, regardless of their reactivities with the monoclonal antibodies. In contrast, parasites obtained from cattle inoculated with parasitized erythrocytes showed no antigenic alteration over a 2 month observation period. The results suggest that antigenic alteration of T. sergenti during persistent infection is related to whether the parasites proliferate through extraerythrocytic schizont stage in cattle or sporozoite and other sexual stages in tick vector.

Expression of a 32 kilodalton Theileria sergenti piroplasm surface protein by recombinant baculoviruses

Previous studies detected a single amino acid substitution (Ala196 to Gly196) between cDNA clones encoding a 32 kDa antigen (p32) of Theileria sergenti (Chitose stock) obtained from a persistently infected calf. In this study, 2 different recombinant baculoviruses (pAc/p32-Ala196 and pAc/p32-Gly196) were constructed for the expression of p32. Molecular masses of the polypeptides produced in Spodoptera frugiperda cells infected with the recombinant baculoviruses were the same as that of authentic p32. pAc/p32-Ala196 produced additional polypeptides, with molecular masses higher than 32 kDa, which resulted from differential N-glycosylation as revealed by endo N-glycosidase treatment. The results indicate that a single amino acid substitution may lead to a conformational change in p32 which affected post-translational modification of recombinant products.

Analysis of mixed parasite populations of Theileria sergenti using cDNA probes encoding a major piroplasm surface protein

The gene for the 32 kDa surface protein (p32) of Theileria sergenti was cloned into lambda gt11 and its nucleotide sequence was determined. The gene encodes a protein of 283 amino acids as deduced from its nucleotide sequence with a 22 residue N-terminal signal peptide. Using this cDNA as a probe we have isolated another two clones from a cDNA library with a CDM8 vector system derived from the same parasite stock. Comparison with three cDNA clones revealed differential polyadenylation and differences in sequences of non-coding regions. Within the coding regions, there were nucleotide transitions which affected the Pst I-restriction site, and one of the transitions was also accompanied by an amino acid substitution (Ala to Gly). Southern blot analysis showed hybridization pattern changes among the parasites isolated from individual calves at different times after infection. From these results, we conclude that at least 3 genetically different parasite populations may coexist, and the transition to predominant parasite populations might occur during persistent infections in a host, possibly to evade the host immune responses.

Characterization of epitopes on a 32 kDa merozoite surface protein of Theileria sergenti

Epitopes on a 32 kDa protein, which is an immunodominant major surface protein of Theileria sergenti, recognized by anti-merozoite monoclonal antibodies were characterized. The results of a competitive binding assay between monoclonal antibodies indicated that there were at least three epitopes in this protein. The presence of repeated epitopes was suggested by using two-site enzyme-linked immunosorbent assay. The protein was partitioned into the detergent phase of Triton X-114 extracts, indicating that the 32 kDa protein is an integral membrane protein. Periodate treatment of 32 kDa protein implies that one epitope of the epitopes recognized by monoclonal antibody has a carbohydrate moiety.

Analysis of the genes encoding immunodominant piroplasm surface proteins of Theileria sergenti and Theileria buffeli by nucleotide sequencing and polymerase chain reaction

The nucleotide sequences of the cDNAs encoding a 33-kDa piroplasm protein of Theileria sergenti (p33) and a similar protein of Theileria buffeli (p34) were determined. Both of the genes contained an open reading frame of 849 base pairs. The predicted amino acid sequence of p33 and p34, consisting of 283 residues, showed 82% similarity. A transmembrane hydrophobic domain and signal peptides were predicted. The polymerase chain reaction was used to amplify p33/34 genes from the piroplasm DNA of T. sergenti, T. buffeli and Theileria orientalis. Following amplification, p33 and p34 genes were clearly differentiated using the restriction enzymes sites that were not shared between them. These results indicated that p33 and p34 were conserved molecules among these Theileria species, and the genes that encode p33/34 proteins were suitable for discrimination of T. sergenti from T. buffeli/T. orientalis.