Theileria equi RAP-1a and RAP-1b proteins contain immunoreactive epitopes and are suitable candidates for vaccine and diagnostics development.
Abstract: Theileria equi is an obligate intracellular protozoan parasite that causes severe hemolytic anaemia in most equid species. Similar to other apicomplexan parasites, T. equi contains rhoptries whose contents have been implicated in host cell invasion and formation of the parasitophorous vacuole that is crucial for survival of the species within cells. Despite their importance, the composition of T. equi rhoptries and their role(s) in host cell invasion remain unexplored. To gain insight into these issues, we evaluated the expression, immunogenicity, and functional roles of two T. equi rhoptry-associated proteins abbreviated as RAP-1a and RAP-1b. The full-length RAP-1a protein was expressed to perform the analysis but our efforts to express the full-length RAP-1b protein failed due to an unknown reason. We therefore generated synthetic immunogenic peptides that map onto the N- and C-termini of the RAP-1b protein as an alternative approach. Our findings show that both proteins are expressed in the extracellular and intra-erythrocytic merozoite stages of T. equi. Serological analyses show that T. equi-infected horses mount antibody responses that recognise both proteins and correlate with a decrease in T. equi load in both acutely and persistently infected horses. In vitro neutralisation studies show that the T. equi RAP-1a protein contains neutralisation-sensitive epitopes as antibodies developed against the protein significantly inhibited the parasites from invading equine erythrocytes. Conversely, antibodies developed against the RAP-1b synthetic peptides did not neutralise parasite invasion, showing that the protein regions on which the peptides were based are not required for T. equi invasion. Overall, the data shows that T. equi rhoptries and their contents are involved in invasion of host cells and supports T. equi RAP-1 proteins as candidates for developing novel serodiagnosis tools and vaccines.
Published by Elsevier Ltd.
Publication Date: 2022-03-19 PubMed ID: 35318949DOI: 10.1016/j.ijpara.2022.01.004Google Scholar: Lookup
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- Journal Article
- Research Support
- U.S. Gov't
- Non-P.H.S.
Summary
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This study explores two proteins found in the Theileria equi, a parasite which can cause severe anaemia in horses. Highlighting the role of these proteins in the infection process and how the immune response of the host recognises them, the research presents these proteins as potential marks to develop new diagnostic methods and vaccines against the parasite.
Background
- Theileria equi is a parasitic microorganism which can infect different species of equids, leading to severe haemolytic anaemia.
- Like other similar parasites, T. equi uses a structure called rhoptries to invade host cells and form a protective compartment (parasitophorous vacuole), crucial for its survival inside those cells.
- The composition and exact role of the T. equi’s rhoptries have not been fully investigated, prompting the need for further research.
Study Design and Results
- The authors focused on two proteins associated with the rhoptries, RAP-1a and RAP-1b, studying their expression, immunogenicity, and potential role in the infection process.
- While the full-length RAP-1a protein was successfully expressed for the study, the RAP-1b had to be represented by synthetic peptides – short chains of amino acids – due to unsuccessful attempts to produce the whole protein.
- Results showed that both proteins are indeed expressed during the major stages of the T. equi’s life cycle, that is, when the parasite is within and outside the host’s cells.
- Serological tests – which measure the response of the immune system to these proteins – showed that infected horses mount an immune response against RAP-1a and RAP-1b, and that this response is associated with a reduction in the parasite load.
In Vitro Neutralisation
- The study also analysed whether the proteins could be neutralised – i.e., have their functionality blocked – by antibodies developed against them.
- Results showed that antibodies against the RAP-1a protein could significantly inhibit the invasion of the parasite into equine erythrocytes.
- However, antibodies against the RAP-1b peptides did not neutralise the parasite’s invasion, indicating that the regions of the protein represented by the peptides are not necessary for the infection process.
Conclusions and Implications
- The study concluded that RAP-1a and RAP-1b proteins, found in the T. equi’s rhoptries, play a role in the infection of host cells.
- The immune response these proteins elicit, and the ability of antibodies to block the function of RAP-1a, support their potential to serve as targets for the development of new diagnostic tools and vaccines against T. equi.
Cite This Article
APA
Onzere CK, Fry LM, Bishop RP, Da Silva M, Madsen-Bouterse SA, Bastos RG, Knowles DP, Suarez CE.
(2022).
Theileria equi RAP-1a and RAP-1b proteins contain immunoreactive epitopes and are suitable candidates for vaccine and diagnostics development.
Int J Parasitol, 52(6), 385-397.
https://doi.org/10.1016/j.ijpara.2022.01.004 Publication
Researcher Affiliations
- Department of Veterinary Microbiology & Pathology, Washington State University, P.O. Box 647040, Pullman, WA 99164, USA. Electronic address: cynthia.onzere@wsu.edu.
- Department of Veterinary Microbiology & Pathology, Washington State University, P.O. Box 647040, Pullman, WA 99164, USA; Animal Disease Research Unit, Agricultural Research Service, US Department of Agriculture, P.O. Box 646630, Pullman, WA 99164, USA.
- Department of Veterinary Microbiology & Pathology, Washington State University, P.O. Box 647040, Pullman, WA 99164, USA.
- Department of Veterinary Microbiology & Pathology, Washington State University, P.O. Box 647040, Pullman, WA 99164, USA.
- Department of Veterinary Microbiology & Pathology, Washington State University, P.O. Box 647040, Pullman, WA 99164, USA.
- Department of Veterinary Microbiology & Pathology, Washington State University, P.O. Box 647040, Pullman, WA 99164, USA.
- Department of Veterinary Microbiology & Pathology, Washington State University, P.O. Box 647040, Pullman, WA 99164, USA.
- Department of Veterinary Microbiology & Pathology, Washington State University, P.O. Box 647040, Pullman, WA 99164, USA; Animal Disease Research Unit, Agricultural Research Service, US Department of Agriculture, P.O. Box 646630, Pullman, WA 99164, USA. Electronic address: carlos.suarez@usda.gov.
MeSH Terms
- Animals
- Cattle
- Epitopes
- Horse Diseases / diagnosis
- Horse Diseases / prevention & control
- Horses
- Merozoites
- Theileria
- Theileriasis / prevention & control
- Vaccines
Citations
This article has been cited 3 times.- Poh KC, Oyen K, Onzere CK, Kappmeyer LS, Bastos RG. Haemaphysalis longicornis ticks are unable to transstadially transmit Theileria haneyi to horses. Front Vet Sci 2025;12:1572944.
- Onzere CK, Bastos RG, Bishop RP, Suarez CE, Fry LM. Expression of IL-10 and TGF-β1 in horses experimentally infected with T. equi merozoites is associated with antibody production but not modulation of pro-inflammatory responses. Front Immunol 2024;15:1370255.
- Hötzel I, Suarez CE. Structural definition of babesial RAP-1 proteins identifies a novel protein superfamily across Apicomplexa. Sci Rep 2023 Dec 15;13(1):22330.
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