Theileria equi claudin like apicomplexan microneme protein contains neutralization-sensitive epitopes and interacts with components of the equine erythrocyte membrane skeleton

Authors: ONZERE, CYNTHIA - Washington State University; Fry, Lindsay; BISHOP, RICHARD - Washington State University; SILVA, MARTA - Washington State University; BASTOS, REGINALDO - Washington State University; KNOWLES, DONALD - Washington State University; Suarez, Carlos

Submitted to: Scientific Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/2021
Publication Date: 4/29/2021
Citation: Onzere, C.K., Fry, L.M., Bishop, R.P., Silva, M.G., Bastos, R.G., Knowles, D.P., Suarez, C.E. 2021. Theileria equi claudin like apicomplexan microneme protein contains neutralization-sensitive epitopes and interacts with components of the equine erythrocyte membrane skeleton. Scientific Reports. 11. Article 9301. https://doi.org/10.1038/s41598-021-88902-4.
DOI: https://doi.org/10.1038/s41598-021-88902-4

Interpretive Summary: Theileria equi is a globally distributed, tick-transmitted blood parasite of horses. The parasite causes significant economic losses due to restriction of international movement of infected horses, reduced ability of infected horses to work (e.g. traction, riding, sporting, etc.), medical costs, and death of valuable animals. Apart from stringent testing efforts, prevention of equine piroplasmosis is largely based on tick control measures and anti-protozoal drug treatment, as there are not yet vaccines available to prevent infection or clinical disease. In this study, we sought to determine the role of a parasite protein, known as claudin like apicomplexan microneme protein (CLAMP), in parasite infection of equine red blood cells. We found that CLAMP is important for red cell invasion, and that it is expressed by multiple red-cell associated parasite stages. Most importantly, we found that infected horses mount a strong antibody response to CLAMP, indicating it is a potential candidate antigen for use in development of a vaccine or diagnostic assay.

Technical Abstract: Theileria equi (T. equi) is a widely distributed apicomplexan parasite that causes severe hemolytic anemia in equid species. Unfortunately, there is no effective vaccine for control of the parasite and understanding the mechanism that T. equi utilizes to invade host cells is crucial for vaccine development. Unlike most apicomplexan species studied to date, the role of micronemes in T. equi invasion is unknown. In this regard, we assessed the role of the T. equi claudin like apicomplexan microneme protein (CLAMP) in the invasion of equine erythrocytes as a first step in understanding the function of the organelle in the parasite. Our findings show that the protein is expressed in the merozoite and intraerythrocytic developmental stages and it is essential for host cell invasion. We further determined that CLAMP interacts with the a-and ß- spectrin chains in the initial stages of T. equi invasion and maintains these interactions while also associating with the anion-exchange protein, tropomyosin, band 4.1 and cytoplasmic actin 1 in the inner cell membrane. We also established that T. equi infected horses mount robust antibody responses against CLAMP indicating that the protein is immunogenic and therefore a viable vaccine candidate.