Cloning and Expression of Immunogenic Regions of EMA-1 Gene of Theileria equi From Infected Horses

Diversity among the pathogenic strains of Theileria equi (T. equi), a major agent of equine piroplasmosis, can affect the appropriate detection of parasite and host immunization. Production of recombinant surface proteins from an infected horse in natural endemic area provides a reliable tool for immunodiagnosis of parasite. Regarding this, the present study was targeted toward the cloning, expression, and purification of the immunogenic regions of equine merozoite antigen 1 (EMA-1 gene), as one of the most important immunodominant surface proteins in T. equi, from naturally infected horses in Iran. The immunogenic region of EMA-1 gene was amplified using the blood of infected horses. EMA-1 gene was cloned into pET26b vector. Then, recombinant plasmids (pET 26b-EMA-1) were transformed into competent E. coli BL21 (DE3) cells. Cloning was confirmed by polymerase chain reaction (PCR), restriction enzyme assays, and DNA sequence analysis. The recombinant protein was expressed using isopropyl β-D-1-thiogalactopyranoside as an inducer, purified using nickle-nitrilotriacetic acid column, and then confirmed by 10% sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and dot blot analysis utilizing Anti-His Tag antibody. Furthermore, the immunoreactivity of recombinant protein against the serum of the infected horses was evaluated using dot blot analysis. The PCR product analysis showed a 750-bp band belonging to immunogenic regions of EMA-1 gene. Sequence analysis revealed that cloned EMA-1 and protein had 94% and 97% homology to EMA-1 sequences submitted to GenBank from different countries, respectively. Restriction enzyme and sequence analyses confirmed the subcloning and correction of the orientation of inserted gene. The SDS-PAGE analysis confirmed the expression of EMA-1 protein with a 28-kDa band. The results of the dot blot analysis revealed that the horse serum containing antibody against T. equi could react with the purified recombinant protein. Purified EMA-1 protein can be used as a reliable tool for the future development of diagnostic tests or vaccines.