Eimeria (E.) tenella, the causative agent of avian coccidiosis, employs apical complex proteins like RON2 for host cell invasion. While EtRON2 has been well-studied, its paralogs remain poorly characterized. This study investigated EtRON2_L1-1, a RON2 homolog, for its structural features, stage-specific expression, and vaccine potential. Bioinformatic analysis revealed EtRON2_L1-1 shares only 23.46% amino acid identity with EtRON2, lacks a signal peptide, and contains three transmembrane domains. Expression profiling revealed distinct transcriptional and translational regulations, with peak mRNA levels in sporulated oocysts and highest protein expression in sporozoites, indicative of post-transcriptional control. Immunofluorescence studies showed stage-dependent localization patterns: cytoplasmic distribution in free sporozoites transitioning to apical end during host cell invasion. In vitro neutralization assays established EtRON2_L1-1 's involvement in invasion, with specific antibodies exhibiting dose-dependent inhibition (13% at 50μg/mL to 42% at 400μg/mL). Vaccination trials demonstrated that while 100μg pCAGGS-EtRON2_L1-1 significantly improved weight gain and reduced oocyst output compared to controls, its protective efficacy was inferior to pCAGGS-EtRON2_L2, particularly in mitigating intestinal lesions. These findings characterize EtRON2_L1-1 as a functionally distinct RON2 paralog involved in host cell invasion, with partial but promising vaccine potential that requires further optimization for effective coccidiosis control.

To Cite This Article: Tang W, Liu M, Zhao X, Shi B, Qi W, Dong H and Li K, 2025. Characterization and vaccine potential of EtRON2_L1-1, a novel RON2 paralog in Eimeria tenella. Pak Vet J. http://dx.doi.org/10.29261/pakvetj/2025.312