"Expression of a recombinant chimeric capsid-nucleocapsid protein from bovine leukemia virus genotype 1 for the diagnosis of enzootic bovine leukosis".

Bovine Leukemia Virus (BLV) is the causative agent of enzootic bovine leukosis (EBL), a neoplastic disease responsible for significant economic losses in the cattle industry. While diagnostic tests primarily target the capsid (p24) and envelope (gp51) proteins, the immunodiagnostic potential of the nucleocapsid protein (p12) remains underexplored. This study aimed to express a recombinant chimeric capsid-nucleocapsid protein (p24-p12) from BLV genotype 1 and evaluate its diagnostic performance. Following in silico epitope prediction, an 851 bp fragment of the gag gene encoding the chimeric protein (RCP24-12) was cloned, expressed in E. coli, and used to develop an indirect ELISA. The assay was used to test 680 plasma samples from Holstein Friesian cattle and compared to a commercial gp51-based ELISA. Discordant results were resolved by Western blot (WB) using RCP24-12 as antigen. The RCP24-12 ELISA detected antibodies in samples negative by the commercial test. Using a composite reference standard (commercial ELISA + WB), the in-house assay demonstrated a sensitivity of 88.8% and a specificity of 79.2%. These findings indicate that the recombinant chimeric protein p24-p12 is a promising antigen for the serological diagnosis of BLV genotype 1 infection, offering improved detection capability over a single-protein (gp51) antigen.