Monoclonal antibodies against Caprine arthritis-encephalitis virus epitopes in the p28 and p55gag viral proteins

► MAbs against CAEV were strongly reactive against p28 and its precursor p55gag. ► p28 contains a linear epitope detergent-stable, not altered by β-ME treatment. ► The epitope in p55gag was susceptible to denaturing treatments of SDS and β-ME. ► The findings suggest the p28 epitope is presented differently from p55gag epitope. The genome of the Caprine Arthritis-Encephalitis Virus (CAEV) encodes the polycistronic precursor protein p55gag. Proteolytic cleavage of p55gag generates the viral core proteins. Some studies suggest that the CAEV p55gag protein contains epitopes or antigenic determinants for these core proteins. This work reinforces this hypothesis and demonstrates that monoclonal antibodies (MAbs) that are directed against the capsid protein (p28) of CAEV are also reactive against the precursor p55gag protein and the intermediate cleavage products, p44, p36 and p22. The major activity of the MAbs was directed against p28. The MAbF12 binding site in p28 was found to be a linear epitope with a structure that is stable after SDS treatment and remains unaltered after β-mercaptoethanol (β-ME) treatment. The MAbF12 binding site in the p55gag, p36 and p22 proteins was found to be a linear epitope with cross-linked sulphide bonds. In conclusion, these findings suggest that the p28 epitope is presented differently from the epitope in the polycistronic precursor protein p55gag. The highly immunogenic p28 contains a linear epitope that is detergent-stable and is not altered by β-ME treatment, whereas the p55gag epitope contains a linear epitope susceptible to denaturing agents.