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A 120-amino-acid polypeptide selected from the transmembrane protein region (tTM) and the major capsid protein p26 of bovine immunodeficiency-like virus (BIV) were expressed as fusion proteins from recombinant baculoviruses. The antigenic reactivity of both recombinant fusion proteins was confirmed by Western blot with bovine and rabbit antisera to BIV. BIV-negative bovine sera and animal sera positive for bovine syncytial virus and bovine leukemia virus failed to recognize the recombinant fusion proteins, thereby showing the specificity of the BIV Western blot. One hundred and five bovine serum samples were tested for the presence of anti-BIV antibodies by the recombinant protein-based Western blot and a reference Western blot assay using cell culture-derived virions as test antigens. There was a 100% concordance when the p26 fusion protein was used in the Western blot. However, the Western blot using the tTM fusion protein as its test antigen identified four BIV-positive bovine sera which had tested negative in both the p26 recombinant-protein-based and the reference Western blot assays. This resulted in the lower concordance of 96.2% between the tTM-protein-based and reference Western blot assays. The results of this study showed that the recombinant p26 and tTM proteins can be used as test antigens for the serodetection of BIV-infection in animals.

To provide a convenient and sensitive method for the detection of equine arteritis virus (EAV)-specific serum antibodies, we developed an immunoblot assay employing the EAV nucleocapsid (N) and membrane (M) proteins expressed in a procaryotic expression vector (pMAL-c2) for the production of recombinant maltose-binding (MBP) fusion proteins (MBP-N and MBP-M). The antigenic reactivity of the recombinant fusion proteins and their Xa factor cleavage EAV products was confirmed by immunoblot using horse antisera to EAV. Some horse sera, however, showed immune reactivity to the MBP fusion partner protein. Based on a total of 32 horse sera analyzed for the presence of EAV antibodies by immunoblot, using the MBP-N or -M fusion proteins and the Xa factor cleavage EAV products, and in the serum neutralization test, there was 100% concordance between the assays. Sera from horses experimentally infected with EAV were reactive in the immunoblot test with both the MBP-N and the MBP-M fusion proteins by day 14 after EAV exposure. The reactivity continued to the end of the experiment at day 145 after infection. This immune reactivity correlated with the detection of neutralizing antibodies in the serum samples. Based on these findings, the recombinant N and M proteins might be useful for serodetection of EAV-infected animals.