EXPRESSION CLONING AND HUMORAL IMMUNE-RESPONSE TO THE NUCLEOCAPSID AND MEMBRANE-PROTEINS OF EQUINE ARTERITIS VIRUS

To provide a convenient and sensitive method for the detection of equi ne arteritis virus (EAV)-specific serum antibodies, we developed an im munoblot assay employing the EAV nucleocapsid (N) and membrane (M) pro teins expressed in a procaryotic expression vector (pMAL-c2) for the p roduction of recombinant maltose-binding (MBP) fusion proteins (MBP-N and MBP-M). The antigenic reactivity of the recombinant fusion protein s and their Xa factor cleavage EAV products was confirmed by immunoblo t 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 p roducts, and in the serum neutralization test, there was 100% concorda nce between the assays, Sera from horses experimentally infected with EAV were reactive in the immunoblot test with both the MBP-N and the M BP-M fusion proteins by day 14 after EAV exposure, The reactivity cont inued to the end of the experiment at day 145 after infection. This im mune reactivity correlated with the detection of neutralizing antibodi es in the serum samples, Based on these findings, the recombinant N an d M proteins might be useful for serodetection of EAV-infected animals .