SYNTHESIS OF RECOMBINANT BACULOVIRUSES EXPRESSING THE OUTER CAPSID PROTEIN VP2 OF 5 BTV SEROTYPES AND THE INDUCTION OF NEUTRALIZING ANTIBODIES TO HOMOLOGOUS AND HETEROLOGOUS BTV SEROTYPES

DNA representing RNA segment L2 of 5 different bluetongue virus (BTV) serotypes (BTV-1, -2, -11, -13 and -17) corresponding to the gene that codes for the BTV neutralization antigen VP2, have been inserted individually into baculovirus transfer vectors in lieu of the 5' coding region of the polyhedrin gene of Autographa californica nuclear polyhedrosis virus (AcNPV). After co-transfection of Spodoptera frugiperda cells with wild-type AcNPV DNA in the presence of the derived transfer vector DNAs, polyhedrin-negative recombinant baculoviruses were recovered. When S. frugiperda cells were infected with each of these viruses, protein was made similar in size and antigenic properties to the authentic BTV VP2 protein. To evaluate the biological activities of these proteins, antibodies were raised to them in guinea pigs. The neutralization capabilities of these antisera were tested against homologous and, for two of the higher titered sera, heterologous BTV serotypes. Each antiserum neutralized the infectivity of the homologous virus serotype. In heterologous virus challenges, the serum raised to the VP2 protein of BTV-13 also neutralized the infectivity of BTV-1, and to lesser extents BTV3, -16, -8 and -9 (BTV-2, -10, -11, -15 were not tested). The serum raised to the VP2 of BTV-17 neutralized BTV-20 and -21, and to lesser extents BTV-4 and -8 (again, BTV-2, -10, -11, -15 were not tested).