NUCLEOCAPSID PROTEIN-N OF LELYSTAD VIRUS - EXPRESSION BY RECOMBINANT BACULOVIRUS, IMMUNOLOGICAL PROPERTIES, AND SUITABILITY FOR DETECTION OF SERUM ANTIBODIES

The ORF7 gene, encoding the nucleocapsid protein N of Lelystad virus ( LV), was inserted downstream of the P10 promoter into Autographa calif ornica nuclear polyhedrosis virus (baculovirus), The resulting recombi nant baculovirus, designated bac-ORF7, expressed a 15-kDa protein in i nsect cells. This proteid was Similar in size to the N protein express ed by LV in CL2621 cells when it was analyzed on sodium dodecyl sulfat e-polyacrylamide gels, The N protein expressed by bac-ORF7 was immunop recipitated with anti-ORF7 peptide serum, porcine convalescent-phase a nti-LV serum, and N protein-specific monoclonal antibodies, indicating that this N protein had retained its native antigenic structure. The recombinant N protein was immunogenic in pigs, and the porcine antibod ies raised against this protein recognized LV in an immunoperoxidase m onolayer assay, However, pigs vaccinated twice with approximately 20 m u g of N protein were not protected against a challenge with 10(5) 50% tissue culture infective doses of LV. Experimental and field sera dir ected against various European and North American isolates reacted wit h the N protein expressed by bac-ORF7 in a blocking enzyme-linked immu nosorbent assay, Therefore, the recombinant N protein may be useful fo r developing diagnostic assays for the detection of serum antibodies d irected against different isolates of LV.