Immunological characterization of the VSV nucleocapsid (N) protein expressed by recombinant baculovirus in Spodoptera exigua larva: use in differential diagnosis between vaccinated and infected animals

Vesicular stomatitis is a viral disease of cattle, pigs, and horses. The disease is characterized by vesicular lesions on the epithelium of the mouth, feet, and teats. The pathological lesions are virtually indistinguishable from that of foot-and-mouth disease. We have developed a recombinant baculovirus that expresses the nucleocapsid (N) protein of the New Jersey serotype of vesicular stomatitis virus (VSVNJ) in insect cells (Sf9) and larvae (Spodoptera exigua). The gene was expressed under control of the polyhedrin promoter as a fusion or nonfusion protein. The recombinant N protein expressed in insect cells could not be distinguished from N protein produced in VSVNJ-infected CHO cells by immunological and biochemical analyses. The level of expression of N as a percentage of the total protein in Sf9 cells was 41% for the fusion and 60% for the nonfusion protein. Higher level (68%) of expression of the nonfusion N protein was obtained in larvae. Recombinant N protein was used in an ELISA to distinguish animals vaccinated with a recombinant VSV glycoprotein from those exposed to the whole virus by infection or classical vaccine. Lysate of a single infected larva (0.2-0.3 g) was adequate for coating ELISA plates to perform 10,000 serum assays in duplicate.