Protective effect of individual glycoproteins of Newcastle disease virus expressed in insect cells: the fusion protein derived from an avirulent strain had lower protective efficacy.

Recombinant hemagglutinin-neuraminidase (rHN) and fusion (rF) glycoproteins of virulent and avirulent strains of Newcastle disease virus (NDV) expressed by using baculovirus expression system were used to investigate their protective immunization effects in chickens. The efficacy of immunization with these recombinant proteins was evaluated by challenge infection. The chickens immunized with either rHN or rF protein of a virulent strain or rHN protein of an avirulent strain were completely protected from the lethal infection of virulent NDV. On the other hand, the rF protein of an avirulent strain, in which precursor F protein was not cleaved, showed lower protective effects. Significant levels of specific antibodies against respective proteins were detected in sera from survivors, whereas relatively lower levels of antibodies were found in chickens which were killed by challenge infection. These data indicate that either HN or F protein alone could induce protective immune responses and the cleavage of F protein might be important for its immunological potential.