Characteristics of glycoprotein B of equine herpesvirus 1 expressed by a recombinant baculovirus.

A recombinant baculovirus (Bac-EgB) containing the complete open reading frame of equine herpesvirus 1 glycoprotein B (EHV-1 gB) expressed recombinant products of 107-133 kDa, 58-75 kDa and 53-57 kDa, corresponding to EHV-1 gB precursor, large and small subunits respectively. High molecular mass products (>200 kDa) in the Bac-EgB infected insect cells were consistent with oligomerisation of the recombinant EHV-1 gB products, and analysis with tunicamycin and endoglycosidases indicated that the baculovirus-expressed gB contained N-linked sugars with high mannose and hybrid chains. N-terminal amino acid sequence analysis of the gB forms revealed identical signal and endoproteolytic cleavage sites to those of gB in EHV-1 infected mammalian cells, and authenticity of processing and transport was supported by the presence of EHV-1 gB antigen at the surface of infected insect cells. Immunogold labelling and electron microscopy of recombinant baculovirus particles indicated that the recombinant gB was also present in baculovirus envelopes. Bac-EgB infected insect cells were able to induce low levels of complement dependent virus neutralising antibody, and have been shown to evoke protective immune responses in murine models of respiratory disease and abortion.