Bovine herpesvirus 4 glycoprotein B is indispensable for lytic replication and irreplaceable by VSVg

Background: Bovine herpesvirus 4 (BoHV-4) is a gammaherpesvirus, belonging to Rhadinovirus genus, with no clear association with disease. However, there is increasing evidence of its secondary pathogenic role in cases of post-partum metritis in cattle. BoHV-4 Open Reading Frame 8 (ORF8) codifies for glycoprotein B (gB) that shows a heterodimeric structure, composed of two subunits and covalently linked by disulfide bonds and responsible for host cell adhesion through binding to heparan sulfates associated with cellular proteoglycans. Here we describe the generation of several tagged soluble forms of gB ectodomain, in order to test their ability to neutralize BoHV-4 infection. Results: The results show, however, that none of these soluble forms are able to block viral infectivity. To better understand the role of gB during BoHV-4 lytic replication, a recombinant BoHV-4 was generated by homologous recombination from a BoHV-4 cloned as a Bacterial artificial chromosome (BAC) (pBAC-BoHV-4-A), in which most of the BoHV-4 gB ORF was substituted by the insertion of a DNA stuffer selectable cassette. The resulting recombinant BoHV-4 genome (pBAC-BoHV-4-A Delta gB-KanaGalK) was completely unable to reconstitute infectious replicating viral particles (Infectious Replicating Viral Particles, IRVPs) and to replicate when transfected in permissive cell lines in comparison to its revertant clone (pBAC-BoHV-4-Delta gB-Rev) or pBAC-BoHV-4-A parental clone. Conclusion: This demonstrates that the BoHV-4 replicating cycle is dependent on gB. Moreover, when gB was deleted from a recombinant BoHV-4 genome delivering an heterologous glycoprotein, Vesicular Stomatitis Virus Glycoprotein (VSVg), VSVg was unable to complement gB. This study provides direct evidence that gB is necessary for BoHV-4 lytic replication.