B Virus (Macacine herpesvirus 1) Glycoprotein D Is Functional but Dispensable for Virus Entry into Macaque and Human Skin Cells

Abstract

Glycoprotein D (gD) plays an essential role in cell entry of many simplexviruses. B virus (Macacine herpesvirus 1) is closely related to herpes simplex virus 1 (HSV-1) and encodes gD, which shares more than 70% amino acid similarity with HSV-1 gD. Previously, we have demonstrated that B virus gD polyclonal antibodies were unable to neutralize B virus infectivity on epithelial cell lines, suggesting gD is not required for B virus entry into these cells. In the present study, we confirmed this finding by producing a B virus mutant, BV-ΔgDZ, in which the gD gene was replaced with a lacZ expression cassette. Recombinant plaques were selected on complementing VD60 cells expressing HSV-1 gD. Virions lacking gD were produced in Vero cells infected with BV-ΔgDZ. In contrast to HSV-1, B virus lacking gD was able to infect and form plaques on noncomplementing cell lines, including Vero, HEp-2, LLC-MK2, primary human and macaque dermal fibroblasts, and U373 human glioblastoma cells. The gD-negative BV-ΔgDZ also failed to enter entry-resistant murine B78H1 cells bearing a single gD receptor, human nectin-1, but gained the ability to enter when phenotypically supplemented with HSV-1 gD. Cell attachment and penetration rates, as well as the replication characteristics of BV-ΔgDZ in Vero cells, were almost identical to those of wild-type (wt) B virus. These observations indicate that B virus can utilize gD-independent cell entry and transmission mechanisms, in addition to generally used gD-dependent mechanisms.

Importance: B virus is the only known simplexvirus that causes zoonotic infection, resulting in approximately 80% mortality in untreated humans or in lifelong persistence with the constant threat of reactivation in survivors. Here, we report that B virus lacking the gD envelope glycoprotein infects both human and monkey cells as efficiently as wild-type B virus. These data provide evidence for a novel mechanism(s) utilized by B virus to gain access to target cells. This mechanism is different from those used by its close relatives, HSV-1 and -2, where gD is a pivotal protein in the virus entry process. The possibility remains that unidentified receptors, specific for B virus, permit virus entry into target cells through gD-independent pathways. Understanding the molecular mechanisms of B virus entry may help in developing rational therapeutic strategies for the prevention and treatment of B virus infection in both macaques and humans.