Entry and tropism of herpes simplex virus.

Abstract

HSV-1 and HSV-2 entry was examined to determine whether these viruses recognize the same non-heparan sulfate receptor(s). Studied in a saturation blocking assay, the viruses bound a common, saturable component(s) during infectious entry. This component is not heparan sulfate (HS) and is involved in some event of stable binding. Infection by BHV-1, vaccinia or PRV was not inhibited to the same extent, thus showing specificity. Null mutant viruses lacking either glycoprotein B, C, H or I did not lose blocking ability. Therefore these glycoproteins are not essential for interaction with the saturable component. Viruses lacking glycoprotein D did not block infection showing that gD is needed for stable attachment. These results indicate that HSV-1 and HSV-2 bind via gD to common receptors on susceptible cells. Just how many receptors are in common remains to be determined. Several approaches were taken to further explore HSV entry events. Stable binding was reduced, but not eliminated under conditions of reduced sulfate. This indicates that HS is not essential for HSV entry. A recently discovered human membrane protein, currently named the herpesvirus entry mediator (HVEM), was tested for involvement in virus entry. Infectious yields of HSV-1 and HSV-2, but not PRV or vaccinia, increase in swine cells stably transfected with the HVEM gene. Rate of entry and rate of penetration studies showed that presence of HVEM increases efficiency of HSV entry and penetration into swine cells. However, HVEM allowed for faster entry of HSV-2 than HSV-1. Interactions with other yet unidentified membrane components may further differentiate HSV-1 from HSV-2. Though the viruses were found to bind common receptors, they may be using different sets of multiple receptors on the susceptible cells with HVEM being one of that set.