Stable attachment for herpes simplex virus penetration into human cells requires glycoprotein D in the virion and cell receptors that are missing for entry-defective porcine cells.

Clonal porcine kidney cell lines that are non-permissive for herpes simplex virus (HSV) infection produced five orders of magnitude less virus than human cells, contained heparan sulfate (HS), and are restricted only at HSV entry. By fluorescent activated cell sorting, we examined HSV attachments to porcine and human cells. Stable attachment to susceptible human embryonic lung (HEL) cells occurred with infectious wild-type virus, complemented gD or gH mutant viruses, or non-infectious virus lacking gH. On HEL cells, mutant virus lacking gD bound to heparan sulfate, but failed to stably bind. None of these viruses stably attached to SK6-A7 cells, one of the non-permissive porcine cell clones. However, HSV could replicate in these cells when entry was mediated by polyethylene glycol. These results confirm that, in neutral pH entry of HSV, (i) multiple attachments to HS and non-HS components lead to penetration, (2) stable attachment before penetration is one required function of gD, but not gH, and (3) for stable attachment, gD interacts directly, or indirectly through another viral or cellular component, with receptors that are present on human cells, but absent for entry-defective porcine cells. Easily propagated clonal porcine cells are a novel resource to investigate stable attachment, the molecular mechanisms of gD functions, and the viral and cellular components that allow HSV entry and spread.