Homologous and heterologous interference requires bovine herpesvirus-1 glycoprotein D at the cell surface during virus entry

Expression of glycoprotein D (gD) of alphaherpesviruses protects cells from superinfection by homologous and heterologous viruses by a mechanism termed interference. We recently showed that MDBK cells expressing bovine herpesvirus (BHV)-1gD (MDBK(gD)) resist BHV-1, pseudorabies virus (PRV) and herpes simplex virus-1 (HSV-1) but not the more closely related BHV-5 infection as determined by the number of plaques produced. However, the plaque size is reduced in all four viral infections suggesting a block in cell-to-cell transmission. Here, we show that MDBK cells expressing truncated BHV-1 gD, designated MDBK(t-gD), secreted soluble gD and were fully susceptible to infection by all the four viruses when the cells were washed prior to infection. When MDBK cells or MDBK(t-gD) cells were treated with medium containing truncated gD prior to infection, they partially resisted BHV-1, PRV and HSV-1 but not BHV-5. Interestingly, both BHV-1 and BHV-5 formed normal-sized plaques in MDBK(t-gD) cells suggesting that the viruses were able to spread efficiently. Thus BHV-1 gD is required at the cell surface at the time of infection in order to block BHV-1, HSV-1 and PRV infections, consistent with a common coreceptor for the three gDs.