Superinfection Exclusion of Alphaherpesviruses Interferes with Virion Trafficking.

Superinfection exclusion (SIE) is a phenomenon in which a primary viral infection interferes with secondary viral infections within that same cell. Although SIE has been observed across many viruses, it has remained relatively understudied. A recently characterized glycoprotein D (gD)-independent SIE of alphaherpesviruses presents a novel mechanism of coinfection restriction for herpes simplex virus 1 (HSV-1) and pseudorabies virus (PRV). In this study, we evaluated the role of multiplicity of infection (MOI), receptor expression, and trafficking of virions to gain greater insight into potential mechanisms of alphaherpesvirus SIE. We observed that high-MOI secondary viral infections were able to overcome SIE in a manner that was independent of receptor availability. We next assessed virion localization during SIE through live microscopy of fluorescently labeled virions and capsid assemblies. Analysis of these fluorescent assemblies identified changes in the distribution of capsids during SIE. These results indicate that SIE during PRV infection inhibits viral entry or fusion while HSV-1 SIE inhibits infection through a postentry mechanism. Although the timing and phenotype of SIE are similar between alphaherpesviruses, the related viruses implement different mechanisms to restrict coinfection. Most viruses utilize a form of superinfection exclusion to conserve resources and control population dynamics. gD-dependent superinfection exclusion in alphaherpesviruses is well documented. However, the undercharacterized gD-independent SIE provides new insight into how alphaherpesviruses limit sequential infection. The observations described here demonstrate that gD-independent SIE differs between PRV and HSV-1. Comparing these differences provides new insights into the underlying mechanisms of SIE implemented by two related viruses.