In the absence of glycoprotein I (gI), gE determines bovine herpesvirus type 5 neuroinvasiveness and neurovirulence

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Abstract
Bovine herpesvirus type 5 (BHV-5) is an alphaherpesvirus that causes fatal encephalitis in calves. Envelope glycoproteins E (gE) and gI of alphaherpesviruses are important for the pathogenesis in vivo. Previously the authors determined that BHV-5 gE is important for BHV-5 neurovirulence. To determine the role of gI in BHV-5 neurovirulence, the authors have constructed gI-deleted and gI-revertant BHV-5 and analyzed their neuropathogenic properties in a rabbit seizure model. Following intranasal infection, 40% of the rabbits infected with the gI-deleted virus showed severe neurological signs. gI-deleted BHV-5 invaded all the central nervous system (CNS) structures invaded by the gI-revertant BHV-5; however, the number of neurons infected by the gI-deleted virus was similar or slightly reduced (two to four fold). Thus, the gI-deleted virus retained significant neurovirulence and/or neuroinvasive properties when compared with the gE-deleted BHV-5. Pulse-chase analysis revealed that the gE of gI-deleted virus was processed to a larger and a diffused 94- to 100-kDa protein (instead of 94 kDa). The 94- to 100-kDa protein was processed in the Golgi with delayed kinetics but it was endoglycosidase H (EndoH) resistant. In cells infected with gI-deleted virus, there was a reduction in cell-surface gE expression compared to wild-type, which correlated to reduced amount of gE processed in the Golgi. The authors believe that in the absence of gI, BHV-5 gE is sufficient for BHV-5 neurovirulence.