Anterograde transport of herpes simplex virus proteins in axons of peripheral human fetal neurons: an immunoelectron microscopy study

Herpes simplex virus (HSV) reactivates from latency in the neurons of dorsa l root ganglia (DRG) and is subsequently transported anterogradely along th e axon to be shed at the skin or mucosa. Although we have previously shown that only unenveloped nucleocapsids are present in axons during anterograde transport, the mode of transport of tegument proteins and glycoproteins is not known. We used a two-chamber culture model with human fetal DRG cultiv ated in an inner chamber, allowing axons to grow out and penetrate an agaro se barrier and interact with autologous epidermal cells in the outer chambe r. After HSV infection of the DRG, anterograde transport of viral component s could be examined in the axons in the outer chamber at different time poi nts by electron and immunoelectron microscopy (IEM). In the axons, unenvelo ped nucleocapsids or focal collections of gold immunolabel for nucleocapsid (VP5) and/or tegument (VP16) were detected. VP5 and VP16 usually colocaliz ed in both scanning and transmission IEM. In contrast, immunolabel for glyc oproteins gB, gC, and go was diffusely distributed in axons and was rarely associated with W5 or VP16. In longitudinal sections of axons, immunolabel for glycoprotein was arrayed along the membranes of axonal vesicles. These findings provide evidence that in DRG axons, virus nucleocapsids coated wit h tegument proteins are transported separately from glycoproteins and sugge st that final assembly of enveloped virus occurs at the axon terminus.