Egress of alphaherpesviruses: comparative ultrastructural study

Area of Science:

• Virology
• Cell Biology
• Microbiology

Background:

• Alphaherpesviruses, including equine herpesvirus 1 (EHV-1), herpes simplex virus 1 (HSV-1), infectious laryngotracheitis virus (ILTV), and pseudorabies virus (PrV), are significant pathogens.
• Understanding viral egress is crucial for developing antiviral strategies.

Purpose of the Study:

• To investigate and visualize the egress mechanisms of four alphaherpesviruses using electron microscopy.
• To compare the morphogenesis and egress pathways of EHV-1, HSV-1, ILTV, and PrV in infected cell lines.

Main Methods:

• Infected cell lines of various origins were analyzed using transmission electron microscopy.
• Immunogold labeling with a trans-Golgi network (TGN)-specific antiserum was employed.
• Studies utilized pseudorabies virus (PrV) mutants lacking glycoproteins gB and gH.

Main Results:

• Intranuclear assembly is followed by budding at the inner nuclear membrane, forming enveloped particles in the perinuclear space.
• Egress from the perinuclear cisterna involves fusion with the outer nuclear membrane, visualized for HSV-1 and EHV-1.
• Intracytoplasmic nucleocapsids are enveloped at the trans-Golgi network (TGN), forming mature virions distinct from those in the perinuclear space.
• Glycoproteins gB and gH are dispensable for the egress of PrV.

Conclusions:

• A deenvelopment-reenvelopment process similar to that observed in other herpesviruses occurs during the maturation of EHV-1, HSV-1, and ILTV.
• The membrane fusion events during viral egress differ significantly from those involved in virus entry and cell-to-cell spread.