Mechanism of reduction of virus release and cell-cell fusion in persistent canine distemper virus infection.
Canine distemper virus (CDV), a mobillivirus related to measles virus causes a chronic progressive demyelinating disease, associated with persistence of the virus in the central nervous system (CNS). CNS persistence of morbilliviruses has been associated with cell-to-cell spread, thereby limiting immune detection. The mechanism of cell-to-cell spread remains uncertain. In the present study we studied viral spread comparing a cytolytic (non-persistent) and a persistent CDV strain in cell cultures. Cytolytic CDV spread in a compact concentric manner with extensive cell fusion and destruction of the monolayer. Persistent CDV exhibited a heterogeneous cell-to-cell pattern of spread without cell fusion and 100-fold reduction of infectious viral titers in supernatants as compared to the cytolytic strain. Ultrastructurally, low infectious titers correlated with limited budding of persistent CDV as compared to the cytolytic strain, which shed large numbers of viral particles. The pattern of heterogeneous cell-to-cell viral spread can be explained by low production of infectious viral particles in only few areas of the cell membrane. In this way persistent CDV only spreads to a small proportion of the cells surrounding an infected one. Our studies suggest that both cell-to-cell spread and limited production of infectious virus are related to reduced expression of fusogenic complexes in the cell membrane. Such complexes consist of a synergistic configuration of the attachment (H) and fusion (F) proteins on the cell surface. F und H proteins exhibited a marked degree of colocalization in cytolytic CDV infection but not in persistent CDV as seen by confocal laser microscopy. In addition, analysis of CDV F protein expression using vaccinia constructs of both strains revealed an additional large fraction of uncleaved fusion protein in the persistent strain. This suggests that the paucity of active fusion complexes is due to restricted intracellular processing of the viral fusion protein.
Meertens
Nadine
N
Department of Clinical Veterinary Medicine, Division of Clinical Research, University of Bern, 3012 Bern, Switzerland.
Stoffel
Michael H
MH
Cherpillod
Pascal
P
Wittek
Riccardo
R
Vandevelde
Marc
M
Zurbriggen
Andreas
A
D000818:Animals; D015153:Blotting, Western; D002450:Cell Communication; D002522:Chlorocebus aethiops; D004216:Distemper / Q000473:pathology* / Q000821:virology; D004217:Distemper Virus, Canine / Q000378:metabolism*; D005455:Fluorescent Antibody Technique / Q000379:methods; D015967:Gene Expression Regulation, Viral; D006023:Glycoproteins / Q000378:metabolism; D018613:Microscopy, Confocal; D008854:Microscopy, Electron / Q000379:methods; D012333:RNA, Messenger / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014357:Trypsin / Q000494:pharmacology; D014709:Vero Cells / Q000648:ultrastructure / Q000821:virology; D014760:Viral Fusion Proteins / Q000378:metabolism; D014764:Viral Proteins / Q000378:metabolism
D006023:Glycoproteins; D012333:RNA, Messenger; D014760:Viral Fusion Proteins; D014764:Viral Proteins; C023587:protein M (glycoprotein); C076619:F protein, Phocine distemper virus; D014357:Trypsin