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Variability of persisting MHV RNA sequences constituting immune and replication-relevant domains
C Bergmann1, E Dimacali, S Stohl
1Department of Neurology, Howard Hughes Medical Institutes, University of Southern California School of Medicine, Los Angeles 90033, USA. cbergman@hsc.usc.edu
Virology
|May 28, 1998
Summary
Persistent mouse hepatitis virus infection in the central nervous system involves viral RNA without infectious virus. Genetic analysis revealed mutations, but not immune escape, contributing to chronic demyelination.
Area of Science:
- Neurovirology
- Immunology
- Molecular Biology
Background:
- Mouse hepatitis virus (JHM strain) causes persistent central nervous system infections in survivors of acute illness.
- Chronic demyelination is associated with persistent JHMV infection, characterized by detectable viral RNA but no infectious virus.
- Understanding the mechanisms of viral persistence, immune evasion, and replication defects is crucial.
Purpose of the Study:
- To investigate viral RNA mutations in acutely and persistently infected mouse brains.
- To determine if mutations in specific viral genes (ECS, M, N) are associated with persistence or immune evasion.
- To assess the role of cytotoxic T cell (CTL) pressure in selecting for viral variants during persistent infection.
Main Methods:
- Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to analyze viral RNA sequences.
- Sequencing focused on the encapsidation sequence (ECS), matrix (M) protein transmembrane domains, and a nucleocapsid (N) protein CTL epitope.
- Mutations were compared between acutely and persistently infected mouse brains, including in different host immune backgrounds (H-2d vs. H-2b).
Main Results:
- The ECS showed minimal variability, suggesting low replication levels during persistence.
- M gene sequences remained stable during persistence, despite mutations during acute infection.
- N gene mutations were random and not selected for during persistence, with one exception (Pro to Ser substitution). A mutation reducing CTL recognition was found in both responder and nonresponder mice, indicating it does not drive persistence via CTL escape.
Conclusions:
- Viral RNA persistence in the CNS is not driven by selection for immune escape variants, particularly CTL escape.
- Low-level replication and random mutations, rather than specific adaptive changes, characterize persistent JHMV infection.
- The findings suggest that immune evasion through CTL escape is not a primary factor in establishing chronic demyelination in immunocompetent adult hosts.