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The pathogenicity of the M9 mutant of Semliki Forest virus in immune-compromised mice
Abstract:
The role of immune mechanisms in the pathogenicity of the M9 mutant of Semliki Forest virus (SFV) has been examined by the use of immune-deficient and immune-suppressed mice. In immune-competent BALB/c and C57BL/6 mice, the lesions in the central nervous system (CNS) were characterized by acute demyelinating meningoencephalomyelitis. Myelin vacuolation and demyelination were more severe in BALB/c mice than in mice with a C57BL background. The mortality was 12% and 29% respectively. Treatment with cyclophosphamide or sodium aurothiomalate did not greatly alter the type of lesion produced, although mortality was increased. Lesions were less severe in nude (T-lymphocyte-deficient) mice and more severe in beige (natural killer cell-deficient) mice than in most immune-competent mice. Mortality was marginally increased in nude mice but not in beige mice. Demyelination in nude mice was followed rapidly by remyelination. Immune modification did not significantly alter the titres of virus in the brain at 7 days post-infection and infectious virus had been cleared from the brain by 14 days in all cases. Degenerating oligodendrocytes were detected in the CNS of all immune-modified mice examined at day 7. This study therefore suggests that both immune mechanisms and destruction of oligodendrocytes play a role in the production of demyelination by M9.
Insights
This study investigated Semliki Forest virus (SFV) M9 mutant pathogenicity using immune-deficient mice. Findings suggest both immune responses and oligodendrocyte damage contribute to demyelination in the central nervous system (CNS).
Area of Science:
- Neurovirology
- Immunology
- Pathology
Background:
- Semliki Forest virus (SFV) is a neurotropic alphavirus.
- The M9 mutant of SFV exhibits distinct pathogenic properties.
- Understanding the role of the immune system in SFV-induced central nervous system (CNS) disease is crucial.
Purpose of the Study:
- To elucidate the role of immune mechanisms in the pathogenicity of the SFV M9 mutant.
- To investigate the contribution of immune-deficient and immune-suppressed mice models to understanding SFV M9 pathogenesis.
- To determine the relationship between immune responses, demyelination, and viral clearance in the CNS.
Main Methods:
- Utilized immune-deficient (nude, beige) and immune-suppressed (cyclophosphamide, sodium aurothiomalate treated) mice.
- Administered SFV M9 mutant to various mouse models, including immune-competent BALB/c and C57BL/6.
- Assessed central nervous system (CNS) lesions, demyelination severity, mortality rates, and viral titers at 7 and 14 days post-infection.
Main Results:
- Immune-competent mice exhibited acute demyelinating meningoencephalomyelitis, with more severe lesions in BALB/c compared to C57BL/6 mice.
- Lesions were less severe in T-lymphocyte-deficient (nude) mice and more severe in natural killer cell-deficient (beige) mice.
- Degenerating oligodendrocytes were observed in the CNS of immune-modified mice, indicating direct cellular damage alongside immune-mediated effects. Viral clearance occurred by 14 days post-infection in all groups.
Conclusions:
- Both immune mechanisms and direct destruction of oligodendrocytes contribute to demyelination caused by the SFV M9 mutant.
- The specific immune cell deficiencies influence the severity of CNS pathology and demyelination.
- Further research into the interplay between viral replication, immune response, and glial cell damage is warranted for SFV M9 pathogenesis.