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Age dependence of viral expression. Electron microscopic and immunoperoxidase studies of Measles virus replication in
Abstract:
The hamster neurotropic strain of measles virus inoculated intracerebrally into BALB/c mice causes a uniformly fatal encephalitis with production of infectious virus in 1- to 2-day-old suckling mice but a 31 per cent mortality with production of measles virus antigen without production of infectious virus in 4-week-weanling mice (8). These two groups of animals were studied using routine electron microscopy and the immunoperoxidase technique in order to determine the nature of the measles virus antigen produced in each situation. Suckling animals showed numerous cytoplasmic viral inclusions in neurons and glia. This nucleocapsid material stained specifically with rabbit antiserum to measles virus antigen overlayed with peroxidase-conjugated goat antirabbit gamma-globulin. Histologic and electron microscopic study of weanling mice revealed rare necrotic cells and occasional loose clusters of neurons with depolymerized ribosomes. Immunoperoxidase staining showed diffuse cytoplasmic staining of similar groups of neurons and dendritic processes without evidence of nucleocapsid material. These differences in virus replication appear to be a function of the maturation of the host cell rather than the measles virus. Hamster neurotropic virus infection of the weanling mouse is an example of a potentially fatal virus infection in which viral replication is defective at a stage prior to assembly of nucleocapsid material; thus, no direct morphologic evidence that the cause of the clinical disease is a viral infection is present.
Insights
Measles virus causes fatal encephalitis in young mice but only antigen production in older mice. This difference in measles virus replication is due to host cell maturation, not the virus itself.
Area of Science:
- Virology
- Neuroscience
- Immunology
Background:
- Measles virus infection in mice can lead to encephalitis.
- Host factors influence viral replication and disease severity.
Purpose of the Study:
- To investigate the nature of measles virus antigen production in mice of different ages.
- To determine if host cell maturation affects measles virus replication.
Main Methods:
- Intracerebral inoculation of hamster neurotropic measles virus into suckling and weanling BALB/c mice.
- Routine electron microscopy and immunoperoxidase staining.
- Analysis of viral inclusions, nucleocapsid material, and antigen distribution.
Main Results:
- Suckling mice exhibited fatal encephalitis with infectious virus and cytoplasmic viral inclusions containing nucleocapsid material.
- Weanling mice showed lower mortality with measles virus antigen in the cytoplasm but no infectious virus or nucleocapsid material.
- Immunoperoxidase staining confirmed measles virus antigen in both groups, but nucleocapsid structures were only observed in suckling mice.
Conclusions:
- Host cell maturation, not the measles virus strain, dictates the stage of viral replication.
- Weanling mice infected with measles virus demonstrate defective replication prior to nucleocapsid assembly.
- This study provides a model for studying potentially fatal viral infections with defective replication in mature host cells.