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Peripheral blood mononuclear phagocytes mediate dissemination of murine cytomegalovirus
C A Stoddart1, R D Cardin, J M Boname
1Department of Microbiology and Immunology, Stanford University School of Medicine, California 94305-5402.
Abstract:
Cytomegalovirus is transmitted with blood and organs from seropositive individuals, although the particular leukocyte population harboring latent or persistent virus remains poorly characterized. Murine cytomegalovirus, tagged with the Escherichia coli lacZ gene, was used to identify cells in which virus replicates during acute infection of immunocompetent mice. Recombinant murine cytomegaloviruses, RM461, RM460, and RM427, were constructed to express beta-galactosidase under control of the human cytomegalovirus ie1/ie2 promoter/enhancer. The lacZ gene was inserted between the ie2 and sgg1 genes in RM461 and RM460, disrupting a 0.85-kb late transcript that was found to be dispensable for replication in cultured cells as well as for infection of mice. In BALB/c mice, lacZ-tagged and wild-type viruses exhibited a similar 50% lethal dose and all had the capacity to latently infect the spleen. Peripheral blood mononuclear phagocytes were the major infected leukocyte cell type, as demonstrated by the ability of infected cells to adhere to glass and to phagocytize latex beads; however, these cells did not exhibit typical monocyte markers. Plaque assay for virus and 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside (X-Gal) staining of frozen sections of organs from infected mice revealed that the major target organs included the spleen, adrenal glands, liver, and salivary glands, although tissues as diverse as brown fat and lungs were also involved. Individual blue-staining cells were readily identified in all infected tissues. These studies identified a mononuclear phagocyte, possibly a macrophage or dendritic cell precursor, as the vehicle of virus dissemination during acute infection, and demonstrate the utility of using lacZ-tagged murine cytomegalovirus for tropism, pathogenesis, and latency studies.
Insights
Murine cytomegalovirus (MCMV) infection in mice reveals that mononuclear phagocytes, likely macrophage or dendritic cell precursors, are key carriers of the virus during acute infection. This study highlights the use of lacZ-tagged MCMV for tracking viral spread and persistence.
Area of Science:
- Virology
- Immunology
- Cell Biology
Background:
- Cytomegalovirus (CMV) transmission occurs via blood and organs from infected individuals.
- The specific leukocyte populations harboring latent or persistent CMV are not well understood.
- Identifying these cells is crucial for understanding CMV pathogenesis and transmission.
Purpose of the Study:
- To identify the leukocyte cell types infected by murine cytomegalovirus (MCMV) during acute infection.
- To characterize the role of these cells in viral dissemination and latency.
- To demonstrate the utility of lacZ-tagged MCMV for studying viral tropism and pathogenesis.
Main Methods:
- Construction of recombinant MCMV strains (RM461, RM460, RM427) engineered to express beta-galactosidase (lacZ) under the human CMV ie1/ie2 promoter/enhancer.
- Infection of immunocompetent BALB/c mice with lacZ-tagged and wild-type MCMV.
- Analysis of infected tissues using plaque assays and X-Gal staining to identify blue-staining (lacZ-positive) cells.
- Characterization of infected peripheral blood mononuclear cells based on adherence and phagocytic properties.
Main Results:
- lacZ-tagged MCMV exhibited similar virulence and latency capacity as wild-type MCMV in mice.
- Peripheral blood mononuclear phagocytes were identified as the primary infected leukocyte type, displaying phagocytic capabilities but not typical monocyte markers.
- Major target organs for MCMV infection included the spleen, adrenal glands, liver, and salivary glands, with involvement also noted in brown fat and lungs.
- Individual infected cells were readily identifiable in all examined tissues.
Conclusions:
- Mononuclear phagocytes, potentially macrophage or dendritic cell precursors, serve as the primary vehicles for MCMV dissemination during acute infection.
- lacZ-tagged MCMV is a valuable tool for investigating MCMV tropism, pathogenesis, and latency.
- Further research into these infected cell types can inform strategies for controlling CMV infection and transmission.