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Chapter 27 : Polyomaviruses
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Polyomaviruses are widely distributed in humans and other animal species. Polyomaviruses were initially considered a genus within the family Papovaviridae, which included papillomaviruses and polyomaviruses. Simian virus 40 (SV40) produces renal involvement in its simian host, as do JC virus (JCV) and BK virus (BKV) in humans. The major known site of BKV persistence is the renal tubular epithelium, and persistent infection of renal tubular epithelium cells, like that seen with JCV and with mouse pneumotropic virus (MPtV), appears to involve not a state of viral latency but rather ongoing productive infection at low level. Those which predispose to progressive multifocal leukoencephalopathy (PML) are not fully understood. A group of investigators has attempted to duplicate PCR isolation of polyomaviruses from the same tumor material in different laboratories. In this study, PCR analysis of the same 225 brain tumor samples was carried out in two geographically separated laboratories. Earlier, the use of PCR analysis of cerebrospinal fluid (CSF) enabled specific diagnosis in 80 to 90% of cases. Highly active antiretroviral therapy (HAART) has been shown to reduce viral load of JCV in CSF, however, and while CSF PCR remains a valuable diagnostic tool in this setting, the diagnostic yield in patients treated with HAART has been shown to be reduced to 57.5%. Recently, based on the observation that JCV binds to the serotonin receptor, one study reported stabilization of disease and improvement in PML lesions following treatment with the serotonin reuptake inhibitor, mirtazapine.
Taxonomic relationships of the major polyomaviruses.
Electron micrograph of BKV extracted from human fetal kidney cells, concentrated by ultracentrifugation, and stained with 2% phosphotungstic acid, showing characteristic 42-nm particles.
Viral gene transcription maps of SV40 (A), BKV (B), and JCV (C) DNAs. The checkerboard area on the thick solid line indicates the portion of the RR. The thin dashed line indicates intron sequences spliced out of large T-Ag. (Adapted from references 33 [A], 100 [B], and 4 [C].)
(A) Identification of SV40 T-Ag by immunofluorescence in transformed simian TC-7 kidney cells. Cells were grown in a monolayer and reacted with monoclonal antibodies PAb 416, PAb 108, and PAb 101 directed against T-Ag as described by O’Neill et al. ( 78a ). (B) Naïve TC-7 cells (not containing T-Ag-encoding DNA sequences) reacted with monoclonal antibodies as in panel A (negative control).
Western blot of SV40 T-Ag and p53 from transformed human cells. SV40 T-Ag was immunoprecipitated in even-numbered lanes and p53 was immunoprecipitated in odd-numbered lanes, and the immunoprecipitates were subjected to electrophoresis in agarose gels and analyzed by Western blotting using a cocktail of antibodies to T-Ag or p53 ( 95 ). The illustration shows that immunoprecipitation of either protein results in coprecipitation of the second protein.
Interaction of JCV, BKV, and SV40 with primary cultures of human fetal brain or glial cells. Cells were infected with a 1/10 dilution of the Mad-1 strain of JCV or a 1/1,000 dilution of SV40 or BKV (~1 infectious unit per cell). Cells were transferred to 22-mm square glass coverslips after 2 weeks for the Mad-1-infected cells and immediately after inoculation for cultures infected with BKV or SV40. In JCV-infected cells, cytopathic effect did not appear until 3 to 4 weeks. In cultures infected with BKV or SV40, cytopathic effect became extensive within 8 to 10 days. (A) Uninfected human fetal brain cells containing relatively small, moderately stained nuclei. (B) Mad-1-infected human fetal brain cells with large nuclei and multinucleated cells. There were also occasional giant multinucleated cells that contained many nuclei (not shown) and also some cells with small nuclei, similar to those in uninfected cells (arrowheads in panels B and C). (C) SV40-infected cells, also with large, darkly staining nuclei. Some nuclei were reticulated or mottled (double arrows), but multinucleated cells were rare. (D) BKV-infected cells. Again, the nuclei were enlarged and intensely stained. Multinucleated cells were again rare. Some nuclei contained what appeared to be doughnut-shaped nucleoli (arrows). This was unique to BKV infection (Wright’s stain; magnification, ×152).
Polyomavirus persistence as a chronic productive infection, as shown in a kidney of a nonimmunosuppressed mouse 6 months after inoculation with murine pneumotropic (K) virus. Arrows indicate the presence of viral nucleic acids (A), T-Ag (B), and Vp1 antigen (C) indicative of viral replication in renal tubular epithelial cells.
Section from edge of a PML lesion, stained for polyomavirus common structural antigen and labeled using immunoperoxidase techniques. There is extensive loss of myelin. Oligodendrocytes have enlarged nuclei that exhibit intense staining for common structural antigen. Giant astrocytes within the lesion remain unlabeled. Magnification, ×216.
Section of PML-affected brain probed for JCV nuclei acids using in situ hybridization methods. Large numbers of exposed emulsion grains, indicative of specific hybridization, overlie nuclei of infected oligodendrocytes. Magnification, ×200.
T2 weighted magnetic resonance image of a patient developing PML in the setting of AIDS. Multifocal areas of demyelination are seen as areas of increased signal, appearing white against the darker background. (Courtesy of Jay Tsuruda.)
Major human and animal polyomaviruses a
Functions of early and late polyomavirus-encoded proteins a