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J. Virol., 06 1996, 3852-3862, Vol 70, No. 6
M Lavignon and L Evans
Mixed retroviral infections frequently exhibit pseudotyping, in which the
genome of one virus is packaged in a virion containing SU proteins encoded
by another virus. Infection of mice by Moloney murine leukemia virus
(M-MuLV), which induces lymphocytic leukemia, results in a mixed viral
infection composed of the inoculated ecotropic M-MuLV and polytropic MuLVs
generated by recombination of M-MuLV with endogenous retroviral sequences.
In this report, we describe pseudotyping which occurred among the
polytropic and ecotropic MuLVs in M-MuLV-infected mice. Infectious center
assays of polytropic MuLVs released from splenocytes or thymocytes of
infected mice revealed that polytropic MuLVs were extensively pseudotyped
within ecotropic virions. Late in the preleukemic stage, a dramatic change
in the extent of pseudotyping occurred in thymuses. Starting at about 5
weeks, there was an abrupt increase in the number of thymocytes that
released nonpseudotyped polytropic viruses. A parallel increase in
thymocytes that released ecotropic M-MuLV packaged within polytropic
virions was also observed. Analyses of the clonality of preleukemic
thymuses and thymomas suggested that the change in pseudotyping
characteristics was not the result of the emergence of tumor cells.
Examination of mice infected with M-MuLV, Friend erythroleukemia virus, and
a Friend erythroleukemia virus-M-MuLV chimeric virus suggested that the
appearance of polytropic virions late in the preleukemic stage correlated
with the induction of lymphocytic leukemia. We discuss different ways in
which pseudotypic mixing may facilitate leukemogenesis, including a model
in which the kinetics of thymic infection, modulated by pseudotyping and
viral interference, facilitates a stepwise mechanism of leukemogenesis.
Copyright © 1996, American Society for Microbiology
A multistep process of leukemogenesis in Moloney murine leukemia virus- infected mice that is modulated by retroviral pseudotyping and interference
Laboratory of Persistent Viral Diseases, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, Hamilton, Montana 59840, USA.
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