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Journal of Virology, September 1998, p. 7048-7056, Vol. 72, No. 9
Department of Biochemistry and Molecular
Biology1 and
Department of
Pathology,2 University of Southern California
School of Medicine, Los Angeles, California 90033, and
Center
for Retrovirus Research and Department of Veterinary Biosciences,
Ohio State University, Columbus, Ohio 432103
Received 6 April 1998/Accepted 20 May 1998
A new provirus clone of feline leukemia virus (FeLV), which we
named FeLV-A (Rickard) or FRA, was characterized with respect to viral
interference group, host range, complete genome sequence, and in vivo
pathogenicity in specific-pathogen-free newborn cats. The in vitro
studies indicated the virus to be an ecotropic subgroup A FeLV with
98% nucleotide sequence homology to another FeLV-A clone (F6A/61E),
which had also been fully sequenced previously. Since subgroup B
polytropic FeLVs (FeLV-B) are known to arise via recombination between
ecotropic FeLV-A and endogenous FeLV (enFeLV) env elements,
the in vivo studies were conducted by direct intradermal inoculation of
the FRA plasmid DNA so as to eliminate the possibility of coinoculation
of any FeLV-B which may be present in the inoculum prepared by
propagating FeLV-A in feline cell cultures. The following observations
were made from the in vivo experiments: (i) subgroup conversion from
FeLV-A to FeLV-A and FeLV-B, as determined by the interference assay,
appeared to occur in plasma between 10 and 16 weeks postinoculation
(p.i.); (ii) FeLV-B-like recombinants (rFeLVs), however, could be
detected in DNA isolated from buffy coats and bone marrow by PCR as
early as 1 to 2 weeks p.i.; (iii) while a mixture of rFeLV species
containing various amounts of N-terminal substitution of the endogenous
FeLV-derived env sequences were detected at 8 weeks p.i.,
rFeLV species harboring relatively greater amounts of such substitution
appeared to predominate at later infection time points; (iv) the
deduced amino acid sequence of rFeLV clones manifested striking
similarity to natural FeLV-B isolates, within the mid-SU region of the
env sequenced in this work; and (v) four of the five cats,
which were kept for determination of tumor incidence, developed thymic
lymphosarcomas within 28 to 55 weeks p.i., with all tumor DNAs
harboring both FeLV-A and rFeLV proviruses. These results provide
direct evidence for how FeLV-B species evolve in vivo from FeLV-A and
present a new experimental approach for efficient induction of thymic
tumors in cats, which should be useful for the study of retroviral
lymphomagenesis in this outbred species.
0022-538X/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Pathogenicity Induced by Feline Leukemia Virus,
Rickard Strain, Subgroup A Plasmid DNA (pFRA)
*
Corresponding author. Mailing address: Department of
Pathology, University of Southern California School of Medicine, 2011 Zonal Ave., Los Angeles, CA 90033. Phone: (323) 442-1184. Fax: (323)
442-3049. E-mail: royburma{at}hsc.usc.edu.
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