1 Department of Virology and Preventive Medicine, Gunma University Graduate School of Medicine, 3-39-22 Showa-machi, Maebashi, Gunma 371-8511, Japan
2 Department of Dermatology, Gunma University Graduate School of Medicine, 3-39-22 Showa-machi, Maebashi, Gunma 371-8511, Japan
Correspondence
Hiroo Hoshino
hoshino{at}med.gunma-u.ac.jp
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ABSTRACT |
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INTRODUCTION |
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It has been known for a long time that retroviruses are, in general, more UV-resistant than other RNA viruses containing genomes of a similar length (Henderson et al., 1992; Levinson & Rubin, 1966
; Murphy & Gordon, 1981
; Owada et al., 1976
). As for the dose required to reduce the infectivity to 10 % (D10), it has been reported that the D10 values of murine leukaemia virus (MuLV), bovine leukaemia virus (BLV) and human immunodeficiency virus type 1 (HIV-1) are 370, 220 and 280 J m2, respectively (Guillemain et al., 1981
; Yoshikura, 1989
). Unexpectedly, we found that the D10 of HTLV-I was as low as about 20 J m2 and that the reverse transcription of HTLV-I was a highly UV-sensitive stage. We investigated and discuss possible mechanisms that could explain the high UV sensitivity of HTLV-I.
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METHODS |
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Virus preparation.
To prepare cell-free virus samples, 8C/HTLV-IMEL5, 8C/HTLV-I2M, PG-4/HTLV-IMT-2, MT-2 and FLK cells were seeded at 6·25x105 ml1 and incubated for 2 days. Cells and debris were removed from the culture supernatants by low-speed centrifugation, and the supernatants were passed through 0·45 µm filters. The filtrates were dispensed into small aliquots and stored at 110 °C until use.
UV irradiation and dosimetry.
Aliquots of 700 µl of supernatants that contained one of these virus samples was placed in the centre of a 35 mm plastic culture plate, kept on ice to eliminate thermal effects and gently agitated to ensure uniform irradiation. UV irradiation was carried out under a low-pressure mercury vapour lamp. The incident UV dose rate was determined using a spectroline DRC-100X dosimeter (Spectronics).
Determination of the UV sensitivities of HTLV-I and BLV.
The 8C/Tax1 cells recently established by us were used for the infectivity assay. The 8C/Tax1 cells were seeded in 2 ml medium in flat-bottomed 6-well plates at 2·5x104 cells ml1. The following day, after irradiation of the viruses with UV light, the cells were infected with 300 µl of HTLV-I or BLV preparations at 37 °C for 1 h in duplicate. The inocula were removed, the cells were washed once with culture medium and then fresh medium was added to the plates. The culture medium was changed at 3 and 6 days. The next day, the cells were fixed with methanol and stained with Giemsa solution and syncytial plaque were counted using an inverted microscope. Cells that contained more than four nuclei were considered to be syncytia and lesions that consisted of three or more syncytia were judged to be plaques. Syncytium numbers in control cultures were about 200 per well for each experiment. Variation of experimental data for each point was within 10 % of corresponding mean value.
UV sensitivity of VSV.
8C cells were seeded into 35 mm plastic culture plates at 6·0x105 cells ml1. The following day, VSV was inactivated with UV light and the cells were infected with 300 µl of VSV preparations at 37 °C for 1 h in duplicate. The cells were washed once with culture medium and medium containing agar was overlaid onto the plates. The next day, cells were stained with neutral red and numbers of plaques were counted using an inverted microscope.
UV sensitivity of cells.
8C, 8C/Tax1 or HeLa cells were seeded in 4 ml medium in 35 mm plastic culture plates at 500 cells ml1. The following day, after removal of the medium and irradiation of the cells with UV light at 012 J m2, fresh medium was added to the wells. After 7 days, cell colonies were counted.
UV sensitivities of HTLV-I and BLV determined by PCR.
8C cells were seeded in 1 ml medium in flat-bottomed 12-well plates at 2x104 cells ml1. Each virus was irradiated with UV. Target 8C cells were then infected with viruses at 37 °C for 1 h, washed with PBS once and incubated for 24 h as described previously (Haraguchi et al., 1994; Yang et al., 1994). The m.o.i. was about 1 for each virus. Cells were lysed with buffer that contained 10 mM Tris/HCl (pH 8·0), 1 mM EDTA, 0·45 % NP-40 (Sigma), 0·45 % Tween 20 (Sigma) and 20 mg protease K ml1 (Sigma), incubated at 52 °C for 2 h and heated at 96 °C for 10 min to inactivate the protease K. To detect viral DNA by PCR, 15 µl reaction mixture that contained 10 mM Tris/HCl (pH 8·3), 50 mM KCl, 1·5 mM MgCl2, each dNTP at 2 mM, 60 ng sense and antisense PCR primers and Taq DNA polymerase (Roche) was added to 5 µl cell lysate. PCR using the various primers shown in Figs 3(a) and 5(a)
was performed in a thermal cycler (Perkin-Elmer Cetus). The PCR cycle was repeated 2537 times under the following conditions: denaturation at 94 °C for 1 min, annealing at 55 °C for 45 s and extension at 72 °C for 1 min. Amplified products were then separated by electrophoresis in an agarose gel containing ethidium bromide as described elsewhere (Haraguchi et al., 1994
). We checked contamination of proviral DNA in virus inocula by PCR. No band was detected when PCR was done soon after inoculation of HTLV-I or BLV, indicating that neither proviral DNA in viral stocks nor strong stop DNA in virus stocks affected the results obtained. In addition to UV-irradiated viruses, cells were infected with serially diluted virus samples. We estimated the D10 by comparing the intensities of the PCR bands obtained with the UV-irradiated viruses with those bands obtained with diluted viruses, especially those obtained with the 1/10 dilution. That is, the intensity of each band was determined by densitometry and plotted on a semi-log graph and D10 values were determined using these graphs. D10 values determined using different PCR primers for a virus are expected to be dependent on the target size of UV irradiation. There should be an inverse proportional relationship between the D10 values and the target sizes of the virus genome examined, if the virus genome is homogeneously sensitive to UV. That is, the formula, D10xtarget size (bp)=constant is expected to be pertinent to UV-inactivation of each virus. Expected data are shown using dotted lines in Figs 4 and 6
.
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H-R-N, 5'-CGTCCGCCGTCTAGGTAAGTT-3'; H-U5-R, 5'-TGTGTTCTATGTTTCTCTCC-3'; H-gag-N, 5'-GGAGCCTTACCACACCTTCG-3'; H-gag-R, 5'-AGGCTGGACGACTAACACCTT-3'; H-pX1-N, 5'-CCACCCAGAGAACCTCTAAA-3'; H-pX2-N, 5'-TTGCATCTCCCCTTCGAAGA-3'; H-pX-R, 5'-GGGTGTACAGGTTTTGGGGC-3'; H-U3L-N, 5'-TGATACTGACTATGGGCC-3'; H-U3R-N, 5'-AGCGTGGAGACAGTTCAGGA-3'; B-R-N, 5'-CTTCTCCTGAGACCCTCGTG-3'; B-U5-R, 5'-TGTTTGCCGGTCTCTCCTGG-3'; B-gag-N, 5'-AACGGGTACCCTAACCCAACAA-3'; B-gag-R, 5'-GGGTTCCTTAGGACTCCGTC-3'; B-pX1-N, 5'-GGGATCCATTACCTGATAA-3'; B-pX2-N, 5'-TTCCCCGGGACTCCAATGAA-3' and B-pX-R, 5'-TGGGTCTCGCAGGTGAGCGT-3'. The first H and B mean HTLV-I and BLV and the last N and R mean sense and antisense, respectively. The primer locations in the HTLV-I and BLV genomes are shown in Figs 3(a) and 5(a).
Construction of chimeric MoMuLVs.
We constructed chimeric MoMuLVs that contain HTLV-I and BLV sequences as follows: fragments of HTLV-I or BLV were inserted into a MoMuLV genome vector containing the green fluorescent protein (GFP) gene after the pol region, pMX-GFP. When cells were infected with MoMuLVs containing the gene for GFP near the 3' end of their genomes, GFP was expressed in the cells. That is, DNA fragments containing the pX(PPT)-U5 regions, i.e. from the polypurine tract (PPT) to U5 (823 bp) of HTLV-I and BLV, were obtained by PCR using the primer pairs H-pX2-N and H-U5-R, and B-pX2-N and B-U5-R, respectively. The fragments were cloned into the NotI site of the expression plasmid pMX-GFP to obtain the plasmids pMX-GFP-HTLV-I and pMX-GFP-BLV. They were transfected into Phoenix-E packaging cells for the production of recombinant ecotropic MoMuLVs and recombinant viruses were harvested. Recombinant viruses were irradiated with UV light as described above and N4R human cells expressing ecotropic MoMuLV receptors were infected with these viruses to detect GFP-expressing cells by flow cytometry (Cyto Ace-100).
UV sensitivities of chimeric pX(PPT)-U5 MoMuLVs.
N4R cells were seeded at 2·5x104 cells ml1. The next day, cells were infected with chimeric viruses in the presence of polybrene. Cells were incubated for 4 days and detached with trypsin and the infection level was determined by flow cytometry. About 30 % of cells were judged to be positive for GFP after infection of the non-irradiated chimeric viruses.
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RESULTS |
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The number of plaques began to decrease at 2·3 J m2 and almost completely inactivated at 14 J m2. The D10 of VSV was estimated to be about 6 J m2 (Fig. 1b).
UV sensitivity of cells
HTLV-I and VSV were so UV-sensitive that we examined the UV sensitivity of the cells as a control. 8C cells were seeded and were irradiated the following day with UV light. After 7 days, we counted viable cell colonies and determined the D10 for colony formation of the cells. Colony formation of the 8C cells was completely inhibited at 6 J m2 and the D10 of the 8C cells was about 3 J m2 (data not shown). We also used 8C/Tax1 or HeLa cells for this assay and obtained similar results: their D10 values were about 35 J m2. Since these data were similar to those previously reported in normal lymphocytes and chronic lymphoid leukaemia lymphocytes (Bogdanov et al., 1997), we considered our determination of UV dose to be accurate.
Viral DNA formation after infection of cells with UV-irradiated viruses
We examined whether the difference in UV sensitivity between HTLV-I and BLV could be detected shortly after infection, i.e. at the stage of reverse transcription. 8C cells were infected with HTLV-IMEL5 or BLV irradiated with UV and cell lysates were made 24 h later and examined for the formation of viral DNA by using PCR and gag primers (Fig. 3a, b) that were located in the region about 7·5 kb from the start of reverse transcription. In addition to UV-irradiated viruses, serially diluted virus samples were also used to infect the cells to determine quantitatively the D10 by PCR: representative results are shown in Fig. 3(cf). Fig. 3(cd) shows the effect of virus dilution on the PCR assay, and Fig. 3(ef) shows the result of infection with irradiated viruses. The D10 values of the two viruses were estimated by comparing the intensities of the PCR bands obtained with the UV-irradiated viruses with those of the bands obtained with 1/10 diluted viruses (Fig. 3g, h
). The D10 values of HTLV-IMEL5 and BLV were estimated to be 25 and 135 J m2, respectively. These data are similar to those determined with the infectivity assays (Fig. 1a
). These findings revealed that the marked difference in UV sensitivity between HTLV-I and BLV was already detected at the reverse transcription step in which the negative strands of the virus genome are found.
We then used several PCR primer pairs located in different regions of the virus genome (Fig. 3a) and examined at which stage of reverse transcription a difference in D10 was initially detected. We plotted the D10 values determined by PCR using the tax1 and gag regions of the PCR primers on a semi-log graph (Fig. 4
). The difference in UV sensitivity between HTLV-I and BLV was even detected using PCR primers located in the R-U5 region (Table 1
). The curve for BLV declined gradually as reverse transcription proceeded, while that for HTLV-I declined steeply from the tax1 gene to the gag gene and to the end of reverse transcription of the viral RNA (Fig. 4
). As for HTLV-I, we noticed that there seemed to be an inverse relationship between D10 and the distance of the region examined from the start of reverse transcription, as shown by the dotted line in Fig. 4
.
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UV sensitivity of the pX(PPT)-U5 region of HTLV-I and BLV
Since a marked difference in the UV sensitivity of HTLV-I and BLV was apparent during reverse transcription of the U5-tax1 region (Figs 4 and 6), we investigated whether the difference in UV sensitivity between the HTLV-I and BLV genomes was due to differences in their RNA sequences in this region. Therefore, we constructed chimeric MoMuLVs (MoMuLV GFP-HTLV-I and MoMuLV GFP-BLV) by inserting an 823 bp sequence of HTLV-I or BLV, pX(PPT)-U5, into pMX-GFP to produce MoMuLV GFP chimeric viruses. In these viruses, most of the MoMuLV genome RNA would be reverse transcribed after HTLV-I and BLV pX(PPT)-U5 RNA.
Recombinant viruses were irradiated with UV and inoculated into N4R cells. Fluorescent cells were detected by flow cytometry 4 days after infection. The proportions of GFP-positive N4R cells infected with non-irradiated MoMuLV GFP, MoMuLV GFP-HTLV-I and MoMuLV GFP-BLV were 35, 23 and 20 %, respectively. Next, each virus was irradiated at 20, 100 and 500 J m2 and used to infect N4R cells. The proportions of GFP-positive N4R cells were, 26, 17 and 0·9 % for MoMuLV GFP, 19, 13 and 1·0 % for MoMuLV GFP-HTLV-I and 16, 9 and 0·6 % for MoMuLV GFP-BLV, respectively, indicating that the three viruses were similarly inactivated in proportion to the irradiation dose. The D10 values of these three viruses were calculated to be about 420 J m2 and were similar to the reported D10 of MoMuLV, 370 J m2, determined by an infectivity assay (Guillemain et al., 1981). We concluded that no special UV-sensitive sequence was present in the 823 bp of the pX (PPT)-U5 regions of HTLV-I and BLV.
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DISCUSSION |
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There seems to have been no report describing the effect of UV irradiation on several phases of the progression of reverse transcription. Under our assay conditions for PCR, PCR bands would be detected once a negative-strand DNA is formed by reverse transcription. We showed that the D10 values determined by infectivity (syncytium formation assay) and viral DNA formation (PCR that will detect negative-strand DNA formation using the gag PCR primer pair) were similar (Table 1). This finding suggests that retroviruses are inactivated by UV because their negative-strand DNA is not completely synthesized.
As a target, putative UV-sensitive viral structures have already been mentioned in the literature. Lovinger et al. (1975) examined the UV sensitivity of reverse transcriptase and concluded that at least 510 % of the loss of infectivity in irradiated retrovirus preparations may be due to viral polymerase inactivation. Owada et al. (1976)
examined the UV inactivation of avian sarcoma virus and concluded that inactivation is caused not only by RNA damage but also damage in RNAprotein linkage as well as polymerase inactivation. Henderson et al. (1992)
studied HIV-1 and stated that the formation of dimers (uracil dimers) after UV-irradiation alone is not effective for virus inactivation, because reverse transcriptase has the ability to read through the damaged bases. The nucleotide, including the linear sequence as well as its secondary or tertiary structures, has been supposed to be a major target for UV inactivation. However, reports on RNA photobiology are very limited. It has been supposed that the formation of pyrimidine hydrates and cyclobutadipyrimidines is important in the UV inactivation of RNA viruses, as it is for DNA viruses (Murphy & Gordon, 1981
).
There has not been an easy assay to quantify the infectivity of cell-free HTLV-I therefore, we used a new method that we established recently, where we could detect the formation of syncytia 1 week after infection of Tax-1-expressing 8C cells by cell-free HTLV-I. The D10 values of two cosmopolitan (Japanese) strains, 2M and MT-2, and one Melanesian strain, MEL-5, of HTLV-I were about 20 J m2 by this method. The D10 of VSV determined using a plaque formation assay was 6 J m2. Thus, HTLV-I was still more UV-resistant than VSV.
We thought of the possibility that, if an irradiated virus infects cells, which harbour part of the viral gene, the D10 obtained would be higher than the actual value. If so, we would not be able to determine an accurate D10 when we used target cells that have previously been transfected with a viral gene. Therefore, if we use 8C/Tax1 cells that contain the tax1 gene, the D10 of HTLV-I would be observed to be higher than the real D10 determined using cells without the tax1 gene. However, the D10 of HTLV-I in our experiments was still very low. Since the UV sensitivity determined by PCR using 8C cells not transfected with the tax1 gene (Figs 36) was similar to that determined by the infectivity assay using 8C/Tax1 cells, we concluded that the transfection of target cells by the tax1 gene did not greatly influence the results of UV inactivation of HTLV-I.
As shown in Figs 4 and 6, the difference in UV sensitivity between HTLV-I and BLV was already observed at a very early stage of reverse transcription or before formation of the strong-stop DNA. Thus, this stage of the reverse transcription of HTLV-I RNA was already very sensitive to UV. We constructed chimeric MoMuLVs that contained 823 bp fragments of the HTLV-I or BLV origins and tested their UV sensitivities. We could hardly detect any difference in UV sensitivity between the two chimeric MoMuLVs. This result suggests that the primary RNA sequence itself is not a determinant of the high UV sensitivity of HTLV-I.
It is expected that there will be an inverse relationship between the UV target size of RNA or DNA and the corresponding D10 when the UV target is homogeneously sensitive to damage induced by UV irradiation: (value of D10)x(target genome size)=constant. We examined whether this was true for HTLV-I and BLV. The D10 values determined by infectivity assays of HTLV-I and BLV were about 17 and 180 J m2, respectively (Fig. 1a; Table 1
); the target sizes of UV irradiation are about 8·5 kb. Thus, D10 values for the UV target size of 300 bp are calculated to be about 480 and 5100 J m2 for HTLV-I and BLV, respectively, whereas the experimental values were 370 and 480 J m2, respectively (Table 1
). For HTLV-I, there was a good correlation between experimentally obtained values and calculated values while, for BLV, there was an apparent discrepancy, as shown in Figs 4 and 6
. This finding suggests that HTLV-I is susceptible to UV damage according to its target RNA size, while UV-irradiated BLV genomes may not be damaged proportionally to their genome sizes.
Several possibilities to explain the difference in UV sensitivity between HTLV-I and BLV can be suggested: (i) the genomic RNA sequence of HTLV-I contains more UV-sensitive sequences, for example pyrimidine dimers, than that of BLV, (ii) the abilities of the reverse transcriptases of HTLV-I and BLV to read through UV-damaged lesions are different, (iii) the first-strand transfer (jump) step of HTLV-I is especially vulnerable to UV irradiation, (iv) the virion structures of HTLV-I and BLV are different, especially the nucleocapsid (NC) and RNA complex structures or (v) recombination between RNA genomes in virions takes place much more readily during reverse transcription of BLV than of HTLV-I.
The first possibility seems unlikely, as we showed that chimeric MoMuLVs harbouring the HTLV-I and BLV tax1-LTR regions of 823 bp were similarly resistant to UV irradiation. Their D10 values were about 420 J m2, similar to that of the parental MoMuLV strain, suggesting that a factor(s) other than linear RNA sequence may be responsible for the difference in UV sensitivity. Even in the case of RNA, pyrimidine dimers have been thought to be a major target of UV irradiation (Murphy & Gordon, 1981). Therefore, we counted the pyrimidine dimers in HTLV-I and BLV as well as MoMuLV, and found that HTLV-I and BLV had quite similar patterns of pyrimidine dimer constitution (data not shown).
The second possibility also seems unlikely because UV-irradiated VSV RNA similarly functioned as a template to make cDNA using reverse transcriptase of either HTLV-I or BLV (data not shown). Figs 4 and 6 showed that the first-strand transfer (jump) step did not markedly affect the reverse transcription efficiency of HTLV-I and BLV.
A recent report by Morcock et al. (2002) suggested that the fourth possibility cannot be ruled out. Morcock et al. (2002)
examined the affinity of NC proteins of retroviruses for their RNA: an NC protein of HTLV-I, p15, is more than 100-fold more loosely associated with HTLV-I RNA than NC proteins of other retroviruses, for example BLV, HIV-1 or simian immunodeficiency virus. Namely, there is a possibility that reverse transcriptase can read through UV-damaged viral RNA more readily if viral RNA is tightly associated with NC protein. Another possibility may be that RNA tightly associated with NC protein is less vulnerable to UV irradiation than that loosely associated with NC protein, like HTLV-I RNA. The D10 of BLV was still smaller than that of HIV-1, as reported by others (Yoshikura, 1989
) and according to the report by Morcock et al. (2002)
. NC protein of BLV is still less tightly associated with viral RNA than that of HIV-1. These findings seems to favour the fourth possibility.
Lastly, the recombination of virus genomes during reverse transcription could partly explain the results obtained for BLV. Retroviruses contain two equivalent RNA genomes in their virions. It has been reported that chimeric viruses are readily made in retroviruses when cells are infected with different types of virus (Telesnitsky & Goff, 1997). If recombination between two virus genomes in the same virions takes place during reverse transcription, UV-damaged lesions in one RNA strand may be rescued by the other intact strand. Even if this is the case, HTLV-I should lack this recombination ability, since its UV sensitivity can be explained by its target genome size, as shown in Figs 4 and 6
. In contrast, other retroviruses, including BLV, may have this activity.
We showed that, among the retroviruses examined so far, HTLV-I had the most UV-sensitive infectivity and that the reverse transcription of all the regions of the HTLV-I genome was similarly sensitive to UV irradiation, whereas there was a discrepancy between the UV target size of the BLV genome and its sensitivity to UV irradiation. The mechanisms underlying these observations remain to be investigated further. Our findings may be helpful to solve an old question: why are retroviruses so resistant to UV irradiation?
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ACKNOWLEDGEMENTS |
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REFERENCES |
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Bogdanov, K. V., Chukhlovin, A. B., Zaritskey, A. Y., Frolova, O. I. & Afanasiev, B. V. (1997). Ultraviolet irradiation induces multiple DNA double-strand breaks and apoptosis in normal granulocytes and chronic myeloid leukemia blasts. Br J Haematol 98, 869872.[CrossRef][Medline]
Clapham, P., Nagy, K. & Weiss, R. A. (1984). Pseudotypes of human T-cell leukemia virus types 1 and 2: neutralization by patients' sera. Proc Natl Acad Sci U S A 81, 28862889.[Abstract]
Fan, N., Gavalchin, J., Paul, B., Wells, K. H., Lane, M. J. & Poiesz, B. J. (1992). Infection of peripheral blood mononuclear cells and cell lines by cell-free human T-cell lymphoma/leukemia virus type I. J Clin Microbiol 30, 905910.[Abstract]
Fischinger, P. J., Peebles, P. T., Nomura, S. & Haapala, D. K. (1973). Isolation of RD-114-like oncornavirus from a cat cell line. J Virol 11, 978985.[Medline]
Gessain, A., Barin, F., Vernant, J. C., Gout, O., Maurs, L., Calender, A. & de The, G. (1985). Antibodies to human T-lymphotropic virus type-I in patients with tropical spastic paraparesis. Lancet 24, 407410.
Guillemain, B., Mamoun, R., Astier, T. & Duplan, J. F. (1981). Mechanism of early and late polykaryocytosis induced by the bovine leukaemia virus. J Gen Virol 57, 227231.[Abstract]
Haapala, D. K., Robey, W. G., Oroszlan, S. D. & Tsai, W. P. (1985). Isolation from cats of an endogenous type C virus with a novel envelope glycoprotein. J Virol 53, 827833.[Medline]
Haraguchi, Y., Yang, D. W., Handa, A., Shimizu, N., Tanaka, Y. & Hoshino, H. (1994). Detection of neutralizing antibodies against human T-cell leukemia virus type 1 using a cell-free infection system and polymerase chain reaction. Int J Cancer 59, 416421.[Medline]
Henderson, E. E., Tudor, G. & Yang, J. Y. (1992). Inactivation of the human immunodeficiency virus type 1 (HIV-1) by ultraviolet and X irradiation. Radiat Res 131, 169176.[Medline]
Hinuma, Y., Nagata, K., Nanaoka, M., Nakai, M., Matsumoto, T., Kinoshita, K. I., Shirakawa, S. & Miyoshi, I. (1981). Adult T-cell leukemia: antigen in an ATL cell line and detection of antibodies to the antigen in human sera. Proc Natl Acad Sci U S A 78, 64766480.[Abstract]
Hoshino, H., Shimoyama, M., Miwa, M. & Sugimura, T. (1983). Detection of lymphocytes producing a human retrovirus associated with adult T-cell leukemia by syncytia induction assay. Proc Natl Acad Sci U S A 80, 73377341.[Abstract]
Hoshino, H., Clapham, P. R., Weiss, R. A., Miyoshi, I., Yoshida, M. & Miwa, M. (1985). Human T-cell leukemia virus type I: pseudotype neutralization of Japanese and American isolates with human and rabbit sera. Int J Cancer 36, 671675.[Medline]
Hoshino, H., Nakamura, T., Tanaka, Y., Miyoshi, I. & Yanagihara, R. (1993). Functional conservation of the neutralizing domains on the external envelope glycoprotein of cosmopolitan and melanesian strains of human T-cell leukemia/lymphoma virus type I. J Infect Dis 168, 13681373.[Medline]
Jacobson, S., Raine, C. S., Mingioli, E. S. & McFarlin, D. E. (1988). Isolation of an HTLV-1-like retrovirus from patients with tropical spastic paraparesis. Nature 331, 540543.[CrossRef][Medline]
Levinson, W. & Rubin, H. (1966). Radiation studies of avian tumor viruses and of Newcastle disease virus. Virology 28, 533542.[CrossRef][Medline]
Lovinger, G. G., Ling, H. P., Gilden, R. V. & Hatanaka, M. (1975). Effect of UV light on RNA-directed DNA polymerase activity of murine oncornaviruses. J Virol 15, 12731275.
Miyoshi, I., Kubonishi, I., Yoshimoto, S., Akagi, T., Ohtsuki, Y., Shiraishi, Y., Nagata, K. & Hinuma, Y. (1981). Type C virus particles in a cord T-cell line derived by co-cultivating normal human cord leukocytes and human leukaemic T cells. Nature 294, 770771.[Medline]
Miyoshi, I., Yoshimoto, S., Taguchi, H., Kubonishi, I., Fujishita, M., Ohtsuki, Y., Shiraishi, Y. & Akagi, T. (1983). Transformation of rabbit lymphocytes with T-cell leukemia virus. Gann 74, 14.[Medline]
Morcock, D. R., Katakam, S., Kane, B. P. & Casas-Finet, J. R. (2002). Fluorescence and nucleic acid binding properties of bovine leukemia virus nucleocapsid protein. Biophys Chem 97, 203212.[CrossRef][Medline]
Murphy, T. M. & Gordon, M. P. (1981). Photobiology of RNA viruses. In Comprehensive Virology, Methods Used in the Study of Viruses, vol. 17, pp. 285349. Edited by H. Fraenkel-Conrat & R. Wangeer. New York: Plenum.
Nagy, K., Clapham, P., Cheingsong-Popov, R. & Weiss, R. A. (1983). Human T-cell leukemia virus type I: induction by syncytia and inhibition by patients' sera. Int J Cancer 32, 321328.[Medline]
Osame, M., Usuku, K., Izumo, S., Ijuchi, N., Amitani, H., Igata, A., Matsumoto, M. & Tara, M. (1986). HTLV-I associated myelopathy, a new clinical entity. Lancet 3, 10311032.
Owada, M., Ihara, S., Toyoshima, K., Sugino, Y. & Kozai, Y. (1976). Ultraviolet inactivation of avian sarcoma viruses: biological and biochemical analysis. Virology 69, 710718.[CrossRef][Medline]
Poiesz, B. J., Ruscetti, F. W., Gazdar, A. F., Bunn, P. A., Minna, J. D. & Gallo, R. C. (1980). Detection and isolation of type C retrovirus particles from fresh and cultured lymphocytes of a patient with cutaneous T-cell lymphoma. Proc Natl Acad Sci U S A 77, 74157419.[Abstract]
Sagata, N., Yasunaga, T., Ogawa, Y., Tsuzuku-Kawamura, J. & Ikawa, Y. (1984). Bovine leukemia virus: unique structural features of its long terminal repeats and its evolutionary relationship to human T-cell leukemia virus. Proc Natl Acad Sci U S A 81, 47414745.[Abstract]
Soda, Y., Shimizu, N., Jinno, A., Liu, H. Y., Kanbe, K., Kitamura, T. & Hoshino, H. (1999). Establishment of a new system for determination of coreceptor usages of HIV based on the human glioma NP-2 cell line. Biochem Biophys Res Commun 258, 313321.[CrossRef][Medline]
Telesnitsky, A. & Goff, S. P. (1997). Reverse transcriptase and the generation of retroviral DNA. In Retroviruses, pp. 144145. Edited by J. M. Coffin, S. H. Hughes & H. E. Varmus. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory.
Van der Maaten, M. J. & Miller, J. M. (1975). Replication of bovine leukemia virus in monolayer cell cultures. Bibl Haematol 43, 360362.[Medline]
Yanagihara, R., Nerukar, V. R. & Ajdukiewicz, A. B. (1991). Comparison between strains of human T lymphotropic virus type I isolated from inhabitants of the Solomon Islands and Papua New Guinea. J Infect Dis 164, 443449.[Medline]
Yoshikura, H. (1989). Thermostability of human immunodeficiency virus (HIV-1) in a liquid matrix is far higher than that of an ecotropic murine leukemia virus. Jpn J Cancer Res 80, 15.[Medline]
Received 18 August 2003;
accepted 30 March 2004.
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