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Unité des Virus Lents (Unité de Recherche Associée 1930, Centre National de la Recherche Scientifique), Institut Pasteur, Paris, France
| Abstract |
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, IL-2, IL-10, and IL-12 in the brains of
SJL/J mice, B10.S mice, and the two lines of congenic mice during the
first 2 wk following inoculation. We found a greater expression of
IFN-
and IL-2 mRNA in the brains of B10.S mice compared with those
of SJL/J mice. Also, the ratio of IL-12 to IL-10 mRNA levels was higher
in B10.S mice. However, the cytokine profiles were the same for the two
lines of resistant congenic mice and for susceptible SJL/J mice.
Therefore, the difference of Th1/Th2 balance between the B10.S and
SJL/J mice is not due to the Ifng locus and does not
account for the difference of susceptibility of these mice to
persistent infection. | Introduction |
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has a major role in limiting viral
persistence and the demyelinating disease, as shown by studying mice
that lack the IFN-
R (IFN-
Ro/o) (6) or by treating
mice with a neutralizing anti-IFN-
Ab (7, 8). These results and
the fact that, according to the current view, IFN-
plays a central
role in Th1/Th2 balance and in the outcome of murine infections in
general (9, 10, 11), made the Ifng gene a good candidate gene
for the control of Theilers virus persistence. In the present work,
we studied the Ifng gene and the cytokine profiles of SJL/J
and B10.S mice following inoculation with Theilers virus. We also
used congenic mice to confirm the presence of a susceptibility gene in
the Ifng region and to test the role of the Ifng
gene and Th1/Th2 balance in the difference of susceptibility between
the SJL/J and B10.S strains. | Materials and Methods |
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SJL/J mice were purchased from Janvier (Saint-Berthevin,
France); and B10.S-H2S/Sg McdJ mice were obtained from The Jackson
Laboratory (Bar Harbor, ME). Two lines of congenic mice, named
SJL.10(70/14) and SJL.10(233/237), were obtained after 10 successive
backcrosses of an (SJL/J x B10.S)F1 toward the SJL/J
parent followed by brother/sister mating. These mice were selected
because they have the B10.S allelic form of the D10 Mit70
and D10 Mit14 markers (line SJL.10(70/14)) or the D10
Mit233 and D10 Mit237 markers (line SJL.10(233/237))
(Fig. 4
). The sequence of these markers is available at
http://www.genome.wi.mit.edu/cgi-bin/mouse/index. A detailed
description of these lines will be given elsewhere (F.B., unpublished
observations). Mice of 34 wk of age were inoculated intracranially
with 104 PFU of the DA strain of Theilers virus in 40
µl of PBS buffer.
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A 3-kb fragment containing the promoter of the Ifng
gene (GenBank accession number M28381) was amplified by PCR from the
genomic DNA of SJL/J and B10.S mice. The DNA fragments were subcloned
in the Bluescript KS vector (Stratagene, Cambridge, U.K.) and sequenced
using the Sequenase kit (Amersham, Arlington Heights, IL). Two
polymorphisms were detected between the two mouse strains: a mutation
in an SphI restriction enzyme site of the SJL/J genome
(GCATGC
ACATGC) and a 16-bp deletion, which we named
D10Pas4, just upstream of the TATA box (see
Results). The following PCR primers were designed to study
D10Pas4: 5'-GAATCCCACAAGAATGGCACAG-3' and
5'-CGAAGGCTCCTCGGGATTA-3'. PCR reactions with these primers were
conducted under standard conditions with buffer (1.5 mM
Mg2+) and Taq DNA polymerase from Life
Technologies (Eragny, France) (at 94°C for 2 min, followed by 40
cycles of 94°C for 40 s, 55°C for 40 s, 72°C for
15 s). Amplified DNA was analyzed in 5% agarose gels.
Microsatellite allele sizes in inbred strains and subspecies were as
follows:
206 bp for strains 129/Sv, A/J, BALB/cByJIco, B10.S,
C3H/HeOuJIco, C57BL/6JIco, C57BR, CB20, CBA/JIco, DBA/2JIco, DDK, DW,
FVB/NPas, MAI, MBT, PL/J, PWK/Pas, and SEG;
190 bp for the MOLD,
SJL/JIco, SPR, and STF strains.
The published sequence of the mouse IFN-
cDNA (12) was used to
prepare a specific RT-PCR probe. BAC 232G19 from Research Genetics
(Huntsville, AL) was digested with EcoRI restriction enzyme
and hybridized with the probe. The fragments that hybridized were
cloned in the Bluescript vector and used to sequence the exon/intron
junctions using primers designed from the published cDNA sequence. The
exons of the SJL/J and B10.S strains were amplified from genomic DNA
using primers designed from the exon/intron junction sequences. They
were cloned with the TOPO TA cloning kit (Invitrogen, San Diego, CA)
and sequenced with the Sequenase kit. The following primers were used
for genomic DNA amplification: For exons 1 and 2,
5'-AAGTTCTGGGCTTCTCCTCC-3' and 5'-CATGTCACCATCCTTGGGAA-3'; for exon 3,
5'-TCCCTGTTGTTTCTAATGGG-3' and 5'-CACCTCCTAGCTTTATCAGC-3'; for exon
4, 5'-GATTTCCATCTTCACTGACC-3' and 5'-TGGGACAATCTCTTCCCCAC-3'.
Quantification of viral RNA in CNS
The assay has been described in detail previously (13). Briefly, total RNA was extracted from the spinal cord. Five-fold dilutions of the RNA solutions were dotted on Hybond-C extra filters (Amersham). The filters were hybridized with a virus-specific 32P-labeled cDNA probe, washed, and exposed overnight against x-ray-sensitive films. In some experiments, the amount of viral RNA was measured by RT-PCR as described for cytokines (see below).
Detection of cytokine mRNA by RT-PCR
The method is similar to that described by Monteyne et al. (14).
Brain tissue and cultured cells were lysed in TRIzol reagent (Life
Technologies). The mixture was extracted with chloroform, and the RNA
was precipitated with isopropanol, washed in ethanol, and finally
resuspended in 50 µl of water. Randomly primed cDNA was prepared from
5 µg of RNA using 200 U of Moloney murine leukemia virus reverse
transcriptase (Life Technologies) according to the manufacturers
instructions. cDNA was amplified by PCR with a Gene Amp kit (Life
Technologies) in a 9600 reactor (Perkin-Elmer Cetus, Norwalk, CT), with
40 cycles for cytokines and 25 cycles for actin and Theilers virus
mRNA. Using these numbers of cycles avoided reaching saturation. The
primers used for the PCR reaction were as follows: IL-2,
5'-GTCCTGCAGGCATGTACAGC-3' and 5'-AGGGCTTGTTGAGATGATGC-3'; IL-10,
5'-CCCAGAAATCAAGGAGCATTTG-3' and 5'-CATGTATGCTTCTATGCAGTTG-3';
IL-12, 5'-CAACGTTGCATCCTAGGATCG-3' and 5'-GCACATCAGACCAGG-3'; IFN-
,
5'-GACAATCAGGCCATCAGCAAC-3' and 5'-CGCAATCACAGTCTTGGCTAA-3';
actin, 5'-ATGGATGACGATATCGCTGC-3' and 5'-GCTGGAAGGTGGACAGTGAG-3';
Theilers virus, 5'-TCTAGATCTAGACTATTCAAGTTCGAGAATGGGGA-3' and
5'-GAATTCGAATTCGAATTCGCCACCATGGGAACGGACAACGCCGAA-3'. The size
of the amplified fragment was 500 bp, 250 bp, 1060 bp, 500 bp, 1060 bp,
and 800 bp for, respectively, IL-2, IL-10, IL-12, IFN-
, actin, and
Theilers virus. The integrity of the RNA and the efficacy of reverse
transcription were assessed by amplifying the actin cDNA with 25 PCR
cycles.
The PCR products were analyzed in 1% agarose gels containing ethidium
bromide, transferred to Hybond-N+ filters (Amersham), and
hybridized overnight at 65°C with internal probes labeled with
32P. The intensity of each hybrid band was quantitated with
a PhosphorImager (Molecular Dynamics, Sunnyvale, CA) under conditions
for which intensity is proportional to the amount of radioactivity. The
ratios between cytokine (or virus) and actin RNA levels were calculated
after subtraction of nonspecific background. The sequences of the
internal probes were as follows: IL-2, 5'-CCTGAGCAGGATGGAGAATT-3';
IL-10, 5'-GCTGGAAGACCAAGGTGTCTACAAGGC-3'; IL-12,
5'-TGGAATGGCGTCTCTGTCTGC-3'; IFN-
, 5'-TCGCCTTGCTGTTGCTGA-3';
actin, 5'-CGTACCACAGGCATTGTGATGG-3'; Theilers virus,
5'-CCTATTACAAGTGTGACCTTGA-3'. Each experimental point shown in
Results corresponds to the mean value obtained with at least
three mice. The cytokine mRNA/actin mRNA ratio varies from experiment
to experiment due to small variations of efficiency of PCR
amplification, membrane blotting, and hybridization as well as to
variations of the specific activity of the probe. Therefore, only
ratios obtained in the same experiment can be compared.
In vitro stimulation of spleen cells and lymphocyte proliferation assay
Fresh spleen cells from SJL/J, B10.S, or congenic mice, cultured in RPMI 1640 medium (Life Technologies) supplemented with 10% FCS, were stimulated with 5% of a cell supernatant containing the 145-2C11 anti-CD3 Ab (a gift of O. Leo, Université Libre de Bruxelles, Rhode Saint-Genèse, Belgium). For cytokine mRNA detection, RNA was extracted from 107 cells after 24 h of culture. For the proliferation assay, [3H]thymidine (0.5 mCi/well) was added to the cultures (2.5 105 cells/well) for the last 6 h of a 72-h incubation period.
| Results and Discussion |
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Because the Ifng gene was a good candidate to explain
the difference of susceptibility of the SJL/J and B10.S strains, we
cloned and sequenced the gene from both strains. There were no
differences in the coding part of the gene (data not shown). However,
we found a 16-bp deletion, which we called D10Pas4, in
the Ifng promoter of the SJL/J mouse (Fig. 1
). We screened a large number of inbred
mouse strains and found the deletion in strains MOLD, SPR, and STF but
not in strains 129/Sv, A/J, B10.S, BALB/cByJIco, C3H/HeOuJIco,
C57BL/6JIco, C57BR, CB20, CBA/JIco, DBA/2JIco, DDK, DW, FVB/NPas, MAI,
MBT, PL/J, PWK/Pas, and SEG.
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by glucocorticoids
(16). The deletion decreases the distance between the two elements by
one and and half helix turns and changes their spatial orientation.
Because this could affect the activity of the promoter (17, 18), we
measured the level of IFN-
mRNA in the brains of SJL/J and B10.S
mice during the first week after inoculation, a time period during
which both strains are infected at similar levels. Because the level of
viral RNA starts to decline in resistant mice around day 7
postinoculation, we assume that biochemical events leading to clearance
would be operating during the first week. We observed a peak of IFN-
mRNA expression at day 6 postinoculation in the case of the B10.S
mouse. In contrast, the level of IFN-
mRNA reached a plateau at day
5 postinoculation in the SJL/J mouse (Fig. 2
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Two lines of congenic mice, named SJL.10(70/14) and
SJL.10(233/237), were obtained as described in Materials and
Methods. They possess the Ifng gene and varying amounts
of the surrounding region of the B10.S parent on an SJL/J background
(Fig. 4
) (F.B., unpublished
observations). Both lines were significantly more resistant to
persistent infection than the SJL/J parent (Fig. 4
), which demonstrates
the existence of a susceptibility locus in the Ifng region.
Fig. 4
also shows that this region accounts for 80% of the difference
of susceptibility between the SJL/J and B10.S strains. Because
Ifng is the only locus for which there is a significant
linkage with susceptibility in a (SJL/J x B10.S)F1 x
B10.S backcross (5), it is unlikely that the rest of the susceptibility
is due to a single locus. Rather, it probably involves several genes
and/or interactions between genes.
To determine whether a locus in the Ifng region is
responsible for the difference of Th1/Th2 balance described above for
the SJL/J and B10.S strains, we examined the levels of IFN-
, IL-2,
IL-10, and IL-12 mRNA in the brains of SJL/J mice and of the two lines
of resistant congenic mice during the first week postinoculation. As
shown in Fig. 5
, the levels of IFN-
and IL-2 mRNA and the ratio of IL-12 to IL-10 mRNA were the same for
the SJL/J and SJL.10(70/14) mice. The same result was obtained
with SJL.10(233/237) congenic mice (data not shown). Therefore, the
Ifng region is not responsible for the difference of Th1/Th2
balance observed between the SJL/J and B10.S strains, although it
accounts for most of the difference of susceptibility between these
strains (Fig. 4
). These results demonstrate that the Th1/Th2
balance is not the major factor in resistance/susceptibility to
persistent infection in this system.
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limits an infection and that there
is a correlation among mouse strains between Th1/Th2 responses and
resistance/susceptibility has been taken as evidence for the role of
Th1 responses in resistance. Our results illustrate how such an
assumption can be improper in the absence of direct genetic proof, such
as that provided by congenic animals.
IFN-
Ro/o animals (6) and treatment of resistant mice
with an anti-IFN-
Ab (7) showed that IFN-
restricts
Theilers virus expression during persistent infection. This finding
is not in contradiction with the results reported here. In the present
case, the effect of IFN-
on late disease is the same for the SJL/J
and the B10.S strains. Knockout mice and immunological manipulations
such as treatments with neutralizing mAbs uncover genes and biochemical
pathways with essential roles in pathogenesis but which are not
necessarily responsible for differences of susceptibility between
strains.
T cell proliferation and IL-2 production after in vitro stimulation
The proliferative response of T lymphocytes after stimulation with
anti-CD3 mAbs is controlled by a gene that has been mapped to the
region containing the D10Mit14 marker (19). To examine
whether this gene was involved in the control of the persistence of
Theilers virus, we compared the proliferative response of T cells
from the SJL/J, B10.S, SJL.10(70/14), and SJL.10(233/237) strains. As
shown in Fig. 6
, T cells from B10.S mice
proliferated more and secreted more IL-2 than T cells from the SJL/J or
SJL.10(233/237) strains; there were no differences when comparing T
cell proliferation and IL-2 mRNA expression for the SJL/J and
SJL.10(233/237) mice. The same result was obtained with the
SJL.10(70/14) congenic strain (data not shown). Therefore, the gene
that controls the T cell-proliferative response is not in the
Ifng region and must be different from that which controls
the susceptibility to Theilers virus persistent infection.
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| Footnotes |
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2 Current address: SmithKline Beecham Biologicals, 89 Rue de lInstitut, 1330 Rixensart, Belgium. ![]()
3 Address correspondence and reprint requests to Dr. Michel Brahic, Unité des Virus Lents (Unité de Recherche Associée 1930, Centre National de la Recherche Scientifique), Institut Pasteur, 75724 Paris Cedex 15, France. E-mail address: ![]()
Received for publication October 28, 1998. Accepted for publication March 23, 1999.
| References |
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interferon is critical for resistance to Theilers virus-induced demyelination. J. Virol. 69:7286.[Abstract]
results in acceleration of Theilers virus-induced demyelinating disease. J. Neuroimmunol. 55:143.[Medline]
: biology and role in pathogenesis. Adv. Immunol. 62:61.[Medline]
(MuIFN-
) cDNA and its expression in heterologous mammalian cells. J. Interferon Res. 5:511.[Medline]
promoter confer activation-specific expression in T cells. J. Exp. Med. 178:1483.
promoter by glucocorticoids and dominant negative mutants of c-Jun. J. Biol. Chem. 270:12548.This article has been cited by other articles:
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E. L. Oleszak, J. R. Chang, H. Friedman, C. D. Katsetos, and C. D. Platsoucas Theiler's Virus Infection: a Model for Multiple Sclerosis Clin. Microbiol. Rev., January 1, 2004; 17(1): 174 - 207. [Abstract] [Full Text] [PDF] |
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S. Vigneau, P.-S. Rohrlich, M. Brahic, and J.-F. Bureau Tmevpg1, a Candidate Gene for the Control of Theiler's Virus Persistence, Could Be Implicated in the Regulation of Gamma Interferon J. Virol., May 15, 2003; 77(10): 5632 - 5638. [Abstract] [Full Text] [PDF] |
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S. Aubagnac, M. Brahic, and J.-F. Bureau Bone Marrow Chimeras Reveal Non-H-2 Hematopoietic Control of Susceptibility to Theiler's Virus Persistent Infection J. Virol., May 3, 2002; 76(11): 5807 - 5812. [Abstract] [Full Text] [PDF] |
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