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Department of Molecular Microbiology and Immunology, University of Southern California/Norris Comprehensive Cancer Center, Keck School of Medicine at University of Southern California, Los Angeles, CA 90089
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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, that of CD8 cells requires Fas and not
perforin or TNF- pathways. Fas ligand is expressed on
liver-infiltrating cells, pointing to death by fratricide that causes
almost complete disappearance of virus-specific CTL 4 wk after
infection. CTL elimination is virus dose dependent, and high doses
induced high alanine aminotransferase values, elevated expression of
Fas ligand on CD8 cells, and increased CD8 cell migration into the
infected liver. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Understanding the immunoregulatory pathways by which the liver induces
unresponsiveness is of much interest, not only to facilitate successful
liver transplantation but also to overcome failure of the immune system
to successfully eliminate microbial infections. In fact, a number of
viruses, among them hepatitis B
(HBV)3 and
hepatitis C virus (HCV), are known to cause chronic infections, often
leading to liver cirrhosis and death (5, 6, 7). Therefore,
the question arises whether the failure of the liver to successfully
eliminate viral infections may in part be because of its
tolerance-inducing activity. To investigate this, use was made of a
viral infection model in which a replication-deficient adenovirus,
expressing the 
-galactosidase (lacZ) gene, is
injected into mice. This had been shown to result in massive infection
and viral gene expression in the liver, which in turn induces a strong
T cell-mediated immune response (8, 9). Here we report
that the T cell response to viral Ags, expressed in the liver, is
terminated at early times after the infection by the induction of cell
death in both CD4 and CD8 cells. Induction of cell death in CD8 cells
is shown to involve Fas, leading to elimination of CTLs able to respond
to virus-infected cells as early as 6 days after the infection. It is
concluded that the liver induces unresponsiveness to non-MHC Ags by a
clonal deletion mechanism.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Pathogen-free female C57BL/6 (H-2b) (B6), B6-pfptm1Sdz (PKO), B6.MRL-Faslpr (lpr), and B6Smn.C3H-FasLgld (gld) mice, 6–12 wk of age, were obtained from The Jackson Laboratory (Bar Harbor, ME). B6/TNFR1/R2 double-deficient (TNFR1/R2KO) mice were generated and generously provided by Dr. Chaim Jacob (Department of Medicine, University of Southern California, Keck School of Medicine, Los Angeles, CA). Bone marrow chimeras were prepared by irradiating mice 950 rad, followed by i.v. injection of 2 x 107 bone marrow cells and 5 x 107 spleen cells. Mice were used for virus infection 1 wk later. For immunization, type 5 adenovirus with deletions in the E1 and E3 region and carrying the lac Z gene was purchased from Microbix Biosystems (Toronto, Ontario, Canada). Virus was propagated in 293 cells as recommended by the supplier. Animals were primed by injection of virus into the tail vein on day 0 (10, 11). Serum ALT was assayed as described (10), with a commercial assay kit (Sigma, St. Louis, MO). For IL-2 treatment, mice were injected with 4 x 105 U recombinant mouse IL-2 (BD PharMingen, San Diego, CA) per day i.p., starting with the day of virus infection until completion of the experiment.
Preparation of liver lymphocytes and fluorometric analysis
Mononuclear cells were isolated from livers as described
previously (10, 11). Liver tissue was passed through a
200-gauge stainless steel mesh in serum-free HBSS, and mononuclear
cells were purified by Percoll gradient centrifugation. RBC contained
in the mononuclear cell preparation were lysed by ammonium chloride.
For FACS analysis, cells were stained with mAbs as described
(11). The following Abs were used: anti-mouse Fc
receptor CD16/CD32 (2.4G2), biotin anti-mouse Fas ligand (FasL;
MFL3), and PE- or FITC-conjugated anti-CD3 (145-2C11), anti-CD4
(GK1.5), anti-CD8 (53-6.7), and anti-NK1.1 (PK136), purchased
from BD PharMingen. For annexin V staining, cells were first incubated
with PE-conjugated anti-CD3, anti-CD4, and anti-CD8
followed by staining with the FITC-annexin V detection kit, according
to the manufacturer’s instructions (Roche Molecular Biochemicals,
Indianapolis, IN). The percentage of annexin V-positive cells in the
CD3+, CD4+, and
CD8+ cell populations were calculated. For FasL
staining, cells were incubated with anti-mouse Fc receptor mAb
CD16/CD32 at 4°C for 10 min, then stained with biotin-conjugated
anti-FasL at 4°C for 30 min. After washing, cells were stained at
4°C for 30 min with PE- or FITC-conjugated streptavidin and FITC- or
PE-conjugated mAb against CD3, CD4, CD8, and NK1.1. FACS analysis was
performed on a FACStarPlus (Becton Dickinson,
Mountain View, CA). The number of CD3+,
CD4+, and CD8+ cells per
liver was calculated by multiplying the measured percentage of each
subpopulation with the total number of mononuclear cells per liver.
Induction of in vitro CTL responses and enzyme-linked immunospot (ELISPOT) assays
Spleen cells were stimulated with irradiated allogeneic
stimulator cells (H-2d) or 5 PFU virus per input
cell in 2-ml Linbro plates (Becton Dickinson, Franklin Lakes, NJ) for 5
days as described (11). Target cells for cytotoxicity
assay were P815 (H-2d) or C57SV
(H-2b) infected with 50 PFU of virus per cell
then incubated for 24 h at 37°C (11). To
demonstrate that cell lysis is attributable to CTL, effector cells were
treated before assay with anti-CD8 Ab (11) and Low-Tox
complement (Accurate Chemical and Scientific, San Diego, CA). For
IFN- ELISPOT assays (11, 12), spleen cells were
restimulated in vitro with virus for 5 days and then seeded with
virus-infected C57SV cells in 96-well plates. To prepare plates, 100
µl of 10 µg/ml purified anti-IFN- (R4-6A2; BD PharMingen)
was pipetted into Multiscreen 96-well filtration plates (Millipore,
Bedford, MA) and incubated overnight at 4°C. Plates were washed three
times and a suspension of 1 x 106 C57SV
cells and 1 x 105 spleen cells in 200 µl
RPMI 1640 10% FCS was added per well and incubated for 24 h at
37°C. After washing the plates three times in PBS 0.05% Tween 20,
100 µl of a solution containing 0.05% Tween 20, 1% BSA, and 5
µg/ml biotin conjugated anti-IFN- Ab (XMG1.2; PharMingen) in
PBS was pipetted into each well and plates incubated overnight at
4°C. A total of 100 µl of a solution containing a 1/400 dilution of
1 mg/ml avidin peroxidase (Sigma) in PBS containing 0.05% Tween 20 and
1% BSA was added per well. After 2 h at room temperature, plates
were washed four times in PBS 0.05% Tween 20. Into each well, 200 µl
of ABE solution (Zymed, South San Francisco, CA) was pipetted, followed
by incubation for 15 min in the dark. After washing in double-distilled
H2O and drying, spots were counted under
microscope.
RT-PCR assays
Liver tissue was harvested and total RNA extracted by the
phenol/chloroform method by using RNAzol B kit (Tel-Test, Friendswood,
TX) (10, 11). RNA (5 µg) was reverse-transcribed to cDNA
in a 50-µl reaction mixture with Superscript II RNase
H- reverse transcriptase and random primers
(Life Technologies, Rockville, MD). For PCR, the equivalent amount of
cDNA product (5 µl) was amplified in a 50-µl reaction mixture
containing 10 mM Tris (pH 8.3), 50 mM KCl, 1.5 mM
MgCl2, 0.2 mM dNTP, 2.5 U Taq DNA
polymerase (Perkin-Elmer, Norwalk, CT), and 1 µM of each specific
primer. The amplification was performed in a Thermoline Gene E
thermocycler (Techne, Cambridge, U.K.) set at 1 min each at 94°C,
58°C, and 72°C for 35 cycles for perforin, FasL, and TNF- and 30
cycles for -actin, followed by an extension at 72°C for 7 min.
After amplification, PCR products were electrophoresed on a 2% agarose
gel and visualized by ethidium bromide staining under UV illumination.
The specific primers for -actin and TNF- were obtained from
Stratagene (La Jolla, CA). Primers for perforin and FasL were:
perforin, sense 5'-CAC AAGTTC GTG CCA GGT GTA-3', antisense 5'-GCA TGC
TCT GTG GAG CTG TTA-3' (13); FasL, sense 5'-CTG GAA TGG
GAA GAC ACA TA-3', antisense 5'-AAA GGT CTT AGA TTC CTC AA-3'
(14).
Histological procedures
To stain lacZ, livers were harvested and immediately frozen in liquid nitrogen. Frozen sections (6 µm) were fixed with 0.5% glutaraldehyde in PBS for 10 min, rinsed twice for 10 min with PBS containing 1 mM MgCl2, and incubated with X-Gal solution (1 mg/ml X-Gal, 5 mM K3Fe(CN)6, 5 mM K4Fe(CN)6, and 1 mM MgCl2 in PBS) at 37°C, 100% humidity for 4 h, then washed twice with distilled water (10, 11).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Injection of adenovirus constructs coding for the lacZ
gene (adeno lacZ) into the tail vein of mice results in
infection and viral gene expression in the liver (8, 9).
This in turn triggers an immune response that is reflected in
mononuclear cell infiltration and increase of liver enzymes in the
serum (10, 11). To monitor viral gene expression, liver
sections were stained for lacZ activity, and the percentage
of positive cells was determined microscopically. Fig. 1
shows that the percentage of
lacZ-expressing hepatocytes is stable during the first 15
days but thereafter decreases and becomes undetectable 4 wk after the
infection. To correlate viral gene expression with liver injury, sera
were assayed for the presence of liver enzymes. As shown in Fig. 1, ALT
values increase by day 3, peak on day 9, and have decreased by day 15,
i.e., at a time at which no decrease in the expression of
lacZ is noticeable. This early decrease of ALT levels, i.e.,
before a decrease of lacZ-expressing hepatocytes, raises the
question as to the reason for the premature termination of liver
injury.
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A shows that cultures from
spleens harvested before the infection or on days 10 and 28 thereafter
respond equally well with the induction of CTL to
H-2d stimulator cells. In contrast, responses to
virus Ags show a much different pattern. There is a low but detectable
response in unprimed spleens and a high response in cells from mice
harvested 10 days after the infection (Fig. 2B). In
contrast, spleen cells from day 28 show a response that is not higher
than that of unprimed controls (Fig. 2B). These results show
that while priming of virus specific CTL is demonstrable at an early
time after the infection, it is undetectable 4 wk later.
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The disappearance of primed CTL from the spleen of virus-infected
mice raises the question of mechanisms that might be involved. Primed
CTL could have left the spleen, or they could have been anergized or
been eliminated by induction of cell death. To examine the latter
possibility, liver mononuclear cells were isolated from infected mice,
stained for annexin V, and analyzed by FACS. Results in Fig. 3A show that in the liver but
not the spleen of infected mice there is an increase of annexin
V-staining lymphocytes on days 6 and 9 after the infection. The cells
that undergo apoptosis stain with anti-CD3 Ab and are therefore T
cells (Fig. 3B). It is important to note that in case of
liver mononuclear cells there is a more than 5-fold increase in the
total number of cells recovered from the liver after the infection,
whereas in the spleen it may be up to 2-fold (10, 11).
Therefore, there is a significant increase of apoptotic T cells in the
liver but not the spleen of virus-infected mice.
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The demonstration of apoptotic T cells in the virus-infected liver
raises questions as to the mechanism responsible for induction of cell
death. To examine which of the known apoptosis-inducing pathways are
involved, the induction of mRNA specific for TNF-, perforin, and
FasL was assayed in liver tissue by RT-PCR. Results in Fig. 4 show that virus infection induces a
significant increase in message for perforin, FasL, and TNF- mRNA.
Therefore, Fas-, perforin-, and TNF--mediated mechanisms could play
a role. To examine the possible involvement of Fas, experiments were
performed in mice lacking Fas or FasL (15, 16). B6-lpr and
B6-gld mice were infected and liver mononuclear cells analyzed for
apoptotic T cells by FACS staining. Results in Fig. 5 show that on day 9 annexin V-staining
cells are demonstrable in both the CD4+ and
CD8+ T cell populations in B6 mice. In B6-lpr and
B6-gld mice the percentage of annexin V-staining
CD4+ cells is identical with that in B6 mice. In
contrast, annexin V-staining CD8+ cells are
virtually absent in both B6-lpr and B6-gld mice. It is important to
note that the majority of T cells in the virus-infected liver are
CD8+ cells (10, 11). Therefore, only
few if any annexin V-staining cells are demonstrable in the
CD3+ cell population. These results show that
apoptosis of CD8+ cells after the viral infection
involves Fas.
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The finding that Fas causes apoptosis of
CD8+ cells raises the question as to which cells
in the liver express FasL and thereby induce cell death. To examine
this, use was made of bone marrow chimeras in which the lymphoid or
liver parenchyma cells express FasL. B6-gld and B6 mice were irradiated
and reconstituted with B6 and B6-gld spleen and bone marrow cells,
respectively. Infection with virus and assay for apoptotic cells
reveals that the percentage of apoptotic CD4+ and
CD8+ cells in B6-gld mice reconstituted with B6
cells is comparable to that of B6 mice reconstituted with B6 cells. In
contrast, in B6 mice, reconstituted with B6-gld cells, death of
CD8+ cells is completely inhibited (Fig. 6A). Therefore, the apoptosis
inducing FasL is not expressed on liver parenchyma cells but rather on
lymphoid cells. Among the mononuclear cells residing in the liver are
cells expressing NK cell surface markers as well as conventional T and
B cells (1, 11). To examine which cells express FasL,
mononuclear cells from livers of virus-infected mice were analyzed by
FACS. Fig. 6, B and C shows that
NK1.1+, CD3+,
CD4+, and CD8+ cells all
increase expression of FasL following the infection. Therefore, death
of CD8+ cells could be caused by any of these
cell populations. However, considering the preponderance of
CD8+ cells in the virus-infected liver, death of
CD8+ cells by companion FasL-expressing
CD8+ cells appears most likely.
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pathways and is inhibited by IL-2
Results in Fig. 5
had shown that apoptosis of
CD8+ but not CD4+ cells is
decreased in Fas- or FasL-deficient mice. This raises the question why
apoptosis of CD4+ cells is independent of the Fas
mechanism and whether it can be explained by lack of Fas expression on
CD4+ cells. To find out, liver-infiltrating
lymphocytes were stained for CD4, CD8, and Fas expression and analyzed
by FACS. Fig. 7 shows that Fas expression
is identical in CD4+ and
CD8+ cells isolated from normal or virus-infected
livers. Therefore, the observation that CD4+
cells undergo apoptosis independent of a functional Fas pathway cannot
be explained by a lack of Fas expression.
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rather than the Fas pathway. To examine this,
perforin deficient B6-PKO mice were infected with virus and liver
mononuclear cells analyzed for annexin V-staining cell populations.
Results in Fig. 8A show that
the percentage of apoptotic CD4+ and
CD8+ cells in PKO mice is indistinguishable from
that of normal mice. To examine the involvement of TNF-, mice
defective for TNFR1 and TNFR2 were tested. Fig. 8B shows
that the percentage of apoptotic CD4+ and
CD8+ cells in TNFR1/2-deficient mice is
indistinguishable from that of normal mice. Therefore, neither perforin
nor TNF- appear to play a role in death of
CD4+ cells. Apoptosis of both
CD4+ and CD8+ cells likely
involves an activation-induced mechanism that should be inhibited by
injection of IL-2. Indeed, results in Fig. 8C show that in
the livers of IL-2-injected mice there is a dramatic decrease of
apoptotic CD4+ and CD8+
cells.
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The demonstration of Fas-dependent apoptosis of
CD8+ cells in livers of virus-infected mice
suggests that the induction of unresponsiveness 4 wk after infection is
the result of elimination of virus-specific CTL (Fig. 2). For this
case, one would predict reduced numbers of virus-specific
CD8+ cells early after the infection. To examine
this, the number of virus-specific, MHC class I-restricted T cells able
to secrete IFN- on incubation with virus-infected targets,
expressing MHC class I Ags, was assayed by ELISPOT. Results in Fig. 9A show that spleen cells from
B6 mice, infected with virus 7 days earlier, contain only about
one-third of the IFN--secreting cells, compared with spleens from
B6-lpr mice. Treatment of cells with anti-CD8 and complement before
ELISPOT assay reveals that the responding cells are predominantly
CD8+ cells. Therefore, the Fas-mediated apoptosis
mechanism reduces the number of virus-specific
CD8+ cells in the spleen at early times after the
infection. Continued elimination of these cells by this mechanism then
accounts for the absence of virus-specific CTL several weeks later
(Fig. 2).
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B shows that suppression of the CTL
response is virus dose dependent as higher doses are more efficient
than lower doses. These results suggest that a high virus dose induces
activation of CTL, up-regulates FasL, and stimulates cell migration
into the liver. The increase of activated, FasL-expressing CTL in the
liver should cause an increase in liver injury concomitant to an
increase in Fas-dependent apoptosis in CD8+
cells. Indeed, it is seen in Table I that
high virus doses stimulate expression of FasL on
CD8+ cells, enhance migration of
CD8+ cells into the virus-infected liver, and
induce high ALT values in the serum. In contrast, low doses, shown to
prime CTL (Fig. 9B), do not induce a significant increase in
ALT values and a much lower recruitment of CD8+
cells into the liver. Importantly, these CD8+
cells express much less FasL.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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In experiments aimed at elucidating the cause of unresponsiveness, it is shown that apoptotic T cells increase in the liver as early as 6 days after the infection. But whereas both CD4+ and CD8+ cells are affected, only apoptosis of CD8+ cells could be demonstrated to involve the Fas pathway. This is unexpected, as a role for Fas in apoptosis of various T cell types is well documented (19, 20, 21). Fas was found to control the expansion of activated T cells during infection with Listeria, which multiplies in various organs, including the liver (22). Fas was also reported to be responsible for superantigen-induced deletion of CD4+ cells (23). Therefore, it is unexpected that elimination of CD8+ but not CD4+ cells is attributable to the Fas mechanism. The possibility that this is caused by lack of Fas expression was excluded by the demonstration of similar levels of Fas on both T cell types. However, consistent with the notion that death of both CD4+ and CD8+ cells involves an activation-induced mechanism is that injection of IL-2 inhibits cell death of both types of cells.
These results raise a number of intriguing questions. One pertains to
the cells that provide activation and Fas-induced apoptosis signals. It
is well documented that despite the fact that the liver has a
relatively low expression of MHC Ags (24, 25), both MHC
class I and II molecules can be demonstrated on hepatocytes
(26). Therefore, viral epitopes may be presented on
hepatocytes for recognition by CD8+ or
CD4+ cells, especially after up-regulation of MHC
molecules by IFN- produced by NK and T cells (11, 24).
Hepatocytes lack costimulatory receptor ligands and therefore would be
able to transmit signal 1 only, which by itself would be paralytic and
therefore lead to T cell anergy or T cell death.
That hepatocytes are able to function as APCs is demonstrated by the fact that allogeneic hepatocytes sensitize MHC class I-specific CTL in vitro (27). However, CTL activity was found to be limited by CTL death unless a costimulatory signal was provided by IL-2 (27). Therefore, priming and subsequent death of CTL in cultures stimulated by allogeneic hepatocytes may well reflect reactions responsible for T cell death in the virus-infected liver. It is important to note here that both naive and activated T cells continuously migrate through the parenchyma and periportal field of the liver and that activated T cells proliferate in the periportal areas (28). Therefore, T cell death may well be induced during Ag recognition on hepatocytes in the liver.
The liver had been shown to attract activated CD8+ cells (29) and proposed to serve as a graveyard for T cells undergoing Ag-induced cell death (1, 30). Therefore, it is quite possible that virus-specific T cells are primed in the periphery, then migrate into the liver where they undergo restimulation by virus-infected hepatocytes that induces apoptosis. Alternatively, T cell activation and T cell death could be induced outside the liver, leading to accumulation of dying cells in the liver.
These considerations raise the question as to where the death-inducing
FasL may be expressed. It had been shown that CD40 signaling can induce
expression of FasL on hepatocytes during chronic allogeneic liver
rejection (31) and that FasL can be expressed on hepatomas
(32). However, our experiments aimed at demonstrating FasL
expression on liver parenchyma cells during induction of apoptosis in
CD8+ cells in bone marrow chimeras were negative.
Rather, we report that viral infection up-regulates expression of FasL
on NK1.1+, CD4+ and
CD8+ cells, pointing to death of
CD8+ cells by either of these cell populations.
Indeed, effector cells with respective phenotypes are well documented
to cause FasL-mediated target cell lysis (33, 34, 35, 36).
However, it seems likely that apoptosis of CD8+
cells is primarily caused by CD8+ cells.
Consistent with this, high doses of virus that are effective in
suppressing virus-specific CTL responses, induce a large increase in
CD8+ cells in the liver and strongly up-regulate
FasL expression on these cells. Published data also support the notion
that CTL may die by Fas-mediated fratricide. Thus, incubation of CTL
with target cells able to induce expression of FasL had been shown to
induce Fas-mediated CTL death in vitro (37). Moreover, HSV
1 infection of mice causes activation-induced fratricide in
virus-specific CTL via the Fas mechanisms (38). Therefore,
the finding here that CTL die by Fas-mediated and activation-dependent
cell death in the liver is not unprecedented. In contrast, it is not
known why CTL elimination in mice infected with lymphocytic
choriomeningitis virus does not proceed via the Fas pathway. It is also
noteworthy that despite our demonstration that TNF- mRNA is induced
in the virus-infected liver, no evidence for a role of this cytokine in
T cell apoptosis was obtained. Death of CD8+
cells by TNF- had been reported (39).
Our experiments show that the elimination of virus-specific CTL by the Fas mechanism is Ag dose dependent, as high doses of virus favor disappearance of primed CTL, whereas low doses promote their survival. These findings have important implications for immune responses to allogeneic liver transplants and viral liver infections. Liver transplants establish large numbers of MHC-expressing cells capable of inducing T cell priming as well as T cell death. The finding in mice that after transplantation, T cells migrate into the liver and then die is consistent with a liver-induced apoptosis mechanism (4). Also consistent is that injection of IL-2 has been reported to cause the rejection of allogeneic liver transplants (4).
Important implications from these results apply to viral infections of the liver in humans. Both HCV and HBV infections often become persistent, leading to chronic hepatitis (6, 7). Although the failure of the immune system to successfully eliminate virus likely has a number of reasons, one of them may be the elimination of virus-specific T cells. Indeed, it has been reported that in HCV-infected patients 0.1% of all T lymphocytes are eliminated in the liver each day (40). If the majority of these T cells were to be HCV specific, this would result in removal of effector cells destined to eliminate the infection. Our finding here that the viral dose is a determining factor in the elimination of virus-primed T cells is consistent with the finding that HBV-infected patients with a high viral load have a lower frequency of virus-specific T cells, compared with patients who have eliminated the virus (41). Moreover, drug-induced reduction of viral load in HBV-infected patients has been shown to correlate with recovery of HBV-specific T cell responses (42). Therefore, it is quite possible that the lack of a sufficient response to infection with HBV and HCV is in part attributable to a virus dose-dependent elimination of virus-specific T cells in the infected liver.
In summary, it is shown here that expression of foreign Ags in the liver induces a transient cell-mediated immune response that appears to be limited by the induction of cell death in CD4+ and CD8+ cells. Although apoptosis of CD8+ cells was shown to proceed by a Fas-mediated mechanism, that of CD4+ cells could not be demonstrated to involve the Fas pathway. FasL is shown to be expressed on various lymphocytes, among those CD8+ cells, which cause a virus dose-dependent elimination of virus-specific CTL. These findings identify an important mechanism of T cell elimination, which could in part be responsible for acceptance of liver allografts in rodents and failure of the cell-mediated immune system to successfully eliminate certain viral infections in the liver.
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Gunther Dennert, University of Southern California/Norris Comprehensive Cancer Center, 1441 Eastlake Avenue, M/S #73, Los Angeles, CA 90089-9176.
3 Abbreviations used in this paper: HBV, hepatitis B virus; HBC, hepatitis C virus; B6, C57BL/6; FasL, Fas ligand; PKO, B6-pfptm1Sdz; lpr, B6.MRL-Faslpr; gld, B6Smn.C3H-FasLgld; ALT, alanine aminotransferase; ELISPOT, enzyme-linked immunospot assay; lacZ, -galactosidase.
Received for publication August 1, 2000. Accepted for publication December 18, 2000.
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References |
|---|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
-inducing factor up-regulates Fas ligand-mediated cytotoxic activity of murine natural killer cell clones. J. Immunol. 157:3967.[Abstract]
interferon. J. Exp. Med. 162:1645. is necessary for T-cell-mediated elimination of recombinant adenovirus-infected hepatocytes in vivo. Proc. Natl. Acad. Sci. USA 92:7257./+ T cells and expansion of NK1.1+ TCR-/
+ T cell development in CD3 
-deficient mice. J. Exp. Med. 182:891.24+ T cells and rapid elimination of effector cells by apoptosis. Eur J. Immunol. 28:3448.[Medline]
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K. Klugewitz, F. Blumenthal-Barby, A. Schrage, P. A. Knolle, A. Hamann, and I. N. Crispe Immunomodulatory Effects of the Liver: Deletion of Activated CD4+ Effector Cells and Suppression of IFN-{gamma}-Producing Cells After Intravenous Protein Immunization J. Immunol., September 1, 2002; 169(5): 2407 - 2413. [Abstract] [Full Text] [PDF]
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 S. H. Gregory and E. J. Wing Neutrophil-Kupffer cell interaction: a critical component of host defenses to systemic bacterial infections J. Leukoc. Biol., August 1, 2002; 72(2): 239 - 248. [Abstract] [Full Text] [PDF]
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E. Zuniga, C. C. Motran, C. L. Montes, H. Yagita, and A. Gruppi Trypanosoma cruzi Infection Selectively Renders Parasite-Specific IgG+ B Lymphocytes Susceptible to Fas/Fas Ligand-Mediated Fratricide J. Immunol., April 15, 2002; 168(8): 3965 - 3973. [Abstract] [Full Text] [PDF]
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Z.-X. Liu, H. Nishida, J.-W. He, M. M. C. Lai, N. Feng, and G. Dennert Hepatitis C Virus Genotype 1b Core Protein Does Not Exert Immunomodulatory Effects on Virus-Induced Cellular Immunity J. Virol., February 1, 2002; 76(3): 990 - 997. [Abstract] [Full Text] [PDF]
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