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Department of Microbiology, Immunology, and Parasitology, LSU Medical Center, New Orleans, LA 70112
| Abstract |
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mRNA
and decreased the expression of HSV-1-infected cell polypeptide 27 mRNA
in the trigeminal ganglion during the acute (day 6 postinfection)
infection of mice, as determined by reverse transcription-PCR. However,
there was no change in the viral load from the eye or trigeminal
ganglion when comparing the AED-treated with the vehicle-treated mice.
Neutralization Abs to IFN-
, -ß, or -
/ß, but not control Ab,
blocked the protective effect following AED exposure, confirming the
involvement of type I IFN in the enhancement of survival in AED-treated
mice. Collectively, these results identify innate immunity as a key
component in augmenting the survival of HSV-1-infected mice following
AED treatment. | Introduction |
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B
, which binds
to NF-
B and blocks translocation to the nucleus, ultimately
antagonizing cytokine gene transcription (7, 8). This recent revelation
of the intracellular action of glucocorticoids may, in part, explain
the immunosuppressive characteristics of glucocorticoids. Similar to
glucocorticoids, the major secretory product of the human adrenal gland
dehydroepiandrosterone
(DHEA)3 has also been
found to modify the immune system. DHEA augments IL-2 but not IL-4
production by activated splenic lymphocytes (9) and freshly isolated
CD4+ T cells (10). Presumably, the direct action of DHEA on
lymphocytes (9) is mediated through receptors found within the target
cells (11, 12). Likewise, DHEA has been found to protect mice from
viral lethality (13, 14, 15), enhance the Ab titer to influenza vaccination
in aging adults (16), and show a reciprocal correlation with deficient
IL-2 production by lymphocytes from patients with systemic lupus
erythematosus (17). While the mechanism(s) involved in the
immunoprotective and immunopotentiating effects of DHEA has not been
elucidated, one pathway reportedly involves antagonizing the action
elicited by glucocorticoids (18, 19).
The antiviral effects of DHEA are dependent upon the mode of delivery,
with the s.c. route showing the greatest efficacy (13). In the skin,
DHEA is converted to 5-androsten-3ß-17ßdiol (androstenediol, AED)
(20), which binds to estrogen receptors (21). The administration of AED
is superior to DHEA in protecting mice from the lethality of bacterial
and viral infections (22). Moreover, both AED and another metabolic
product of DHEA, androstenetriol (5-androstene-3ß-17ß-triol, AET)
have been found to counter the immunosuppressive effects of the steroid
hydrocortisone on lymphocyte proliferation, and mitogen-induced IL-2
and IL-3 production in vitro, while DHEA is without effect (23, 24).
Recently, the administration of AED in mice infected with influenza
virus was shown to decrease mortality associated with the infection,
enhance IFN-
production by draining lymph node and splenic
lymphocyte populations, and antagonize the elevated corticosterone
levels associated with the infection (25). Collectively, the
observations suggest that DHEA, through the metabolic products AED and
AET, antagonizes the immunosuppressive effects of glucocorticoids
elicited following infection. However, the presence of DHEA receptors
in cells of the immune system (11, 12) and the direct action of DHEA
and its metabolites on cytokine production (9, 10, 23, 24, 25) suggest that
these hormones may have additional immunoregulatory properties of
biologic relevance in addition to the antiglucocorticoid action
(26).
The present study was undertaken to assess the protective effects of AED on herpes simplex virus type 1 (HSV-1)-induced mortality. The immune response to ocular HSV-1 infection is well defined, involving innate (27, 28), cellular (29, 30), and humoral immunity (31, 32). Since the previous viral models characterizing the effects of DHEA and AED on survival employed viral pathogens that induce a rapid death, it was hypothesized that the protective effect mediated by AED would primarily modify some aspect of the innate, nonadaptive immune response. Within this first line of defense, neutrophils (33), macrophages (34, 35), NK cells (36), and cytokines (e.g., type I IFN) (37, 38) are candidates previously shown to be involved in monitoring HSV-1 infection. Consequently, the present study focuses on the early immune (cytokine) events within the immediate vicinity of HSV-1 replication following ocular infection including the eye and trigeminal ganglion (TG).
| Materials and Methods |
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Vero and CV-1 African monkey kidney cell lines were obtained from the American Type Culture Collection (Rockville, MD). Cells were cultured in complete media (RPMI 1640; Mediatech, Washington, DC) containing 5% FBS (Life Technologies, Gaithersburg, MD) and an antibiotic/antimycotic solution (Sigma Chemical Company, St. Louis, MO). Cells were incubated at 37°C, 5% CO2, 95% humidity. HSV-1 was grown up and harvested as previously described (39).
Infection of mice
Female ICR mice (2534 g; Harlan Sprague-Dawley, Indianapolis, IN) were anesthetized by i.p. administration of 0.1 ml of PBS containing xylazine (6.6 mg/kg) and ketamine (100 mg/kg). Following scarification, tear film was blotted from the eyes and the mice were inoculated with 210 plaque forming units (pfu) of HSV-1 (McKrae strain) in each eye in a volume of 3 µl. Infection was verified by swabbing the eyes 2 to 3 days postinfection (p.i.), placing the swabs in CV-1 monolayer cultures, and observing the cultures for cytopathic effects. Animals were assessed for survival following inoculation with virus or killed by CO2 asphyxiation at days 3, 6, and 30 days p.i. Blood was collected via the vena cava, and the eyes and TG were removed. TGs and eyes were processed for RNA isolation and serum was obtained from the clotted blood. Animals were handled and maintained in accordance with the National Institutes of Health Guidelines on the Care and Use of Laboratory Animals (40).
Treatment of mice
AED 3-sulfate (henceforth referred to as AED) (Sigma Chemical
Co.) was reconstituted in a 1:1 DMSO:ethanol ratio that was then added
to water for a final concentration of 10, 50, or 100 µg/ml of AED in
0.05% DMSO:ethanol. Following the inoculation of mice with HSV-1, the
drinking water of the mice was replaced with either water containing
the AED or vehicle (0.05% DMSO:ethanol). Due to the precipitation of
AED within 96 h following reconstitution, the treated water was
replaced every 72 h. In indicated experiments, mice received
rabbit anti-mouse IFN-
/ß (Access Biomedical, San Diego, CA;
1,000 neutralizing U), IFN-
(Hycult Biotechnology, Uden, The
Netherlands; 1,000 neutralizing U), IFN-ß (Access Biomedical; 1,000
neutralizing U), or normal rabbit Ig at the time of infection and 3 and
6 days p.i.
Reverse transcription (RT)-PCR
RT-PCR of TG was performed as described (39). Briefly, TG RNA
was extracted in Ultraspec 228 RNA isolation reagent (Biotecx Inc.,
Houston, TX). First strand cDNA was synthesized using AMV reverse
transcriptase (Promega Corp., Madison, WI). PCR was performed in a
thermal cycler (Ericomp
cycler I; Ericomp, San Diego, CA) with 35
cycles of 94°C (for 1.25 min)
57 to 60°C (for 1.25
min)
72°C (for 0.5 min). PCR primers for
glyceraldehye-3-phosphate dehydrogenase (GAPDH), infected cell
polypeptide 27 (ICP27), IFN-
, TNF-
, latency-associated transcript
RNAs (LAT), IL-10, and RANTES were as previously described (39).
IFN-
(consensus sequence for IFN-
1, -2, and -7) and CD8 primer
sequences were obtained from Clontech Laboratories, Inc. (Palo Alto,
CA). Primers for IL-6 were 5'-TTCCATCCAGTTGCCTTCTTGG-3' (sense) and
5'-CTTCATGTACTCCAGGTAG-3' (antisense), yielding a 359-bp product.
Primers for IFN-induced protein 10 kDa and JE/monocyte chemoattractant
protein-1 (MCP-1) yielding 431- and 582-bp products, respectively, and
the settings for the amplification of the specific products were as
described (41). Following electrophoresis of the amplified product,
ethidium bromide-stained PCR products were visualized with a Bio-Rad
1000 gel documentation system (Bio-Rad, Hercules, CA). Densitometric
analysis of gel images was performed using molecular analysis 3.3
software (Bio-Rad).
Measurement of HSV-1 titers in the tissues
TG, eyes, and cerebella were removed 5 to 6 days p.i. and homogenized in 0.8 ml of RMPI 1640 containing 5% FBS in 2.0-ml microfuge tubes. Homogenates were clarified by centrifugation for 1 min at 13,000 x g. HSV-1 titer in clarified supernatants was determined by plaque assay. Viral load was calculated as pfu x sample volume/tissue weight and expressed in pfu/ml.
Corticosterone determination
Sera from killed animals were assayed for corticosterone levels
by radio immunoassay (RIA; ICN Biomedicals, Costa Mesa, CA). All
samples were assayed in duplicate and collected at 10:00 AM. The
corticosterone levels were extrapolated from the standard curve
(Rf
0.9900).
Statistics
One-way analysis of variance and Scheffe multiple comparison test were used to determine significant (p < 0.05) differences between the indicated groups using the GBSTAT program (Dynamic Microsystems, Inc., Silver Springs, MD).
| Results |
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AED was assessed for its effects on the survival of mice ocularly
infected with HSV-1. The results show that greater than 80% of
vehicle-treated animals succumbed to the infection compared with 38 and
30% of mice treated with 10 and 50 µg/ml of AED, respectively (Fig. 1
). Similar to vehicle, mice treated with
100 µg/ml were not able to manage the viral infection, with only 25%
of the animals surviving although there was a modest delay in mortality
compared with vehicle-treated animals (Fig. 1
). There were no apparent
differences in the consumption of water containing the AED between the
HSV-1-infected groups of mice, which might explain the difference in
the survival curve.
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To determine whether AED reduced the replication of virus during
the acute stage of infection, HSV-1-infected mice treated with or
without AED were screened for infectious virus. Although there was a
tendency for a decrease in infectious virus in the eye and more in the
TG of AED-treated mice, there were no significant differences in the
viral titers in the eye, TG, or cerebellum (Fig. 2
). However, only 45% (5 of 11) of the
AED-treated mice had detectable virus in the cerebellum compared with
73% (8 of 11) of vehicle-treated mice. These results suggest that AED
treatment antagonizes the spread of HSV-1 from the site of inoculation
to the central nervous system.
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Since a previous study has shown that AED administered s.c. could
antagonize the increase in corticosterone following an intranasal
influenza infection (25), corticosterone levels were determined in mice
treated with AED (50 µg/ml) or vehicle. The results show no
differences in the serum corticosterone levels 3, 6, or 30 days p.i.
when comparing the vehicle-treated with the AED-treated animals,
suggesting that the antiglucocorticoid properties reported for AED are
not applicable in this model system (Fig. 3
).
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mRNA in the eye and TG,
respectively, during acute HSV-1 infection
To determine whether AED modifies the expression of cytokine genes
during the course of HSV-1 infection, RT-PCR was performed to monitor
viral and cytokine transcript expression using eye and/or TG samples
obtained 3, 6, and 30 days p.i. Three days p.i., MCP-1 gene expression
was elevated in the eye of AED-treaed mice (Fig. 4
and Table I
). When the PCR was conducted through a
range of cycles from 20 to 35, MCP-1 mRNA expression was significantly
elevated in the AED-treated animals, confirming the qualitative RT-PCR
(data not shown). Similar to MCP-1, the immediate early gene ICP27 of
HSV-1 was elevated in the AED-treated mice compared with vehicles
(Fig. 4
and Table I
). No other transcripts analyzed in the eye were
found to be significantly different when comparing the two groups of
animals (Table I
). Samples obtained from the TG of vehicle- and
AED-treated mice 3 days p.i. showed no significant differences in any
of the transcripts tested (Fig. 5
and
Table II
). However, both CD8 and RANTES
mRNA levels were elevated in the AED-treated group. Likewise, ICP27
gene expression in the TG was detected in two of eight AED-treated mice
compared with zero of eight vehicle-treated controls.
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and decrease in ICP27 mRNA
levels in AED-treated mice compared with vehicle controls (Fig. 6
mRNA ranging
from 20 to 35 cycles confirmed the qualitative differences between the
AED- and vehicle-treated groups (data not shown). No other transcripts
assessed were found to be different between the two groups of treated
animals.
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, IFN-
, CD8, and
RANTES) in the TG comparing AED-treated with vehicle-treated mice 30
days p.i. (data not shown). Type I IFNs are involved in the protective effect in HSV-1-infected mice following AED administration
Since AED-treated mice were found to have elevated IFN-
and
lower ICP27 mRNA levels in the TG during the early, acute (day 6
p.i.) stages of the infection, the involvement of type I IFNs in the
protective effect of the AED-treated animals was investigated. Similar
to previous results, 33% of the vehicle-treated HSV-1-infected mice
survived acute infection (Fig. 7
).
However, mice exposed to AED in the drinking water and treated with
control Ab showed a significant improvement in survival (74%) of acute
infection. When AED-treated mice were administered neutralizing Abs to
IFN-
/ß or IFN-
, the survival was reduced to nearly the same
level as the vehicle-treated, HSV-1-infected animals, supporting the
RT-PCR data showing involvement of IFN-
in AED-mediated protection
(Fig. 7
). All the AED-treated animals administered neutralizing Ab to
IFN-ß succumbed to acute infection, suggesting a key, protective role
for IFN-ß during the acute ocular infection with HSV-1.
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| Discussion |
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and decrease in IL-10 production by
Ag-stimulated lymphocytes in virally infected mice administered AED
(22, 23, 24, 25), it could be concluded that AED acted primarily to reduce
circulating corticosteroid levels during infection and thereby blocked
the immunosuppressive effects mediated by this hormone. Similar to
previous studies, ocular HSV-1 infection resulted in a significant rise
in corticosterone levels during the acute stages. However, AED
treatment had no effect on the steroid levels during this time period.
The data suggest the anticorticosteroid action of AED is not a
consideration in the current study. The discrepancy between the present
and previous studies may reside in the route of administration of the
compound. Previous studies have focused on the administration of AED
s.c. in a single bolus (22, 23, 24, 25). In the present study, AED was
administered through the drinking water throughout the time course of
the infection. Consequently, the metabolism of the compound via these
two routes of treatment may greatly influence the action of the drug on
physiologic processes, including immunocompetence. However, consistent
with previous studies showing the antiviral nature of AED in vivo,
the current investigation shows AED was found to significantly
enhance the survival of HSV-1-infected mice.
Following ocular inoculation with HSV-1, the virus replicates in
the eye, spreads to the sensory nerve endings, and by retrograde
transport travels to the neuronal cell bodies within the TG (42).
The result of the penetration and replication of the virus in the
sensory ganglia is an intense inflammatory response (43). The control
of viral replication during this period is crucial in eliminating the
spread of the virus into the central nervous system, resulting in
fulminating encephalitis. Accordingly, the immune response within the
first 3 to 7 days p.i. will ultimately dictate the outcome of the
infection. Inspection of cytokine transcripts in the TG during this
time period showed a significant increase in IFN-
expression in the
AED-treated mice. This increase coincided with a decrease in the viral
transcripts ICP27 and LAT. Furthermore, the administration of
neutralizing Abs to IFN-
or IFN-
/ß but not control Ab blocked
the protective effect observed in the AED-treated mice, confirming the
observation assessing IFN-
gene expression within the TG of the
AED-treated mice. Collectively, these results suggest that type I IFN
is the primary mechanism by which AED treatment affords protection from
death in the ocular HSV-1-infected mice. However, differences were
observed when comparing Ab to IFN-
and IFN-ß. AED-treated mice
administered anti-IFN-
or IFN-
/ß Ab succumbed to the
infection at a level similar to the vehicle-treated mice, whereas all
mice treated with anti-IFN-ß Ab died. Since IFN-ß is linked to
a single gene whereas IFN-
is part of a multigene family (44), it is
difficult to determine the nature of the neutralizing capacity of the
anti-IFN-
Ab relative to the Ab directed against IFN-ß.
However, the PCR data using oligonucleotide primers that are specific
for IFN-
1, -2, and -7 and showing increases in the mRNA expression
following AED treatment suggest that one or more of these subtypes of
IFN-
are likely candidates in the protective effect following AED
treatment. Therefore, it is imperative to identify which of the IFN-
subtypes is involved in the protective effect mediated through AED
against HSV-1 infection before a comparison in the efficacy of the
subtype of IFN-
to IFN-ß can be determined. Nevertheless, the
results of the present study are consistent with previous findings
illustrating the central role of the type I IFNs in controlling HSV-1
replication during acute infection in vitro (37, 38) and in vivo (27, 28). Type I IFNs are also thought to promote a Th1 response (45) and
the generation and maintenance of memory CD8+ cells
(46), both of which are important attributes for the host during a
viral infection.
The present study found that low to moderate concentrations (1050 µg/ml) of AED in the drinking water antagonized viral-induced mortality while a higher concentration (100 µg/ml) had no protective effect. Although monitoring of individual mice for the consumption of AED was not determined, there were no obvious differences in the volume of vehicle- or AED-containing water consumed between groups of mice, which might explain the differences in the protective effect. It is possible that other neuroendocrine processes are involved upon reaching a threshold level of AED in the circulation that might influence the outcome of the viral infection in the central nervous system.
During the early events of HSV-1 replication in the eye, AED-treated mice displayed elevated levels of both MCP-1 and ICP27 gene expression compared with the vehicle-treated controls. The increased replication of HSV-1 in the eye of AED-treated mice as indicated by the expression of ICP27 may result in a greater degree of tissue pathology associated with an increase in MCP-1 in response to the infection. The increase in MCP-1 synthesized from immune and nonimmune sources within the eye would predictably enhance the extravasation of monocytes into the inflamed site (47, 48), providing an increase in Ag processing, presentation, and type I IFN induction compared with the normal course of the infection. An association of MCP-1 but not RANTES gene expression with herpes stromal keratitis has previously been found (41) and is consistent with the present results supporting the role of MCP-1 in tissue inflammation in the eye.
Since infectious HSV-1 was found in 45% of the cerebella of
AED-treated mice and 73% of vehicle-treated controls, AED does not
prevent death of the animal by preventing the spread of virus to the
central nervous system. Therefore, AED may function in an additional
capacity within the brain to reduce the sequela of HSV-1 pathogenesis
(i.e., encephalitis) unrelated to the enhancement of type I IFN by AED.
However, the enhancement of IFN-
is required to protect the animal
from undergoing encephalitis. Similar to another study (22), the
present investigation found that AED had no direct effect on viral
replication (data not shown), implying that another extrinsic property
(e.g., neuroendocrine hormone modulation) besides the induction of IFN
might play a role in antagonizing the pathogenesis of HSV-1 within the
central nervous system. The fact that AED did not significantly reduce
the viral load in the tissues examined but reduced the mortality of the
animals is similar to a recent finding investigating HSV-1-induced
pneumonia (49). In that study, inhibition of inducible nitric oxide
synthase was found to suppress viral pneumonia even though higher viral
titers in the lung were found. The authors concluded that the
inflammatory response rather than the cytopathic effect of the virus
resulted in pneumonia. However, in the present study, both AED- and
vehicle-treated mice presented with intense periocular inflammation.
Moreover, by RT-PCR the mice exhibited insignificant differences in the
levels of cytokine and CD8 transcripts within the TG with the exception
of IFN-
, suggesting that both groups of animals are undergoing a
similar inflammatory response. Consequently, future studies will be
required to further characterize the immunologic and nonimmunologic
parameters that antagonize HSV-1 replication in both peripheral and
central nervous systems in the context of the AED treatment regimen
employing both oral and s.c. routes of administration.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Daniel J. J. Carr, Department of Microbiology, Immunology, and Parasitology, LSU Medical Center Box P6-1, 1901 Perdido Street, New Orleans, LA 70112-1393. ![]()
3 Abbreviations used in this paper: DHEA, dehydroepiandrosterone; AED, androstenediol (5-androstene-3ß, 17ß-diol); AET, androstenetriol (5-androstene-3ß, 7ß, 17ß-triol); HSV-1, herpes simplex virus type 1; TG, trigeminal ganglion; p.i., postinfection; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; ICP27, infected cell polypeptide 27; LAT, latency-associated transcript; MCP-1, monocyte chemoattractant protein-1; pfu, plaque forming unit. ![]()
Received for publication September 9, 1997. Accepted for publication November 19, 1997.
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