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*
Third Department of Medicine (Neurology), Shinshu University School of Medicine, Matsumoto, Japan; and
Department of Immunology, Juntendo University School of Medicine, Tokyo, Japan
| Abstract |
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and IFN-
in the spleen cells was decreased. The delayed-type
hypersensitivity and T cell proliferative response specific for TMEV
were decreased by this treatment. In contrast, treatment with Abs to
B7-2, resulted in no effect on TMEV-IDD. These data suggest that B7-1
is critically involved in the pathogenesis of TMEV-IDD and that Abs to
B7-1 could be a novel therapeutic approach in the clinical treatment of
demyelinating diseases such as human multiple
sclerosis. | Introduction |
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Persistent CNS virus infection in susceptible mouse strains triggers clonal expansion and differentiation of TMEV-specific MHC class II-restricted effector delayed-type hypersensitivity (DTH) (Th1) cells that are poorly controlled by normal immunoregulatory mechanism. Activated Th1 cells, specific for viral capsid protein, release proinflammatory cytokines in the CNS, resulting in the subsequent recruitment and activation of mononuclear phagocytes that initiate myelin destruction via both direct and bystander mechanisms (13, 14).
Full activation of T cells requires two signals from APCs. The first signal, the binding of the TCR to its Ag-MHC ligand, provides specificity. The second signal is provided by costimulatory molecules expressed on APCs. Of the known costimulatory molecules, the family of proteins termed B7 appears to be the most potent. The B7 costimulatory pathway involves at least two molecules, B7-1 (CD80) (15) and B7-2 (CD86) (16). The B7 molecules on the APC, B7-1 and B7-2, are the counterreceptors for CD28 and CTLA-4 (17). This costimulatory signal controls T cell activation and suppression and involves the induction of Th1/Th2 cell from Th0 cell (18). Blocking B7-1 interactions during T cell activation induces functional inactivation in Th1 cells, leading to a state of hyporesponsiveness or anergy (19). In experimental autoimmune encephalomyelitis (EAE), another model of MS, encephalitogenic CD4+ Th1 cells play an important role in pathogenesis. In the mouse EAE system, several researchers examined the effect of anti-B7 Abs. The suppressive effect of anti-B7-1 mAb treatment and the aggravated effect of anti-B7-2 mAb treatment have been reported (18, 20, 21, 22, 23). Pope et al. showed that B7-1 and B7-2 were also expressed on the surface of macrophages/microglia and CD4+ T cells in the CNS of TMEV-infected mice (24). These findings suggest that the B7 costimulatory molecule may play an important role in the pathogenesis of TMEV-IDD.
As far as we know, the effect of anti-B-7 mAbs on TMEV-IDD has not been studied yet. We recently generated mAbs to mouse CD80 (RM80) and CD86 (PO3) (25). By utilizing these mAbs, we examined the separate roles of the different costimulatory molecules B7-1 (CD80) and B7-2 (CD86) in TMEV-IDD.
| Materials and Methods |
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Female pathogen-free SJL/J mice from The Jackson Laboratory (Bar Harbor, ME) were housed and cared for in an approved facility, in accordance with the National Institutes of Health guidelines.
Virus
The BeAn 8386 strain of TMEV was propagated in baby hamster kidney (BHK)-21 cells grown in DMEM supplemented with 7.5% donor calf serum and purified by isopyknic centrifugation on Cs2SO4 gradients as previously described (26).
mAbs
A rat IgG2a mAb to mouse CD80 (RM80) and a rat IgG2b to mouse CD86(PO3) were obtained from PharMingen (San Diego, CA) (25). Hybridoma cells that produce these mAbs were cultured in RPMI 1640 supplemented with 10% FBS and 0.1% gentamicin. These cells were injected into nude mice; mAbs harvested as ascites were purified with the use of a protein G affinity column. All of these mAbs were prepared in PBS at 1 mg/ml.
Injection of mice with TMEV
For i.c. inoculation of virus, 1.3 x 106 PFU of virus in 30 µl were administered into the right cerebral hemisphere of mice anesthetized with methoxyflurane. This inoculum consistently induces neurological signs in susceptible mouse strains (27).
Treatment with mAbs
Six- to eight-wk-old female SJL/J mice were separated into
groups (A-E). Group A mice (control) were treated with PBS. In each
experiment, TMEV was injected into SJL/J mice i.c. at day 0. mAbs
(RM80, PO3, M18/2(nonspecific rat IgG2a mAb)) were injected i.p. into
mice on days 4 and 14 after i.c. infection with TMEV at a dose of 500
µg at a volume of 100 µl/mouse per injection. Details of the
experimental design are given in Table I
.
We performed this mAb treatment experiment three times. In one
experiment, five groups of mice were under investigation
(n = 20 for each group). Before experiments, five mice
were blindly selected from each group for histological study, and
another five mice were also blindly selected from each group for
immunological studies such as TMEV-specific DTH, TMEV-specific T cell
proliferation assay, and enumeration of cytokine-producing cells assay.
Other mice were clinically observed until 80 days post i.c. infection
(n = 10 for each group).
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TMEV-infected mice were examined daily for clinical symptoms of demyelination. Mice were allowed to walk on a polyethylene (Dynalab, Rochester, NY) walking board and observed for exhibition of symptoms including a waddling gait, extensor spasms, paralysis, loss of righting reflex, incontinence, and hunched posture. Neurological signs were recorded using the following grading system: normal = 0, slight waddling gait = 1, waddling gait = 2, spastic hind limb paralysis = 3, and severe hind limb paralysis accompanied by incontinence = 4 (28). These clinical scores have been shown to be indicative of demyelination (29). A clinical score was recorded daily for each mouse in each experiment using this grading system. The mean clinical score for each group of mice on each day was calculated by dividing the sum of all clinical scores of the mice in a given group by the number of mice in that group.
Histology
In each experiment, mice were blindly selected from each group (n = 5 from each group) beforehand for histological examination and sacrificed on day 40 post i.c. infection. Since we had repeated this experiment three times, 15 mice from each group were histologically examined. Mice were perfused under anesthesia by the intraventricular route with 4% paraformaldehyde in PBS, pH 7.4. Spinal cords were removed, fixed in 4% paraformaldehyde and 2.5% glutaraldehyde in PBS, and embedded in epoxy resin. These epoxy-embedded (1 µm thick) sections were stained with toluidine blue. These sections from 12 segments/mouse were read under light microscopy, and grading was done in a blinded fashion by two independent investigators who were unaware of the treatment each animal had received. The score for inflammation was determined according to the following criteria: 0, none; 1, a few inflammatory cells; 2, numerous scattered cells with an occasional perivascular cuff; 3, many perivascular cuffs; and 4 and 5, increasing perivascular infiltration and subarachnoid inflammation. The extent of demyelination was determined according to the following scoring system: 0, no demyelination; 1, a few scattered naked axons; 2, small groups of naked axons; and 3, large groups of demyelinated axons with confluent plaques of demyelination (30).
Ag-specific DTH
A 24-h ear swelling assay was used to quantitate DTH (31). Before experiments, five mice were also blindly selected from each group for immunological studies. At 36 days post i.c. infection, prechallenge ear thickness of these mice was determined using a Mitutoyo digimatic micrometer (Mitutoyo, Tokyo, Japan). Subsequently, 5 µg of purified TMEV in 10 µl of saline was injected into the dorsal surface of the ear using a Hamilton syringe fitted with a 30-gauge needle. Twenty-four hours later, ear thickness was again measured, and the increase in thickness was expressed in units of 10-4 inches. Ear swelling reactions were due to mononuclear cell infiltration and showed typical DTH kinetics (i.e., minimal swelling at 4 h and maximal swelling at 24 to 48 h).
T cell proliferation assay
After DTH measurement, the same mice were sacrificed. Spleen cells were harvested from three animals in each group and pooled. Cells (5 x 105) were cultured in 96-well flat-bottom microculture plates in RPMI 1640 containing 0.5% syngeneic mouse serum, 5 x 10-5 M 2-ME and antibiotics. Triplicate cultures were stimulated with three different concentrations of UV-inactivated TMEV (0.5, 5, and 10 µg) and were incubated for 72 h in a humidified atmosphere of 5% CO2 and 95% air. Cultures were then pulsed with 1.0 µCi of [3H] dThd and harvested 24 h later. Measurement of [3H]dThd incorporation was determined using a scintillation counter and expressed as cpm. Background proliferation was less than 1/7 of TMEV-specific proliferation.
Anti-TMEV Ab and anti-TMEV subclass titration
TMEV-specific Ab titers were determined using ELISA as described earlier (32) utilizing sera from individual mice. Briefly, 0.3 µg of purified virus was used to coat microtiter plates. A BSA solution (0.3 µg) was also used to coat the plates, to serve as a negative control. Unless otherwise stated, 2-fold serial diluents of sera starting from a 1:100 (20 x 100) dilution were reacted with the Ags on the microtiter plates and then with goat anti-mouse secondary Ab conjugated with alkaline phosphatase (KPL, Gaithersburg, MD). For anti-TMEV subclass Ab titration, sera were reacted with the Ag on the microplates and then with biotinylated rat monoclonal anti-mouse IgG subclass Ab (Zymed, San Francisco CA). After the plates were washed, streptavidin-alkaline phosphatase was added to each well, and the plates were incubated. After the plates were again washed, substrate (p-nitrophenyl phosphate) for the enzyme was added, and the enzyme reaction was colorimetrically measured by an ELISA reader (Bio-Rad, Hercules, CA) at 410 nm. The Ab titers of ELISA represent log2 x 100.
Cytokine assay by ELISA
The concentration of circulating cytokines, such as TNF-
,
IFN-
, IL-4, or IL-10, were measured using commercially available
ELISA kits (Genzyme, Cambridge, MA).
Enumeration of cytokine-producing cells
On day 40 post i.c. infection, spleen cells from the same mice
used for Ag-specific DTH and T cell proliferation assay
(n = 5 from each group) were harvested from animals in
each group. The levels of TNF-
, IFN-
, IL-4, or IL-10 producing
spleen cells were examined using an ELISPOT assay. The original reverse
ELISPOT assay (33) was modified by using nitrocellulose
membrane (Bio-Rad). Wells were filled (50 µl/well) with monoclonal
hamster anti-murine TNF-
, IFN-
, IL-4, or IL-10 mAbs (Genzyme)
at a concentration of 10 µg/ml in 0.5% BSA in PBS overnight at
4°C. Unabsorbed Abs were removed, and wells were washed with PBS. The
plates were then blocked with 1% BLOTTO (nonfat dry milk) for 2 h
at 37°C. The outer surface of the nitrocellulose membrane was
carefully dried. Spleen cells (1 x
105/well) in the culture medium (RPMI 1640
supplemented with 10% FBS and 0.1% gentamicin) were dispensed among
individual wells (100 µl/well). Plates were then incubated for
48 h at 37°C in a humidified, 5% CO2
atmosphere and were washed three times with Tris-buffered saline with
Tween 20 (TBST). Fifty µl of a 1:250 dilution of polyclonal rabbit
anti-murine TNF-
, IFN-
, IL-4, or IL-10 Abs (Genzyme) was
added to each well followed by incubation for 2 h at 37°C.
Plates were washed with TBST again and were treated with 50 µl of 1
µg/ml alkaline phosphatase-conjugated goat anti-rabbit IgG (KPL)
for 2 h at 37°C. After another washing with TBST, cytokines
secreted by single cells were visualized by adding a mixture of
nitro-blue tetrazolium and 5-bromo-4-chloro-3-indole phosphate (Life
Technologies, Grand Island, NY). The color reaction of the enzyme was
halted after 30 min by washing with water, and spots were enumerated
under x40 magnification.
Statistical analysis
Clinical scores were analyzed using the Mann-Whitney U test; other results were statistically evaluated using the Student t test (StatView program, Abacus Concepts, Berkeley CA). A p value of <0.05 was considered statistically significant.
| Results |
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The results of experiments are summarized in Fig. 1
and Table II
.
Control animals (Group A, nontreated; group B, treated with control mAb
M18/2) showed the typical disease course of TMEV-IDD. On day 40, about
35% of mice showed clinical signs such as waddling gait, extensor
spasm, and hind leg paralysis; mean clinical scores were 2.8 in group A
and 2.7 in group B, respectively. On day 80, all mice from groups A, B,
and D (treated with anti-B7-2 mAb) and with E (treated with both
anti-B7-1 mAb and anti-B7-2 mAb) developed TMEV-IDD; the mean
clinical scores were 3.6 in group A and 3.5 in group B. In contrast,
only 6.7% (1/15) of mice treated with anti-B7-1 mAb (group C) had
clinical signs on day 40; the mean clinical score was 1.3. On day 80,
40% (4/10) of mice treated with anti-B7-1 mAb had clinical signs
with a mean clinical score of 1.9. These results demonstrate that
clinical signs of demyelinating disease are significantly suppressed
(p < 0.01) in animals treated with
anti-B7-1 mAb (group C), as compared with those in control groups
(groups A and B). In addition, we could not detect any significant
differences in other treatment groups (groups D and E) that received
either anti-B7-2 alone or together with anti-B7-1 mAb.
Representative mice were blindly selected from each group
(n = 5 from each group) for histological examination
and sacrificed on day 40 post i.c. infection. The characteristic
perivascular and parenchymal mononuclear cell infiltration and
extensive demyelination in the white matter of spinal cord were
observed in mice from groups A, B, D, and E (Fig. 2
A). The inflammation scores and
demyelination scores were significantly lower in mice from group C
(p < 0.01) than those from control groups
(Fig. 2
B, Table II
).
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Virus-specific DTH, as measured by the ear-swelling assay, is
known to correlate strongly with susceptibility to TMEV
(31). DTH has been shown to be mediated by the Th1
lymphocyte subset (34). To compare the clinical signs and
the level of TMEV-specific DTH, we assessed the level of DTH 36 days
after viral infection in mice selected for immunological examination
(n = 5 from each group). The levels of DTH at 36 days
postinfection in mice of control groups (groups A and B) were increased
at almost the same levels previously reported (35).
Conversely, they were significantly lower (p <
0.01) in mice treated with neutralizing anti-B7-1 Ab (group C).
These results show that administration of anti-B7-1 mAb inhibits
the level of TMEV-specific DTH. The levels of DTH at 36 days
postinfection in mice treated with anti-B7-2 mAb, and mice treated
with both anti-B7-1 mAb and anti-B7-2 mAb, were increased to
similar levels of control groups (Fig. 3
A).
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T cell proliferative responses have been used frequently to assess
the level of response of CD4+ T helper cells to the virus
(36). After DTH measurement, same mice were sacrificed on
day 40 post i.c. infection. Spleen cells were taken out and used for
examination for TMEV-specific T cell proliferation and ELISPOT assay.
When the TMEV-specific T cell proliferative responses of mice treated
with neutralizing anti-B7-1 mAb were compared with those of control
groups, we observed a distinct difference (Fig. 3
B).
These results may indicate that administration of anti-B7-1 mAb
inhibits the ability of TMEV-specific T cell proliferation of
TMEV-specific mouse spleen cells or inhibits the generation of
TMEV-specific T cells at the precursor level. TMEV-specific T cell
proliferative responses of mice treated with anti-B7-2 mAb, and
mice treated with both anti-B7-1 mAb and anti-B7-2 mAb, were
increased to almost the same levels as those of control groups.
TMEV-specific Ab responses
We examined the Ab responses in the experimental groups of mice to
determine a possible effect of anti-B7-1 and anti-B7-2 Abs on
the production of TMEV-specific Abs. Sera were taken from all mice of
each group (n = 10 from each group) on day 56 and day
80 post i.c. infection. On day 56, there was no significant difference
in the TMEV-specific Ab levels among the six groups. We also explored
whether Ab isotypes were affected. We detected IgG1 and IgG2b Abs in
all groups, with no significant difference among the five groups. We
also detected IgG2a Ab in control groups (Groups A, B, D, and E), but
not in the anti-B7-1 mAb neutralizing Ab-treated group (group C)
(Fig. 4
). These results indicate that,
despite an unaltered level of total Abs, there is a lack of IgG2a
component in animals treated with anti-B7-1 neutralizing Abs. This
result is consistent with the suppression of Th1 response since IgG2a
production is dependent on the presence of Th1 population.
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After DTH measurement, the same mice (n = 5 from
each group) were sacrificed on day 40 post i.c. infection. Spleen cells
were taken out and used for ELISPOT assay. We could not detect any
TNF-
, IFN-
, IL-4, or IL-10 in the sera from animals of any
groups. The levels of cytokine-producing cells in the spleens of
animals were also assessed using the ELISPOT method. TNF-
production
by spleen cells from mice treated with neutralizing Abs to B7-1 was
significantly suppressed (p < 0.01) compared
with other groups (Fig. 5
A).
IFN-
production by spleen cells from mice treated with anti-B7-1
neutralizing Abs was also significantly suppressed
(p < 0.01) compared with other groups (Fig. 5
B). No significant differences in the production of
Th2-derived cytokines such as IL-4 and IL-10 were observed among all
groups (Fig. 5
, C and D). No cytokine
production by spleen cells was detected in uninfected mice. These
results suggest that production of proinflammatory cytokines such as
TNF-
and Th1 cell-derived inflammatory cytokines such as IFN-
was
down-regulated in TMEV-infected mice treated with anti-B7-1
neutralizing Abs.
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| Discussion |
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(50). CD80 (B7-1) is preferentially
up-regulated on T and B cells and macrophages of the CNS during EAE and
in acute CNS plaques from patients with multiple sclerosis (22, 51). The effects of anti-B7 mAbs in mouse EAE have been
reported. In myelin basic protein (MBP)-induced mouse EAE system, the
proliferation and IL-2 production of MBP-specific lymph node cells
(LNC) were inhibited, and the clinical signs were reduced by using
CTLA4Ig (52). They also showed that anti-CD80 (B7-1)
mAb blocked development of the first disease episode and anti- CD86
(B7-2) mAb had no effect. Injection of CTLA4Ig on day 2
postimmunization protected the disease, but combined anti-CD80
(B7-1) mAb and anti-CD86 (B7-2) mAb treatment on day 2
resulted in marked exacerbation of disease (20). The same
group also showed that administration of anti-CD80 (B7-1) in
actively induced EAE resulted in almost complete suppression of
clinical disease. Administration of both anti-CD80 (B7-1) mAb and
anti-CD86 (B7-2) mAb on day 2 resulted in a delay in disease onset
and reduced disease severity, but disease suppression was not as
complete as with anti-CD80 (B7-1) alone. Conversely, anti-CD86
(B7-2) mAb treatment resulted in modest disease exacerbation. In vitro
activation of MBP-specific lymph node cells was inhibited by the
combination of anti-B7-1 mAb plus anti-B7-2 mAb, but not
individually (21). The opposite results reported in Refs.
20 and 21 with the injection of both anti-B7-1 mAb and
anti-B7-2 mAb may be due to the different protocols for disease in
induction. In Ref. 20 , the authors used a pertussis toxin-dependent
model of actively induced EAE. In Ref. 21 , the authors used a pertussis
toxin-independent model of active EAE (involving two injections of MBP)
and adoptively transferred EAE. Kuchroo et al. showed that anti-B7-1 mAb drove naive MBP-specific helper T cells along a Th2 pathway whereas anti-B7-2 mAb favored Th1 development. Administration of anti-B7-1 mAb inhibited the generation of Th1 cells and ameliorated the disease, whereas injection of anti-B7-2 mAb inhibited the generation of Th2 cells and worsened the disease. Blocking B7 molecules in vivo did not inhibit the generation of Ag-specific T cells, consistent with the in vitro differentiation results, but affected the cytokine profiles of the responding T cells (18). Millers group showed preferential up-regulation of B7-1 during the course of relapsing EAE and a selective increase in its functional costimulatory activity relative to B7-2 in relapsing EAE. When these Abs were administered during the first remission after the acute phase of the disease, anti-B7-2 treatment had no effect, whereas blockade of B7-1/CD28 interactions using the F(ab) fragments of anti-B7-1 resulted in the blockade of disease relapses (22). Taken together, in the mouse EAE system, administration of anti-B7-1 mAb ameliorates and that of anti-B7-2 mAb worsens the disease, and the various EAE results suggest a requirement for B7-1 in the pathogenesis. These results are similar to our study. In TMEV-IDD, anti-B7-1 mAb treatment suppressed the disease. Our study showed this treatment also suppressed TMEV-specific T cell proliferation and DTH, and down-regulated proinflammatory and Th1 cell-derived inflammatory cytokines. These result suggest that inhibition of encephalitogenic CD4+ Th1 cell activation caused by this treatment may lead to the suppression of TMEV-IDD. Though anti- B7-2 mAb treatment did not change the clinical course of demyelination, this treatment may suppress Th2 cell function. It is interesting to note that treatment with both anti-B7-1 mAb and anti-B7-2 mAb had no effect on TMEV-IDD. Suppression of both Th1 and Th2 cells may not change the Th1-Th2 balance and eventually lead to demyelination. However, the effect of both anti-B7-1 mAb and anti-B7-2 mAb treatment is controversial in EAE. In another autoimmune disease model, autoimmune diabetes of nonobese diabetic (NOD) mouse, anti-B7-2 mAb treatment prevented, whereas anti-B7-1 exacerbated, the disease (53, 54). Since Th1-type cytokines should mediate disease in nonobese diabetic mice (55), these results may suggest that the concept B7-1 costimulation preferentially results in development of Th1 cells whereas B7-2 results in the development of Th2 cells may be overly simplified. The conflicting results between immune-mediated demyelinating disease and autoimmune diabetes may be due to the difference in the nature of APCs on the side of the autoimmune disease, or the presence of the blood-brain barrier. Although the importance of the role of CD28/B7 costimulatory signals in the regulation TMEV-IDD has been shown in this study, further investigation should be needed in the pathogenesis of demyelinating disease. Finally, since methods of clinical therapy of MS are still incomplete, it is important to examine the possibility of anti-cytokine therapy, including mAb to B7-1.
| Footnotes |
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2 Address correspondence and reprint requests to Dr. Chang-Sung Koh, Third Department of Medicine (Neurology), Shinshu University School of Medicine, 3-1-1 Asahi, Matsumoto 390-8621, Japan. E-mail address: ![]()
3 Abbreviations used in this paper: MS, multiple sclerosis; TMEV, Theilers murine encephalomyelitis virus; TMEV-IDD, TMEV-induced demyelinating disease; EAE, experimental autoimmune encephalomyelitis; DTH, delayed-type hypersensitivity; i.c., intracerebral. ![]()
Received for publication July 8, 1999. Accepted for publication September 17, 1999.
| References |
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gt11 system: different patterns of antibody reactivity among different mouse strains. J. Neuroimmunol. 27:173.[Medline]
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