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Regular Articles |
From the Institute of Neurology,*
University of Vienna,
Vienna, Austria; Department of
Neuroimmunology,
Max Planck Institute for
Neurobiology, Martinsried, Germany; and Department of
Pathology,
Dartmouth Medical School, Lebanon,
New Hampshire
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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In vitro studies have identified a variety of mechanisms that lead to apoptosis of T cells. Several of these mechanisms may also operate in the CNS in vivo. Apoptosis may ensue in the course of antigen presentation9 either induced by excessive antigen in the lesions10 or caused by unbalanced signaling by CNS antigen-presenting cells.11-13 Alternatively, various antigen-independent mechanisms of apoptosis may be involved. Steroids induce apoptosis of T cells in the thymus,14 and in the course of EAE, glucocorticoid levels peak at the time of recovery,15 when T-cell apoptosis is most prominent.8 Cytokines such as transforming growth factor-ß, which can induce T-cell apoptosis in vitro,16 are locally produced in EAE lesions.17 Furthermore, activation of the Fas-dependent cell death pathway may be involved. In inflammatory eye lesions, as an example, T cells undergo Fas-FasL induced apoptosis caused by abundant expression of FasL in the corneal epithelium and retina.18
To comprehend the mechanisms operating in the CNS in vivo, a number of unresolved questions need to be addressed: Is apoptosis unique to certain autoreactive T-cell clones such as myelin basic protein (MBP)-specific T cells, or is it a general feature of T cell-mediated CNS autoimmunity? Is apoptosis restricted to the autoantigen-specific T cells or are all incoming T cells destroyed, regardless of their antigen specificity? Which resident cells in the CNS are essential for apoptosis induction and, more specifically, is apoptosis dependent on major histocompatibility complex-restricted antigen presentation by facultative resident antigen-presenting cells such as astrocytes or microglial cells?
This study addresses these questions in several different models of EAE. A transgenic model used allowed unequivocal identification of transferred autoantigen-specific or secondarily recruited "bystander" T cells in the lesions and also permitted their fate to be discerned during local proliferation and destruction. Our data suggest that the CNS possesses a mechanism of T-cell elimination by apoptosis that is not dependent on the presence of the antigen for which the T cell is specific, nor does it require the activation of the lymphocyte that enter the CNS.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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For the induction of EAE and for the production of
antigen-specific T-cell lines, 6–12-week-old inbred Lewis rats or
TK-tsA transgenic rats were used that were either purchased from
Charles River (Sulzfeld, Germany) or provided by the local animal
facilities from the Max Planck Institute for Psychiatry (Martinsried,
Germany). The production of the TK-tsA transgenic Lewis rats has been
described before.19
These animals harbor 250 to 300 copies
of a transgene cassette encompassing the thymidine kinase (TK) promoter
of herpes simplex virus, the temperature-sensitive simian virus 40 T
antigen tsA58/dl884 (tsA), and simian virus 40 polyadenylation and
splice sites. Northern blot analysis for tsA58 mRNA of thymus cells
from transgenic animals showed that the transgene is not expressed and,
thus, can be used as a stable genomic marker of otherwise normal Lewis
rat cells. For the production of bone marrow chimeras, Lewis rats were
obtained from Charles River Laboratories (Wilmington, MA), and DA rats
were supplied by Bantin and Kingman Breeders (Fremont, CA). The
(DA x Lewis) F1 hybrids that served as bone marrow
donors were generated in the animal colony at Washington University
(St. Louis, MO) from these two parental stocks. Briefly, the bone
marrow chimeras were created by lethally irradiating (1,000 rad)
2-month-old DA rats and subsequently infusing 108
bone
marrow cells from the (DA x Lewis) F1 via the tail
vein, as described previously20
(Table 1)
. All animals were maintained in
accordance with United States and German institutional and federal
guidelines for the treatment of rodents.
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The specific establishment of the different T-cell lines is
described in detail in the respective publications cited in Table 1
. In
general, 8 to 12-week-old Lewis rats or TK-tsA-transgenic Lewis rats
were immunized with 0.05–0.2 mg of various peptides in 0.2 ml complete
Freund's adjuvant. Draining lymph nodes were isolated 9 to 13 days
after sensitization, and stable T-cell lines were established as
described.6
Briefly, these cells were propagated by
alternating cycles of antigen-driven T-cell activation, using
irradiated syngeneic thymus cells as antigen-presenting cells, and
interleukin (IL)-2-dependent expansion of activated T cells. Phenotype
and antigen specificity of these cells was determined as reported
elsewhere.21
Induction of EAE
Adoptive transfer experiments were performed using freshly activated T-cell blasts specific for MBP, MOG, myelin-associated glycoprotein (MAG), and S100b after 72 hours of stimulation with the appropriate antigen. T-cell blasts, dependent on the cell line varying in numbers, were injected intravenously. EAE in the radiation bone marrow chimeras and respective controls was induced by intravenous injection of 107 MBP-specific Lewis T lymphoblasts. In the TK-tsA experiments, EAE was induced in 8 to 12-week-old TK-tsA transgenic rats by injection of normal Lewis MBP-specific T blasts. Alternatively, EAE was induced in 8 to 12-week-old Lewis rats by passive transfer of freshly activated (TK-tsA) MBP-specific T-line blasts. A third experiment comprised Lewis rats that received (TK-tsA) OVA-specific T lymphocytes, either as freshly activated T-cell blasts or as completely resting cells no longer able to respond to IL-2. In some of these animals the Tk-tsA OVA T cells were co-transferred with MBP-reactive Lewis T-cell blasts. The animals were examined daily for clinical signs of EAE, which was scored on the following scale: 0, healthy; 1, complete loss of tail tonus; 2, additional hind limb weakness; 3, hind limb paralysis and incontinence; 4, complete paralyses; and 5, death.
Sampling and Embedding
At various time points after T-cell transfer, animals were perfused with 4% paraformaldehyde in phosphate-buffered saline under deep anesthesia. The brain and spinal cord were removed and fixed in the same fixative for an additional 3 hours. This material was then embedded in paraffin. Paraffin sections 3 µm thick from spinal cord were cut and used for general pathological screening, in situ hybridization (ISH) for TK-tsA, in situ tailing (IST) for detection of DNA fragmentation, and immunocytochemistry.
ISH for TK-tsA
ISH was performed as described earlier,22 with the addition that, before acetylation, the sections were incubated in 10 mmol/L citric acid (pH 6.0) and microwave treated (five times for 5 minutes each, 700 W). Digoxygenin-labeled TK/tsA DNA probe, corresponding to the transgene cassette, was generated by random priming, according to the DIG DNA labeling and detection kit instructions (Boehringer Mannheim, Indianapolis, IN). For use in the ISH, the probe was diluted 1:100.
Immunocytochemistry
Immunocytochemistry was performed with a biotin-avidin technique as described in detail by Vass et al.23 The following primary antibodies were used: W3/13 (recognizing T cells; DAKO, Glostrup, Denmark) and proliferating cell nuclear antigen (PCNA; recognizing proliferating cells; DAKO). In case of double labeling for PCNA and W3/13, sections were primarily stained for PCNA by using a triple alkaline phosphatase anti-alkaline phosphatase system as described earlier in Breitschopf et al22 with nitroblue tetrazolium/5-bromo-4-chloro-3-indolyl phosphate as substrate. Next, W3/13 was stained with the same alkaline phosphatase anti-alkaline phosphatase system but visualized with Fast Red. This resulted in PCNA+ nuclei stained black and W3/13+ T cells (cytoplasm and cell membrane) stained red. To analyze nuclear condensation indicative for apoptosis, all sections were counterstained with hematoxylin.
IST
To detect cells with DNA fragmentation, IST was performed as described by Gold et al.24 Briefly, 3-µm paraffin sections from spinal cord were deparaffinized, treated with chloroform, and air dried. Next, sections were incubated in 50 µl of the reaction mixture (5 µl 10x tailing buffer, 1 µl digoxigenin-labeled nucleotides, and 44 µl transferase). As a secondary step, the sections were incubated with an alkaline phosphatase anti-digoxigenin F(ab')2 antibody at a dilution of 1:250. Alkaline phosphatase was visualized with nitroblue tetrazolium/5-bromo-4-chloro-3-indolyl phosphate. All materials for the IST were obtained from Boehringer Mannheim. Subsequently, the sections were stained with monoclonal antibody W3/13 as described above.
Quantification of (Apoptotic) T Cells
TK-tsA-positive cells were quantified in spinal cord cross-sections. Per cross-section the numbers of nonapoptotic (one or two distinctive spots; see Results) or apoptotic (diffuse labeling over the entire nucleus; see Results) cells were counted in the various compartments (parenchyma, meninges, and perivascular space of blood vessels). In general, from each animal, three cross-sections representing a total area of 10 mm2 were studied. In case of low numbers of infiltrating TK-tsA-positive cells (such as by injection of OVA-specific T cells), a total of five cross-sections were investigated. The total numbers of infiltrating T cells were quantified in the various compartments on spinal cord cross-sections. In the case of TK-tsA animals, these W3/13-stained sections were consecutive to the sections used for ISH. Apoptotic W3/13+ T cells were distinguished from nonapoptotic T cells by morphological criteria (nuclear condensation and fragmentation).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Apoptotic cells were identified in W3/13-stained sections by their
characteristic nuclear changes, ie, the condensation of chromatin and
nuclear fragmentation (Figure 1a)
. DNA
fragmentation in these cells was confirmed by their positive reaction
in IST-stained sections.8
T-cell apoptosis was found in all
models of EAE (induced by MBP-, MOG-, MAG-, and S100-reactive T cells)
despite quite pronounced variations in the patterns of inflammation in
these different conditions25
(Figure 2a)
. In general, apoptotic T cells were
dispersed throughout the CNS parenchyma, although in larger or
confluent lesions where inflammatory cells were densely packed,
apoptotic cells occurred in clusters of variable size (Figure 1b)
.
Because in vitro apoptosis of T cells frequently follows a
transient phase of cell cycle activation and/or
proliferation,26
we studied, by using the cell cycle marker
PCNA, whether these clustered T cells also might proliferate and
thereafter rapidly undergo apoptosis. Double staining for PCNA and
W3/13 showed that on day 4 of EAE, PCNA+ cells were only
found in the parenchyma. Considering the size and shape of the nucleus,
most of these cells were identified as macrophages (Figure 1c)
.
PCNA+ T cells were found to be extremely rare (one to two
cells/section) and in some cases appeared to have a condensed nucleus,
indicating that these cells were undergoing apoptosis (Figure 1, d and e)
. This sparse proliferation of T cells in the CNS confirms the
results from Ohmori et al,27
who used bromodeoxyuridine
labeling to detect proliferating T cells in the CNS. None of the cells
in the apoptotic clusters showed labeling for PCNA, opposing the view
that such clusters developed from a local expansion of
antigen-stimulated T-cell clones.
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The distribution of W3/13+ T cells in spinal cord
cross-sections was quantified by counting the numbers of T cells in
parenchyma, meninges, and perivascular space. As shown in Figure 2a
,
the distribution of T cells on day 6 of EAE induced by MBP-, MAG- or
S100-specific T cells in the different compartments of the CNS are
similar. In these models, most T cells are located in the parenchyma.
In the MOG EAE model, infiltration in the CNS parenchyma for as yet
unknown reasons is impeded, and thus, lymphocytes to a large extent are
retained in the meninges and perivascular space. From these
W3/13+ T cells in the various models, we quantified the
proportion of apoptotic W3/13+ cells in the different
compartments of the CNS. The results (Figure 2b)
show that apoptotic T
cells are present in the CNS neuroectodermal parenchyma, whereas
connective tissue compartments such as meninges and the perivascular
space are almost completely devoid of apoptotic T cells. This finding
strongly suggests that T-cell apoptosis relies on cellular factors or
contacts with cells exclusively present in the parenchyma.
Antigen Presentation by Parenchymal Glial Cells Is Not a Prerequisite for T Cell Apoptosis
Evidence that apoptosis of T cells depends on a parenchymal
component is supported by in vitro data showing that antigen
presentation by astrocytes or microglia but not by
thymocytes12,28,29
triggers programmed cell death of
encephalitogenic T cells. To investigate whether such a role of
resident microglia or astrocytes in vivo might be
demonstrated, we quantified the number of (apoptotic) T cells in the
spinal cord of bone marrow chimeras and control Lewis rats on day 6
after transfer of Lewis MBP-specific T cells. In these chimeric
animals, antigen presentation to the injected Lewis MBP-specific T
cells by resident CNS cells is precluded because of the mismatch
between the major histocompatibility complex expressed on the resident
cells and the major histocompatibility complex restriction requirements
of the infiltrating T cells.20,30
The results (Table 2)
revealed that in both chimeric and
control animals, high numbers of T lymphocytes infiltrated the spinal
cord. As in all other MBP T-cell models investigated, in chimeric
animals the majority of T cells were present in the parenchyma with
lower numbers of T cells in meninges and perivascular space.
Quantification of apoptotic T cells (Table 2)
in the parenchyma
revealed a similar percentage of T cells undergoing apoptosis in both
chimeric and control animals. Earlier studies in bone marrow chimeras
have shown that, despite the absence of antigen presentation by
CNS-resident glial cells, the induction, progression, and regression of
EAE is very similar to that in animals with major histocompatibility
complex-matched CNS-resident antigen-presenting cells.20,31
Our observation that apoptosis of lymphocytes is retained in chimeric
animals further delineates that antigen-induced apoptosis by resident
astrocytes or microglial cells cannot be held responsible for
down-regulation of inflammation in the CNS.
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The definition of the type of T cells undergoing apoptosis in the
CNS during EAE is essential to unravel the mechanisms responsible for
destruction of these lymphocytes. To address this question, we used a
transgenic Lewis rat with a high number of copies of foreign DNA in its
genome, which is not transcribed into mRNA but allows reliable
identification of transferred T cells even when they undergo several
cycles of proliferation or are destroyed by apoptosis. ISH with the
TK-tsA DNA probe performed on the spinal cord of such TK-tsA transgenic
animals revealed labeling as one or two distinctive spots over the
nucleus of each individual cell (Figure 1, f and g)
. In the various ISH
reactions performed on the CNS of TK-tsA transgenic animals, a labeling
efficiency of 80 to 91% was reached. ISH on nontransgenic Lewis rats
showed a background labeling of less than 0.5% of cells. In EAE
animals, apoptotic T cells instead of the distinctive spots showed a
strong diffuse labeling over the entire nucleus (Figure 1i)
. In some
cases, pinched-off apoptotic bodies were seen close to these condensed
nuclei (Figure 1, j and k)
. Obviously, the diffuse labeling of
TK-tsA+-degenerating T cells is a result of the DNA
cleavage in apoptotic cells, thereby spreading the multiple copies
of TK-tsA genome (which in hemizygous animals lie in a tandem
repeat on one chromosome) over the entire nucleus.
MBP-Specific T Cells Are Abundant at Early Stages of EAE and Are Destroyed by Apoptosis
MBP-specific T cells during the course of EAE were quantified by
counting the number of TK-tsA-positive nuclei in the spinal cord. Two
hours and 24 hours after injection of TK-tsA MBP-specific T cells,
these cells were found in the CNS only in very low numbers (Table 3)
. The number of MBP-specific T cells
dramatically increased on day 4 after cell transfer. At this time
point, high numbers of MBP-specific T cells were present in the
meninges, perivascular space, and the CNS parenchyma (Figure 1h)
.
Quantification revealed that at this time point, high numbers of
MBP-specific T cells in the parenchyma were undergoing apoptosis (Table 4)
, whereas in the meninges and perivascular space no apoptotic
MBP-specific T cells were present.
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.
However, given that the total numbers of T cells remained the same
(Table 3)
, at this time point large numbers of host-derived,
secondarily recruited T cells apparently infiltrated the CNS.
Also in the meninges and perivascular space, the percentage of
MBP-specific T cells decreased (Table 3)
, showing an 83% reduction in
numbers compared with a 46% reduction of total T cells. Similarly, in
comparison with day 4, the percentage of apoptotic MBP-reactive T cells
declined (Table 4)
.
At day 9 of EAE, both the numbers of MBP-specific T cells and the total
T-cell population were drastically reduced (Figure 3)
. In the parenchyma, the MBP-specific T
cells still comprised 24% of all T cells, whereas, in the meninges and
perivascular space, only sporadically were MBP-specific T cells found
(Table 3)
. The numbers of apoptotic T cells were also decreased at this
late stage of EAE (Figure 3)
. At this period, the vast majority of
apoptotic T cells were unlabeled, the MBP-specific T cells contributing
only 21% of all apoptotic T lymphocytes (Table 4)
.
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The results described above implied that the numbers of
MBP-specific apoptotic T cells could not account for all of the
apoptotic W3/13+ T cells in the spinal cord at the various
time points of EAE. To demonstrate apoptosis of host-derived T cells
directly, we therefore induced EAE in TK-tsA rats by injection of
wild-type Lewis MBP-specific T cells. In this experimental paradigm,
all TK-tsA-labeled T cells are host-derived. On day 4, the first
host-derived inflammatory cells were detected in the meninges,
perivascular space, and parenchyma. At this time point, most apoptotic
T cells were unlabeled, with only few TK-tsA+ apoptotic
cells in the parenchyma (Figure 1, l to n)
. During the course of EAE,
the percentage of these host-derived apoptotic T cells gradually
increased until a maximum of 56% was reached on day 9 (Table 4)
.
Although this experiment established that secondarily recruited
host-derived T lymphocytes undergo apoptosis in inflammatory CNS
lesions, it does not answer the question whether these host-derived
cells are autoreactive or of irrelevant antigen specificity.
Both Activated and Resting OVA-Reactive T Cells Are Recruited into EAE Lesions and Locally Undergo Apoptosis
To determine whether apoptosis of lymphocytes in the nervous
system is confined to autoreactive T cells or whether it affects T
cells of any specificity, we transferred TK-tsA-labeled, OVA-specific T
cells in the presence or absence of Lewis MBP-specific T cells (Table 5)
. In the absence of EAE induced by
MBP-specific T cells, 4 days after transfer, OVA-specific T cells were
not found in the CNS. In contrast, in animals with transfer EAE
(MBP-reactive T cells and OVA-specific T cells injected on day 0),
OVA-specific T cells had been recruited to the CNS lesions on day 4 of
EAE (Figure 1o)
. In these animals, almost 10% of all T cells in the
CNS were derived from the OVA-specific T-cell line. Resting
OVA-specific T cells transferred to EAE rats also appeared in the CNS
lesions, although to a much lower extent than their activated
counterparts (Figure 1q)
. In both the resting and activated
OVA-specific T-cell populations that found their way into the CNS
parenchyma after adoptive transfer, the presence of apoptotic cells
could be documented (Figure 1, p and r)
. In fact, the percentage of
apoptotic cells was even higher among the resting than among the
activated OVA-specific T lymphocytes, even though the overall number of
resting cells entering the CNS was lower than the activated type (Table 5)
.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The experiments using TK-tsA transgene-labeled, MBP-specific T cells demonstrate that in the early stage of EAE (day 4), almost 50% of all T cells found in the target organ are derived from the encephalitogenic, CNS antigen-specific population. Although homing and/or the selective retention of antigen-specific T cells is not the main subject of the current study, this observation is potentially important, because it challenges the longstanding dogma that antigen-specific T cells only constitute a very small percentage (less than 1%) of all lymphocytes in lesions in preclinical/clinical stages of EAE.32-34 Our data, however, are in line with the results from others who in early phases of monophasic EAE found high numbers30,35 of antigen-specific T cells in CNS lesions. A possibility is that parenchymal infiltration of T cells differs extensively between chronic EAE in mice32-34 and the acute monophasic EAE in rats as presented here. Alternatively, the finding of low numbers of antigen-specific T cells may result from tracing methods (autoradiography) that largely underestimated the actual number of antigen-specific T cells in the CNS parenchyma.
Several observations indicate that antigen-induced apoptosis may contribute to the elimination of antigen-specific T cells in the CNS. Critchfield et al10 showed that intravenous treatment with soluble MBP improved the clinical course of EAE, possibly by high-dose antigen-induced apoptosis of MBP-specific T cells. Similarly, in experimental autoimmune neuritis, intravenous injection of recombinant P2 protein prevented clinical experimental autoimmune neuritis and led to a profound increase of apoptotic cells in the sciatic nerve.36 The elimination of TK-tsA+ MBP-specific T cells confirms the results from Tabi et al,37 who described elimination of Vß8.2+ antigen-specific T cells. Although in our system antigen-specific cells appear to die by apoptosis, our observations do not support a mechanism by which only CNS antigen-specific cells are eliminated. In fact, nonspecifically recruited, host-derived T cells also died in the CNS, a process especially prominent in the late stage of the disease. Because host-derived cells could theoretically contain a large pool of CNS-reactive T lymphocytes,38 OVA-specific T cells were transferred to animals destined to develop EAE, and they likewise were found to undergo apoptosis in the CNS in high proportions. This finding is in contrast to that of Tabi et al,37 who provided indirect evidence for selective survival of OVA-reactive T cells and, thus, concluded that apoptosis in EAE is restricted to the antigen-specific T cells. In their model, these authors could not differentiate the injected OVA-specific T cells from the co-transferred MBP-specific T cells. Indirect evidence showing that T cells isolated from the CNS proliferated strongly after stimulation with OVA, whereas no proliferation after MBP stimulation was achieved, was therefore used as an argument that only antigen-specific T cells were selectively eliminated. It may be clear from their work, as well as from that of others,11,12,28,35 that antigen-specific T cells in the CNS become anergic. However, our results show that apoptosis in the CNS also proceeds independently of anergy.
Recent work in human brain focused on Fas-induced apoptosis as a mechanism to eliminate inflammatory T cells. Fas+ T cells and FasL+ microglial cells and macrophages have been demonstrated in the brain from multiple sclerosis patients,39,40 suggesting that Fas-induced apoptosis of T cells by microglial cells may occur. In addition, apoptosis of activated T cells may also be induced by Fas-FasL interactions between T cells themselves,41 expression of both Fas and FasL on apoptotic T cells in rat EAE lesions has been described.42 Arguing against a role for Fas-FasL-induced apoptosis in EAE are data showing that T-cell apoptosis is not abolished in EAE lesions of lpr and gld mutant mice, although they lack functional Fas or FasL.43
Another mechanism that at least in vitro can induce death of T cells involves corticosteroids. High-dose corticosteroid treatment augments apoptosis in inflammatory lesions of EAE44 as well as experimental autoimmune neuritis.45 The contribution of endogenous corticosteroids to T-cell apoptosis in the natural course of EAE is less clear. Lymphocytes undergo apoptosis in the CNS parenchyma but not in the meninges, the perivascular space, or at the inoculation site after active immunization.8 Equal, if not greater, levels of apoptosis would be expected at such locations if systemic corticosteroids were responsible. Moreover, the induction of EAE in adrenalectomized rats revealed only a minor reduction in the level of apoptotic cells in the inflammatory CNS lesions in comparison.46
Thus, the question arises whether the CNS hosts a mechanism of T-cell elimination unrelated to the described Fas-dependent, antigen-specific or corticosteroid-induced mechanisms.47 One possible group of apoptosis-inducing factors in the CNS might be galectins. Galectins are ß-galactoside-binding proteins that are present on hepatic sinusoidal endothelial cells and thymic epithelial cells and have been shown to induce apoptosis in various populations of thymocytes as well as in mature T lymphocytes.48 Another mechanism involved in the elimination of T cells could be the down-regulation of IL-2 and inhibition of lymphocyte proliferation by sialic acid-containing glycosphingolipids (gangliosides).49 Such moieties are widely distributed in the CNS.50 Gangliosides may do so by binding to the IL-2 receptor of T lymphocytes.51 This down-regulation of IL-2 alone can make T cells susceptible to several mechanisms of apoptosis including the corticosteroid-induced type.9,16
As shown in this study and former studies8,37 the rate of T cell apoptosis in the nervous system during acute EAE is exceptionally high and differs strongly from T cell apoptosis during inflammatory diseases in the skin (dermatomyositis) or muscle (myositis) where it is nearly absent.47,52 Whether in multiple sclerosis (MS) brain T cell apoptosis is operating efficiently is not clear. Apoptosis of CD3+ T cells can be observed in MS brain but the numbers are low and not in any way comparable to the incidence of apoptosis in acute monophasic EAE.53 However, we have recently studied T cell apoptosis in a case of acute disseminated encephalitis (ADEM), a disease more closely comparable to acute EAE.54 Apoptosis rates in this case reached about 30% of all T cells, which equals the incidence of apoptosis in acute EAE (Bauer J, Stadelmann C, Bancher C, Jellinger K, and Lassmann H, manuscript in preparation). This suggests that in principle, human and rodent brains have similar mechanisms for elimination of T cells. Whether the low incidence of apoptotic T cells in MS is a consequence of the disease's chronicity or whether this reflects a disturbed mechanism of T cell elimination has to be determined in future studies.
In conclusion, our study shows that the neuroectodermal CNS parenchyma provides a very efficient instrument of T-cell destruction by apoptosis. A new and important finding is that the mechanism(s) active in the CNS parenchyma affects not only the T cells specific for a CNS antigen, but eliminates all T-cell populations that arrive in inflammatory brain lesions regardless of specificity or activation state. This fundamental program for T-cell deletion in the CNS can then be further assured by a variety of antigen- or activation-dependent T-lymphocyte deletion processes. Overall, the existence of multiple, potentially synergistic T-cell depletion mechanisms in the neural parenchyma makes the CNS an extremely hostile environment for these cellular elements of the immune system.
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Acknowledgements |
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Footnotes |
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Supported by the Deutsche Forschungsgemeinschaft Sonderforschungsbereich 217 (Projekt C12), by the European Community Biotechnology programme BIO-960174, by Austrian Science Foundation grant P10608-Med, and by grant NS27321 (to WFH).
Accepted for publication June 5, 1998.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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and tumor necrosis factor (TNF)-
. J Exp Med 1997, 20:305-316
ß T lymphocytes for apoptosis. Nature 1991, 353:858-861[Medline]
B-crystallin, a small heat shock protein. Nature 1995, 375:798-801[Medline]
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 B. P. Schlitt, M. Felrice, M. L. Jelachich, and H. L. Lipton Apoptotic Cells, Including Macrophages, Are Prominent in Theiler's Virus-Induced Inflammatory, Demyelinating Lesions J. Virol., April 1, 2003; 77(7): 4383 - 4388. [Abstract] [Full Text] [PDF]
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M. Djerbi, K.-B. Abdul-Majid, M. Abedi-Valugerdi, T. Olsson, R. A. Harris, and A. Grandien Expression of the Long Form of Human FLIP by Retroviral Gene Transfer of Hemopoietic Stem Cells Exacerbates Experimental Autoimmune Encephalomyelitis J. Immunol., February 15, 2003; 170(4): 2064 - 2073. [Abstract] [Full Text] [PDF]
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 W. Lu, M. Bhasin, and S. E. Tsirka Involvement of Tissue Plasminogen Activator in Onset and Effector Phases of Experimental Allergic Encephalomyelitis J. Neurosci., December 15, 2002; 22(24): 10781 - 10789. [Abstract] [Full Text] [PDF]
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L.-Y. Kwok, H. Miletic, S. Lutjen, S. Soltek, M. Deckert, and D. Schluter Protective Immunosurveillance of the Central Nervous System by Listeria-Specific CD4 and CD8 T Cells in Systemic Listeriosis in the Absence of Intracerebral Listeria J. Immunol., August 15, 2002; 169(4): 2010 - 2019. [Abstract] [Full Text] [PDF]
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J. S. Haring, L. L. Pewe, and S. Perlman Bystander CD8 T Cell-Mediated Demyelination After Viral Infection of the Central Nervous System J. Immunol., August 1, 2002; 169(3): 1550 - 1555. [Abstract] |
