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*
Cellular Immunology Laboratory, Institut National de la Santé et de la Recherche Médicale, CJF 9711, Hôpital Pitié-Salpêtrière, Paris, France;
Unité de Biologie Moleculaire du Gène, Institut National de la Santé et de la Recherche Médicale, Unité 277, Institut Pasteur, Paris, France; and
Centre National de la Recherche Scientifique, Unité Mixte de Recherche 7627, Hôpital Pitié-Salpêtrière, Paris, France
| Abstract |
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islet cells (rat insulin promoter-HA mice) and
islet-specific Tc1 and Tc2 cells were generated in vitro from
HA-specific CD8+ cells of TCR transgenic mice (CL4-TCR
mice). One million Tc1 cells, differentiated in vitro in the presence
of IL-12, transferred diabetes in 100% of nonirradiated adult rat
insulin promoter-HA recipients; the 50% diabetogenic dose was 5
x 105. Highly polarized Tc2 cells generated in the
presence of IL-4, IL-10, and anti-IFN-
mAb had a relatively low,
but definite, diabetogenic potential. Thus, 5 x 106
Tc2 cells caused diabetes in 6 of 18 recipients, while the same dose of
naive CD8+ cells did not cause diabetes. Looking for the
cause of the different diabetogenic potential of Tc1 and Tc2 cells, we
found that Tc2 cells are at least as cytotoxic as Tc1 cells but their
accumulation in the pancreas is slower, a possible consequence of
differential chemokine receptor expression. The diabetogenicity of
autoreactive Tc2 cells, most likely caused by their cytotoxic activity,
precludes their therapeutic use as regulators of
autoimmunity. | Introduction |
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or TNF-
(1). However, not
long after the description of Th1 and Th2-like Th cells, an analogous
functional division of the CD8+ T cell subset was
also revealed (2, 3, 4), and the Tc1/Tc2 terminology was
later introduced by Sad et al. (5). Two main types of Tc2
cells have been described, apparently depending on the conditions of in
vitro T cell differentiation. In one of the early reports,
CD8+ T cells stimulated with PMA and ionomycin in
the presence of IL-4 were found to produce IL-4, IL-5, and IL-10; they
lost cytotoxic activity and CD8 expression, and provided cognate help
to B cells (6). Noncytotoxic CD8+ T
cell clones, which expressed CD40 ligand and helped B cells, were also
described by Cronin et al. (7). However, in other models,
Tc2 cells of an apparently different type were described. These Tc2
cells exerted perforin-mediated cytotoxicity; expressed the CD8
-
and
-chains; secreted IL-4, IL-5, and IL-10; and provided bystander,
but not cognate, help to B cells. The cytokine profile of Tc2 cells
generated by stimulation with alloantigen, H-Y Ag, or specific peptide
was found to be stable both in vitro (5) and in vivo
(8). Functional in vivo assays demonstrated that Tc2 cells
are able to trigger a delayed-type hypersensitivity reaction and have
strong graft-vs-lymphoma activity (9, 10, 11). Interestingly,
upon adoptive transfer, in vitro-polarized influenza virus
hemagglutinin
(HA)3-specific Tc2
cells were found to be inefficient in clearing influenza virus
infection (12). In another model, in vitro-generated
tumor-reactive Tc2 cells were less efficient in eliminating lung tumors
than Tc1 cells (13). Tc2-like CD8+ cells have been detected in diverse pathological conditions in humans as well as in mice. CD8+ T cells producing type 2 cytokines were found in the respiratory tract, mediastinal lymph nodes, and spleen of mice infected with influenza virus (14, 15, 16). Furthermore, Tc2 cells seem to be involved in human pathology, because IL-4-producing CD8+ cells have been detected in patients with AIDS and Job-like syndrome and also in lepromatous leprosy (17, 18, 19). A functional role for IL-4- and IL-5-producing T cells has been suggested in experimental bronchial hyperreactivity; development of IL-5-producing CD8+ cells was detected in lymphocytic choriomeningitis virus (LCMV) TCR transgenic mice undergoing a Th2 immune response against OVA emulsified in incomplete Freund adjuvant immunized concomitantly with LCMV peptide via the airways (20). These Tc2 cells were found to trigger a lung eosinophilic cell infiltration upon challenge with the viral Ag.
However, no data are available on the role of Tc1 and Tc2 cells in
autoimmunity. Like CD4+ cells,
CD8+ cells are also known to have an important
role in both the induction and the down-regulation phase of
organ-specific autoimmune diseases, such as insulin-dependent diabetes
mellitus (IDDM) and experimental allergic encephalomyelitis (EAE; Ref.
21, 22, 23, 24, 25, 26). According to most of the experimental data
available, autoreactive Th1 cells are effectors, whereas Th2 cells are
regulators, of the autoimmune tissue damage in organ-specific
autoimmunity (27, 28), so an analogous functional division
of Tc1-Tc2 cells might also apply. Furthermore,
CD8+ cells were found to be mediators of oral
tolerance to autoantigens (29). Whether these
TGF-
-producing CD8+ cells are related to the
Tc2 cells described in other models has not been determined. However,
investigation of the potential Ag-specific immunoregulatory activity of
Tc2 cells is of theoretical, as well as practical, interest; if
autoreactive Tc2 cells were found to be devoid of diabetogenic
potential they could be tested as regulators of the destructive
autoimmune response mounted by Tc1 and Th1 cells.
The aim of this study was to explore the role of autoreactive Tc1 and
Tc2 cells in an organ-specific autoimmune disease, IDDM, employing an
adoptive transfer model based on the use of HA-specific T cells from
TCR transgenic mice (CL4-TCR mice) and recipients rat insulin promoter
(RIP)-HA transgenic mice expressing HA in the pancreatic
cells
(30, 31). This approach enabled us to generate high purity
autoreactive Tc1 and Tc2 populations from naive
CD8+ cells, providing the means to compare
directly the pathogenic potential of Tc1 and Tc2 effectors expressing
the same TCR. Tc2 cells produced small amounts of IFN-
and high but
variable amounts of IL-4 and IL-10. We found that Tc1 and Tc2 cells had
similar levels of cytotoxic activity. However, pancreas-specific homing
and proliferative capacity of Tc2 cells was lower than that of Tc1
cells. Transferred to adult, nonirradiated RIP-HA recipients, Tc1 cells
were highly diabetogenic, while Tc2 cells had a definite, but reduced,
diabetogenic potential.
| Materials and Methods |
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The CL4-TCR transgenic mouse line (30) expresses an
H-2Kd-restricted TCR (V
10; V
8.2) against
the influenza virus HA transmembrane peptide amino acids 512520
(IYSTVASSL). RIP-HA mice, used as recipients in the adoptive transfer
experiments, express HA specifically in the pancreatic
cells
(31). The CL4-TCR and RIP-HA transgenic mice, both
backcrossed 68 times with BALB/c mice, were bred in a conventional
animal facility, while normal BALB/c mice were purchased from
IFFA-Credo (St-Germain-sur-lArbresle, France).
In the adoptive transfer experiments, nonirradiated, 6- to 8-wk-old RIP-HA hemizygote recipients were injected i.v. with different doses of naive or preactivated CL4 CD8+ T cells in 0.2 ml PBS. Glucosuria was tested daily using Multistix 8 SG test strips (Bayer Diagnostics, Puteaux, France). Mice that had glucosuria for 2 consecutive days were considered to be diabetic; control measurements confirmed that these mice had more than 3.5 g/L glucose in their blood. Severely diabetic mice were euthanized.
Cell culture
CL4 spleen and lymph node single-cell suspensions were incubated
with anti-CD8
mAb (CT-CD8a; Caltag, Burlingame, CA) and positive
selection of CD8+ cells was performed by
magnetic-activated cell sorting magnetic beads and separation columns
(Miltenyi Biotech, Bergish Gladbach, Germany). The efficacy of the
selection was controlled by flow cytometry; the resulting cell
suspension typically contained more than 80%
V
8+, CD8+,
CD62Lhigh, CD25-
lymphocytes and less than 2% contaminating CD4+
cells.
To obtain Tc1 cells, 5 x 105 purified CL4
CD8+ T cells were stimulated with 5 x
106 irradiated syngeneic spleen cells in 2 ml
complete DMEM supplemented with 10% FCS (Life Technologies, Paisley,
Scotland) containing 1 µM HA peptide, 1 ng/ml IL-2, and 20 ng/ml
IL-12. On day 3, the cultures were split into four aliquots and fed
with fresh medium containing IL-2. For the generation of Tc2 cells,
5 x 105 CL4 CD8+ T
cells were stimulated with 5 x 106 spleen
cells in the presence of 1 µM HA peptide, 1 ng/ml IL-2, 80 ng/ml
IL-4, 20 ng/ml IL-10, and 10 µg/ml anti-IFN-
mAb. On day 3,
the cultures were split into two to four aliquots and fed with fresh
medium. On day 6, cells were harvested and living cells were collected
by Ficoll density separation and washed with tissue culture medium at
least three times.
The polarized Tc1 and Tc2 cells were then used in adoptive transfer experiments. Their cytokine production was assessed in parallel by restimulating 106 cells with 5 x 106 irradiated BALB/c spleen cells in 2 ml complete DMEM in the presence of 1 µM HA peptide. Splenocytes and pancreatic lymph nodes were removed from RIP-HA mice 4 days after adoptive transfer of either 20 x 106 Tc1 or Tc2 cells. Single-cell suspensions were incubated (8 x 105 cells/well) in the presence or absence of 1 µM HA peptide. Supernatants were collected after 48 h incubation, aliquoted, and stored at -20°C until the cytokine determination by ELISA test was performed.
Cytokines, ELISA, and flow cytometry
Recombinant mouse IL-2, IL-4, and IL-10 were purchased from R&D
Systems (Minneapolis, MN). Recombinant mouse IL-12 was a gift from Dr.
Stanley Wolf, Genetics Institute (Cambridge, MA). The neutralizing
anti-IFN-
mAb (clone XMG1.2) used in the Tc2 culture was purchased
from PharMingen (San Diego, CA).
Cytokines were determined by sandwich ELISA using Cytoset matched Ab
pairs and recombinant cytokine standards (Biosource International,
Camarillo, CA). IFN-
: polyclonal rabbit anti-mouse IFN-
capture Ab and biotinylated anti-IFN-
mAb (clone DB-1); IL-10:
anti-IL-10 capture mAb (clone JES5-SXC1) and biotinylated
anti-IL-10 mAb (clone JES5-2A5); IL-4: anti-IL-4 capture mAb
(clone BVD4-1D11) and biotinylated anti-IL-4 mAb (clone BVD4-24G2).
The cytokine ELISA were performed according to the instructions of the
supplier using Costar (Cambridge, MA) enxyme immunoassay plates (No.
3590) and Biosource streptavidin-HRP conjugate.
The anti-CD8 (clone CT-CD8a) and anti-CD4 (clone CT-CD4) mAbs
were purchased from Caltag Laboratories (Burlingame, CA) while the
anti-B220 (clone RA3-6B2), anti-V
8 (clone F23.1) and
anti-CD25 (clone 7D4) mAbs were obtained from PharMingen.
Intracellular IFN-
was detected by FITC-labeled anti-IFN-
mAb
(clone XMG1.2) using FITC-labeled clone R3-34 as an isotype control
mAb (PharMingen). Tc1 and Tc2 cells were previously
stimulated for 5 h with 1 µg/ml PMA (Sigma, St. Louis, MO) and 1
µg/ml ionomycin (Sigma); after the first hour, 3 µM monensin
(Sigma) was added. Fixation and membrane permeabilization were
performed using 2% paraformaldehyde and 0.1% saponin,
respectively.
FACS analysis was performed by a FACScan flow cytometer (Becton Dickinson, Mountain View, CA), and the data were analyzed using CellQuest software (Becton Dickinson).
Cytotoxicity assay
The cytotoxic effect of Tc1 and Tc2 cells on P815 mastocytoma cells (H-2d) pulsed with 1 µM HA peptide was assessed as previously described (32). To assess the contribution of the perforin pathway in the cytotoxic activity, the cytotoxicity test was performed in the presence or absence of 4 mM EGTA and 3 mM MgCl2.
Tracing of adoptively transferred CD8+ cells
In some experiments, Tc1 or Tc2 cells labeled with an intracellular fluorescent dye, 5,6-carboxy-succinimidyl-fluorescein-ester (CFSE; Molecular Probes, Eugene, Oregon), were used for adoptive transfer experiments. For the labeling, the cell suspension (5 x 107 cells/ml) was incubated for 10 min with 5 mM CFSE at 37°C, then the reaction was stopped by adding cold medium and the cells were washed three times. One or 4 days after the cell transfer, the recipients were sacrificed. Spleen and pancreas single cell suspensions were prepared using a wire mesh and a syringe plunger and the percentage of the CFSE-labeled cells in the lymphocyte forward light scatter-side light scatter gate and the mean fluorescence level of positive cells were determined by FACS analysis.
RNase protection assay
Total RNA was prepared from 107 Tc1 or Tc2
cells, at day 6 after initiation of the culture under polarizing
conditions, either before or after 12 h of in vitro restimulation
with 10 µg/ml of plate-bound anti-CD3 mAb (clone 2C11;
PharMingen) using the RNA Plus extraction kit (Quantum Biotechnologies,
Montréal, Canada). Ribonuclease protection assays were performed
with the RiboQuant kit (PharMingen) using the mCR-5 and the mCR-6
radiolabeled probe sets (PharMingen) according to the manufacturers
recommended protocol. The dried gel was placed on film and developed at
-70°C. Quantitation of the radioactivity on the gel was performed
using a high-resolution
-imager (Biospace, Paris, France) allowing
us to obtain a direct measurement of numeric images obtained from
actual counting of
-particles emitted. Data were normalized against
the L32 and GAPDH housekeeping genes.
Intracellular [Ca2+] measurements
Cells (107/ml) were incubated in HBSS with
Ca2+ and Mg2+ (pH 7.4),
containing 2.5 µM fura 2-AM (Molecular Probes) for 60 min at 37°C
in the dark. Cells were washed twice with HBSS, and resuspended at
2 x 106/ml. Two milliliters were placed in
a continuously stirred cuvette at 37°C in a fluorometer (Perkin-Elmer
LS-5B, Bois dArcy, France). Fluorescence was monitored at
ex1 = 340 nm,
ex2 =
380 nm, and
em = 510 nm. Data were recorded
every 200 ms. The following recombinant chemokines were tested at 50
nM: RANTES, macrophage inflammatory protein (MIP)-1
, eotaxin,
secondary lymphoid tissue chemokine (SLC), I309, fractalkine, IL-8, and
IFN-inducible protein 10 (IP-10) (all from PeproTech, Rocky Hill, NJ).
Calcium concentrations were calculated using the following equation as
described (33):
[Ca2+]i = 225 x
(R -
Rmin)/(Rmax -
R) x Sf380/Sb380. Rmax and
Rmin were evaluated in 1 mM
Ca2+ containing medium by lysing the cells with
0.5% Triton X-100 for Rmax
(Rmax = 9.4), followed by the addition of 3
mM EGTA for Rmin
(Rmin = 1.5).
| Results |
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The extent of Tc1- or Tc2-type cell differentiation was controlled
by restimulating the purified cells in vitro and measuring the
production of prototypic type 1 (IFN-
) and type 2 (IL-4 and IL-10)
cytokines. Tc1 cells harvested after 6 days of culture in the presence
of IL-12 and restimulated with APC and peptide were invariably found to
produce large amounts of IFN-
and no detectable IL-4 or IL-10 (Fig. 1
). In our initial experiments, we found
that IL-4, IL-10, and anti-IFN-
mAb synergize in inducing
Tc2-type differentiation. The presence of IL-4 alone in the culture
resulted in a mixed cytokine profile, but the addition of IL-10 to the
culture elevated the production of both IL-4 and IL-10, while
anti-IFN-
mAb decreased the production of IFN-
(Fig. 1
).
Because the most complete Tc2-type polarization was obtained in the
presence of IL-2, IL-4, IL-10, and anti-IFN-
mAb, this protocol
was chosen for the adoptive transfer experiments. The individual Tc2
cell populations used in the additional experiments produced variable
quantities of the three cytokines measured. However, the results of the
cell transfer experiments shown in Fig. 5
were obtained using highly
polarized Tc2 cells, which, according to our arbitrarily but a priori
established criteria, produced at least a 2-fold higher level of both
IL-4 and IL-10 than IFN-
. Six of 14 independent Tc2 populations fell
into this category; the supernatant of these cells contained 169
± 61 pg/ml IFN-
, 1435 ± 409 pg/ml IL-4, and 5868 ± 1943
pg/ml IL-10 (mean ± SEM).
|
|
Both Tc1 and Tc2 cells collected on day 6 stained homogeneously for the
transgenic V
8.2 TCR chain and contamination with
CD4+ cells was less than 1%. Cells were highly
activated in both cases and showed only slight differences in the CD25
and CD62 ligand expression between the two cell subsets (Fig. 2
and data not shown). A varying
percentage of the Tc1 cells, typically about 50%, and a minor fraction
of Tc2 cells were found to be CD8low (Fig. 2
).
The CD8low and the CD8high
cells had identical side-scatter/forward-scatter characteristics and
similar levels of TCR and CD25 expression (data not shown).
|
, we performed
intracellular cytokine staining to assess the cellular source of this
production. After 5 h of incubation in the presence of PMA,
ionomycin, and monensin, over 85% of Tc1 cells were highly positive
for IFN-
. The majority of Tc2 cells were also positive; however, a
heterogeneity was found in the level of IFN-
and the mean
fluorescence intensity of IFN-
high Tc2 cells
was lower than that of corresponding Tc1 cells (Fig. 3
present in the culture supernatant of most of our Tc2 cultures
was not due to contamination with Tc1 cells, but rather to a
low/intermediate level of IFN-
production by Tc2 cells.
|
|
CL4-TCR Tc1 cells transferred into adult, nonirradiated, RIP-HA
transgenic recipients induced diabetes reproducibly. The 50%
diabetogenic dose was 5 x 105, and as few
as 105 cells were sufficient to cause diabetes at
a low frequency (Fig. 5
). High cell doses
(106 or more) invariably caused disease 45 days
after the cell transfer, while, in the case of lower cell doses, a
longer time (up to 3 wk) was necessary for the development of
glucosuria (Fig. 5
). Tc1 (107 cells) transferred
into nontransgenic control recipients (n = 5) did not
cause diabetes.
To assess the diabetogenic potential of Tc2 cells, a relatively high
cell dose, 5 x 106 cells, was chosen. This
number of Tc1 cells, which corresponds to 10 times the 50%
diabetogenic dose, always transferred diabetes within 45 days (Fig. 5
). Highly polarized Tc2 cells (5 x 106)
were found to have a definite, but reduced, diabetogenic activity.
Overall, 6 of 18 mice injected with Tc2 cells developed diabetes.
Therefore, Tc1 cells were more than 10 times more diabetogenic than Tc2
cells (Fig. 5
). Tc2 cells were nonetheless more diabetogenic than naive
CD8+ cells, because the same dose of purified
naive CD8+ cells, 5 x
106, did not transfer diabetes (Fig. 5
). However,
higher doses of naive cells were not completely harmless, because
107 naive cells caused diabetes in 2 recipients
of 11 (data not shown).
As previously described (8), the polarized phenotype of
HA-specific Tc1 and Tc2 cell populations was stable in vivo.
Splenocytes and pancreatic lymph node cells from RIP-HA mice adoptively
transferred 4 days earlier with 20 x 106
Tc1 cells specifically produced large amounts of IFN-
but no
detectable IL-4 or IL-10 in response to HA peptide in vitro (Fig. 6
). Conversely, splenocytes and
pancreatic lymph node cells from RIP-HA mice adoptively transferred
with 20 x 106 Tc2 cells produced both IL-4
and IL-10 as well as low levels of IFN-
in response to HA peptide
(Fig. 6
). No cytokine production was detected using splenocytes or
pancreatic lymph node cells from uninjected RIP-HA control mice. This
indicates that Tc1 and Tc2 cells retain their cytokine profile in vivo
and that a phenotype switch is not likely to explain induction of
diabetes in Tc2 recipients.
|
To look for possible causes of the different diabetogenic
potential of Tc1 and Tc2 cells we compared the homing and proliferation
of Tc1 and Tc2 cells in the pancreas and the spleen. In these
experiments, the transferred Tc1 or Tc2 cells had previously been
labeled with CFSE and homing of the transferred cells was monitored by
flow cytometry. Furthermore, a comparison of the mean fluorescence
level of CFSE-positive cells enabled us to assess the difference
between the number of divisions performed by Tc1 and Tc2 cells. The
homing and proliferation of Tc1 and Tc2 cells in the spleen was
comparable on both days 1 and 4 after the transfer (Fig. 7
). In contrast, in the pancreas, there
were 2.0 times more Tc1 than Tc2 cells on day 1, but by day 4 this
difference had increased to 6 times more. Furthermore, the decreased
CFSE content of Tc1 cells in the pancreas on day 4 indicated that they
had divided on average twice more than Tc2 cells (Fig. 7
).
|
, IP-10, fractalkine, and I309) confirmed the somewhat higher
surface expression of functional CCR5 on Tc1 as compared with Tc2
cells, and the lack of CXCR2 and CCR3 on both cell types (Fig. 8
|
| Discussion |
|---|
|
|
|---|
In accordance with literature data, Tc1 and Tc2 cells generated according to our protocol were phenotypically similar. However, a surprising feature of our model is the partial loss of the CD8 molecule, which was more pronounced in Tc1 than in Tc2 cells. The contribution of an expanded minor CD4-CD8- compartment to the recovered cell population is highly improbable, because our cultures start with highly purified, positively selected CD8+ cells and because the CD8low Tc1/Tc2 cells still express the molecule at a low level. Therefore, a partial loss of the CD8 marker by the originally positive cells would seem the more plausible explanation. A similar loss of CD8 expression has been described by Erard et al. (6) in the case of CD8+ cells stimulated with PMA and ionomycin, or allogeneic thymoma cells, in the presence of IL-4. A loss of the CD8 molecule is also known to occur in the case of CD8+ cells stimulated by mitogens, and has also been described as a means to silence autoreactive CD8+ T cells (34, 35). However, it is interesting that CL4-TCR CD8+ cells stimulated with APC and peptide can also lose the CD8 molecule, especially in light of the fact that activation of CL4-TCR-expressing T cells by Ag-pulsed APC or by soluble monomeric MHC-peptide complexes was found to be CD8-dependent (30, 36). Because the decrease in the expression level of CD8 was less marked in Tc2 than in Tc1 cells, the reduced expression of this molecule cannot explain the lower diabetogenic potential of the Tc2 cells.
We found that Tc2 cells, though they are much more diabetogenic than naive CD8+ cells, do not induce diabetes as efficiently as Tc1 cells. Analogous adoptive transfer experiments performed with Th1 and Th2 cells gave consistent results: transferred islet-specific Th2 cells did not cause disease in immunocompetent recipients (37, 38). However, whether autoreactive Th2 cells were protective depended on the model. In the adoptively transferred diabetes model of Katz et al. (37) Th2 cells could not protect against the damage caused by Th1 cells. In EAE models, Th2 cells were either protective (39, 40), or harmless but inefficient in suppressing the disease induced by Th1 cells (41). However, Th2 cells caused diabetes in severely immunocompromised nonobese diabetic mouse (NOD).SCID mice (42). Furthermore, myelin basic protein-specific Th2 cells caused CNS inflammation in an analogous experimental setup (43).
In our system, the reduced diabetogenic potential of the Tc2 cells
might be due to different factors. Differential cytokine production
could contribute to this effect. Indeed, an important pathogenic role
has been proposed for IFN-
in IDDM based on experiments involving
transgenic expression of IFN-
in
islet cells, treatment of NOD
mice with neutralizing anti-IFN-
mAbs, or use of IFN-
- or
IFN-
R-deficient mice (44, 45, 46, 47, 48). Our preliminary results
indicate that 2 x 106 Tc1 cells from
IFN-
-deficient CL4-TCR mice fail to transfer diabetes in RIP-HA mice
(our unpublished results) suggesting that the reduced pathogenic
potential of Tc2 cells could be due to their low level of IFN-
production. Another possibility is that the IL-4 or IL-10
produced by the Tc2 cells might protect the recipients from the
cell damage. Nevertheless, the role of these two cytokines remains
ambiguous. Local expression of IL-4 has been shown to prevent the
autoimmune rejection of transplanted islet grafts (49),
while IL-4 is not required for control of either autoimmune diabetes
(50) or EAE (51). Interestingly, IL-10 has
been found to have a dual role in the development of autoimmune tissue
damage. Though administration of IL-10, considered to be a prototypic
immunosuppressive cytokine, decreased the incidence of diabetes in NOD
mice (52), local expression of IL-10 in the pancreas of
NOD mice led to CD4- and B cell-independent CD8+
infiltration of the organ (53, 54).
Another potential explanation for the different pathogenicity of Tc1
and Tc2 cells could be their different homing and proliferative
properties. By analogy, islet-specific diabetogenic Th1 and
nondiabetogenic Th2 cells have been found to have different kinetics of
migration to the pancreas (55). The migration pattern of
mouse Th1 and Th2 is correlated with differential expression of
chemokine receptors (56). In particular, CCR5 is
preferentially expressed on Th1 cells, whereas its ligands (RANTES,
MIP-1
, and MIP-1
) are expressed in the pancreas during
development of destructive autoimmune insulitis in NOD mice (55, 57). It is tempting to speculate that the higher expression of
CCR5 on Tc1 as compared with Tc2 cells, previously reported by Cerwenka
et al. (12) and confirmed in this report, contributes to
the preferential recruitment of Tc1 cells in the pancreas. Conversely,
CCR7 expression on Tc2 cells could promote their homing in secondary
lymphoid tissues, which constitutively express SLC (56, 58) and this interaction may prevent T cells from responding to
agonist MHC-peptide complexes (59). However, the
difference in homing capacity seems to be quantitative rather than
qualitative (55). In our model, 1 day after the injection,
slightly more CFSE-labeled Tc1 than Tc2 cells were found in the
pancreas of the recipients while on day 4 the difference was more
marked; six times more Tc1 than Tc2 cells were found in the pancreas of
recipients. This increase might have been due to different homing, or
to different rates of proliferation of the two cell subsets because the
decreased amount of CFSE in Tc1 cells indicated a higher number of cell
divisions. This reduced pancreas-specific homing/proliferation,
combined with the different cytokine profile, might contribute to the
compromised diabetogenic potential of Tc2 cells.
In contrast, the residual diabetogenic potential of our Tc2 populations might be explained by their retained cytotoxic activity. Fully in line with the observation of Cerwenka et al. (12), our Tc2 cells generated in vitro by stimulation with APCs and specific peptide were cytotoxic. Because EGTA abolished the cytotoxic activity of both Tc1 and Tc2 cells, the cytotoxicity in both cases seems to be preferentially mediated by perforin rather than by alternative pathways. Literature data on the Fas-L-dependent killing by in vitro cultured Tc1 and Tc2 cells are equivocal. Although cytotoxicity of both Tc1 and Tc2 cells was almost completely abolished in perforin-/- mice, Fas-L mediated killing was demonstrable by wild-type Tc1 or, in other models, by both Tc1 and Tc2 cells (9, 10, 60, 61). The interpretation of these data is currently difficult.
Perforin-dependent lysis seems to be a major mechanism of
cell
damage in IDDM, because the incidence of spontaneous diabetes was
drastically decreased in NOD mice lacking perforin (21).
Furthermore, a lack of perforin blocked the development of diabetes,
but not insulitis, in an adoptive transfer model based on the use of
LCMV-GP transgenic mice (22). Being a necessary mechanism
of tissue damage in diabetes, the cytotoxic activity of the Tc2
populations could explain their diabetogenic capacity.
In conclusion, although highly polarized Tc2 cells are more diabetogenic than naive CD8+ cells, they are more than 10 times less diabetogenic than Tc1 cells. This difference between Tc1 and Tc2 cells may due to a combination of several factors, namely differences in cytokine production, proliferative capacity, and homing pattern. The diabetogenicity of autoreactive Tc2 cells, caused most likely by their cytotoxic activity, precludes their clinical use to down-regulate autoimmunity.
| Acknowledgments |
|---|
| Footnotes |
|---|
2 Address correspondence and reprint requests to Dr. Roland Liblau at Cellular Immunology Laboratory, Institut National de la Santé et de la Recherche Médicale, CJF 9711, 105 bd de lHopital, Paris 75013, France. ![]()
3 Abbreviations used in this paper: HA, hemagglutinin; LCMV, lymphocytic choriomeningitis virus; IDDM, insulin-dependent diabetes mellitus; EAE, experimental allergic encephalomyelitis; RIP, rat insulin promoter; NOD, nonobese diabetic mouse; IP-10, IFN-inducible protein 10; MIP, macrophage inflammatory protein; SLC, secondary lymphoid tissue chemokine; CFSE, 5,6-carboxy-succinimidyl-fluorescein-ester. ![]()
Received for publication November 22, 1999. Accepted for publication September 8, 2000.
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