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Institute for Medical Microbiology and Hygiene, Department of Immunology, University of Freiburg, Freiburg, Germany
| Abstract |
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| Introduction |
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We have addressed this issue in a transfer model using H8-transgenic (tg) mice ubiquitously expressing the CD8 T cell epitope gp33 from lymphocytic choriomeningitis virus (LCMV) (11) and TCR-tg mice specific for gp33 (12). Naive T cells from TCR-tg mice transfused into H8-tg mice are rapidly tolerized. In the present study we show that stimulation via anti-CD40 interferes with peripheral tolerance induction and activates self-reactive TCR-tg cells to cause immunopathology in this transfer system. The break of tolerance via anti-CD40 stimulation was B cell independent and did not require CD28/B7 interactions.
| Materials and Methods |
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C57BL/6 (B6) mice were obtained from our breeding colony and from Harlan Winkelmann (Borchen, Germany). Thy1.1+ P14 TCR-tg mice, line 327, specific for amino acids 3341 (GP33 epitope) of the LCMV glycoprotein (12, 13) and H8-tg mice ubiquitously expressing the LCMV gp33 epitope as a transgene (11) have been described previously. H8-tg mice had been generated on a B6 background. TCR-tg mice deficient in CD28 and H8-tg mice deficient in B cells were generated through breeding with B6.CD28-/- mice (14) and B6.µMT mice (15), respectively. Female or male mice were used at 816 wk of age. Mice were bred and kept in a conventional animal house facility.
Virus
The LCMV-WE isolate used in this study was originally obtained from R. Zinkernagel (University Hospital, Zurich, Switzerland). Mice were infected i.v. with 200 PFU and viral titers were determined in a virus plaque assay as described (16).
Adoptive cell transfers and anti-CD40 Ab treatment
Spleen cells containing 105 TCR-tg cells were injected (i.v.) into nonirradiated B6 or H8-tg mice. Anti-CD40 treatment was performed by i.p. injection of 100 µg of anti-CD40 mAb, clone FGK45 (17). Unless otherwise indicated, Abs were given on the day of cell transfer and 2 days afterward.
Flow cytometry
Lymphocytes were resuspended in PBS containing 2% FCS and 0.1%
NaN3 at a concentration of
106107 cells/ml, followed
by incubation at 4°C for 20 min with 100 µl of appropriately
diluted mAb. For PBL staining 10 U/ml heparin was added to the staining
buffer. The following mAb were used: CD4 (clone GK1.5), CD8 (clone
53-6.7), CD25 (clone 7D4), CD44 (clone IM7), CD45R/B220 (clone
RA3-6B2), CD62L (clone MEL-14), CD69 (clone H1.2F3), CD90.1 (clone
OX-7), TCR V
2 (clone B20.1), and TCR V
8 (clone MR5-2). Abs were
purchased from BD PharMingen (San Diego, CA). The mAb were directly
labeled with FITC or PE, or were biotinylated. For the latter,
PE-streptavidin (both from BD PharMingen) was used as a secondary
reagent for detection. Cells were analyzed on a FACSort flow cytometer
(BD Biosciences, Mountain View, CA) using CellQuest software (BD
Biosciences). Before analysis of PBL, RBCs were lysed using FACS Lysing
Solution (BD PharMingen).
Immunohistochemistry
Spleen or liver sections (57 µm) were cut on a cryostat microtome, air dried, fixed in acetone, and blocked with TBS containing 5% mouse serum and with the DAKO Biotin Blocking System (DAKO, Hamburg, Germany). Anti-Thy1.1-biotin, anti-CD8-biotin, and anti-B220-biotin (all from BD PharMingen) were used as primary mAb followed by streptavidin-conjugated alkaline phosphatase (StreptAB Complex/AP; DAKO) and alkaline phosphatase substrate kit I (Vector Laboratories, Burlingame, CA). Sections were counterstained with Mayers hemalum.
Serum GLDH activity
Blood (200 µl) taken from the tail vein was collected in serum separator tubes (MICROTAINER Brand Serum Separator Tube; BD Biosciences) and centrifuged for 20 min at 3300 x g, and sera were analyzed for glutamate dehydrogenase (GLDH; units per liter).
| Results |
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To study self-reactive T cells in an environment ubiquitously
expressing the self-Ag, CD8 T cells (105) from
TCR-tg mice specific for the gp33 epitope of LCMV were adoptively
transferred into H8-tg mice (H8 mice) expressing the GP33 epitope as a
transgene driven by the H-2Kb promoter. Twelve
days after transfer, H8 recipient mice were infected with LCMV to test
the responsiveness of the transferred TCR-tg cells. As a control,
TCR-tg cells were transferred into non-tg recipient mice. The donor
TCR-tg cells (Thy1.1+) were traced in recipient
mice (Thy1.2+) by flow cytometry using
Thy1.1-specific mAb. Without LCMV infection,
Thy1.1+ cells were at detection limit in both
types of recipient mice. After LCMV infection, a massive in vivo
proliferation of donor TCR-tg cells was found in B6 recipient mice but
not in H8 mice (Fig. 1
A). Lack
of in vivo proliferation of TCR-tg in H8 mice was unlikely due to
impaired viral replication, because host CD8 T cells proliferated
strongly (12 vs 50% CD8+ of PBL) after LCMV
infection.
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2), CD44, CD62L, CD25, and CD69
revealed that these cells exhibited an activated phenotype. Parking
TCR-tg cells in H8 mice for 6 days strongly impaired their
proliferative response to LCMV (Fig. 1Break of tolerance induction in H8 mice by anti-CD40 Ab treatment
Several recent reports indicate that priming vs tolerance
induction of T cells is strongly influenced by the activation state of
the APC (18, 19, 20, 21, 22). Therefore, we wondered whether
stimulation of APC by agonistic anti-CD40 mAb interfered with
peripheral tolerance induction of the transferred self-reactive TCR-tg
cells in H8 mice. Indeed, this was the case, because TCR-tg cells
proliferated vigorously in anti-CD40-treated H8 recipients without
LCMV infection (Fig. 2
A,
left and middle panels). TCR-tg cells adoptively
transferred into anti-CD40-treated B6 mice did not expand (Fig. 2
A, right panels). The induced TCR-tg cells in
anti-CD40-treated H8 mice exhibited an activated phenotype with
up-regulated CD25 and CD44 and down-regulated CD62L expression (Fig. 2
B). Without Ab treatment, TCR-tg cells remained at
detection limit. In absolute numbers, the transferred TCR-tg cells
(105) expanded >100-fold, since within 1
wk
107 Thy1.1+
cells were recovered from the spleen of CD40-treated H8 recipient mice
(Fig. 3
). Titration experiments further
revealed that transfer of as few as 1000 TCR-tg cells was sufficient to
yield significant (
40% Thy1.1+ of total CD8)
expansion of donor cells in the host (Fig. 2
C). Clonal
expansion of TCR-tg cells peaked 1 wk after transfer and treatment, and
at this time point all mice showed clinical symptoms including ruffled
fur, hunched posture, cachexia, and ataxia. About half of the mice had
to be killed due to their moribund stage. The surviving mice recovered
rapidly, and TCR-tg cells declined gradually and were no longer
detectable 45 wk after transfer (Fig. 2
D). Together, these
data show that CD40 triggering of APC in H8 mice abolished induction of
peripheral tolerance and induced vigorous proliferation of
self-reactive CD8 T cells in vivo.
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Lymphocytes in H8 mice may serve as potential target cells for the
activated TCR-tg cells. Therefore, spleens of anti-CD40-treated H8
mice were examined by immunohistology. As illustrated in Fig. 4
A, top panels,
expansion of TCR-tg cells was accompanied by severe immunopathological
alterations of the splenic architecture: TCR-tg cells
(Thy1.1+) were distributed all over splenic white
and red pulp areas, the few remaining CD4 T cells exhibited a diffuse
localization, and the size of B cell follicles was severely reduced.
Accordingly, the absolute numbers of CD4 and B cells in the spleen were
strongly decreased in H8 mice that received both Abs and TCR-tg cells
(Fig. 3
). It is likely that this decrease is due to cell elimination by
activated TCR-tg cells, because Con A blast spleen cells from H8 mice
can serve as target cells for activated TCR-tg cells in vitro
(11) and H8 spleen cells have been shown to be rapidly
eliminated by gp33-specific CTL in vivo (23).
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Most CD40-expressing cells in lymphoid organs are B cells
(4). To examine whether CD40-activated B cells were
essential in breaking peripheral tolerance induction of self-reactive T
cells, H8 mice lacking B cells (H8.µMT mice) were used as recipient
mice. Nonetheless, TCR-tg cells transferred into anti-CD40-treated
H8.µMT mice proliferated as vigorously as in H8 mice (Fig. 5
A).
Up-regulation of the costimulatory molecules CD80 and CD86 is thought
to be important for the improved stimulating properties of activated
APC. To test the role of these costimulatory molecules, transfer
experiments with TCR-tg cells from CD28-deficient mice were performed.
Because these TCR-tg cells were Thy.1.2+, donor
cells were traced in the recipient mice by Abs (V
8, V
2) specific
for the tg TCR. Surprisingly, TCR-tg cells lacking CD28 proliferated as
vigorously as T cells from wild-type mice in anti-CD40-treated H8
mice (Fig. 5
B). Moreover, H8 recipients of
CD28-/- TCR-tg cells exhibited similar
pathology (e.g., destruction of splenic architecture, impaired
survival) as recipients of wild type TCR-tg cells (data not shown).
Thus, neither B cells nor CD28-mediated costimulation were essential in
breaking tolerance induction of self-reactive T cells in H8 mice by
anti-CD40 treatment.
| Discussion |
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In the model used by Garza et al. (21), injection of
soluble LCMV peptides together with anti-CD40 Abs induced diabetes
in (RIP-LCMV x LCMV TCR) double-tg mice. These mice expressed
LCMV glycoprotein on pancreatic
-islet cells and the corresponding
Ag receptor on almost all T cells. The system described here is
distinct from this model because H8 mice were "spiked" with only a
few (103105) TCR-tg cells
which proliferated vigorously and induced hepatitis and destruction of
lymphoid organs after anti-CD40 treatment. Nonetheless, both
studies point to potential hazards using systemic CD40 stimulation as a
therapeutic approach. In this context, it is noteworthy that transient
elevations of serum liver transaminases up to grades 3 and 4 had been
observed in patients treated with recombinant human CD40 ligand
(9). Furthermore, a recent report has demonstrated that tg
overexpression of CD40 ligand in murine epidermis results in chronic
skin inflammation and systemic autoimmunity (24).
Interestingly, pathology in this model could be transferred by CD8 but
not by CD4 T cells from diseased animals.
Clonal expansion of TCR-tg cells in anti-CD40-treated H8 mice was followed by anergy and peripheral deletion. This indicated that the activating properties of the APC were transient only after injection of anti-CD40 Abs. This result fits well with a recent study by den Boer et al. (25) demonstrating that T cell immunity induced by injection of a tolerogenic peptide together with anti-CD40 Ab treatment rapidly declines. Activated CD8 T cells have been shown to trigger maturation of DCs in vitro (26). However, the decline of TCR-tg cells indicates that the large number of the induced TCR-tg effector cells in CD40-treated H8 were unable to sustain the activating properties of DC in vivo when anti-CD40 Abs became limiting.
The results presented here differ considerably from similar adoptive transfer experiments using Ld-alloreactive CD8 T cells from 2C TCR-tg mice (27). In this study, agonistic anti-CD40 Abs induced only minimal expansion of 2C TCR-tg cells after transfer into H-2b/d F1 mice. A more sustained expansion of TCR-tg cells in that system required help from CD154-expressing CD4 T cells; therefore, the authors concluded that anti-CD40 agonism cannot completely mimic the physical presence of CD4 T cells. The discrepancy between this finding and our results could be due to 1) the different type of Ag (alloreactive vs MHC-restricted) studied, 2) the particular properties of the anti-CD40 mAb (FGK115 vs FGK45) used, or 3) the different affinities of the two tg TCRs (2C vs P14).
Tolerance induction in the presence of excessive Ag is well documented. Induction of peripheral tolerance by adoptive transfer of TCR-tg cells into Ag-bearing hosts was first shown in the HY model (28) and subsequently also in other Ag systems (29, 30, 31, 32). Similarly, T cell tolerance induced by injection of high doses of soluble peptides (12, 33, 34) or by exhaustive differentiation in the presence of high viral Ag load (35) has been demonstrated. These findings led to the hypothesis that Ag load and distribution primarily determine whether priming or tolerance occurs (36). Transgenic gp33 expression in H8 mice was under the control of promoter and regulatory regions of the H-2Kb MHC class I gene (11). In addition, anti-CD40 Ab treatment did not increase H-2Kb cell surface expression on B cells and DC in these mice (data not shown). Thus, gp33 Ag load and distribution probably did not differ in control and anti-CD40-treated H8 mice. Nevertheless, the fate of the transferred TCR-tg cells differed dramatically. Therefore, our data strongly suggest that the differentiation stage of the APC is considerably more important than Ag load and distribution in determining whether priming or tolerance occurs in the presence of excessive Ag.
The type of APC responsible for the break of T cell tolerance induction by CD40 ligation in vivo has not yet been defined. Our data demonstrate that B cells were not essential for this process. This result agrees with Diehl et al. (19), using soluble peptides to tolerize T cells. Besides B cells, DC, macrophages, parenchymal, microglial, and endothelial/epithelial cells also express CD40 (4, 37, 38, 39). In light of their well-established role in T cell activation (40), stimulated DC are the most likely candidates for the conversion of T cell tolerance to T cell priming. CD40 ligation of DC leads to up-regulation of the costimulatory molecules CD80 and CD86 (41), thereby enhancing their stimulating capacities. Interestingly, induction of CD80/86 expression on DC was not crucial in breaking tolerance in H8 mice, because TCR-tg cells from CD28-deficient mice expanded in a similar number to TCR-tg cells from wild-type mice. Therefore, induction of other stimulatory molecules or augmented production of proinflammatory cytokines (42, 43, 44, 45) may compensate or may even play the key roles in "licensing" APCs for CD8 T cell activation. Further progress in understanding priming and tolerance induction of T cells will depend on the identification of these factors.
In conclusion, this study provides further in vivo evidence for the fundamental concept that the activation state of the APC, most likely DC, is crucial in determining whether interaction of T cells with Ag leads to clonal expansion and acquisition of effector T cell function or to tolerance by ignorance, anergy, or deletion. In addition, our data suggest the need for caution in systemically activating APC in vivo by CD40 ligation in the presence of potentially self-reactive CD8 T cells.
| Acknowledgments |
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| Footnotes |
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2 Address correspondence and reprint requests to Dr. Hanspeter Pircher, Institute for Medical Microbiology and Hygiene, Department of Immunology, Hermann-Herder-Strasse 11, University of Freiburg, D-79104 Freiburg, Germany. E-mail address: pircher{at}UKL.uni-freiburg.de ![]()
3 Abbreviations used in this paper: DC, dendritic cell; tg, transgenic; LCMV, lymphocytic choriomeningitis virus; GLDH, glutamate dehydrogenase. ![]()
Received for publication October 24, 2001. Accepted for publication March 21, 2002.
| References |
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heavy chain class switching. Immunity 5:319.[Medline]
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