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Inhibits Presentation of a Tumor/Self Peptide by CD8
- Dendritic Cells Via Potentiation of the CD8+ Subset1
Department of Experimental Medicine, University of Perugia, Italy
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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greatly enhances their
inhibitory activity on Ag presentation by the other subset, blocking
the ability of IL-12-treated CD8- DC to overcome
suppression. In contrast, IFN- has no direct effects on the APC
function of the latter cells and does not interfere with IL-12
signaling. The negative regulatory effect triggered by IFN- in
CD8+ DC appears to involve interference with tryptophan
metabolism in vivo. Through tryptophan depletion affecting T cell
responses, IFN- acting on CD8+ DC may thus contribute to
regulation of immunity to tumor/self peptides presented by the
CD8- subset. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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production by NK cells and directs Th1 development
(5, 6, 7). IFN-, in turn, acts on monocytes to augment
IL-12 secretion. Thus, IL-12 and IFN- comprise a positive feedback
system that is probably required for optimal production of IL-12 in
vivo (8). This particularly applies to the early response
to foreign entities, such as conserved molecules on bacteria and other
evolutionarily distant organisms (9). DC also respond to
endogenous Ags, including tumor and self-peptides (10).
While the activity of DC focused outward toward the recognition of
microbial Ags may be regulated primarily via Th2 cytokines (11, 12), the activity of DC focused inward could be down-regulated
directly by Th1-associated proinflammatory and cytotoxic molecules,
including IFN- and NO (13, 14). There is now enough
evidence to support a protective role for TNF-
(15) and
IFN- (16) in experimental models of T cell-mediated
autoimmunity. In many of these models, the immunosuppressive activity
of proinflammatory cytokines is believed to involve regulatory effects
on APC (16). Myeloid APC, including macrophages, play a complex role in regulating T cell responses. It has long been recognized that some (inflammatory) macrophages support T cell activation whereas other macrophage phenotypes suppress T cell proliferation. To do so, macrophages have several effector mechanisms at their disposal, including production of cytotoxic or cytostatic molecules, such as PGE2, NO, and cytokines. In addition, some macrophages inhibit microbial infections by producing indoleamine 2,3-dioxygenase (IDO), which catabolizes tryptophan. It has been recently suggested that IDO-mediated tryptophan catabolism by macrophages may represent an important mechanism to suppress T cell responses in vivo during pregnancy, autoimmunity, tumor growth, and chronic infection (17).
On studying the presentation in vivo of a tumor/self peptide in DBA/2
mice (18, 19), we have previously found that the APC
function of myeloid CD8- DC is normally
inhibited by a minority population of CD8+ DC,
and yet the former cells could be primed by IL-12 to overcome
inhibition (20, 21, 22). In the present study, we have further
investigated cytokine modulation of CD8- and
CD8+ DC in this experimental model. We have found
that IFN- exerts profound immunosuppressive effects on the
generation of T cell reactivity in vivo to the tumor/self peptide and
that the cytokine acts on CD8+ DC to enhance
inhibition of peptide presentation by the other subset. Of interest,
the inhibitory activity induced by IFN- and mediated by
CD8+ DC was completely removed by the addition of
a competitive inhibitor of IDO activity to the
CD8+ DC cultures. These data may imply a negative
feedback loop involving IFN- and tryptophan catabolism in the
regulation of IL-12-dependent immunity initiated or sustained by
CD8- DC.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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DBA/2J (H-2d) and BALB/c
(H-2d) mice were obtained from Charles River
Laboratories (Calco, Milan, Italy). Male mice were used at the age of
2–4 mo. Murine rIL-12 was a generous gift from Dr. B. Hubbard
(Genetics Institute, Cambridge, MA). IL-12 was 98.8% pure, as assessed
by SDS-PAGE, and endotoxin contamination was <0.9 EU/mg on
Limulus amebocyte assay. The sp. act. of the
purified rIL-12 preparation, measured as ability to stimulate
proliferation in human phytohemagglutinin-activated blasts, was
3.1 x 106 U/mg. Murine rTNF, rGM-CSF,
and rIFN- were obtained from Genzyme (Boston, MA). Endotoxin was
removed from all solutions containing cytokines with Detoxi-gel
(Pierce, Rockford, IL), resulting in endotoxin contamination below the
detection limit (0.05 EU/ml) of a specific assay (Coatest Endotoxin,
Chromogenix AB, Mölndal, Sweden) (20).
Cytofluorometric analysis of surface expression of the IFN- receptor
-chain involved the use of biotinylated rat IgG to murine CD119
(clone GR20; PharMingen, San Diego, CA) according to standard
procedures. The IDO inhibitor
1-methyl-DL-tryptophan (23) was
purchased from Aldrich (Milan, Italy).
Peptides
Source and sequence of peptides used in this study are described elsewhere (18, 24). Peptides were synthesized on solid phase using either F-moc for transient NH2-terminal protection (P815AB) or t-Boc chemistry (influenza virus nucleoprotein peptide (NP) 147–155), purified by means of reverse-phase HPLC and characterized by amino acid analysis.
DC preparation
DC were prepared from collagenase-treated spleens (collagenase
type IV, Sigma, St. Louis, MO), as described (20, 21). The
recovered cells were routinely >96% CD11c+ and
appeared to consist of 90–95% CD8- and
5–10% CD8+ cells. For preparation of
CD8+ and CD8-
fractions (22), purified DC were separated using a
positive selection column and CD8 MicroBeads (Miltenyi Biotec,
Bergisch Gladbach, Germany). The recovered
CD8- cells typically contained <0.8%
contaminating CD8+ DC and were referred to as
the CD8- fraction, whereas the
CD8+ fraction was made up of 
80%
CD8+ DC.
Immunization and skin test assay
Cytokine treatments of DC (20, 25) were performed
at 37°C by an 18-h incubation with 100 ng/ml rIL-12, 50 U/ml
rTNF-, 20 ng/ml GM-CSF, or 200 U/ml (unless otherwise stated)
rIFN- before peptide pulsing. Control cultures were incubated with
medium alone. In selected experiments, 1-methyl-tryptophan (2 µM) was
added to the cultures during cytokine activation. For in vivo priming,
cells were pulsed with 5 µM P815AB (or NP) peptide at 37°C for
2 h. Cells were then irradiated (3000 rad) and washed, and each
mouse received an i.v. injection of 3 x 105
unfractionated DC, CD8- DC, or a mixture of
CD8- and 3% CD8+ DC. A
skin test assay was employed for measuring class I-restricted
delayed-type hypersensitivity (DTH) responses to the peptide used for
immunization, as described (18, 19). Results were
expressed as the increase in footpad weight of peptide-injected
footpads over that of vehicle-injected counterparts. Data are the
mean ± SD for at least six mice per group. The statistical
analysis was performed using Student’s paired t test by
comparing the mean weight of experimental footpads with that of control
counterparts (18, 19, 20, 21, 22). The data reported are from
representative experiments, and experiments with similar results were
performed three to six times.
Nuclear extracts and EMSA
DC were stimulated for 15 min with rIL-12 (100 ng/ml), rIFN-
(200 U/ml), or a combination of both, and nuclear extracts were
prepared as previously described (20). All DNA binding
reactions were conducted for 20 min at room temperature in a final
volume of 20 µl. The reactions were started by adding 10 µg of
nuclear protein extract to a reaction mix containing 1 µg of
poly(dI·dC)·(dI·dC) (Pharmacia, Uppsala, Sweden), 4 µl of 5x
binding buffer (50 mM Tris, pH 7.5, 250 mM NaCl, 5 mM EDTA, 25% (v/v)
glycerol, and 5 mM DTT), and 20,000 cpm (0.1 ng) of the NF-
B
[-32P]ATP-labeled dsDNA oligonucleotide
(5'-AGAGGGGACTTTCCGAGAGGC-3'). The whole sample was then loaded on
a 5% native polyacrylamide gel in Tris-borate-EDTA buffer. After
electrophoresis, gels were dried and separated protein-DNA complexes
were visualized by autoradiography using Kodak XAR5 films (Eastman
Kodak, Rochester, NY).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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ablates IL-12-induced
adjuvanticity
Our previous studies have shown that IL-12 in vitro confers
priming ability on purified DC pulsed with a tumor peptide (P815AB)
before transfer into recipient hosts. In particular, transfer of
unfractionated DC exposed sequentially to IL-12 and P815AB confers skin
test reactivity mediated by CD8+ T cells on
prospective recipients of an intrafootpad challenge with the tumor
peptide. To investigate whether other cytokines in addition to IL-12
might modulate the APC function of splenic DC, the purified cells
(>96% CD11c+) were exposed to different
cytokines (TNF-, GM-CSF, or IFN-), either singly or in
combination with IL-12, before peptide pulsing and transfer into
recipient mice to be assayed at 2 wk for footpad reactivity to P815AB
(Fig. 1
). Unlike IL-12, none of the
tested cytokines was able to activate the APC function of DC. The
addition of TNF- or GM-CSF did not affect the adjuvant activity of
IL-12. Most strikingly, the presence of IFN- during DC activation
with IL-12 completely ablated the adjuvanticity of the latter cytokine.
When different concentrations of IFN- were tested for possible
reversal of IL-12 activity, we found that the inhibitory effect of
IFN- was associated with cytokine concentrations 
25 U/ml (Fig. 2).
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does not affect IL-12-induced activation of NF-B
The adjuvant effect of IL-12 on DC is mediated by interaction with
a specific high-affinity receptor, and signaling through this receptor
involves nuclear localization of the transcription factor NF-B
(20). Therefore, we became interested in ascertaining
whether the inhibitory activity of IFN- on IL-12-induced
adjuvanticity could involve interference with IL-12 signaling. Using
EMSA analysis, we investigated nuclear uptake of NF-B complexes in
DC exposed to IFN- in combination with IL-12. Nuclear extracts were
obtained from DC cultures treated with IL-12, IFN-, or a combination
of both. Fig. 3 shows that, using an
NF-B probe from authentic NF-B sites (20), both
IL-12- and IL-12 plus IFN--treated DC displayed nuclear
translocation of the transcription factor. In fact, IFN- per se
appeared to result in detectable activation of NF-B. Consistent with
these data was the observation (data not shown) that IFN- would not
affect the expression of IL-12-induced changes in DC, such as increased
class II molecule expression (26) and autocrine production
of IL-12 (20, 21). Most importantly, these data suggested
that the inhibitory effect of IFN- on IL-12-induced adjuvanticity
did not involve a direct action on CD8- DC,
which have been shown to represent a primary target for IL-12 activity
in our model system (22).
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acts selectively on CD8+ DC to impair peptide
presentation
Two populations of DC can be distinguished in the mouse spleen,
the CD8+ DEC-205+
CD11b- and CD8-
DEC-205- CD11b+,
representing putative lymphoid-related and putative myeloid-related DC,
respectively (27, 28, 29, 30). We have previously shown that
unlike unfractionated DC, highly purified CD8-
cells are capable of effective presentation of P815AB in the absence of
the CD8+ component. However, the presence of as
few as 3% CD8+ DC blocks effective presentation
of P815AB by CD8- DC when a mixture of
peptide-pulsed cells of the two subtypes is transferred into recipient
hosts. Externally added IL-12 will act on CD8-
DC to allow the cells to overcome suppression (22). To
determine whether the CD8- and
CD8+ components of the DC cultures in the
experiments above might contribute differentially to the inhibitory
effect of IFN-, splenic DC were fractionated to yield a population
of >99% CD8- cells and a fraction highly
enriched in CD8+ cells (22). After
pulsing with P815AB, cells were injected into recipient hosts that were
assayed for footpad reactivity to P815AB. CD8-
DC were administered either singly or in combination with 3%
CD8+ cells, and either fraction was used either
as such or after cytokine treatment. As expected, Fig. 4A shows that the blockade of
T cell reactivity resulting from the addition of
CD8+ cells to the CD8-
fraction was reversed by preexposure of the latter cells to IL-12.
Cotreatment of CD8- DC with IL-12 and IFN-
did not impair the adjuvant activity of the former cytokine. In
contrast, exposure of CD8+ DC to IFN-
completely blocked the adjuvant effect exerted by IL-12 on the
CD8- fraction. No effect was displayed by
IFN- on the ability of the CD8- fraction
alone to present P815AB in an immunogenic fashion. Additional groups
(not reported in the figure) confirmed the previous finding that IL-12
lacks direct effects on CD8+ DC.
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does not affect presentation of P815AB by
CD8- DC raised the possibility that the two DC
subsets may respond differently to IFN-, and in fact both
CD8+ and CD8- DC were
found to express comparable amounts of transcripts specific for the
- and ß-chains of the IFN- receptor (data not shown). In
addition, Fig. 4
B shows comparable expressions of surface
IFN- receptor -chain as assessed by immunofluorescence analysis
of CD8- and CD8+
DC. Inhibitory activity of CD8+ DC in BALB/c mice
In DBA/2 mice, the ratio of CD8+ to
CD8- DC is considerably lower than in the other
mouse strains so far examined, where the CD8-
and CD8+ subtypes each account for 50% of the
whole splenic DC population (22, 28, 30). To ascertain
whether our observations with the P815AB peptide made in the DBA/2
strain could be extended to other strains, we resorted to
H-2-compatible BALB/c mice, in which almost equal proportions of
CD8- and CD8+ DC are
detected. Fig. 5 shows the effect of
sensitization with P815AB using unfractionated or fractionated DC,
either untreated or exposed to IL-12 or IFN-. In particular, a group
of mice received CD8- cells admixed with 3%
CD8+ cells at the time of peptide pulsing.
Similar to the results obtained in the DBA/2 strain, we found that the
unfractionated splenic DC population was incapable of effective
presentation of P815AB. Yet, the CD8- fraction
alone was highly effective in priming hosts to the peptide, an effect
that was negated by the addition of CD8+ DC.
However, the blockade of DTH induction resulting from the copresence of
CD8+ and CD8- DC was
reversed by preexposure of the latter cells to IL-12. Finally,
injection of IL-12-treated CD8- DC admixed with
IFN--treated CD8+ DC resulted in no detectable
DTH activity.
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in the inhibitory activity of
CD8+ DC
It has been recently shown that human monocyte-derived macrophages
suppress T cell proliferation in vitro via IFN--mediated induction
of IDO (31). Because cells synthesizing IDO modulate T
cell proliferation by reducing tryptophan concentrations in local
tissue microenvironments, tryptophan catabolism may represent a general
mechanism in T cell suppression (17). In our model system
with P815AB, we have previously hypothesized that production of IL-10
may represent a means whereby CD8+ DC regulate
the activity of the myeloid lineage (22). Experiments were
designed to investigate the possible contribution of IDO production to
the suppressive activity of CD8+ DC either under
basal condition or after activation with IFN-. The compound
1-methyltryptophan is known to be a potent competitive inhibitor of IDO
activity both in vivo (32) and in vitro (31).
To determine whether IDO induction contributes to
CD8+ DC effects, cultures of the latter cells
were exposed overnight to 1-methyltryptophan in vitro before peptide
pulsing, mixing with CD8- DC, and transfer into
recipient hosts. The effect of the addition of the inhibitor of IDO
activity was studied in both untreated and IFN--treated
CD8+ DC. Fig. 6
shows that inhibition of IDO did not affect the basal negative
regulatory role of CD8+ DC added to the cultures
of myeloid DC. In contrast, blockade of IDO activity completely ablated
the inhibitory effect of IFN--treated CD8+ DC
on peptide presentation by IL-12-treated
CD8- DC.
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To investigate whether the distinct patterns of activity observed
with different DC subsets pulsed with P815AB could also be observed
with evolutionarily distant Ags, we used a reference viral peptide, the
influenza virus NP 147–155 (24). In an experimental model
analogous to that of P815AB, peptide-pulsed DC were transferred into
recipient hosts either as such or after cell fractionation and/or
exposure to IFN- in vitro. After 2 wk, the animals were assayed for
class I-restricted skin test reactivity (Fig. 7). Different from the recipients of
P815AB-pulsed DC, the animals receiving whole DC populations pulsed
with NP were able to mount a significant DTH response, an effect that
could not be negated by pretreatment of the DC with IFN-. Transfer
of purified CD8- DC, either alone or in
combination with 3% CD8+ cells, resulted in a
DTH response that was quantitatively similar to that of the
unfractionated DC. Exposure of CD8+ DC to IFN-
before peptide pulsing and mixing with CD8- DC
had no effect on the onset of DTH to the viral peptide.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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and activated T cells (34). In several
experimental models, proinflammatory cytokines may ameliorate
autoimmunity, depending on timing and level of production and
presumably via interference with the APC function
(16). On studying the immune response to a synthetic tumor/self peptide in DBA/2 mice (35), we have previously found that peptide-loaded DC transferred into recipient hosts can present Ag in a tolerogenic or immunogenic fashion (19), depending on whether or not CD8+ DC are present in the transferred population (22). Thus, it appears that only myeloid CD8- DC are responsible for the activation of a Th1-like response to P815AB in our model system. Although these cells appear to be basally suppressed by the lymphoid CD8+ DC subset, they can be primed by IL-12 to overcome suppression (22). These data are apparently in contrast with several recent reports demonstrating that both CD8+ and CD8- splenic DC have strong immunostimulatory potentials for both CD4+ and CD8+ T cells (36, 37, 38, 39). In a study by Maldonado-López et al. (36), splenic CD8+ DC transferred intrafootpad were found to prime an immune response to keyhole limpet hemocyanin that was dominated by Th1 cytokines. In contrast, administration of CD8- DC induced a Th2 response. Ruedl and Bachmann (39) recently showed that both CD8+ and CD8- DC could activate CD8+ T cells in vitro and induce protective anti-viral CTL responses in vivo. Although the reasons underlying such apparently disparate roles of DC subsets in the various experimental models are unclear at present, one crucial aspect in our system may be the use of a tumor/self peptide rather than evolutionarily distant Ags (3). A functional distinction between myeloid and lymphoid DC with regard to immunogenic vs tolerogenic presentation of P815AB may reflect the long-established notion that there are two functional types of DC, one for immunity and one for regulation of tolerance (28, 29, 40, 41). Yet, despite the vast amount of empirical data on the subject, controversy continues to surround the issue of the distinction between myeloid and lymphoid DC at the functional level (42). In addition to functional heterogeneity of DC, the nature of a tumor/self peptide may contribute to explain the failure of unfractionated DC pulsed with P815AB to elicit a DTH response, in contrast to the strong DTH responses elicited by highly immunogenic peptides, including an influenza virus NP. Finally, although class I-restricted DTH is used in this study as the only means of assessing activation of CD8+ T cells specific for the P815AB peptide, it should be noted that the induction of this response correlates with the ability of mice to reject otherwise tumorigenic inocula of mastocytoma cells expressing the P815AB Ag (35).
Therefore, our present data reinforce the notion of a mutually
antagonistic effect of CD8- and
CD8+ DC, with the former cells mediating and the
latter cells opposing immunogenic presentation of a tumor/self peptide.
Interestingly, this study also provides evidence that the suppressive
effect of CD8+ DC is not confined to the DBA/2
strain, but can be evidenced in BALB/c mice even at a
CD8+ to CD8- DC ratio much
lower (3% of lymphoid DC) than that occurring in the unfractionated
splenic population (where the value is about 50%). In addition, the
current investigation demonstrates that the normally considered
proinflammatory cytokine IFN- is, in the context of DC presentation
of a tumor/self peptide, capable of preventing the onset of
IL-12-dependent Th1-type reactivity, which is mediated by
CD8+ T cells but requires
CD4+ lymphocytes for afferent induction
(35, 43). In another experimental model, it has been
recently shown that transfer of DC ex vivo stimulated with IFN-
down-modulates autoimmune diabetes (44).
Our data further suggest the occurrence of a negative feedback system
in which a major effector molecule of acquired immunity, IFN-,
down-regulates Ag presentation by CD8- DC. The
hypothesis of such a loop, and thus of functional cross-regulation
between IFN- and IL-12, is not in conflict with the widely accepted
notion that IFN- activates APC to produce IL-12, which is necessary
for the onset of cell-mediated immunity and is probably required for
the maintenance of autoimmunity (45). In contrast to its
effect on macrophages, IFN- is not a good inducer of IL-12 from DC,
in which IL-12 itself has been shown to be a far better inducer
(20, 21). In autoimmunity, it has been proposed that
proinflammatory cytokines may be required at an early time to induce
self-reactive responses by priming inflammatory Th1 responses; however,
the late expression of the same cytokines could drive the terminal
differentiation and death of T cells, including those engaged in
autoreactive responses (16). In addition, because IL-12
regulates the extent of the IFN- response to a variety of antigenic
stimuli (6, 9), the inhibitory activity of IFN- on DC
function could represent a potent and critical regulatory response in
acquired immunity. However, it should be noted that neither basal
inhibition by CD8+ DC nor induction of inhibitory
activity by IFN- were observed to an evolutionarily distant
influenza virus NP, thus suggesting that the regulatory mechanisms we
have been observing with the P815AB peptide may be restricted to
tumor/self peptides. This would imply that DC are able to discriminate
between tumor/self peptides and evolutionarily distant Ags and would
establish a new paradigm for self/nonself discrimination at the amino
acid level.
Besides being an important effector molecule released by Ag-specific T
cells in acquired immunity, IFN- may also be released by DC. Ohteki
et al. (46) recently reported that
CD8+ DC, but not CD8- DC,
are major producers of IFN- in response to IL-12. Although IL-12 has
no detectable effect on the negative regulatory role of
CD8+ DC in our in vivo model, we have found that
both CD8+ and CD8- DC will
produce IFN- in response to IL-12 in vitro. However, the effect
requires several days of in vitro exposure to IL-12 and cannot be
detected until 3 days of culture (data not shown). These findings
further support the notion that, regardless of its cellular origin, a
late production of IFN- may contribute to down-modulation of an
ongoing immune response.
Although CD8+ DC present a higher, constitutive
expression of IL-10 (22), and IL-10-treated DC are known
to be tolerogenic in vivo (47), the mechanism underlying
the activity of CD8+ DC is still unclear
(30), as is the regulation and physiological role of these
cells in vivo. In the present study, we provide evidence that IFN-
acting through CD8+ DC does not interfere with
IL-12 signaling in the CD8- DC subset.
Furthermore, we obtained evidence suggesting that
CD8+ and CD8- DC may
respond differently to IFN-. In fact, both
CD8+ and CD8- DC were
found to express comparable amounts of transcripts specific for the
- and ß-chains of the IFN- receptor (data not shown) and of
surface -chain molecule.
Also unclear in our experimental model is the issue of whether
CD8+ DC inhibition of P815AB presentation
primarily involves the APC function of CD8- DC
or T cell recognition of the peptide (22, 30). We have
previously shown that peptide-pulsed CD8+ DC not
treated with IFN- produce relatively high amounts of IL-10. However,
in the present study, we failed to detect increased production of IL-10
by CD8+ DC treated with IFN- (data not shown).
Thus, we have explored other possible mechanisms whereby IFN-
potentiates the inhibitory effect of CD8+ DC. In
particular, because IFN--induced tryptophan catabolism may represent
an important mechanism of T cell tolerance by macrophages (17, 31, 32), we have investigated the possible involvement of IDO
induction by IFN- in CD8+ DC. By the use of a
specific inhibitor of IDO activity in vitro, we have obtained evidence
that the IFN- effect on CD8+ DC was reversed
by the blockade of tryptophan catabolism. Of particular interest was
the observation that the inhibitor of IDO had no effect on the basal
inhibition exerted by CD8+ DC, i.e., in the
absence of IFN- and IL-12. Using RT-PCR, we have recently begun to
assess any possible differential expression and/or induction of IDO by
IFN-. Contrary to the results with control macrophage cultures, we
observed high constitutive expression of IDO in both
CD8- and CD8+ DC, which
prevented clear assessment of any differential effects of IFN- on
the two types of DC subsets (data not shown).
While suggesting a role for tryptophan catabolism in T cell tolerance
as induced by DC, these data indicate that the two mechanisms of
CD8+ DC suppression, namely under basal
conditions and after activation with IFN-, may be different. We are
currently evaluating the tryptophan-degrading activity of DC, which
might reflect a multifactored combination of IDO expression, tryptophan
transport into the cells, and intracellular conditions that
posttranslationally affect enzyme activity (31). In any
case, our present data suggest that activation of
CD8+ DC by IFN- in vitro results in the
production of functional IDO, which may cause depletion of tryptophan
in vivo in local tissue microenvironments and subsequent inhibition of
T cell responses. This could represent an important mechanism whereby
IFN- and CD8+ DC regulate immune
responses.
Because of the exquisite sensitivity of CD8+ DC
to physiologic concentrations of IFN- (represented in our study by
25 U/ml), our present data may shed light on the physiological roles of
functionally distinct DC subsets, on the mechanisms whereby
proinflammatory cytokines exert immunosuppressive activity, and on the
relationship between tryptophan catabolism and T cell tolerance. The
large number of studies performed to analyze interactions between
cytokines and responses to self-peptides indicates the extreme
complexity of the cytokine network. Consequently, the regulation that
cytokines superimpose on self-reactivity is a finely tuned balance
between activation and down-modulation (16). Factors such
as the duration of cytokine exposure and the type of APC involved are
likely to strongly influence the balance. We speculate that DC might
discriminate self from nonself in an inflammatory context dominated by
IFN-. Such a property of DC would help to explain the many and
apparently disparate roles of IFN- in acquired immunity.
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Acknowledgments |
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Paolo Puccetti, Department of Experimental Medicine, Pharmacology Section, University of Perugia, Via del Giochetto, I-06123 Perugia, Italy.
3 Abbreviations used in this paper: DC, dendritic cells; DTH, delayed-type hypersensitivity; IDO, indoleamine 2,3-dioxygenase, NP, nucleoprotein peptide.
Received for publication February 18, 2000. Accepted for publication May 22, 2000.
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References |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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production by CD8+ lymphoid dendritic cells. J. Exp. Med. 189:1981.This article has been cited by other articles:
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 C. Orabona, M. T. Pallotta, C. Volpi, F. Fallarino, C. Vacca, R. Bianchi, M. L. Belladonna, M. C. Fioretti, U. Grohmann, and P. Puccetti SOCS3 drives proteasomal degradation of indoleamine 2,3-dioxygenase (IDO) and antagonizes IDO-dependent tolerogenesis PNAS, December 30, 2008; 105(52): 20828 - 20833. [Abstract] [Full Text] [PDF]
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A. De Luca, C. Montagnoli, T. Zelante, P. Bonifazi, S. Bozza, S. Moretti, C. D'Angelo, C. Vacca, L. Boon, F. Bistoni, et al. Functional yet Balanced Reactivity to Candida albicans Requires TRIF, MyD88, and IDO-Dependent Inhibition of Rorc J. Immunol., November 1, 2007; 179(9): 5999 - 6008. [Abstract] [Full Text] [PDF]
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 R. Metz, J. B. DuHadaway, U. Kamasani, L. Laury-Kleintop, A. J. Muller, and G. C. Prendergast Novel Tryptophan Catabolic Enzyme IDO2 Is the Preferred Biochemical Target of the Antitumor Indoleamine 2,3-Dioxygenase Inhibitory Compound D-1-Methyl-Tryptophan Cancer Res., August 1, 2007; 67(15): 7082 - 7087. [Abstract] [Full Text] [PDF]
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P. Feunou, S. Vanwetswinkel, F. Gaudray, M. Goldman, P. Matthys, and M. Y. Braun Foxp3+CD25+ T Regulatory Cells Stimulate IFN-{gamma}-Independent CD152-Mediated Activation of Tryptophan Catabolism That Provides Dendritic Cells with Immune Regulatory Activity in Mice Unresponsive to Staphylococcal Enterotoxin B J. Immunol., July 15, 2007; 179(2): 910 - 917. [Abstract] [Full Text] [PDF]
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 M. D. Chiesa, S. Carlomagno, G. Frumento, M. Balsamo, C. Cantoni, R. Conte, L. Moretta, A. Moretta, and M. Vitale The tryptophan catabolite L-kynurenine inhibits the surface expression of NKp46- and NKG2D-activating receptors and regulates NK-cell function Blood, December 15, 2006; 108(13): 4118 - 4125. [Abstract] [Full Text] [PDF]
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S. Agaugue, L. Perrin-Cocon, F. Coutant, P. Andre, and V. Lotteau 1-Methyl-Tryptophan Can Interfere with TLR Signaling in Dendritic Cells Independently of IDO Activity J. Immunol., August 15, 2006; 177(4): 2061 - 2071. [Abstract] [Full Text] [PDF]
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M. L. Belladonna, U. Grohmann, P. Guidetti, C. Volpi, R. Bianchi, M. C. Fioretti, R. Schwarcz, F. Fallarino, and P. Puccetti Kynurenine Pathway Enzymes in Dendritic Cells Initiate Tolerogenesis in the Absence of Functional IDO J. Immunol., July 1, 2006; 177(1): 130 - 137. [Abstract] [Full Text] [PDF]
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M. S. von Bergwelt-Baildon, A. Popov, T. Saric, J. Chemnitz, S. Classen, M. S. Stoffel, F. Fiore, U. Roth, M. Beyer, S. Debey, et al. CD25 and indoleamine 2,3-dioxygenase are up-regulated by prostaglandin E2 and expressed by tumor-associated dendritic cells in vivo: additional mechanisms of T-cell inhibition Blood, July 1, 2006; 108(1): 228 - 237. [Abstract] [Full Text] [PDF]
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C. Orabona, P. Puccetti, C. Vacca, S. Bicciato, A. Luchini, F. Fallarino, R. Bianchi, E. Velardi, K. Perruccio, A. Velardi, et al. Toward the identification of a tolerogenic signature in IDO-competent dendritic cells Blood, April 1, 2006; 107(7): 2846 - 2854. [Abstract] [Full Text] [PDF]
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P. J. O'Connell, X. Wang, M. Leon-Ponte, C. Griffiths, S. C. Pingle, and G. P. Ahern A novel form of immune signaling revealed by transmission of the inflammatory mediator serotonin between dendritic cells and T cells Blood, February 1, 2006; 107(3): 1010 - 1017. [Abstract] [Full Text] [PDF]
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 J. Tsukada, A. Ozaki, T. Hanada, T. Chinen, R. Abe, A. Yoshimura, and M. Kubo The role of suppressor of cytokine signaling 1 as a negative regulator for aberrant expansion of CD8{alpha}+ dendritic cell subset Int. Immunol., September 1, 2005; 17(9): 1167 - 1178. [Abstract] [Full Text] [PDF]
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J. R. Gordon, F. Li, A. Nayyar, J. Xiang, and X. Zhang CD8{alpha}+, but Not CD8{alpha}-, Dendritic Cells Tolerize Th2 Responses via Contact-Dependent and -Independent Mechanisms, and Reverse Airway Hyperresponsiveness, Th2, and Eosinophil Responses in a Mouse Model of Asthma J. Immunol., August 1, 2005; 175(3): 1516 - 1522. [Abstract] [Full Text] [PDF]
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C. Orabona, M. L. Belladonna, C. Vacca, R. Bianchi, F. Fallarino, C. Volpi, S. Gizzi, M. C. Fioretti, U. Grohmann, and P. Puccetti Cutting Edge: Silencing Suppressor of Cytokine Signaling 3 Expression in Dendritic Cells Turns CD28-Ig from Immune Adjuvant to Suppressant J. Immunol., June 1, 2005; 174(11): 6582 - 6586. [Abstract] [Full Text] [PDF]
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S. Bozza, F. Fallarino, L. Pitzurra, T. Zelante, C. Montagnoli, S. Bellocchio, P. Mosci, C. Vacca, P. Puccetti, and L. Romani A Crucial Role for Tryptophan Catabolism at the Host/Candida albicans Interface J. Immunol., March 1, 2005; 174(5): 2910 - 2918. [Abstract] [Full Text] [PDF]
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 F. Fallarino, R. Bianchi, C. Orabona, C. Vacca, M. L. Belladonna, M. C. Fioretti, D. V. Serreze, U. Grohmann, and P. Puccetti CTLA-4-Ig Activates Forkhead Transcription Factors and Protects Dendritic Cells from Oxidative Stress in Nonobese Diabetic Mice J. Exp. Med., October 18, 2004; 200(8): 1051 - 1062. [Abstract] [Full Text] [PDF]
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F. Fallarino, C. Asselin-Paturel, C. Vacca, R. Bianchi, S. Gizzi, M. C. Fioretti, G. Trinchieri, U. Grohmann, and P. Puccetti Murine Plasmacytoid Dendritic Cells Initiate the Immunosuppressive Pathway of Tryptophan Catabolism in Response to CD200 Receptor Engagement J. Immunol., September 15, 2004; 173(6): 3748 - 3754. [Abstract] [Full Text] [PDF]
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 B. L. Colvin, A. E. Morelli, A. J. Logar, A. H. Lau, and A. W. Thomson Comparative evaluation of CC chemokine-induced migration of murine CD8{alpha}+ and CD8{alpha}- dendritic cells and their in vivo trafficking J. Leukoc. Biol., February 1, 2004; 75(2): 275 - 285. [Abstract] [Full Text] [PDF]
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B.-G. Xiao, X.-C. Wu, J.-S. Yang, L.-Y. Xu, X. Liu, Y.-M. Huang, B. Bjelke, and H. Link Therapeutic potential of IFN-{gamma}-modified dendritic cells in acute and chronic experimental allergic encephalomyelitis Int. Immunol., January 1, 2004; 16(1): 13 - 22. [Abstract] [Full Text] [PDF]
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U. Grohmann, R. Bianchi, C. Orabona, F. Fallarino, C. Vacca, A. Micheletti, M. C. Fioretti, and P. Puccetti Functional Plasticity of Dendritic Cell Subsets as Mediated by CD40 Versus B7 Activation J. Immunol., September 1, 2003; 171(5): 2581 - 2587. [Abstract] [Full Text] [PDF]
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U. Grohmann, F. Fallarino, R. Bianchi, C. Orabona, C. Vacca, M. C. Fioretti, and P. Puccetti A Defect in Tryptophan Catabolism Impairs Tolerance in Nonobese Diabetic Mice J. Exp. Med., July 7, 2003; 198(1): 153 - 160. [Abstract] [Full Text] [PDF]
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P. Terness, T. M. Bauer, L. Rose, C. Dufter, A. Watzlik, H. Simon, and G. Opelz Inhibition of Allogeneic T Cell Proliferation by Indoleamine 2,3-Dioxygenase-expressing Dendritic Cells: Mediation of Suppression by Tryptophan Metabolites J. Exp. Med., August 19, 2002; 196(4): 447 - 457. [Abstract] [Full Text] [PDF]
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F. Fallarino, U. Grohmann, C. Vacca, R. Bianchi, M. C. Fioretti, and P. Puccetti CD40 Ligand and CTLA-4 Are Reciprocally Regulated in the Th1 Cell Proliferative Response Sustained by CD8+ Dendritic Cells J. Immunol., August 1, 2002; 169(3): 1182 - 1188. [Abstract] [Full Text] [PDF]
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M. L. Belladonna, J.-C. Renauld, R. Bianchi, C. Vacca, F. Fallarino, C. Orabona, M. C. Fioretti, U. Grohmann, and P. Puccetti IL-23 and IL-12 Have Overlapping, but Distinct, Effects on Murine Dendritic Cells J. Immunol., June 1, 2002; 168(11): 5448 - 5454. [Abstract] [Full Text] [PDF]
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A. L. Mellor, D. B. Keskin, T. Johnson, P. Chandler, and D. H. Munn Cells Expressing Indoleamine 2,3-Dioxygenase Inhibit T Cell Responses J. Immunol., April 15, 2002; 168(8): 3771 - 3776. [Abstract] [Full Text] [PDF]
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F. Fallarino, C. Vacca, C. Orabona, M. L. Belladonna, R. Bianchi, B. Marshall, D. B. Keskin, A. L. Mellor, M. C. Fioretti, U. Grohmann, et al. Functional expression of indoleamine 2,3-dioxygenase by murine CD8{alpha}+ dendritic cells Int. Immunol., January 1, 2002; 14(1): 65 - 68. [Abstract] [Full Text] [PDF]
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U. Grohmann, F. Fallarino, R. Bianchi, M. L. Belladonna, C. Vacca, C. Orabona, C. Uyttenhove, M. C. Fioretti, and P. Puccetti IL-6 Inhibits the Tolerogenic Function of CD8{{alpha}}+ Dendritic Cells Expressing Indoleamine 2,3-Dioxygenase J. Immunol., July 15, 2001; 167(2): 708 - 714. [Abstract] [Full Text] [PDF]
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U. Grohmann, M. L. Belladonna, C. Vacca, R. Bianchi, F. Fallarino, C. Orabona, M. C. Fioretti, and P. Puccetti Positive Regulatory Role of IL-12 in Macrophages and Modulation by IFN-{{gamma}} J. Immunol., July 1, 2001; 167(1): 221 - 227. [Abstract] [Full Text] [PDF]
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H. Hochrein, K. Shortman, D. Vremec, B. Scott, P. Hertzog, and M. O'Keeffe Differential Production of IL-12, IFN-{{alpha}}, and IFN-{{gamma}} by Mouse Dendritic Cell Subsets J. Immunol., May 1, 2001; 166(9): 5448 - 5455. [Abstract] [Full Text] [PDF]
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U. Grohmann, F. Fallarino, S. Silla, R. Bianchi, M. L. Belladonna, C. Vacca, A. Micheletti, M. C. Fioretti, and P. Puccetti CD40 Ligation Ablates the Tolerogenic Potential of Lymphoid Dendritic Cells J. Immunol., January 1, 2001; 166(1): 277 - 283. [Abstract] [Full Text] [PDF]
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F. Fallarino, U. Grohmann, R. Bianchi, C. Vacca, M. C. Fioretti, and P. Puccetti Th1 and Th2 Cell Clones to a Poorly Immunogenic Tumor Antigen Initiate CD8+ T Cell-Dependent Tumor Eradication In Vivo J. Immunol., November 15, 2000; 165(10): 5495 - 5501. [Abstract] [Full Text] [PDF]
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