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Immunobiology Laboratory, Imperial Cancer Research Fund, London, United Kingdom
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Abstract |
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 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
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+ DC consistently display
the highest proportion of HEL-loaded MHC class II molecules. These data
indicate that exogenous Ags can be displayed to T cells in lymphoid
tissues by a large cohort of resident DC whose presentation is
regulated by innate and adaptive stimuli. Our data further reveal the
existence of a feedback mechanism that augments Ag presentation during
cognate APC-T cell interactions. |
Introduction |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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While B cells indeed present constitutively in vivo those Ags acquired
pinocytically (6, 7), other data suggest that this may not
be true of dendritic cells
(DC),4 the most
important APC in regulating T cell responses (8, 9, 10, 11). To
examine the requirements for presentation of a foreign Ag by murine DC
and B cells in vivo, we used the C4H3 mAb specific for
I-Ak in association with the 46–61 fragment of
the model Ag hen egg lysozyme (HEL; Ref. 12). This Ab can
stain APC bearing high levels of processed HEL in vitro and in vivo,
allowing direct measurement of presentation in the absence of ancillary
factors that can influence T cell assays of APC function (6, 7, 12). Using this reagent, we find that although the majority of
DC in lymph nodes is able to process and present HEL in vitro, it is
unable to do so efficiently in vivo unless an activation stimulus is
provided together with the Ag. This stimulus can take the form of a
microbial adjuvant, anti-CD40, or, remarkably, the presence of
Ag-specific T cells and acts to promote and sustain the presentation of
a high frequency of antigenic complexes primarily by
CD8+ DC. Together, these results suggest that
the ability of DC to present Ags in vivo is regulated and coupled to
activation. Activation-linked presentation results in a marked increase
in T cell stimulation.
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Materials and Methods |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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HEL, Con A, Lucifer Yellow, FITC-dextran, and LPS were purchased from Sigma (St. Louis, MO). All reagent stocks were tested for endotoxin content (Limulus amebocyte lysate assay; BioWhittaker, Walkersville, MD) and, if necessary, rigorously depleted of the contaminant by several passes through KuttsuClean (Maruha, Ibaraki, Japan), as recommended by the manufacturer. Residual levels of endotoxin in HEL were below 8 endotoxin units/mg. Repeated depletion with KuttsuClean did not decrease these levels further.
Monoclonal Abs
C4H3 is a rat IgG2b mAb that recognizes residues 46–61 of HEL
in the context of I-Ak (12). All
other mAbs were purchased from PharMingen (San Diego, CA). mAbs used
for in vivo treatment were endotoxin-free 3/23 anti-CD40
(13) and an isotype-matched (rat IgG2a) control Ab. mAbs
used for staining were 10-3.6 and MR5-2, mouse IgG2a specific for
I-Ak and Vß8.1/8.2, respectively; RA3-6B2,
RM4-5, and 53-6.7, rat IgG2a against B220, CD4, and CD8,
respectively; and HL3 and H1.2F3, hamster IgG against CD11c and CD69,
respectively. Irrelevant isotype-matched control Abs were used to
validate the specificity of staining.
Animals
Male and female B10.BR mice were obtained from Harlan U.K. (Bicester, U.K.) and were used at 6–20 wk of age. Mice were injected s.c. with HEL in the base of the tail or in the footpad for analysis of APC in surface inguinal lymph nodes or popliteal nodes, respectively. C4H3 detection of presentation in popliteal lymph nodes could be accomplished using 250–400 µg HEL administered to the footpad in 50 µl PBS. Similar detection in surface inguinal nodes required the injection of 1–4 mg HEL in 100 µl PBS. LPS or mAbs were used alone or in conjunction with HEL at the indicated doses. Control mice were injected with PBS.
Adoptive transfer
For adoptive transfer experiments, cells were taken from mice transgenic for 3A9 TCR, specific for I-Ak/HEL46–61 (14). These mice were purchased from The Jackson Laboratory (Bar Harbor, ME) on a B10.BR background and were bred at the Imperial Cancer Research Fund animal facility. Cells taken from lymph nodes and spleen were labeled with carboxymethyl fluorescein diacetate (Molecular Probes, Eugene, OR) and transferred i.v. (0.5–1 x 107 cells/mouse) into sex-matched B10.BR mice. 3A9 T cells in the recipients (0.2% of lymph node cells) were identified by flow cytometry as fluorescent cells that stained for CD4 and Vß8.2. Experiments using cells from 3A9 mice or from 3A9 mice bred into a recombinase-activating gene-2-/- B10.BR background gave identical results.
Cells
In initial experiments lymph node cell suspensions were prepared by collagenase/DNase digestion (15). However, because commercial supplies of collagenase contain substantial levels of endotoxin, in later experiments LPS-free Liberase (Roche Diagnostics, Lewes, U.K.) was substituted for collagenase. The phenotype and yield of DC obtained by either digestion method were identical (N. Rogers and C. Reis e Sousa, unpublished observations), and all the analysis reported here was unaffected by the digestion protocol.
Flow cytometry
Lymph node cells were stained with C4H3 as described for spleen
(7). Briefly, half of each cell suspension was stained
using unconjugated C4H3, followed by biotinylated mouse
F(ab')2 anti-rat IgG (Jackson
ImmunoResearch, West Grove, PA), except in experiments involving
immunization with anti-CD40, in which biotinylated C4H3 was used
instead. The other half of the sample was stained with biotinylated
10-3.6. All samples were then treated with a cocktail of FITC- or
APC-conjugated anti-CD8, PE-conjugated anti-CD11c,
Tricolor-conjugated streptavidin (Caltag, San Francisco, CA), and FITC-
or APC-conjugated anti-B220 together with an excess of unconjugated
rat IgG and 2.4G2 supernatant (anti-Fc
RII/III)
(16).
Two hundred thousand to 500,000 events were collected on a FACScalibur
cytometer (Becton Dickinson, Mountain View, CA) and analyzed using
FlowJo software (Treestar, San Carlos, CA). Live cells were selected
based on TOPRO exclusion (Molecular Probes) and/or scatter profile. APC
populations were defined as shown in Fig. 1
A. Median, rather than mean,
fluorescence values were determined for each parameter measured, as
medians are a stricter representation of the fluorescence of the
population as a whole.
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Surface inguinal or popliteal lymph nodes were generally pooled
from groups of two or three mice. For analysis of presentation, the
median C4H3 fluorescence for each lymph node APC population was
calculated and normalized by dividing this value by the corresponding
I-Ak median fluorescence (7). This
method takes into account differences in surface
I-Ak levels among APC and any changes in these
levels induced by in vitro culture or immunization (see Figs. 1
and 4).
The normalization procedure also reduces C4H3 values, such that
presentation in normalized samples is only apparent when high levels of
HEL46–61 are presented preferentially over self
peptides (7).
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Results |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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The processing and presentation of HEL protein by B cells and DC
subsets in vitro was assessed by staining whole lymph node cell
populations with the C4H3 Ab after overnight culture in the presence of
HEL. CD11c was used as a marker for DC, which were subdivided into
CD8- and CD8+
populations (Fig. 1A). B cells were identified based on
their expression of B220 and their lack of CD11c expression (Fig. 1A).
In cells cultured in medium alone, the C4H3 Ab stained a subset of
I-Ak molecules loaded with certain unidentified
self peptides (henceforth referred to as background staining; Fig. 1, B and C; Ref. 12). The level of
background staining varied among APC types, but was roughly
proportional to the amount of I-Ak expressed at
the cell surface (Fig. 1, C and D). C4H3 staining
of both B cells and DC increased 6- and 10-fold, respectively, after
culture with HEL protein (Fig. 1, B and C).
Surface I-Ak levels increased by 1.5- and
1.3-fold, respectively, in response to the same Ag (Fig. 1, B and D). Because increases in
I-Ak expression could increase background
staining, to take I-Ak levels into consideration,
median C4H3 fluorescence values were divided by those for
I-Ak (see Materials and Methods).
Normalized values represent the fraction of I-Ak
molecules loaded with HEL46–61 and indicate the
efficiency with which the epitope is generated (7).
Analyzed in this manner, HEL exposure in vitro resulted in an average
increase of 3- to 4-fold in the normalized C4H3 levels of lymph node
APC across multiple experiments (Fig. 1E). Addition of LPS
did not alter the frequency of C4H3 epitopes displayed by B cells or DC
in vitro (Fig. 1, B–E).
Virtually all B cells presented HEL, as assessed by the unimodal C4H3
staining pattern after HEL exposure (Fig. 1B). Surprisingly,
a unimodal C4H3 staining pattern was also seen with both DC subsets
(Fig. 1B), suggesting that the vast majority of lymph node
DC were able to process native HEL in vitro.
CD8+ DC exhibited the highest absolute levels
of C4H3 staining after exposure to HEL (Fig. 1, B and
C). However, these cells also expressed the highest surface
levels of I-Ak after culture (Fig. 1, B and D). When I-Ak levels
were accounted for by normalization, both B cells and DC processed HEL
in vitro with similar efficiency, as reported for spleen APC
(6).
Endotoxin promotes Ag presentation by CD8+ DC in
vivo
To study HEL presentation in vivo, groups of mice were immunized
s.c. in the base of the tail with HEL depleted of endotoxin. Cell
suspensions were prepared from surface inguinal lymph nodes and were
stained with C4H3 or anti-I-Ak. Staining data
were normalized to I-Ak levels (see above) to
give a measure of the proportion of I-Ak
molecules loaded with HEL46–61. As shown in Fig. 2A, B cell presentation of HEL
could be detected in draining inguinal lymph nodes as early as 3 h
after HEL administration to the base of the tail. The response peaked
at 6 h and declined to near background levels by 24 h
postimmunization. Remarkably, there was only a slight increase in the
frequency of C4H3 epitopes detected on CD8+ or
CD8- DC during this period despite
administration of doses of HEL as high as 4 mg/mouse (Fig. 2, B and C). Similar results were obtained in
popliteal lymph nodes following footpad immunization (not shown). The
failure of DC to present HEL at the same level as B cells (Fig. 2, A–C) was not due to lower endocytic activity, as FITC-HEL
and other endocytic tracers accumulated to a greater extent in
popliteal lymph node DC than in B cells after footpad injection (Table I). Thus, in contrast to that in vitro,
DC presentation of exogenous Ags occurs inefficiently in vivo.
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- DC or B cells and actually decreased it
in some experiments (Fig. 2, A and C). However,
the addition of LPS to the HEL inoculum invariably caused a rapid and
sustained increase in the frequency of C4H3 epitopes on
CD8+ DC compared with HEL or LPS alone (Figs. 2B and 4). Similar results were obtained in popliteal lymph
nodes after immunization into the footpad with lower doses of HEL (Fig. 2D). Importantly, the overall increase in C4H3 staining
(Fig. 2, B and D, and Fig. 4) induced by LPS was
not due to an influx of a few CD8+ DC
expressing high levels of C4H3. Rather, the unimodal C4H3 staining
pattern obtained (Fig. 2D) suggests that essentially all
lymph node CD8+ DC were able to process and
present HEL in vivo after coadministration of LPS. In contrast, C4H3
staining of CD8- DC increased only slightly
after HEL immunization, even in the presence of LPS (Fig. 2, C and D). CD8- DC also
displayed higher background levels of C4H3 staining than the
CD8+ subset, consistent with greater surface
expression of I-Ak (Fig. 2D, PBS
control).
LPS coadministration did not increase the retention of endocytic
tracers by lymph node APC (Table I), suggesting that LPS was not simply
promoting Ag uptake. To address whether LPS increased HEL processing,
we examined whether it could similarly promote presentation of
preprocessed Ag. Low levels of C4H3 staining above background were seen
on CD8- DC, but not on
CD8+ DC, after immunization with the synthetic
HEL46–61 peptide in the absence of LPS (Fig. 2E). LPS coadministration increased the frequency of C4H3
epitopes generated by the HEL peptide in CD8+
DC, but had no effect on CD8- DC (Fig. 2E). Thus, LPS activation acts at least in part by improving
peptide loading by CD8+ DC in vivo.
CD40 cross-linking in vivo increases HEL presentation by B cells
and CD8+ DC
To determine whether there were other stimuli that could similarly
activate DC and improve processing and presentation of exogenous Ags,
we examined the effect of CD40 ligation on HEL presentation. CD40
cross-linking has been shown to potently modulate the activity of DC
(17). The frequency of C4H3 epitopes on
CD8+ DC in popliteal nodes was greatly
enhanced and sustained when HEL was administered to the footpads in
conjunction with an agonistic anti-CD40, but not a control, Ab
(Fig. 3B). Interestingly, a
similar picture was seen for B cells, suggesting that although not
responsive to innate stimuli such as LPS, these APC can up-regulate Ag
presentation in response to certain signals (Fig. 3A). As
with LPS, anti-CD40 mAb did not increase the proportion of C4H3
epitopes on CD8- DC (Fig. 3C).
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The effects of anti-CD40 in vivo suggested that Ag
presentation by DC might be increased by molecules displayed by T cells
during activation, which could ligate counter-receptors on DC such as
CD40 or TNF-related activation-induced cytokine receptor. To
investigate whether this occurs physiologically, we adoptively
transferred cells from 3A9 TCR transgenic mice (containing T cells
specific for HEL46–61 and
I-Ak) into syngeneic unirradiated recipients.
Twenty-four hours later the adoptive recipients were immunized with HEL
or PBS. As before, immunization of normal B10.BR controls with HEL
alone increased C4H3 staining primarily on B cells, while the addition
of LPS to the inoculum (positive control) specifically augmented C4H3
staining on CD8+ DC (Fig. 4A). This increase was
disproportionate to any increase in I-Ak levels
(Fig. 4B) and was best illustrated by the increase in the
average normalized C4H3 fluorescence from multiple experiments (Fig. 4C). Interestingly, in 3A9 adoptive recipients HEL alone
similarly resulted in an increase in C4H3 staining of
CD8+ DC, reaching the level obtained in
control mice immunized with HEL and LPS (Fig. 4, A and
D). Again, the increase in C4H3 fluorescence was out of
proportion to any change in I-Ak expression (Fig. 4, B and D). Across multiple experiments this was
reflected in a marked increase in the normalized C4H3 value, as shown
in Fig. 4C. All the transgenic T cells in HEL-immunized
mice, but not in PBS-injected controls, up-regulated CD69, indicating
that they had become activated (not shown). This suggests that T cell
recognition of cognate Ag initiates a feedback mechanism that results
in increased Ag display by some APC.
Increased HEL presentation after adjuvant coadministration results in increased T cell activation
The above results suggested that innate and adaptive
signals that increase DC activation can markedly enhance Ag
presentation, i.e., the delivery of signal 1 to T cells. However,
experiments using the C4H3 Ab to detect presentation in vivo require
the administration of doses of HEL far in excess of those required to
activate HEL-specific T cells. To extrapolate our findings to
physiologically relevant Ag doses, we measured the activation of 3A9 T
cells in vivo in response to HEL alone or HEL plus LPS. We used doses
of Ag that allow formation of enough antigenic complexes to activate T
cells but do not result in a detectable increase in C4H3 binding.
Although 3A9 T cells up-regulated CD69 in response to immunization with
HEL alone, 100-fold higher Ag doses were required to approach the
levels of CD69 seen in response to HEL plus LPS (Fig. 5A). This result demonstrates
that the microbial signal acts as a potent adjuvant to promote T cell
activation. To determine whether this was due to increased Ag
presentation or simply to up-regulation of costimulatory and/or
adhesion molecules after LPS treatment, we measured CD69 up-regulation
on 3A9 T cells in mice immunized with Con A, an Ag that is independent
of MHC presentation but that still depends on other APC-derived signals
for T cell activation. In contrast to its effects on the 3A9 response
to HEL, LPS only slightly increased the activation of 3A9 T cells in
response to Con A (Fig. 5B). Therefore, the addition of LPS
to HEL augments 3A9 activation largely by increasing delivery of signal
1 to T cells rather than costimulatory or other signals.
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Discussion |
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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), but improve Ag loading onto MHC class
II molecules (Fig. 2E). Although it remains possible that
lymph node DC process exogenous Ags exclusively by an extracellular
pathway (24), our results are consistent with the idea
that the MHC class II groove in immature DC is occupied by invariant
chain, which cannot be degraded until the cells receive an activation
signal (10, 11). Because of the exquisite susceptibility of DC to activation by microbes (25), coupling of Ag presentation to DC activation may, therefore, bias DC to present Ags of microbial origin rather than self proteins. This idea fits the proposal that innate recognition of infectious organisms initiates adaptive immunity (5, 26, 27), but extends it to suggest that exposure to microbial stimuli leads not only to up-regulation of costimulatory molecules on APC and consequent increased delivery of signal 2 to T cells (28), but also up-regulation of Ag presentation and increased delivery of signal 1. This has important implications for our understanding of immune function and for vaccine design, because it implies that adjuvants act in part by promoting the formation and display of antigenic complexes by DC. In concert with increases in costimulation and cytokine production, this may facilitate and sustain T cell activation, clonal expansion, and generation of memory cells (29).
In our analysis, C4H3 staining was normalized to the staining obtained
with an Ab against I-Ak (see Materials and
Methods). Normalization is necessary because C4H3 cross-reacts
with a subset of I-Ak molecules loaded with
certain self-peptides (7, 12). Any increase in total MHC
class II levels is likely to increase this background proportionately.
An example of this can be seen after immunization with LPS alone, which
causes an increase in the absolute C4H3 (Fig. 4A) and
I-Ak (Fig. 4B) staining of DC, but
fails to affect the normalized C4H3 value (Fig. 4C).
However, normalization may well underestimate the amount of HEL
presentation in our experiments. It has previously been shown that the
presence of high concentrations of HEL protein can lead to increased
surface I-Ak expression by B cells through rescue
of molecules that would otherwise be targeted for lysosomal degradation
because of failure to be loaded with peptide (30, 31).
Such rescue is consistent with the increase in
I-Ak levels seen after incubation of lymph node
cells with HEL in vitro (Fig. 1, B and D). In
these circumstances, normalization penalizes cells that up-regulate
I-Ak because of HEL loading and effectively
biases the analysis toward those APC presenting the highest levels
of HEL.
The fact that normalized data represent proportion, rather than total
number, of HEL-loaded I-Ak molecules should be
borne in mind when thinking of the implications of our data for T cell
recognition. For example, although the proportion of HEL-loaded
I-Ak molecules on CD8-
DC is lower than that on CD8+ DC after
immunization (Figs. 2 and 4), the fact that the former APC express
higher absolute levels of I-Ak (Fig. 4, B and D) may result in equivalent or higher
absolute levels of HEL-loaded MHC class II. It is not clear at this
stage whether T cell recognition depends only on the absolute levels of
Ag display on APC or is sensitive to the frequency of MHC molecules
loaded with the antigenic peptide. In support of the latter,
self-peptide-loaded MHC complexes can act as TCR antagonists (32, 33), and a high frequency of antigenic complexes on APC has been
associated with increased priming of CD8+ T cells
(34, 35, 36, 37). Although we believe that normalization is
essential for understanding our results, we also include raw median
fluorescence values and FACS profiles in Figs. 1, 2, and 4, which give
an indication of the magnitude of the changes in the actual data and
may show a different hierarchy of presentation by DC subsets.
In contrast to its effect in vivo, LPS did not increase HEL processing
and presentation by either DC subset in vitro (Fig. 1, B–E). This suggests that simply disrupting the tissue and
culturing lymph node cells provide signals analogous to those provided
by LPS in vivo, which result in a marked increase in DC presentation.
Such signals are not present in cultures of bone marrow-derived DC,
which remain relatively quiescent and unable to present HEL until
activated by LPS or CD40 ligation (11). The activation of
DC upon isolation from tissues is a well-known feature
(38) and may also explain the differences in surface MHC
class II levels between DC subsets seen before and after culture. Thus,
freshly isolated CD8+ DC express lower surface
levels of MHC class II than CD8- DC (Fig. 4, B and D), but up-regulate it to a greater degree
in culture (Fig. 1, B and D), in part due to
redistribution of MHC molecules sequestered in intracellular
compartments (N. Rogers and C. Reis e Sousa, unpublished observations).
Interestingly, intracellular sequestration of MHC class II and
expression of invariant chain and cystatin C are more prevalent in
resting CD8+ DC than in
CD8- DC (N. Rogers, O. Schulz, and C. Reis e
Sousa, unpublished observations), consistent with the ability of the
former subset to rapidly load a high frequency of
I-Ak molecules with HEL peptides upon activation
in vivo.
Although lymph node CD8- DC did not display a
high frequency of C4H3 epitopes in our immunization experiments (
Figs. 2–4), they did so after in vitro culture with the Ag (Fig. 1). This
result suggests that the CD8- DC subset is
capable of efficient Ag processing, but that as yet unidentified
signals are required to induce high levels of presentation in vivo.
Such stimuli may include endogenous signals such as recognition of
dying cells (39, 40, 41, 42). Endogenous signals may also explain
the low level HEL presentation by DC in the absence of added adjuvants
(
Figs. 2–4), which appears to be independent of residual endotoxin in
the Ag preparation (our unpublished observations). Given a likely role
for DC in cross-tolerance to tissue Ags (43), it is
interesting to speculate that some signals may induce DC presentation
without causing up-regulation of costimulatory molecules.
Interestingly, presentation of LPS-free HEL by
CD8+ DC can be detected if the mouse has
previously received transgenic naive T cells specific for the Ag (Fig. 4). How can a T cell provide signals that initiate presentation of Ags
by DC if those signals depend on recognizing Ag in the first place? In
other work, we have found that T cell feedback amplifies cytokine
production by DC in vivo, but this is dependent upon prior DC
activation by innate signals (48). It is likely, therefore, that T
cells do not initiate Ag presentation, but simply augment it by
"rewarding" APC expressing small amounts of the right peptide:MHC
complexes. HEL in the absence of added LPS can still be presented by B
cells and also by DC at low levels (Figs. 2 and 4), which may be
sufficient to initiate T cell activation. However, a positive feedback
loop would dramatically increase the responsiveness of naive T cells to
low amounts of Ag during initial T cell activation (Fig. 5).
Amplification of presentation could also, perhaps, allow recruitment of
lower affinity T cells into the priming reaction, effectively leading
to clonal diversification. Positive feedback may be mediated in part
through CD40 cross-linking on the APC by CD40 ligand (CD40L)
up-regulated on the T cell, consistent with the effects of
anti-CD40 Ab on presentation. However, blocking studies with
anti-CD40L Ab to address this issue proved inconclusive. A maximum
inhibition of 20% of the increase in normalized C4H3 staining of DC
was seen after CD40L blockade in 3A9 adoptive recipients (data not
shown). This may indicate our inability to achieve full blockade or,
more likely, may reflect the presence of additional T cell ligands for
CD40 and/or the effect of related molecules such as TNF-related
activation-induced cytokine (44, 45). Studies are underway
to determine the relative contribution to DC activation of DC receptors
for T cell signals.
Langerhans cells freshly isolated from skin and exposed to intact
protein Ags in vitro can generate antigenic complexes that activate
Ag-specific, MHC class II-restricted T cells. However, they rapidly
lose the ability to do so upon culture, a phenomenon termed maturation
(46), which in vivo is thought to be accompanied by
migration of Langerhans cells to the T cell areas of draining lymph
nodes (38, 47). This has often been interpreted to mean
that DC in secondary lymphoid tissues are the end product of the
maturation process. Surprisingly, we find that most freshly isolated
lymph node DC of either subset are capable of processing and presenting
native Ag in vitro and that, given the appropriate stimulus,
CD8+ DC can do so in vivo. Thus, our data
indicate that the great majority of DC in lymph nodes are immature
cells capable of endocytosing Ags that drain to those sites and able to
process and present them at high levels upon receiving an appropriate
stimulus. Similarly, the majority of splenic DC can process and present
native HEL protein (6). One may, therefore, envisage two
mechanisms for Ag presentation in the T cell areas of secondary
lymphoid tissues. One involves the conventional pathway of immigration
into the tissue of DC originally present at the site of antigenic
challenge. Another involves a large cohort of resident immature lymph
node DC, which permanently sample lymph or blood contents and
up-regulate presentation in response to the presence of inflammatory
mediators draining from sites of infection. Some of these DC may also
be capable of phagocytosing incoming tissue DC and represent the Ags
they transported, as recently suggested (40). The
existence of multiple mechanisms for Ag presentation in secondary
lymphoid tissues might exist to ensure amplification of a nascent
response by maximizing the number of DC presenting relevant Ags and
allowing efficient selection of T lymphocytes with the appropriate Ag
specificity.
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Acknowledgments |
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Footnotes |
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2 Address correspondence and reprint requests to Dr. Caetano Reis e Sousa, Immunobiology Laboratory, Imperial Cancer Research Fund, 44 Lincoln’s Inn Fields, Holborn, London, WC2A 3PX U.K.
3 Abbreviations used in this paper: DC, dendritic cells; HEL, hen egg lysozyme; CD40L, CD40 ligand.
4 Ag presentation in this paper is used strictly to denote the display by APC, at the cell surface, of MHC molecules loaded with peptides from the Ag in question.
Received for publication May 8, 2000. Accepted for publication August 10, 2000.
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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molecules can inhibit T cell activation. J. Exp. Med. 190:1627.This article has been cited by other articles:
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 A. Engering, S. J. van Vliet, K. Hebeda, D. G. Jackson, R. Prevo, S. K. Singh, T. B. H. Geijtenbeek, H. van Krieken, and Y. van Kooyk Dynamic Populations of Dendritic Cell-Specific ICAM-3 Grabbing Nonintegrin-Positive Immature Dendritic Cells and Liver/Lymph Node-Specific ICAM-3 Grabbing Nonintegrin-Positive Endothelial Cells in the Outer Zones of the Paracortex of Human Lymph Nodes Am. J. Pathol., May 1, 2004; 164(5): 1587 - 1595. [Abstract] [Full Text] [PDF]
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R. Sporri and C. Reis e Sousa Newly Activated T Cells Promote Maturation of Bystander Dendritic Cells but Not IL-12 Production J. Immunol., December 15, 2003; 171(12): 6406 - 6413. [Abstract] [Full Text] [PDF]
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D. Frleta, R. J. Noelle, and W. F. Wade CD40-mediated up-regulation of Toll-like receptor 4-MD2 complex on the surface of murine dendritic cells J. Leukoc. Biol., December 1, 2003; 74(6): 1064 - 1073. [Abstract] [Full Text]
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 S.-i. Fujii, K. Shimizu, C. Smith, L. Bonifaz, and R. M. Steinman Activation of Natural Killer T Cells by {alpha}-Galactosylceramide Rapidly Induces the Full Maturation of Dendritic Cells In Vivo and Thereby Acts as an Adjuvant for Combined CD4 and CD8 T Cell Immunity to a Coadministered Protein J. Exp. Med., July 21, 2003; 198(2): 267 - 279. [Abstract] [Full Text] [PDF]
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J. E. Buhlmann, S. K. Elkin, and A. H. Sharpe A Role for the B7-1/B7-2:CD28/CTLA-4 Pathway During Negative Selection J. Immunol., June 1, 2003; 170(11): 5421 - 5428. [Abstract] [Full Text] [PDF]
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S. Fillatreau and D. Gray T Cell Accumulation in B Cell Follicles Is Regulated by Dendritic Cells and Is Independent of B Cell Activation J. Exp. Med., January 20, 2003; 197(2): 195 - 206. [Abstract] [Full Text] [PDF]
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E. Muraille, C. De Trez, B. Pajak, M. Brait, J. Urbain, and O. Leo T Cell-Dependent Maturation of Dendritic Cells in Response to Bacterial Superantigens J. Immunol., May 1, 2002; 168(9): 4352 - 4360. [Abstract] [Full Text] [PDF]
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J. A. Williams, S. O. Sharrow, A. J. Adams, and R. J. Hodes CD40 Ligand Functions Non-Cell Autonomously to Promote Deletion of Self-Reactive Thymocytes J. Immunol., March 15, 2002; 168(6): 2759 - 2765. [Abstract] [Full Text] [PDF]
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I. H. Frazer, R. D. Kluyver, G. R. Leggatt, H. Yang Guo, L. Dunn, O. White, C. Harris, A. Liem, and P. Lambert Tolerance or Immunity to a Tumor Antigen Expressed in Somatic Cells Can Be Determined by Systemic Proinflammatory Signals at the Time of First Antigen Exposure J. Immunol., December 1, 2001; 167(11): 6180 - 6187. [Abstract] [Full Text] [PDF]
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0.003, by
t test). Differences among APC or between HEL and HEL
plus LPS groups were not statistically significant.
