Content uploaded by Luc Lebeau
Author content
All content in this area was uploaded by Luc Lebeau
Content may be subject to copyright.
Available via license: CC BY 4.0
Content may be subject to copyright.
Spleen-Resident CD4
+
and CD4
2
CD8a
2
Dendritic Cell
Subsets Differ in Their Ability to Prime Invariant Natural
Killer T Lymphocytes
Emilie Bialecki
1,2,3,4,5
, Elodie Macho Fernandez
1,2,3,4,5
, Stoyan Ivanov
1,2,3,4,5
, Christophe Paget
1,2,3,4,5
,
Josette Fontaine
1,2,3,4,5
, Fabien Rodriguez
1,2,3,4,5
, Luc Lebeau
6
, Christophe Ehret
6
, Benoit Frisch
6
,
Franc¸ois Trottein
1,2,3,4,5
, Christelle Faveeuw
1,2,3,4,5
*
1Center for Infection and Immunity of Lille, Institut Pasteur de Lille, Lille, France, 2Universite
´Lille Nord de France, Lille, France, 3Centre National de la Recherche
Scientifique (CNRS), UMR 8204, Lille, France, 4Institut National de la Sante
´et de la Recherche Me
´dicale (Inserm), U1019, Lille, France, 5Institut Fe
´de
´ratif de Recherche 142,
Lille, France, 6Laboratoire de Conception et Application des Mole
´cules Bioactives, Faculte
´de Pharmacie, CNRS, UMR 7199/Universite
´de Strasbourg, Illkirch, France
Abstract
One important function of conventional dendritic cells (cDC) is their high capacity to capture, process and present Ag to T
lymphocytes. Mouse splenic cDC subtypes, including CD8a
+
and CD8a
2
cDC, are not identical in their Ag presenting and T
cell priming functions. Surprisingly, few studies have reported functional differences between CD4
2
and CD4
+
CD8a
2
cDC
subsets. We show that, when loaded in vitro with OVA peptide or whole protein, and in steady-state conditions, splenic
CD4
2
and CD4
+
cDC are equivalent in their capacity to prime and direct CD4
+
and CD8
+
T cell differentiation. In contrast, in
response to a-galactosylceramide (a-GalCer), CD4
2
and CD4
+
cDC differentially activate invariant Natural Killer T (iNKT) cells,
a population of lipid-reactive non-conventional T lymphocytes. Both cDC subsets equally take up a-GalCer in vitro and in
vivo to stimulate the iNKT hybridoma DN32.D3, the activation of which depends solely on TCR triggering. On the other
hand, and relative to their CD4
+
counterparts, CD4
2
cDC more efficiently stimulate primary iNKT cells, a phenomenon likely
due to differential production of co-factors (including IL-12) by cDC. Our data reveal a novel functional difference between
splenic CD4
+
and CD4
2
cDC subsets that may be important in immune responses.
Citation: Bialecki E, Macho Fernandez E, Ivanov S, Paget C, Fontaine J, et al. (2011) Spleen-Resident CD4
+
and CD4
2
CD8a
2
Dendritic Cell Subsets Differ in Their
Ability to Prime Invariant Natural Killer T Lymphocytes. PLoS ONE 6(10): e26919. doi:10.1371/journal.pone.0026919
Editor: Colin Combs, University of North Dakota, United States of America
Received August 8, 2011; Accepted October 6, 2011; Published October 31, 2011
Copyright: ß2011 Bialecki et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This work was supported by the Institut National de la Sante
´et de la Recherche Me
´dicale (Inserm), the CNRS, the University of Lille Nord de France, the
Pasteur Institute of Lille, and the Institut National du Cancer (INCa, projets libres) under reference R08046EE/RPT08003EEA. The funders had no role in study
design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have declared that no competing interests exist.
* E-mail: christelle.faveeuw@pasteur-lille.fr
Introduction
The dendritic cell (DC) network is essential for the initiation and
the regulation of immune responses. Dendritic cells are specialized
in Ag capture, processing and presentation on MHC molecules
[1]. The interaction of DC with naive T lymphocytes can lead to
different forms of immune responses (type 1, type 2 or type 17
responses or tolerance), the outcome of which depends on the type
of DC as well as their activation state [2]. Along with their ability
to prime naive T lymphocytes and shape the adaptive immune
response, DC also play a major role in the activation of innate
immune cells including NK and invariant NKT (iNKT) cells.
Invariant NKT cells represent an emerging population of ‘‘innate-
like’’ immune cells expressing NK lineage receptors and an
invariant TCRachain (Va14-Ja18 rearrangement in mice and
Va24-Ja18 rearrangement in humans) that pairs with a limited
number of Vbchains. This cell population recognizes exogenous
and self (glyco)lipid Ag presented by the CD1d molecule expressed
by Ag presenting cells, including DC (for reviews, [3–7]). In
response to CD1d-restricted lipids such as a-galactosylceramide
(a-GalCer), a non-mammalian glycolipid Ag with potent anti-
tumor properties [8], iNKT cells rapidly and vigorously produce a
wide array of immunomodulatory cytokines including IFN-cand
IL-4. This explosive response leads to downstream activation of
DC, NK cells, neutrophils and B and T cells with important
outcomes on immune responses and pathologies (for reviews,
[3,7,9,10].
Dendritic cells are heterogeneous and can be classified into
different subtypes according to their phenotype, tissue distribution
and functions. Spleen-resident DC are mainly composed of
conventional DC (cDC) that can be further subdivided into
distinct subtypes, including CD8a
2
cDC, encompassing CD4
+
and CD4
2
subsets, and CD8a
+
cDC, expressing or not the
CD103 molecule [11,12]. Over the last decade, several reports
pointed out a functional dichotomy between CD8a
2
cDC, the
most numerous cDC subtype in the spleen, and CD8a
+
cDC.
Thus, CD8a
+
cDC serve as efficient APC for inducing a Th1
response and, through their cross-presenting capacity, for priming
CTL response whereas CD8a
2
cDC preferentially present
exogenous Ag to prime CD4
+
T cells and to induce Th2 responses
[1,13–16]. More recently, functional differences within CD8a
+
cDC subsets have been underlined. Of major importance is the
recent demonstration that CD8a
+
CD103
+
cDC, a subpopulation
that localises in the marginal zone of the spleen, is critical for
PLoS ONE | www.plosone.org 1 October 2011 | Volume 6 | Issue 10 | e26919
either tolerance induction to cell-associated Ag or cross-priming
in response to systemic activation stimuli [17,18]. Splenic CD8a
2
cDC subsets (now termed CD4
+
and CD4
2
cDC for the sake of
simplicity) are closely related phylogenetically although recent
transcriptomic and proteomic analyses revealed some differences
that may be important for their respective functions [19,20].
Functional studies aimed at comparing CD4
+
and CD4
2
cDC
are very limited and sometimes contradictory. Hochrein et al. first
reported that CD4
2
cDC are more efficient at producing IL-12
after CD40 ligation or TLR stimulation whereas two other
studies reported no major differences in IL-12 production
between the two cDC subsets in response to Leishmania infection
[21–23]. Proietto et al. also reported that CD4
+
cDC are the
main producers of inflammatory chemokines after TLR activa-
tion [24]. The ability of CD4
+
and CD4
2
cDC to prime and
orientate CD4
+
T lymphocytes upon sensitization with OVA
peptide has been studied in steady-state and stressful conditions.
In these systems, both cDC subsets equally primed CD4
+
T
lymphocytes and induced a mixed response. However, it was
noticed that the CD4
2
cDC biased the response towards a more
Th1 direction [23,25], in an IL-12 independent manner [23]. So
far, potential differences in the ability of CD4
+
and CD4
2
cDC
to prime conventional T lymphocytes in response to whole
protein remains undetermined. In the present study, we show
that after sensitization with OVA peptide or whole OVA, and
under steady-state conditions, both CD8a
2
cDC subsets are
comparable in their capacity to prime and direct CD4
+
and
CD8
+
T cell differentiation. In contrast, when sensitized with the
iNKT cell activator a-GalCer, CD4
+
and CD4
2
cDC subsets
markedly differ, both in vitro and in vivo, in their ability to activate
and/or polarize iNKT cells. Thus, our data reveal a novel
functional difference between splenic CD4
+
and CD4
2
cDC
subsets.
Results
CD4
+
and CD4
2
cDC are equivalent in their ability to
activate CD4
+
and CD8
+
T lymphocytes in vitro
There is now evidence that cDC subsets, i.e. CD8a
+
versus
CD8a
2
cDC or CD103
+
versus CD103
2
CD8a
+
cDC, are not
equivalent in their Ag presenting functions [13,16–18]. Whether
CD8a
2
cDC subsets (CD4
+
and CD4
2
) differ in their capacity to
present Ag and activate conventional CD4
+
and CD8
+
T
lymphocytes remains an open question. To address this issue,
CD8a
2
cDC subsets were purified from the spleens of naı
¨ve mice
on the basis of CD11c, CD4, CD8 as well as CD11b expression. In
contrast to previous reports, the CD11b marker was considered in
our sorting strategy to limit contaminating cells, principally in the
CD4
2
cDC fraction (Figure 1A). Thus, all CD8a
2
cDC were
CD11b
+
and the CD4
2
cDC subset contained very few
contaminating cells, such as plasmacytoid DC (Siglec-H
+
)or
CD8
+
cDC precursors (Sirp-a
2
) (Figure 1A). Isolated splenic
CD4
+
and CD4
2
cDC subsets were then assayed for their ability
to prime and direct the differentiation of OVA-specific TCR
transgenic T cells (OT-II) in steady-state conditions. As seen in
Fig. 1B, CD4
+
and CD4
2
cDC loaded with graded doses of the
MHC class II-restricted OVA peptide induced a mixed cytokine
response in OT-II CD4
+
T lymphocytes characterized by
equivalent levels of secreted IFN-cand IL-13, whatever the time
point analysed. Similarly, loading of CD4
+
and CD4
2
cDC with
whole OVA resulted in an equivalent release of IFN-cand IL-13
by OT-II CD4
+
T lymphocytes (Fig. 1C). IL-4 and IL-5 were
undetectable in all culture supernatants. Thus, CD4
+
and CD4
2
cDC pulsed with OVA peptide or whole OVA protein equally
prime CD4
+
T lymphocytes to differentiate into a mixed T cell
population.
The capacity of CD4
+
and CD4
2
cDC to activate CD8
+
T
lymphocytes was next compared. As seen in Fig. 2A, loading of
CD4
+
and CD4
2
cDC with the MHC class I-restricted OVA
peptide SIINFEKL led to a comparable CD8
+
T cell activation, in
terms of IFN-cproduction, although for the highest dose, peptide-
loaded CD4
2
cDC induced more IFN-cbut only at day 3. Thus,
the two cDC subsets present OVA peptide to CD8
+
T
lymphocytes with the same efficacy leading to an equivalent
priming. The cross-presenting ability of both cDC subsets was next
assessed using whole OVA (Fig. 2B). Compared to CD8a
+
cDC
[1,13,14,16], CD8a
2
cDC induced a low, but detectable,
production of IFN-cby OT-I CD4
+
T lymphocytes. As Fig. 2B
shows, the cross-presenting activity of CD4
+
and CD4
2
cDC was
not statistically different. Collectively, these data indicated that
after in vitro challenge with peptide or whole protein, CD4
+
and
CD4
2
cDC have an equivalent capacity to prime naı
¨ve CD4
+
and
CD8
+
T lymphocytes and to induce the differentiation of mixed
effector Th populations.
CD4
+
and CD4
2
cDC differ in their capacity to activate
iNKT cells in vitro
Dendritic cells are particularly well equipped to promote rapid
and potent cytokine release by iNKT cells [26–32]. We first
compared the capacity of CD4
+
and CD4
2
cDC to activate iNKT
cells in vitro. To this end, the two cDC subsets were loaded with the
prototypical lipid Ag a-GalCer, washed and then exposed to
primary iNKT cells. As depicted in Fig. 3A, a-GalCer-loaded
CD4
2
and CD4
+
cDC promoted the production of both IFN-c
and IL-4 by FACS-sorted iNKT cells in a dose-dependent
manner. Interestingly, whilst both cDC subsets induced an
equivalent secretion of IL-4 by iNKT cells, CD4
2
cDC triggered
a significantly higher production of IFN-cby iNKT cells relative
to their CD4
+
counterparts. This effect was observed whatever the
dose of a-GalCer. We hypothesized that this difference could be
due to a differential expression of the CD1d molecule on the DC
surface. However, flow cytometry analysis revealed an equivalent
level of CD1d expression between CD4
2
(MFI of 87956543) and
CD4
+
(MFI of 97106503) cDC subsets in steady-state conditions
(Fig. 3B) as well as after in vitro a-GalCer loading (data not shown).
Moreover, the DN32.D3 hybridoma, the activation of which is
solely due to CD1d/TCR interactions, was activated to a similar
extent by both CD4
+
and CD4
2
cDC (Fig. 3C). These data
suggest that the enhanced ability of CD4
2
cDC to polarize
primary iNKT cells towards a Th1 direction is probably due to co-
factors produced by the former. We investigated the possibility
that IL-12 could be responsible for this phenomenon. Interleukin-
12p40 and p70 proteins were not detected in our co-culture
system, a phenomenon that could be explained by their rapid
capture. In line with this hypothesis, and relative to the control, an
induction of IL-12p35 (but not IL-12p40, not shown) transcripts
was detected in a-GalCer loaded cDC/iNKT cell co-culture
(Fig. 3D). Of interest, the fold induction of IL-12p35 mRNA
synthesis (,160 fold) was more elevated in CD4
2
cDC compared
to CD4
+
cDC (,20 fold). These data suggest that bioactive IL-12
might be involved in the higher ability of a-GalCer pulsed CD4
2
cDC to induce IFN-cby primary iNKT cells. To confirm this
hypothesis, a neutralizing anti-IL-12 Ab was added during the co-
culture. As already reported [33,34], in this system, IFN-c
production by iNKT cells was not fully dependent on IL-12
production by cDC (Fig. 3E). However, the enhanced capacity of
CD4
2
cDC to promote IFN-cproduction by iNKT cells was
totally dependent on IL-12.
Dendritic Cells and Natural Killer T Cell Priming
PLoS ONE | www.plosone.org 2 October 2011 | Volume 6 | Issue 10 | e26919
Figure 1. CD4
+
and CD4
2
cDC are equivalent in their ability to activate CD4
+
T lymphocytes. (A) Splenic CD4
+
and CD4
2
cDC were sorted
on the basis of CD11c, CD11b, CD8 and CD4 expression. The presence of contaminating plasmacytoid DC and CD8a
+
cDC precursors in the CD4
2
cDC
fraction was evaluated by using anti-Siglec-H and Sirp-amAbs, respectively. (B, C) Both cDC subsets were sensitized with graded doses of OVA
peptide (B) or whole OVA (C) and co-cultured for 3 and 5 days with naive CD4
+
T cells purified from OT-II mice. The production of IFN-cand IL-13 was
quantified by ELISA. Results represent the mean 6SD of a representative experiment out of two.
doi:10.1371/journal.pone.0026919.g001
Dendritic Cells and Natural Killer T Cell Priming
PLoS ONE | www.plosone.org 3 October 2011 | Volume 6 | Issue 10 | e26919
CD4
+
and CD4
2
cDC loaded in vivo with a-GalCer
activate iNKT cells differently
We then compared the ability of CD4
+
and CD4
2
cDC, loaded
in vivo with a-GalCer, to activate iNKT cells. Before this, we
verified that both cDC subsets can take up a-GalCer in vivo after
intravenous injection. To this end, Cy5 conjugated to a-GalCer
was synthesized, as shown schematically in Fig. 4A, and tested for
its in vitro iNKT cell activating property. As revealed in Fig. 4B, in
vitro exposure of bone-marrow derived DC to increasing doses of
Cy5-a-GalCer promoted IL-2 production by DN32.D3 hybrid-
oma cells. This effect was dependent on CD1d expression by DC.
Cy5-a-GalCer also induced, in a CD1d-dependent fashion, IFN-c
and IL-4 release by primary iNKT cells (Fig. 4C). We next
compared the in vivo incorporation rate of a-GalCer in cDC
subsets. As shown in Fig. 4D, 2 h after Cy5-a-GalCer adminis-
tration, both CD4
+
and CD4
2
cDC labelled positively and to a
similar extent. Of note, Cy5-conjugated a-GalCer was weakly
incorporated by both cDC subsets 45 min after injection (data not
shown). The ex vivo iNKT cell-activating properties of CD4
+
and
CD4
2
cDC were then compared. To this end, cDC subsets were
sorted from a-GalCer-inoculated mice (2 h) and co-cultured with
iNKT cells. At this time point, cDC subsets equally expressed the
CD1d molecule and exhibited no sign of maturation, as assessed
by flow cytometry (data not shown). As shown in Fig. 4E, in vivo a-
GalCer sensitized CD4
+
and CD4
2
cDC activated the DN32.D3
hybridoma to the same extent although in a less efficient manner
compared to in vitro a-GalCer sensitized cDC (Fig. 3C). These data
are in line with the above results showing no differences in the
incorporation rate of a-GalCer in vivo between the two cDC
subsets. In contrast, when primary cell-sorted iNKT cells were
used, major differences were observed (Fig. 4F). Indeed, CD4
2
cDC promoted IFN-cand IL-4 release by primary cell-sorted
iNKT cells while CD4
+
cDC only promoted a low level of IL-4
secretion.
Discussion
Very few studies have been devoted to investigate the respective
roles of CD4
2
and CD4
+
cDC subsets in immune responses. In
the current study, we showed for the first time that upon peptide
and whole protein challenge, splenic CD4
2
and CD4
+
cDC
equally prime CD4
+
and CD8
+
conventional T lymphocytes in
vitro and that under steady-state conditions, they have a similar
capacity to induce the differentiation of mixed effector Th
populations. In marked contrast, CD4
2
and CD4
+
cDC differ in
their ability to stimulate iNKT cells.
In this study, we compared the activating properties of ex vivo-
isolated CD4
2
and CD4
+
cDC on conventional T lymphocytes
(priming and polarization) as well as on iNKT cells (primary
stimulation), a population of non-conventional T lymphocytes.
Even under stringent sorting conditions, the functions attributed
to cDC subsets may be biased by minor contaminant populations.
In contrast to previous reports [19–25], a particular attention was
paid to the elimination of potential contaminating cells such as
plasmacytoid DC and Sirp-a-negative CD8
+
cDC precursors in
the CD4
2
cDC preparation. We first compared the capacity of
CD4
2
and CD4
+
cDC to prime and orientate naı
¨ve T cells in vitro
using OVA peptide or whole OVA protein, as a model of study.
In agreement with [23,25], we showed that, when pulsed with
OVA peptide, splenic CD4
2
and CD4
+
cDC equally prime naı
¨ve
CD4
+
conventional T cells in vitro. Similarly, no differences
between the two cDC subsets were found in response to whole
OVA. This novel observation indicated that, at least for OVA
and in steady-state conditions, CD4
+
and CD4
2
cDC share
similar endocytic properties as well as an equivalent ability to
trim Ag and present peptide fragments by the MHC class II
molecule. Of note, MHC class II molecules were equally
expressed on both cDC subsets (not shown). Our data also
suggested no differences in the Th directing potential of CD4
+
and CD4
2
cDC in our experimental conditions. This finding is in
line with [25], but not with [23] who showed that CD4
2
cDC
rather favour Th1 polarisation relative to CD4
+
cDC. When
exposed to a MHC class I-restricted peptide, no major differences
in priming activity of CD4
+
and CD4
2
cDC was noticed. Finally,
in accordance with the poor cross-presenting capacity of CD8a
2
cDC [1,13,14], CD4
+
and CD4
2
cDC pulsed with whole OVA
modestly activated OT-I CD8
+
T lymphocytes. In these settings,
CD4
+
and CD4
2
cDC activate OVA-specific CD8
+
T lympho-
cytes to a similar extent. Thus, our study clearly show that, under
steady-state conditions, highly purified CD4
+
and CD4
2
cDC
prime and orientate CD4
+
and CD8
+
T lymphocytes with the
same efficacy. CD8a
2
cDC are particularly well equipped with
innate (microbial) detectors [19,20]. Whether or not functional
differences in terms of both stimulatory and regulatory properties
occur between CD4
+
and CD4
2
cDC during stressful conditions
(i.e. in the context of infection) is unknown at present. Previous
studies suggested that CD4
2
cDC activated in vivo during
Leishmania donovani infection or in vitro upon TLR activation are
more prone to induce a Th1 response than their CD4
+
cDC
counterparts [23,25]. Thus, CD4
2
and CD4
+
cDC may play
different roles in immune responses in the context of exogenous
(microbial) stimulation.
Figure 2. CD4
+
and CD4
2
cDC are equivalent in their ability to
activate CD8
+
T lymphocytes. (A, B) CD4
+
and CD4
2
cDC subsets
were sensitized with graded doses of OVA peptide (A) or whole OVA (B)
and co-cultured for 3 and 5 days with naive CD8
+
T cells purified from
OT-I mice. The production of IFN-cwas quantified by ELISA. Results
represent the mean 6SD of a representative experiment out of two.
doi:10.1371/journal.pone.0026919.g002
Dendritic Cells and Natural Killer T Cell Priming
PLoS ONE | www.plosone.org 4 October 2011 | Volume 6 | Issue 10 | e26919
We next assessed whether CD4
2
and CD4
+
cDC promote
identical primary stimulation of iNKT cells, an ‘‘innate-like’’
immune cell population that reacts to lipid Ag. Previous findings
established that cDC are particularly efficient at activating iNKT
cells in vivo [26,28] and that, in turn, iNKT cells strongly
contribute to DC maturation and functions [35]. Studies from
Farrand et al. and Simkins et al. showed that, after a-GalCer
administration, CD8a
+
CD103
+
(CD207
+
) cDC are dispensable
for the primary activation of iNKT cells but play a key role in
the by-stander activation of immune cells, which occurs
subsequently to primary iNKT cell activation [17,36]. These
data suggested a role for other APC, including CD8a
2
cDC, in
the primary activation of iNKT cells. No studies have so far
evaluated the respective role of CD4
2
and CD4
+
cDC in this
setting. Analysis of CD1d expression revealed no differences
between CD4
2
and CD4
+
cDC freshly sorted from naı
¨ve
animals (Fig. 3B) or in vivo early after a-GalCer inoculation (data
not shown). Moreover, in vitro as well as in vivo sensitization with
a-GalCer triggered an activation of the iNKT cell hybridoma
DN32.D3, as assessed by IL-2 production. These data, and the
Figure 3. CD4
+
and CD4
2
cDC differ
in vitro
in their capacity to activate iNKT cells. (A, C) Sorted CD4
+
and CD4
2
cDC were exposed to
graded doses of a-GalCer and then co-cultured for 48 h with sorted iNKT cells (A) or with the iNKT cell hybridoma DN32.D3 (C). Cytokine production
was quantified by ELISA. Results represent the mean 6SD of 3 (A) or 2 (C) independent experiments. (B) CD1d expression on CD4
+
and CD4
2
cDC
was assessed by flow cytometry. Of note, the staining with the isotype control was identical on both cDC subsets. For clarity, the isotype control on
the CD4
+
, but not CD4
2
, cDC subset is shown. Shown is a representative experiment out of three. (D) Sorted CD4
+
and CD4
2
cDC were exposed, or
not (medium), to a-GalCer (100 ng/ml) and then co-cultured for 6 h with sorted iNKT cells. RNAs were prepared and IL-12p35 (Il12p35) mRNA copy
numbers were measured by quantitative RT-PCR. Data are normalized to expression of Gapdh and are expressed as fold increase over average gene
expression in vehicle-treated cDC. Of note, the basal level of IL-12p40 transcript in ex vivo sorted cDC is relatively elevated (Ct: 25–26) (Ct of gapdh: 20,
Ct of il12p35: 31–32). Data represent the mean 6SD (triplicates) of an experiment out of two performed. (E) a-GalCer-loaded cDC subsets were co-
cultured for 48 h with sorted iNKT cells in the presence of a neutralizing IL-12 Ab or an isotype control Ab. Shown is a representative experiment
(mean 6SD) out of three performed. * p,0.05; ** p,0.01; *** p,0.001.
doi:10.1371/journal.pone.0026919.g003
Dendritic Cells and Natural Killer T Cell Priming
PLoS ONE | www.plosone.org 5 October 2011 | Volume 6 | Issue 10 | e26919
fact that a-GalCer is incorporated with the same kinetics and
efficacy by both cDC subsets in vivo (Fig. 4D), indicated that
CD4
2
and CD4
+
cDC display no differences in their ability to
trigger TCR-dependent activation of iNKT cells. a-GalCer can
directly bind to cell-surface CD1d but a large proportion of it is
internalised and loaded on CD1d in endosomes [37,38]. This
suggests that acquisition and uptake of free a-GalCer in cDC as
well as mechanisms regulating the CD1d Ag presentation
Figure 4. CD4
+
and CD4
2
cDC equally capture a-GalCer
in vivo
but differ in their ability to activate iNKT cells. (A) Representation of
Cy5-conjugated a-GalCer synthesis. (B, C) Bone marrow-derived DC (10
5
/well) from WT and CD1d
2/2
mice were loaded with unconjugated or Cy5-
conjugated a-GalCer (25 and 100 ng/ml) and then co-cultured with either the iNKT cell hybridoma DN32.D3 (10
5
/well) for 24 h (B) or with sorted
primary iNKT cells (10
5
/well) for 48 h (C). Cytokine production was quantified by ELISA. (D) Recipient mice were i.v. injected with Cy5-conjugated
(20 mg), or unconjugated as a control (dotted line), a-GalCer and then Cy5 incorporation by CD4
+
(black) and CD4
2
cDC (grey) was analyzed by flow
cytometry 2 h later. Of note, both cDC subsets had similar profiles using unconjugated a-GalCer. For clarity, we only show the FACS profile for the
CD4
+
cDC subset. Shown are a representative histogram (left panel) and the MFI 6SD (right panel) of three independent experiments. (E, F) Mice
were i.v. injected with a-GalCer (2 mg), cDC subsets were sorted 2 h later and co-cultured with the iNKT cell hybridoma DN32.D3 (E) or with sorted
iNKT cells (F). Cytokine production was quantified by ELISA. Shown is a representative experiment out of three performed. * p,0.05; *** p,0.001.
doi:10.1371/journal.pone.0026919.g004
Dendritic Cells and Natural Killer T Cell Priming
PLoS ONE | www.plosone.org 6 October 2011 | Volume 6 | Issue 10 | e26919
pathway are not profoundly different between the two cDC
subsets.
Activation of primary iNKT cells, unlike iNKT hybridomas, not
only depends on CD1d/Ag mediated TCR triggering, but also on
co-factors produced by DC. This complex interplay between DC
and iNKT cells not only modulates the strength of the iNKT cell
response but also the nature of released cytokines. We found major
differences between CD4
2
and CD4
+
cDC in their capacity to
promote activation of primary iNKT cells, as judged by cytokine
release. In vitro, we consistently observed that CD4
2
cDC induced
more IFN-csecretion by iNKT cells than their CD4
+
cDC
counterparts. Previous reports have shown that, following initial
DC/iNKT cell contact, production of bioactive IL-12 by a-
GalCer loaded DC is necessary for optimal production of IFN-c
by iNKT cells [33,34]. On the other hand, under steady-state
conditions, IL-12 is not required for primary activation of
conventional T lymphocytes [25,39,40]. Of note, there is only a
moderate enhancement (,2 to 3 fold, for both cDC subsets) of
IL12p35 mRNA levels in this condition (data not shown).
However, in contrast to conventional T lymphocytes, our data
show that the enhanced capacity of CD4
2
cDC (compared to
CD4
+
cDC) to promote IFN-cproduction by iNKT cells is IL-12
dependent. This result is in line with the higher capacity of CD4
2
cDC to release bioactive IL-12 under stressed conditions [22]. As a
whole, as is the case after TLR stimulation [22], our data support
the notion that CD4
2
cDC are stronger producers of bioactive IL-
12 after iNKT cell-mediated cDC maturation. The ex vivo
stimulatory activity of CD4
2
and CD4
+
cDC on primary iNKT
cells was next compared. Despite an identical a-GalCer uptake
rate in vivo and a similar level of cell surface CD1d relative to
CD4
2
cDC, CD4
+
cDC failed to trigger IFN-crelease and
promoted a low amount of IL-4 by primary iNKT cells. However,
both cDC subsets were able to activate the iNKT hybridoma
DN32.D3, the activation of which requires less cell surface CD1d/
a-GalCer complex than that of primary iNKT cells. The inferior
ability of CD4
+
cDC to promote IFN-crelease is in agreement
with our in vitro data and can be explained by their weaker IL-12
production following initial contact with iNKT cells. The lower
amplitude of primary iNKT cell activation following contact with
in vivo loaded cDC, relative to in vitro loaded cDC, certainly
amplifies this phenomenon. Moreover, it is possible that the
expression of other co-stimulatory factors by in vivo a-GalCer
loaded CD4
+
cDC is insufficient to promote optimal activation of
iNKT cells (IL-4) in our experimental settings [41,42,43,44]. It is
also possible that expression of inhibitory molecules by CD4
+
cDC
may have altered the threshold for activation of primary iNKT
cells.
To conclude, our data show that, under steady-state conditions,
CD4
2
and CD4
+
cDC equally prime and orientate conventional
T lymphocytes in vitro. This suggests that targeting vaccine Ag to
either DC subset would be without potential benefit. In contrast,
our study shows for the first time, that CD4
2
cDC are more potent
in stimulating iNKT cells, at least in response to the canonical
iNKT cell agonist a-GalCer. It remains to define whether CD4
2
and CD4
+
cDC display a similar behaviour in response to a-
GalCer-based analogues or to more physiological (self lipids)
ligands. The physiological relevance of this novel finding on iNKT
cell-mediated immune responses awaits further studies.
Materials and Methods
Mice
Six- to 8-wk-old male wild type C57BL/6 mice were purchased
from Janvier (Le Genest-St-Isle, France). 8-wk-old male OT-I or
OT-II mice were purchased from Iffa Credo (St. Germain sur
l’Arbresle, France). The generation of CD1d
2/2
mice has been
already described [45]. Mice were bred in our own facility in
pathogen free conditions. Animals were handled and housed in
accordance with the guidelines of the Pasteur institute Animal
Care and Use Committee. All the experiments were performed
after approval by the ethics committee for animal experimentation
from the Nord–Pas de Calais Region (Agreement Nu: 59-350163).
Reagents and Abs
a-GalCer was purchased from Axxora Life Sciences (Coger
S.A., Paris, France). The MHC class I- and MCH class II-
restricted OVA peptides, respectively SIINFEKL and ISQAV-
HAAHAEINEAGR were synthesized by the Institut de Biologie et
Chimie des Prote´ines (Lyon, France). OVA was purchased from
Sigma-Aldrich (Sigma, St Quentin-Fallavier, France). APC-
conjugated monoclonal Abs against mouse CD5, CD11c, PE-
conjugated anti-NK1.1, -CD11b, -CD4, -Sirp-a, FITC-conjugat-
ed anti-CD8, Siglec-H, PercPCy5.5-conjugated anti-CD4,
-CD11b, biotin-conjugated -CD1d, -CD86 and PE-Cy7-conju-
gated anti-CD8, streptavidin and isotype controls were purchased
from BD Pharmingen (Le Pont de Claix, France). Biotin-
conjugated anti-CD40 were purchased from eBioscience (Mon-
trouge, France). The neutralizing goat IgG directed against mouse
IL-12 was from R&D systems (Abingdon, UK) and the isotype
control Ab from Sigma. Cyanine (Cy)5-conjugated a-GalCer was
synthesized according to Kamijuku et al. [46], except that Cy3-
NHS was replaced by Cy5-COOH on the amino-terminal
position of the a-GalCer sphingosine moiety (Fig. 3A). Briefly,
the primary amine compound was stirred in dichloromethane in
the presence of N,N-Diisopropylethylamine and benzotriazole-1-
yl-oxy-tris-(dimethylamino)-phosphonium hexafluorophosphate
with Cy5 to provide a-GalCer-Cy5.
Purification of splenic CD4
2
and CD4
+
cDC subsets
For cDC cell sorting, spleens were treated with type VIII
collagenase (1 mg/ml) (Sigma) at 37uC for 20 min and then
disrupted in PBS supplemented with 2% FCS. After washes, red
blood cells were removed using lysis buffer (Sigma)). For cDC cell
sorting, spleen cells were labeled with APC-conjugated anti-
CD11c, PE-conjugated anti-CD11b, PerCpCy5.5-conjugated
anti-CD4 and FITC-conjugated anti-CD8 mAbs. After cell surface
labeling and washing, cells were electronically sorted using a
FACSAria (Becton Dickinson, MD, USA). Sorted splenic cDC
subsets were at least 98% pure.
Purification of iNKT cells
Perfused livers were minced into small pieces and incubated
with type VIII collagenase (1 mg/ml) and DNase I (1 mg/ml)
(Sigma) at 37uC for 20 min. The liver pieces were then
homogenized and NKT cells were enriched by centrifugation in
a 36%–72% Percoll gradient. Liver mononuclear cells were
labeled with APC-conjugated anti-CD5 and PE-conjugated anti-
NK1.1 mAbs and cells were sorted as described [47]. CD5
+
NK1.1
+
cell purity after sorting was consistently .98%. Sorted
CD5
+
NK1.1
+
cells contain ,90% iNKT cells as assessed by
PBS57-loaded CD1d tetramer and TCRbstaining.
FACS analysis
Briefly, 2610
6
cells/well were plated in 96-well plates,
resuspended in 50 ml of the appropriate combination of Abs
(allowing cDC subset identification) and incubated on ice for
30 min. After washes, biotin-conjugated anti-CD1d, -CD86 or
Dendritic Cells and Natural Killer T Cell Priming
PLoS ONE | www.plosone.org 7 October 2011 | Volume 6 | Issue 10 | e26919
-CD40 Ab or isotype control were added for another 30 min.
Then, PE-Cy7-conjugated streptavidin was added for 20 min.
After the last wash, cells were fixed in 1% paraformaldehyde in
PBS and were analyzed on a LSR Fortessa (Becton Dickinson).
Data were then analyzed using FlowJo software (Treestar, OR,
USA).
Assessment of IL-12 gene expression by quantitative RT-
PCR
Total RNA from DC/iNKT cell co-culture was extracted and
cDNA was synthesized by classical procedures. Quantitative RT-
PCR was carried out in an ABI 7500 Thermocycler (Applied
Biosystems, Foster City, CA) using 0.5 mM of specific primers and
QuantiTect SYBR Green PCR Master Mix (Qiagen). Primers
specific for gapdh 59-TGCCCAGAACATCATCCCTG-39and 59-
TCAGATCCACGACGGACACA-39,Il12p35 59-CACGCTAC-
CTCCTCTTTTTG-39and 59-CAGCAGTGCAGGAATAAT-
GTT-39,Il12p40 59-GACCCTGCCCATTGAACTGGC-39and
59-CAACGTTGCATCCTAGGATCG-39, were designed by the
Primer Express Program (Applied Biosystems) and used for
amplification in triplicate assays. PCR amplification of gapdh was
performed to control for sample loading and to allow normaliza-
tion between samples. DCt values were obtained by deducting the
raw cycle threshold (Ct values) obtained for gapdh mRNA, the
internal standard, from the Ct values obtained for investigated
genes. For graphical representation, data are expressed as fold
mRNA level increase compared to the expression level in vehicle-
treated DC/iNKT cell co-culture.
Dendritic cells and iNKT co-cultures
Bone-marrow DC were prepared as described in [48]. Cell-
sorted cDC subsets (3610
4
/well, 96-well plate) were pulsed with
OVA peptides for 2 h or whole OVA for 6 h, washed and co-
cultured with 1.5610
5
naı
¨ve CD4
+
or CD8
+
T lymphocytes
purified from the spleens of OT-II and OT-I mice, respectively.
After 3 and 5 days, culture supernatants were collected and
cytokine production was analysed by ELISA (R&D Systems and
eBiosciences). For cDC and iNKT cell co-cultures, cDC subsets
(10
4
to 10
5
/well) were pulsed with graded doses of a-GalCer for
4 h, washed, and co-cultured for 48 h with hepatic CD5
+
NK1.1
+
cells (5610
4
cells/well) or the iNKT cell hybridoma DN32.D3
[49] (10
5
cells/well). In some experiments, a-GalCer-loaded cDC
subsets were co-cultured with sorted iNKT cells in the presence of
a neutralizing IL-12 Ab or an isotype control Ab (10 mg/ml). To
study the ex vivo stimulatory capacity of cDC subsets, mice were i.v.
injected with 2 mgofa-GalCer, cDC subsets were sorted 2 h later
and co-cultured (7610
4
cells/well) with 10
5
iNKT cell hybridoma
for 24 h or with 10
5
sorted hepatic iNKT cells for 48 h. Cytokine
production was measured in the culture supernatants by ELISA.
Measurement of Cy5-a-GalCer incorporation by splenic
CD4
2
and CD4
+
cDC subsets
Mice were i.v. injected with Cy5-conjugated a-GalCer (20 mg)
and 45 min or 2 h later, spleen cells were labelled with
appropriate fluorescent Abs to identify splenic cDC subsets.
Spleen cells were acquired on the LSR Fortessa and data analyzed
using the FlowJo software.
Statistics
Results are expressed as the mean 6SD. The statistical
significance of differences between experimental groups was
calculated by an unpaired Student’s t test or an ANOVA1 with
a Bonferroni post test (GraphPad Prism 4 software, San Diego,
CA). Results with a pvalue of less than 0.05 were considered
significant.
Acknowledgments
We are grateful to Dr L. Van Kaer (Vanderbilt University, Nashville, TN)
and Dr A. Bendelac (University of Chicago, IL) for the gift of CD1d
2/2
C57BL/6 mice and the NKT cell hybridoma DN32.D3, respectively. Eric
Diesis (Institut de Biologie et Chimie des Prote´ines, Lyon) is greatly
acknowledged for peptide synthesis. The authors would like to express their
gratitude to Drs Maria Leite de Moraes (Hoˆ pital Necker, Paris) and
Sandrine Henry (CIML, Marseille) for helpful discussions. C. Vendeville is
greatly acknowledged for her technical assistance.
Author Contributions
Conceived and designed the experiments: CF FT BF LL. Performed the
experiments: EB EMF SI CP JF FR CF. Analyzed the data: EB EMF CF
FT. Contributed reagents/materials/analysis tools: CE BF LL CF FT.
Wrote the paper: CF FT.
References
1. Villadangos JA, Schnorrer P (2007) Intrinsic and cooperative antigen-presenting
functions of dendritic-cell subsets in vivo. Nat Rev Immunol 7: 543–555.
2. Coquerelle C, Moser M (2010) DC subsets in positive and negative regulation of
immunity. Immunol Rev 234: 317–334.
3. Bendelac A, Savage PB, Teyton L (2007) The biology of NKT cells. Annu Rev
Immunol 25: 297–336.
4. Cohen NR, Garg S, Brenner MB (2009) Antigen Presentation by CD1 Lipids, T
Cells, and NKT Cells in Microbial Immunity. Adv Immunol 102: 1–94.
5. Godfrey DI, Kronenberg M (2004) Going both ways: immune regulation via
CD1d-dependent NKT cells. J Clin Invest 114: 1379–1388.
6. Taniguchi M, Harada M, Kojo S, Nakayama T, Wakao H (2003) The
regulatory role of Valpha14 NKT cells in innate and acquired immune response.
Annu Rev Immunol 21: 483–513.
7. Van Kaer L, Joyce S (2005) Innate immunity: NKT cells in the spotlight. Curr
Biol 15: R429–431.
8. Kawano T, Cui J, Koezuka Y, Toura I, Kaneko Y, et al. (1997) CD1d-restricted
and TCR-mediated activation of valpha14 NKT cells by glycosylceramides.
Science 278: 1626–1629.
9. Cerundolo V, Silk JD, Masri SH, Salio M (2009) Harnessing invariant NKT
cells in vaccination strategies. Nat Rev Immunol 9: 28–38.
10. Tupin E, Kinjo Y, Kronenberg M (2007) The unique role of natural killer T cells
in the response to microorganisms. Nat Rev Microbiol 5: 405–417.
11. Shortman K, Naik SH (2007) Steady-state and inflammatory dendritic-cell
development. Nat Rev Immunol 7: 19–30.
12. Vremec D, Pooley J, Hochrein H, Wu L, Shortman K (2000) CD4 and CD8
expression by dendritic cell subtypes in mouse thymus and spleen. J Immunol
164: 2978–2986.
13. Dudziak D, Kamphorst AO, Heidkamp GF, Buchholz VR, Trumpfheller C,
et al. (2007) Differential antigen processing by dendritic cell subsets in vivo.
Science 315: 107–111.
14. Heath WR, Belz GT, Behrens GM, Smith CM, Forehan SP, et al. (2004) Cross-
presentation, dendritic cell subsets, and the generation of immunity to cellular
antigens. Immunol Rev 199: 9–26.
15. Maldonado-Lopez R, De Smedt T, Michel P, Godfroid J, Pajak B, et al. (1999)
CD8alpha+and CD8alpha- subclasses of dendritic cells direct the development
of distinct T helper cells in vivo. J Exp Med 189: 587–592.
16. Shortman K, Heath WR (2010) The CD8+dendritic cell subset. Immunol Rev
234: 18–31.
17. Farrand KJ, Dickgreber N, Stoitzner P, Ronchese F, Petersen TR, et al.
(2009) Langerin+CD8alpha+dendritic cells are critical for cross-priming and
IL-12 production in response to systemic antigens. J Immunol 183:
7732–7742.
18. Qiu CH, Miyake Y, Kaise H, Kitamura H, Ohara O, et al. (2009) Novel subset
of CD8{alpha}+dendritic cells localized in the marginal zone is responsible for
tolerance to cell-associated antigens. J Immunol 182: 4127–4136.
19. Edwards AD, Chaussabel D, Tomlinson S, Schulz O, Sher A, et al. (2003)
Relationships among murine CD11c(high) dendritic cell subsets as revealed by
baseline gene expression patterns. J Immunol 171: 47–60.
Dendritic Cells and Natural Killer T Cell Priming
PLoS ONE | www.plosone.org 8 October 2011 | Volume 6 | Issue 10 | e26919
20. Luber CA, Cox J, Lauterbach H, Fancke B, Selbach M, et al. (2010)
Quantitative proteomics reveals subset-specific viral recognition in dendritic
cells. Immunity 32: 279–289.
21. Henri S, Curtis J, Hochrein H, Vremec D, Shortman K, et al. (2002) Hierarchy
of susceptibility of dendritic cell subsets to infection by Leishmania major:
inverse relationship to interleukin-12 production. Infect Immun 70: 3874–3880.
22. Hochrein H, Shortman K, Vremec D, Scott B, Hertzog P, et al. (2001)
Differential production of IL-12, IFN-alpha, and IFN-gamma by mouse
dendritic cell subsets. J Immunol 166: 5448–5455.
23. Maroof A, Kaye PM (2008) Temporal regulation of interleukin-12p70 (IL-
12p70) and IL-12-related cytokines in splenic dendritic cell subsets during
Leishmania donovani infection. Infect Immun 76: 239–249.
24. Proietto AI, O’Keeffe M, Gartlan K, Wright MD, Shortman K, et al. (2004)
Differential production of inflammatory chemokines by murine dendritic cell
subsets. Immunobiology 209: 163–172.
25. Manickasingham SP, Edwards AD, Schulz O, Reis e Sousa C (2003) The ability
of murine dendritic cell subsets to direct T helper cell differentiation is
dependent on microbial signals. Eur J Immunol 33: 101–107.
26. Bezbradica JS, Stanic AK, Matsuki N, Bour-Jordan H, Bluestone JA, et al.
(2005) Distinct roles of dendritic cells and B cells in Va14Ja18 natural T cell
activation in vivo. J Immunol 174: 4696–4705.
27. Chang DH, Osman K, Connolly J, Kukreja A, Krasovsky J, et al. (2005)
Sustained expansion of NKT cells and antigen-specific T cells after injection of
alpha-galactosyl-ceramide loaded mature dendritic cells in cancer patients. J Exp
Med 201: 1503–1517.
28. Fujii S, Shimizu K, Kronenberg M, Steinman RM (2002) Prolonged IFN-
gamma-producing N KT response induced with alpha-galactosylceramide-
loaded DCs. Nat Immunol 3: 867–874.
29. Nieda M, Okai M, Tazbirkova A, Lin H, Yamaura A, et al. (2004) Therapeutic
activation of Valpha24+Vbeta11+NKT cells in human subjects results in highly
coordinated secondary activation of acquired and innate immunity. Blood 103:
383–389.
30. Parekh VV, Wilson MT, Olivares-Villagomez D, Singh AK, Wu L, et al. (2005)
Glycolipid antigen induces long-term natural killer T cell anergy in mice. J Clin
Invest 115: 2572–2583.
31. Tatsumi T, Takehara T, Yamaguchi S, Sasakawa A, Sakamori R, et al. (2007)
Intrahepatic delivery of alpha-galactosylceramide-pulsed dendritic cells sup-
presses liver tumor. Hepatology 45: 22–30.
32. Toura I, Kawano T, Akutsu Y, Nakayama T, Ochiai T, et al. (1999) Cutting
edge: inhibition of experimental tumor metastasis by dendritic cells pulsed with
alpha-galactosylceramide. J Immunol 163: 2387–2391.
33. Hayakawa Y, Takeda K, Yagita H, Van Kaer L, Saiki I, et al. (2001) Differential
regulation of Th1 and Th2 functions of NKT cells by CD28 and CD40
costimulatory pathways. J Immunol 166: 6012–6018.
34. Kitamura H, Iwakabe K, Yahata T, Nishimura S, Ohta A, et al. (1999) The
natural killer T (NKT) cell ligand alpha-galactosylceramide demonstrates its
immunopotentiating effect by inducing interleukin (IL)- 12 production by
dendritic cells and IL-12 receptor expression on NKT cells. J Exp Med 189:
1121–1128.
35. Fujii S, Shimizu K, Smith C, Bonifaz L, Steinman RM (2003) 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 198: 267–279.
36. Simkins HM, Hyde E, Farrand KJ, Ong ML, Degli-Esposti MA, et al. (2010)
Administration of alpha-galactosylceramide impairs the survival of dendritic cell
subpopulations in vivo. J Leukoc Biol.
37. Chiu YH, Jayawardena J, Weiss A, Lee D, Park SH, et al. (1999) Distinct subsets
of CD1d-restricted T cells recognize self-antigens loaded in different cellular
compartments. J Exp Med 189: 103–110.
38. Prigozy TI, Naidenko O, Qasba P, Elewaut D, Brossay L, et al. (2001)
Glycolipid antigen processing for presentation by CD1d molecules. Science 291:
664–667.
39. Schulz O, Edwards AD, Schito M, Aliberti J, Manickasingham S, et al. (2000)
CD40 triggering of heterodimeric IL-12 p70 production by dendritic cells in vivo
requires a microbial priming signal. Immunity 13: 453–462.
40. Seder RA, Gazzinelli R, Sher A, Paul WE (1993) Interleukin 12 acts direct ly on
CD4+T cells to enhance priming for interferon gamma production and
diminishes interleukin 4 inhibition of such priming. Proc Natl Acad Sci U S A
90: 10188–10192.
41. Baev DV, Caielli S, Ronchi F, Coccia M, Facciotti F, et al. (2008) Impaired
SLAM-SLAM homotypic interaction between invariant NKT cells and dendritic
cells affects differentiation of IL-4/IL-10-secreting NKT2 cells in nonobese
diabetic mice. J Immunol 181: 869–877.
42. Leite-De-Moraes MC, Hameg A, Pacilio M, Koezuka Y, Taniguchi M, et al.
(2001) IL-18 enhances IL-4 production by ligand-activated NKT lymphocytes: a
pro-Th2 effect of IL-18 exerted through NKT cells. J Immunol 166: 945–951.
43. Matsumoto G, Kubota E, Omi Y, Lee U, Penninger JM (2004) Essential role of
LFA-1 in activating Th2-like responses by alpha-galactosylceramide-activated
NKT cells. J Immunol 173: 4976–4984.
44. Uchida T, Kinoshita M, Fukasawa M, Habu Y, Shinomiya N, et al. (2007) IL-18
time-dependently modulates Th1/Th2 cytokine production by ligand-activated
NKT cells. Eur J Immunol 37: 966–977.
45. Mendiratta SK, Martin WD, Hong S, Boesteanu A, Joyce S, et al. (1997) CD1d1
mutant mice are deficient in natural T cells that promptly produce IL-4.
Immunity 6: 469–477.
46. Kamijuku H, Nagata Y, Jiang X, Ichinohe T, Tashiro T, et al. (2008)
Mechanism of NKT cell activation by intranasal coadministration of alpha-
galactosylceramide, which can induce cross-protection against influenza viruses.
Mucosal Immunol 1: 208–218.
47. Bialecki E, Paget C, Fontaine J, Capron M, Trottein F, et al. (2009) Role of
marginal zone B lymphocytes in invariant NKT cell activation. J Immunol 182:
6105–6113.
48. Paget C, Mallevaey T, Speak AO, Torres D, Fontaine J, et al. (2007) Activation
of invariant NKT cells by toll-like receptor 9-stimulated dendritic cells requires
type I interferon and charged glycosphingolipids. Immunity 27: 597–609.
49. Bendelac A, Lantz O, Quimby ME, Yewdell JW, Bennink JR, et al. (1995) CD1
recognition by mouse NK1+T lymphocytes. Science 268: 863–865.
Dendritic Cells and Natural Killer T Cell Priming
PLoS ONE | www.plosone.org 9 October 2011 | Volume 6 | Issue 10 | e26919
