The Mannose Receptor Mediates Uptake of Soluble but Not of
Cell-Associated Antigen for Cross-Presentation1
Sven Burgdorf,2Veronika Lukacs-Kornek,2and Christian Kurts3
The mannose receptor (MR) has been implicated in the recognition and clearance of microorganisms and serum glycoproteins. Its
endocytic function has been studied extensively using macrophages, although it is expressed by a variety of cell types, including
dendritic cells (DC). In this study, we investigated its role in Ag presentation by DC using MR?/?mice. Uptake of the model Ag,
soluble OVA, by bone marrow-derived DC and in vitro activation of OVA-specific CD8 T cells (OT-I cells) strictly depended on
the MR. In vivo, MR deficiency impaired endocytosis of soluble OVA by DC and concomitant OT-I cell activation. No alterations
in the DC subtype composition in MR?/?mice were accountable. Uptake of cell-associated OVA was unaffected by MR deficiency,
resulting in unchanged activation of OT-I cells. These findings demonstrate that DC use the MR for endocytosis of a particular
Ag type intended for cross-presentation. The Journal of Immunology, 2006, 176: 6770–6776.
organisms (1). Furthermore, the MR plays a homeostatic role in
the clearance of glycoproteins, such as ?-glucuronidase and pro-
collagen, which are up-regulated in the blood serum during in-
flammation (2). The MR consists of an N-terminal cysteine-rich
domain, a fibronectin type II repeat domain, eight carbohydrate
recognition domains (CRD), a transmembrane domain, and a short
intracellular region (3). The cysteine-rich region mediates binding
to sulfated sugar moieties, whereas the CRD bind glycoproteins
bearing (for instance) terminal mannose, fucose, and, with a lower
affinity, glucose residues (4). Most studies addressing the function
of the MR have used macrophages (5), which use it for uptake of
mannosylated structures such as dextrans (1). In addition to these
cells, the MR has also been detected in liver endothelial cells,
dermal microvascular endothelial cells, monocytes, Langerhans
cells, and dendritic cells (DC) (6).
DC play a central role in the induction of adaptive immune
responses (7). After capturing and internalizing Ag in peripheral
organs, they migrate toward the draining lymph nodes, where they
can activate naive T cells. For activation of CD8?T cells, captured
extracellular Ag are presented on MHC class I molecules (8)—a
process termed cross-presentation—which contributes to the in-
duction of cytotoxicity against many viruses and tumors (9). The
murine DC subpopulation expressing the CD8? homodimer has
he mannose receptor (MR)4is a 180-kDa transmembrane
C-type lectin that functions as an endocytic receptor. It
has been implicated in the recognition of various micro-
been shown to be particularly relevant for cross-presentation of
foreign Ag (10) and of self Ag under homeostatic conditions (11,
12). In the presence of inflammatory stimuli, also CD8?-deficient
DC were able to cross-present (13, 14).
Several receptors mediating Ag uptake in DC have been iden-
tified, such as Fc-receptors, DC-SIGN and DEC205. A role of the
MR in Ag uptake and presentation by DC has been proposed based
on the finding that mannosylated proteins are presented more ef-
ficiently than nonmannosylated ones (15, 16). It is unclear, how-
ever, whether this uptake was due to the MR, because DC express
other receptors, such as DC-SIGN, with affinity for mannosylated
proteins (6, 17). For the same reason, mannan, a polymer of man-
nose, which competitively blocks endocytosis of mannose-rich
structures, cannot be considered a specific inhibitor of the MR. To
overcome these limitations, we have used MR?/?mice to eluci-
date the role of the MR in the uptake and presentation of soluble
vs cell-associated OVA.
Materials and Methods
MR?/?mice on a C57BL/6 (B6) background were generated and provided
by Dr. M. C. Nussenzweig (Rockefeller University, New York, NY) (2).
B6 mice bearing the Kbmutant bm1 (bm1 mice) and OT-I Rag-1?/?mice
on a B6 background were provided by Dr. W. R. Heath (Walter and Eliza
Hall Institute of Medical Research, Melbourne, Australia) (18). For all
experiments, mice between 8 and 16 wk of age bred under specific patho-
gen-free conditions were used in accordance with local animal experimen-
Abs and reagents
All mAb used were purchased from BD Biosciences, except anti-MR Ab
(Serotec) and SF1, which were purified from hybridoma supernatant
(American Type Culture Collection) and used after conjugation with al-
exa488. All reagents, if not specified otherwise, were obtained from
Generation of bone marrow-derived dendritic cells (BMDC)
BMDC were generated using GM-CSF as described previously (19). At
day 7, CD11c?cells isolated by magnetic separation with the autoMACS
system (Miltenyi Biotec) were used for all in vitro experiments. Purity of
CD11c?cells was typically higher than 98%.
Preparation of fluorescent soluble and cell-associated OVA
Soluble OVA was conjugated to a fluorochrome using an alexa647labeling
kit (Invitrogen Life Technologies) according to the manufacturer’s guide-
lines. The labeling procedure involved gel filtration as a final step for
Institute of Molecular Medicine and Experimental Immunology (IMMEI), Friedrich-
Wilhelms-Universita ¨t, Bonn, Germany
Received for publication January 26, 2006. Accepted for publication March 15, 2006.
The costs of publication of this article were defrayed in part by the payment of page
charges. This article must therefore be hereby marked advertisement in accordance
with 18 U.S.C. Section 1734 solely to indicate this fact.
1This work was supported by was supported by a junior research group grant from
the German state of Nordrhein-Westfalen (to C.K.). S.B. was supported by BONFOR
Grant O-173.0009 of the University of Bonn Clinic, Bonn, Germany.
2S.B. and V.L-K. contributed equally to this work.
3Address correspondence and reprint requests to Dr. Christian Kurts, Institute of
Molecular Medicine and Experimental Immunology, Friedrich-Wilhelms-Universita ¨t,
53105 Bonn, Germany. E-mail address: firstname.lastname@example.org
4Abbreviations used in this paper: MR, mannose receptor; DC, dendritic cell; OT-I
cell, OVA-specific CD8 T cell; CRD, carbohydrate recognition domain; bm1 mice,
C57BL/6 mice bearing the Kbmutant bm1; BMDC, bone marrow-derived DC; cLN,
cutaneous lymph node; MFI, mean fluorescence intensity.
The Journal of Immunology
Copyright © 2006 by The American Association of Immunologists, Inc.0022-1767/06/$02.00
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6776 MANNOSE RECEPTOR-MEDIATED AG UPTAKE FOR CROSS-PRESENTATION