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Specialized in Thymus-Independent
Plasma Cell Differentiation of B Cell Subsets
TLR Agonists Selectively Promote Terminal
Hanane Gheit, Chantal Bella and Thierry Defrance
Laurent Genestier, Morgan Taillardet, Paul Mondiere,
2007; 178:7779-7786; ;
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Print ISSN: 0022-1767 Online ISSN: 1550-6606.
Immunologists All rights reserved.
Copyright © 2007 by The American Association of
9650 Rockville Pike, Bethesda, MD 20814-3994.
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The Journal of Immunology
by guest on June 13, 2013
TLR Agonists Selectively Promote Terminal Plasma Cell
Differentiation of B Cell Subsets Specialized in
Laurent Genestier,2*†Morgan Taillardet,2*†Paul Mondiere,*†Hanane Gheit,*†Chantal Bella,‡
and Thierry Defrance3*†
Naive murine B cells are known to proliferate and differentiate in response to LPS or CpG, which bind to TLR4 and TLR9,
respectively. However, the naive murine B cell compartment is heterogeneous and comprises four different B cell subsets:
B-1a, B-1b, marginal zone (MZ), and follicular (FO) B cells. B-1a, B-1b, and MZ B cells are specialized in the response to
thymus-independent Ag, and FO B cells are involved in the response to thymus-dependent Ag. This study was undertaken
to compare those four naive B cell subsets for their responses to TLR agonists. Quantitative RT-PCR analysis revealed that
expression of TLR transcripts differs quantitatively but not qualitatively from one subset to the other. All TLR agonists, with
the exception of flagellin and poly(I:C), stimulate B cell proliferation whatever the subset considered. However, TLR ligation
leads to massive differentiation of B-1 and MZ B cells into mature plasma cells (PC) but only marginally promotes PC
differentiation of FO B cells. Moreover, TLR stimulation strongly up-regulates expression of Blimp-1 and XBP-1S, two
transcription factors known to be instrumental in PC differentiation, in B-1 and MZ B cells but not in FO B cells. Altogether,
our findings suggest that B-1 and MZ B cells are poised to PC differentiation in response to the microbial environment and
that TLR agonists can be instrumental in stimulating Ab-mediated innate immune protection during microbial
The Journal of Immunology, 2007, 178: 7779–7786.
peritoneal and pleural cavities and can be further subdivided into
B-1a (B220lowIgMhighCD11b?CD5?) and B-1b cells (B220low
IgMhighCD11b?CD5?). B-2 cells are primarily located in second-
ary lymphoid organs and comprise two populations designated as
follicular (FO)4B cells (B220?CD23highCD21low) and marginal
zone (MZ) B cells (B220?CD23lowCD21high), respectively (1).
Due to their unique location near the marginal sinus, MZ B cells
are considered critical determinants of host defense directed
against encapsulated blood-borne bacterial Ags (2). Nevertheless,
there is increasing evidence of a broader role for MZ B cells in
both T-independent (TI) and T-dependent (TD) immune responses
he mature naive B cell compartment in the mouse can be
divided into four B cell subsets that belong either to the
B-2 or the B-1 lineage. B-1 cells reside mainly in the
(3, 4). It has recently been documented that B-1b cells are mostly
responsible for the adaptive immune response to TI Ag and exert
a memory function (5, 6). Both B-1a and MZ B cells express
polyreactive specificities with low affinities to a broad range of
Ags and are thus responsible for the production of natural Abs,
thereby contributing to innate immunity (1, 6). Conversely, FO B
are primarily recruited by TD Ags. They lead to germinal center
formation and subsequent production of somatically mutated PC
and memory B cells with high-affinity Ag-binding capacities.
TLRs are pattern recognition receptors that play a central role as
sensors of infection and inducers of innate and adaptive immune
responses (7). Ten TLRs have been described in the mouse so far.
Their most common natural or synthetic agonists include pepti-
doglycan and Pam3CSK4(TLR1/2), bacterial lipoproteins and
MALP2 (TLR2/6), dsRNA and poly(I:C) (TLR3), LPS (TLR4),
flagellin (TLR5), ssRNA and imidazoquinolines (TLR7 and
TLR8), unmethylated CpG oligodeoxynucleotides (TLR9), and
profilin-like molecule (TLR11) (7–10). It has long been known
that certain TLR agonists can deliver B cell stimulatory signals
(11, 12). Furthermore, Ruprecht and Lanzavecchia (13) demon-
strated that TLR stimulation is required along with BCR triggering
and T cell help to sustain optimal proliferation and differentiation
of human naive B cells.
In humans, naive B cells express low to undetectable levels of
TLRs while memory B cells constitutively express several TLRs
that can promote their proliferation and PC differentiation (14, 15).
This observation gave ground to the idea that microbial products
could contribute to maintain a crucial function of the immune sys-
tem. In the mouse, naive B cells proliferate and secrete Igs in
response to LPS and CpG (11, 12), indicating that they express
functional TLR4 and TLR9. However, little is known about the
distribution of TLRs and the impact of their agonists on mouse naive
B cell subsets. In particular, due to their strong contribution to the
*Institut National de la Sante ´ et de la Recherche Me ´dicale, Unite ´ 851, IFR128
Biosciences Lyon-Gerland, Lyon, France;†Universite ´ Claude Bernard Lyon I,
Lyon, France; and‡Plateau technique de cytome ´trie en flux, IFR128 Biosciences
Lyon-Gerland, Lyon, France
Received for publication September 15, 2006. Accepted for publication April
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 grants from the Institut National de la Sante ´ et de la
Recherche Me ´dicale and Sanofi Pasteur.
2L.G. and M.T. contributed equally to this work and therefore share the first
3Address correspondence and reprint requests to Dr. Thierry Defrance, Institut Na-
tional de la Sante ´ et de la Recherche Me ´dicale Unite ´ 851, IFR 128 BioSciences
Lyon-Gerland, 21 Avenue Tony Garnier, Lyon, France. E-mail address: defrance@
4Abbreviations used in this paper: FO, follicular; MZ, marginal zone; TI, thymus
independent; TD, thymus dependent; PC, plasma cell; HPRT, hypoxanthine guanine
phosphoribosyltransferase; ISC, Ig-secreting cell; SN, supernatant.
Copyright © 2007 by The American Association of Immunologists, Inc. 0022-1767/07/$2.00
The Journal of Immunology
by guest on June 13, 2013
not differ significantly from their peritoneal counterpart in terms of
PC differentiation in response to CpG1668.
Under certain aspects, murine MZ and B-1 cells behave like
human memory B cells with which they share the constitutive TLR
expression and enhanced responsiveness to TLR agonists. The pro-
pensity of human memory B cells to differentiate into PC in re-
sponse to TLR agonists has been proposed to provide a means
whereby microorganisms sustain the titers of seric-protective Abs
by continuously reactivating memory B cells in an Ag-independent
fashion. For B-1 and MZ B cells, the physiological role fulfilled by
this functional trait is unknown. B-1 and MZ B cells are involved
in innate humoral functions such as production of gut IgA and
natural Abs that help to prevent spreading of commensal or infec-
tious microorganisms. It is thus tempting to speculate that micro-
bial signals delivered through TLRs could be instrumental in these
functions. The published literature does not support a crucial role
for microbial signals and TLRs in establishment or maintenance of
these innate B cell functions. For example, a recent report from
Pasare and Medzhitov (25) has demonstrated that MyD88-defi-
cient mice express normal serum IgA Abs (although IgA secretion
in the gut had not been explored). Furthermore, contradictory re-
sults have been published regarding the reduction of serum IgM
levels in naive MyD88-deficient mice or MyD88/TRIF double-
deficient mice (25, 26), and natural Abs are still produced in germ-
free mice (27, 28). It cannot formerly be excluded that formation
and replenishment of the pool of natural Abs involves compensa-
tory mechanisms other than TLR signaling or that TLRs can be
triggered by endogenous ligands. Nevertheless, available data
rather support the notion that the unique ability of B-1 and MZ B
cells to become PC upon TLR triggering is instrumental in stim-
ulating Ab-mediated innate immune protection during microbial
infection. It has been demonstrated that naive MyD88 knockout
mice are more vulnerable to bacterial infection (29, 30) than naive
wild-type mice. However, once the adaptive arm of the immune
response has been mobilized by prior vaccination with heat-killed
bacteria, MyD88 knockout mice and wild-type mice are equally
protected from challenge with live bacteria. This indicates that
disruption of the TLR signaling pathway primarily impairs innate
immune protection mechanisms. The recent work from Tedder and
colleagues (6) has revealed that B-1a cells are a crucial component
of innate humoral responses. We thus propose that TLR stimula-
tion in the course of natural infection allows a rapid raise of the
production of protective natural Abs by B-1 and MZ B cells. This
could contribute to reduce the microbial load below life-threaten-
ing levels until the adaptive arm of the immune response becomes
Recent evidence has demonstrated that TLRs may play a pivotal
role in B cell activation (25), suggesting that TLR agonists can be
considered as potential adjuvants for conventional TD Ags. Our
results demonstrating that B-1 and MZ B cells are poised to PC
differentiation in response to TLR agonists suggest that the use of
TLR agonists for adjuvantation of TI vaccines should also be
The authors have no financial conflict of interest.
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7786 IMPACT OF TLR AGONISTS ON NAIVE MOUSE B CELL SUBSETS
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