Supplementum 163 - Swiss Medical Weekly

15 S SWISS MED WKLY 2008;138(Suppl 163) · www.smw.ch
Free Communications 5 – SSAI / SGAI
77
Intestinal bacteria condition dendritic cells to promote IgA
production
J. Massacand1 , P. Kaiser1 , B. Ernst1 , A. Tardivel2 , K. Bürki3 , P.
Schneider2 , N. Harris1 .
1 ETHZ (Schlieren-Zürich, CH); 2 UNIL (Lausanne, CH);
3 UZH (Zürich, CH)
Immunoglobulin A represents the predominant antibody isotype
produced at the intestinal mucosa, where it plays an important role in
limiting the penetration of commensal intestinal bacteria and
opportunistic pathogens. We investigated the role of dendritic cells
(DC) from different tissues of origin in the differentiation of IgA
producing B cells in a co-culture system. We show in mice that
Peyer’s Patch-derived DC (PP-DC) exhibit a specialized phenotype
allowing the promotion of IgA production. PP-DC exhibited increased
production of the B-cell activating factor of the tumor necrosis family
(BAFF) and a proliferation-inducing ligand (APRIL), which were
necessary for IgA production in the absence, but not the presence, of
CD40- or LPS-mediated signalling. In contrast, in the absence of BCR
stimulation no IgA was detected when DC originated from peripheral
lymph nodes. Furthermore DC presence was mandatory for IgA, but
not IgG1 and IgM, production and IgM and IgG1 levels were
comparable and independent of the origin of the DC. Intestinal
bacteria are a unique feature of the mucosal immune system and are
known to play a role in the mucosal immune system development. We
investigated their role in the ability of PP-DC to instruct naïve B cells
to differentiate into IgA producing plasma cells. For this purpose we
compared IgA levels in co-cultures with DC from germ free or SPF
mice. Interestingly, the presence of intestinal commensal bacteria
largely accounted for the preferential IgA production. These data
indicate that exposure to intestinal commensal bacteria, as well as
other intestinal environmental factors, condition DC to promote IgA
production.
78
Double-stranded RNA induces apoptosis in spleen CD8a
dendritic cells
S. Fuertes Marraco1 , L. O’Reilly2 , F. Grosjean1 , P. Romero3 , B. Salaun3 ,
L. Otten1 , A. Strasser2 , H. Acha-Orbea1 . 1 Université de Lausanne
(Epalinges, CH); 2 Walter and Elisa Hall Institute of Medical Research
(Parkville Victoria, AUS); 3 Ludwig Institute of Cancer Research
(Epalinges, CH)
In the event of microbial invasion, dendritic cells (DC) are central to
the detection and processing of pathogen in order to induce efficient
adaptive immune responses.
The Toll-like Receptor (TLR) network is well known to mediate
pathogen detection and potent activation of DC. Thereafter, evidence
on the effect of TLR-ligands on the lifespan of DC is, however,
contradictory and incomplete. While increased survival may enhance
their function, apoptosis may serve to prevent over-activation leading
to autoimmunity and to limit the spread of infection.
In the present project, we made use of novel splenic CD8a DC lines,
derived from tumors in mice transgenic for the SV40 Large T
oncogene under the DC-specific CD11c promoter, where CD8a DC
preferentially transform. They are known to express TLR3 (detecting
dsRNA during viral infection) and to be capable of antigen crosspresentation.
Stimulation of DC lines with PolyIC (synthetic TLR-3 ligand) induces
potent activation, however, dramatic apoptosis is observed after 24-
48 hours. We took advantage of these novel DC lines to characterize
the apoptotic mechanisms involved and extended our studies to
normal DC.
Altogether our results show upregulation of Bim as a key feature of
DC apoptosis and an important role of type I interferon signaling for
induction of cell death in DC lines and wild type DC.
These results provide clues for the optimization of the use of PolyIC
and DC-based strategies for therapeutic purposes.
79
Role of TLR7 and TLR9 in a murine model of SLE
M-L. Santiago-Raber1 , P. Borel1 , S. Uematsu2 , S. Akira2 , S. Izui1 .
1 University of Geneva (Geneva, CH); 2 Osaka University (Osaka, JP)
Background: Systemic Lupus Erythematosus (SLE) is a systemic
autoimmune disorder characterized by the formation of a variety of
autoantibodies and subsequent development of immune complex (IC)
glomerulonephritis, i.e. lupus nephritis. The pathogenesis of SLE is a
complex process, in which MHC-linked and multiple non-MHC-linked
genetic factors contribute to the overall susceptibility of the disease.
More recently, the role of Toll-like receptor 7 (TLR7) and TLR9 in the
development of murine SLE has been suggested. Notably, the Yaa
(Y-linked autoimmune acceleration) mutation, which markedly
accelerates the progression of murine lupus, was identified to be a
translocation from the telomeric end of the X chromosome –
containing the gene encoding TLR7 – onto the Y chromosome.
Methods: To determine the contribution of TLR7 and TLR9 to the
development of SLE, we introduced the tlr7 or tlr9 null mutation into
C57BL/6 mice congenic for Nba2 (NZB autoimmunity 2) locus bearing
the Yaa mutation (B6.Nba2.Yaa) and followed the development of the
pathology.
Results: Males B6.Nba2.TLR7-/Yaa (i.e. bearing a single copy of
TLR7) produced reduced serum levels of IgG autoantibodies (against
DNA and ribonucleoproteins), and also incidence of lupus nephritis.
However, the protection was not complete, since these mice still
developed high titers of anti-chromatin and retroviral gp70-anti-gp70
immune complexes and severe lupus nephritis, which was not the
case in B6.Nba2 male mice lacking the Yaa mutation. In contrast,
mice B6.Nba2.TLR9-/-.Yaa displayed an accelerated development
SLE (50% mortality at 5 month of age vs. 14 month in B6.Nba2.Yaa
controls) with an enhanced development of autoimmune responses
and an increased TLR7-dependant B cell and plasmacytoïd dendritic
cell activation.
Conclusion: Our results indicate that the Yaa-mediated acceleration
of SLE cannot be totally explained by the Tlr7 gene duplication alone,
and that TLR7 and TLR9 play an opposing role on the development of
SLE.
80
CD4+ and CD8+ T-cells exhibit differential requirements for
CCR7-mediated antigen transport during influenza infection
A.K. Heer, N. Harris, M. Kopf, B.J. Marsland.
ETH Zürich (Schlieren, CH)
Upon encounter of viral antigens in an inflammatory environment,
dendritic cells upregulate costimulatory molecules and the chemokine
receptor CCR7, the latter being pivotal for their migration to the
lymph node. By utilizing mice deficient in CCR7, we have examined
the requirement of DC-mediated antigen transport from the lung to
the draining lymph node for the induction of anti-influenza immune
responses in vivo. We found that CCR7-mediated migration of DC
was more crucial for CD8+ T cell than CD4+ T cell responses. Whilst
no specific CD8+ T cell response could be detected in the airways or
lymphoid tissues during the primary infection, prolonged infection in
CCR7-deficient mice did result in a sustained inflammatory
chemokine profile, which led to non-specific CD8+ T cell recruitment
to the airways. The recruitment of influenza-specific CD4+ T cells to
the airways was also below levels of detection in the absence of
CCR7 signaling, although a small influenza-specific CD4+ T cell
population was detectable in the draining lymph node, which was
sufficient for the generation of class-switched anti-influenza
antibodies and a normal CD4+ T cell memory population. Overall, our
data show that CCR7-mediated active antigen transport is
differentially required for CD4+ and CD8+ T cell expansion during
influenza infection.
81
Restricted B-cell receptor diversity converts acute into chronic
LCMV infection
A. Bergthaler 1 , L. Flatz 1 , A. Verschoor 2 , A. Hegazy 2 , M. Holdener 2 ,
K. Fink 2 , B. Eschli 2 , E. Horvath 2 , B. Odermatt 2 , D. Pinschewer 1 .
1 University of Geneva (Geneva, CH); 2 University Hospital of Zurich
(Zurich, CH)
Persistent infections like HIV and HCV represent a great burden to
global health but preventive vaccines remain unavailable. Cytotoxic T
cell responses are key for virus control, but recent results from clinical
HIV trials suggest that coordinate action with other immune
mediators may be needed for vaccine protection. Accordingly, the
contributive role of specific antibodies in resolving chronic virus
infections has recently gained interest.
Here, we studied the contribution of virus-specific B cell responses to
control of lymphocytic choriomeningitis virus (LCMV) infection in
mice, which is also predominantly mediated by cytotoxic T cells. To
circumvent the drawbacks intrinsic to B cell-deficient mouse models
(i.e. disorganized splenic microarchitecture, impaired CD4+ T cell
responses) we exploited a panel of genetically engineered B cellcompetent
mice with differentially restricted B cell receptor (BCR)