The Journal of Experimental Medicine
The Rockefeller University Press $30.00
J. Exp. Med. Vol. 205 No. 13 2995-3006
Systemic lupus erythematosus (SLE) is a chronic
autoimmune disease characterized by the pro-
duction of antibodies against an array of self-
antigens such as double-stranded (ds) DNA and
components of small nuclear ribonucleopro-
teins (snRNPs), including the Sm/RNP anti-
gens (U1, U2, U4-6, and U5 snRNPs), Ro/SS-A
antigens (Y RNAs), and other antigens ( 1 ). Re-
cent evidence strongly suggests that type I IFNs
(IFN-Is), a family of antiviral cytokines, are in-
tegral to the pathogenesis of SLE. Elevated
serum levels of IFN-I and overexpression of
IFN-stimulated genes (ISGs) in the peripheral
blood of SLE patients have been demonstrated
by several groups ( 2 – 4 ). This “ IFN signature ” is
associated with more active disease and the pres-
ence of autoantibodies against dsDNA and the
Sm/RNP and Ro/SS-A antigens ( 5, 6 ).
The etiology of excess IFN-I in SLE is in-
completely understood. Research on innate im-
munity has led to the identifi cation of several
pathways mediating IFN-I production in mam-
malian cells. Toll-like receptor (TLR) 3, a sen-
sor for viral dsRNA, and TLR4, the receptor for
LPS, both stimulate IFN-I secretion through
Pui Y. Lee:
Abbreviations used: ago2, argo-
naute 2; ANA, antinuclear anti-
body; clo-lip, clodronate-
ds, double stranded; IC,
immune complex; IFN-I, type I
IFN; IPS-1, IFN-b promoter
stimulator 1; IRF, IFN regula-
tory factor; ISG, IFN-stimulated
gene; MCP, monocyte che-
moattractant protein; Mda5,
melanoma diff erentiation-associ-
ated gene 5; MFI, mean fl uores-
cence intensity; Mx1, myxoma
response protein 1; MyD88,
myeloid diff erentiation factor
88; PDC, plasmacytoid DC;
PEC, peritoneal exudate cell;
RIG-I, retinoic acid–inducible
gene I; RT-PCR, real-time
quantitative PCR; SLE, systemic
lupus erythematosus; snRNP,
small nuclear ribonucleoprotein;
ss, single stranded; TBK-1,
TANK-binding kinase 1; TLR,
Toll-like receptor; TMPD,
ane; TRIF, Toll/IL-1 receptor
inducing IFN-b; Yaa, Y-linked
TLR7-dependent and Fc ? R-independent
production of type I interferon
in experimental mouse lupus
Pui Y. Lee , 1 Yutaro Kumagai , 3 Yi Li , 1 Osamu Takeuchi , 3 Hideo Yoshida , 1,4
Jason Weinstein , 1 Erinn S. Kellner , 1 Dina Nacionales , 1 Tolga Barker , 1
Kindra Kelly-Scumpia , 1 Nico van Rooijen , 5 Himanshu Kumar , 3
Taro Kawai , 3 Minoru Satoh , 1,2 Shizuo Akira , 3 and Westley H. Reeves 1,2
1 Division of Rheumatology and Clinical Immunology and Center for Autoimmune Disease and 2 Department of Pathology,
Immunology and Laboratory Medicine, University of Florida, Gainesville, FL 32610
3 Laboratory of Host Defense, World Premier International Research Center Immunology Frontier Research Center,
Osaka University, Suita, Osaka 565-0871, Japan
4 Division of Rheumatology and Infectious Diseases, Department of Internal Medicine, Fujita Health University, Toyoake,
Aichi-Ken 470-1192, Japan
5 Department of Molecular Cell Biology, Free University Medical Center, 1007MB Amsterdam, Netherlands
Increased type I interferon (IFN-I) production and IFN-stimulated gene (ISG) expression are
linked to the pathogenesis of systemic lupus erythematosus (SLE). Although the mecha-
nisms responsible for dysregulated IFN-I production in SLE remain unclear, autoantibody-
mediated uptake of endogenous nucleic acids is thought to play a role.
2,6,10,14-tetramethylpentadecane (TMPD; also known as pristane) induces a lupus-like
disease in mice characterized by immune complex nephritis with autoantibodies to DNA and
ribonucleoproteins. We recently reported that TMPD also causes increased ISG expression
and that the development of the lupus is completely dependent on IFN-I signaling (Nacio-
nales, D.C., K.M. Kelly-Scumpia, P.Y. Lee, J.S. Weinstein, R. Lyons, E. Sobel, M. Satoh, and
W.H. Reeves. 2007. Arthritis Rheum. 56:3770 – 3783). We show that TMPD elicits IFN-I
production, monocyte recruitment, and autoantibody production exclusively through a Toll-
like receptor (TLR) 7 – and myeloid differentiation factor 88 (MyD88) – dependent pathway.
In vitro studies revealed that TMPD augments the effect of TLR7 ligands but does not
directly activate TLR7 itself. The effects of TMPD were amplifi ed by the Y-linked autoim-
mune acceleration cluster, which carries a duplication of the TLR7 gene. In contrast, defi -
ciency of Fc ? receptors (Fc ? Rs) did not affect the production of IFN-I. Collectively, the
data demonstrate that TMPD-stimulated IFN-I production requires TLR7/MyD88 signaling
and is independent of autoantibody-mediated uptake of ribonucleoproteins by Fc ? Rs.
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MECHANISM OF INTERFERON PRODUCTION IN EXPERIMENTAL LUPUS | Lee et al.
required to trigger IFN-I production by TLR3 and TLR4
( 7 ), whereas MyD88 mediates TLR7/8 and TLR9 signaling
( 8 – 10 ). We have previously shown that within 2 wk of TMPD
treatment, an accumulation of IFN-I – producing CD11b + Ly6C hi
monocytes can be detected in the peritoneal cavity in wild-
type mice concurrent with increased IFN-I production and
ISG expression ( 27 ). Compared with wild-type mice, the to-
tal number of peritoneal exudate cells (PECs) was signifi cantly
reduced in MyD88 ? / ? mice after TMPD treatment ( Fig. 1 A ).
Toll/IL-1 receptor domain – containing adaptor inducing
IFN- ? (TRIF) ( 7 ). In contrast, TLR7/8 and TLR9 mediate
IFN-I production via myeloid diff erentiation factor 88 (MyD88)
in response to single-stranded (ss) RNA and unmethylated CpG
DNA, respectively ( 8 – 10 ). In addition, cytoplasmic receptors
that recognize intracellular nucleic acids and induce IFN-I
have been described recently. Retinoic acid – inducible gene I
(RIG-I) and melanoma diff erentiation-associated gene 5
(MDA5) recognize cytoplasmic RNA and trigger IFN-I by
activating IFN- ? promoter stimulator 1 (IPS-1; also known as
MAVS, VISA, and CARDIF) and IFN regulatory factor (IRF) 3
( 11 – 14 ). Cytoplasmic DNA binds to a newly described cyto-
plasmic sensor and triggers IFN-I production via a pathway re-
quiring TANK-binding kinase 1 (TBK-1) and IRF3 ( 15, 16 ).
It has been hypothesized that nucleic acids from dying cells
may act as ligands for TLR7/8 and TLR9 to trigger IFN-I
production in SLE. Immune complexes (ICs) formed by auto-
antibodies to DNA and snRNPs help to transport these “ en-
dogenous ligands ” to endosomes where TLR7, 8, and 9 are
normally found ( 17 ). Activation of these TLRs then induces
the production of IFN-I by plasmacytoid DCs (PDCs). This
hypothesis is supported by numerous in vitro studies ( 18, 19 ).
However, therapeutic administration of recombinant IFN- ?
can directly trigger the production of anti-dsDNA antibodies
( 20 ), and in several mouse model of lupus, IFN-I production is
required for the induction of autoantibodies ( 21 – 23 ), suggest-
ing that IFN-I dysregulation may occur upstream of autoanti-
body development. Therefore, it remains controversial whether
nucleic acid – containing ICs in SLE initiate IFN-I production
or act to perpetuate a positive feedback loop of IFN produc-
tion initiated by another factor, such as a viral infection.
Experimental lupus induced by the hydrocarbon oil
2,6,10,14-tetramethylpentadecane (TMPD; also known as
pristane) displays many key immunological and clinical features
of human SLE, including the presence of the IFN signature
and lupus autoantibodies such as anti-dsDNA, -Sm, and -RNP
( 24 – 26 ). Importantly, IFN-I play an essential role in this model,
as the development of glomerulonephritis and production
of autoantibodies (anti-Sm/RNP, -dsDNA, and -Su) are
abolished in IFN-I receptor – defi cient (IFNAR ? / ? ) mice ( 22 ).
Unexpectedly, a population of Ly6C hi immature monocytes
that accumulates in the peritoneal cavity after TMPD treat-
ment, rather than DCs, is the major source of the excess IFN-I
seen in this model ( 27 ). The persistent infl ux of Ly6C hi mono-
cytes and production of IFN-I occur within 2 wk of TMPD
treatment, long before the appearance of autoantibodies against
snRNPs and dsDNA (3 – 5 mo), indicating that the initial wave
of IFN-I production may be independent of the presence of
RNA-containing ICs. In this study, we aimed to elucidate the
mechanism of IFN-I production in TMPD-induced lupus.
TMPD-induced IFN-I production requires MyD88
To identify the mechanism of IFN-I induction by TMPD,
we fi rst analyzed the eff ect of TMPD on mice with defi -
ciency of the adaptor molecules TRIF or MyD88. TRIF is
Figure 1. TMPD-induced IFN-I production requires MyD88.
(A) Comparison of the number of total PECs, Ly6C hi monocytes, and granulo-
cytes 2 wk after TMPD treatment in wild-type ( n = 5), MyD88 ? / ? ( n = 6),
TRIF ? / ? ( n = 4), and IFNAR ? / ? mice ( n = 4). (B) Flow cytometry of perito-
neal cells (box indicates Ly6C hi monocytes and dashed oval indicates
granulocytes). (C) RT-PCR analysis of Mx1 and IRF7 expression in PECs
(normalized to peritoneal cells from an untreated wild-type mouse).
(D) ELISA quantifi cation of MCP-1 in the peritoneal lavage fl uid of TMPD-
treated mice. (E) Flow cytometry analysis of Sca-1 expression on periph-
eral blood mononuclear cells. Mean fl uorescence intensity (MFI) of Sca-1
on B220 + cells is shown. Each bar represents the mean, and error bars
indicate SE. Data are representative of two or more independent experi-
ments. *, P < 0.05 using the Student ’ s t test.
JEM VOL. 205, December 22, 2008
Both Ly6C hi monocytes and granulocytes (defi ned as CD11b +
Ly6G + Ly6C mid ) were decreased by > 90% ( Fig. 1, A and B ).
Importantly, we found that IFN-I induction by TMPD was
completely dependent on MyD88, because elevated expres-
sion of the ISGs myxoma response protein 1 ( Mx1 ) and IRF7 in
PECs was abolished in MyD88 ? / ? mice, as also seen in
IFNAR-defi cient mice ( Fig. 1 C ). The levels of the IFN-
inducible chemokine monocyte chemoattractant protein 1
(MCP-1; also known as CCL2) in the peritoneal lavage fl uid
were also reduced in the absence of MyD88 ( Fig. 1 D ). In
contrast, TRIF defi ciency did not aff ect the accumulation of
PEC populations or the increased expression of ISGs ( Fig. 1,
A – D ). Although we were unable to detect signifi cant changes
in serum IFN- ? / ? levels by ELISA, IFN-I secretion was re-
quired for the response to TMPD, as the up-regulation of
ISGs and recruitment of Ly6C hi monocytes were abolished in
IFNAR ? / ? mice ( Fig. 1, A – D ). The absence of IFN-I signal-
ing, however, did not aff ect the infl ux of granulocytes ( Fig. 1,
A and B ).
The increase in IFN-I after TMPD treatment is not lim-
ited to the peritoneal cavity, as the IFN signature is also de-
tectable in the peripheral blood ( 22 ). We found that surface
expression of the IFN-inducible gene Sca-1 (Ly6A/E) on B
cells was dramatically up-regulated in wild-type mice treated
with TMPD ( Fig. 1 E ). Although Sca-1 is naturally expressed
by certain lymphocyte subsets and hematopoietic stem cells
( 28 ), TMPD induced Sca-1 expression in virtually all B cells
in wild-type, but not IFNAR ? / ? , mice ( Fig. 1 E ). Increased
Sca-1 expression was also evident on CD8 + and CD4 + T cells
(unpublished data). Similar to the pattern of ISG expression in
PECs, the up-regulation of Sca-1 was reduced in MyD88 ? / ?
but not TRIF ? / ? mice ( Fig. 1 E ), further supporting an es-
sential role of MyD88 in IFN-I production in this model.
To address whether the cytoplasmic nucleic acid sensors
also contribute to TMPD-induced IFN-I production, we tested
the eff ect of TMPD on IPS-1 ? / ? and TNF ? / ? TBK1 ? / ? mice
(TBK-1 ? / ? is embryonically lethal unless crossed with mice
defi cient of TNF- ? [ 29 ]). IPS-1 is a required adaptor for in-
tracellular viral RNA detection via RIG-I and MDA5 ( 12 ),
whereas TBK-1 is required for cytoplasmic DNA-induced
IFN-I secretion ( 30 ). The expression of Mx1 and IRF7 in PECs
was comparable in wild-type, IPS-1 ? / ? , TNF ? / ? TBK-1 ? / ? ,
and TNF ? / ? mice ( Fig. 2 ), suggesting that the intracellular
nucleic acid – sensing pathways are not required for IFN-I
production in this model. The patterns of peritoneal cell
infl ux and Sca-1 expression on peripheral blood lympho-
cytes were also similar among these strains (unpublished data).
Collectively, our data indicate that TMPD-elicited IFN-I
production was strictly MyD88 dependent.
TMPD-induced IFN-I production is TLR7 dependent,
Because MyD88 mediates IFN-I induction by TLR7 and
TLR9, we next investigated which of these innate receptors
is responsible for the eff ect of TMPD. 2 wk after TMPD treat-
ment, the number of PECs in TLR9 ? / ? mice was reduced by
? 20% compared with TLR7 ? / ? and wild-type controls. The
numbers of Ly6C hi monocytes and granulocytes were also
reduced in the absence of TLR9, whereas the pattern of the
cellular infl ux remained similar to wild-type animals ( Fig. 3,
A and B ).
Interestingly, TLR7 ? / ? mice exhibited a specifi c reduc-
tion of Ly6C hi monocytes in the peritoneal cavity ( Fig. 3 A ).
Despite the decrease in these immature monocytes, total PEC
counts in TLR7 ? / ? mice were comparable to wild-type con-
trols because of a signifi cant increase in the number of granu-
locytes ( Fig. 3, A and B ). An accumulation of CD11b + Ly6C ?
residential macrophages was also evident in the absence of
TLR7 ( Fig. 3 B ). These patterns are strikingly similar to those
observed in IFNAR ? / ? mice ( Fig. 1, A – D ). Indeed, the in-
creased Mx1 and IRF7 expression and MCP-1 production
were abrogated in TLR7 ? / ? mice ( Fig. 3 C ). Up-regulation
of Sca-1 expression on B cells was also reduced in these mice
after TMPD treatment ( Fig. 3 D ), recapitulating the fi ndings
in MyD88 ? / ? and IFNAR ? / ? mice. On the contrary, ISG
expression in PECs and surface expression of Sca-1 were similar
in TLR9 ? / ? mice compared with wild-type controls. These
fi ndings suggest that although TLR9 may contribute to the
infl ammatory response, IFN-I induction by TMPD was me-
diated primarily by TLR7.
To further defi ne the role of TLR7 in the infl ammatory
response to TMPD, we compared the expression of various
cytokines and chemokines in wild-type and TLR7 ? / ? ani-
mals using a PCR array. After TMPD treatment, perito-
neal cells from wild-type mice displayed dramatically higher
Figure 2. Cytoplasmic nucleic acid sensors do not contribute to
IFN-I production. RT-PCR analysis of Mx1 and IRF7 expression in PECs
from wild-type ( n = 5), IPS-1 ? / ? ( n = 5), TNF ? / ? ( n = 2), and TNF ? / ? TBK-
1 ? / ? ( n = 4) animals (normalized to peritoneal cells from an untreated
wild-type animal). Each bar represents the mean, and error bars indicate
SE. Data are representative of two independent experiments.
MECHANISM OF INTERFERON PRODUCTION IN EXPERIMENTAL LUPUS | Lee et al.
production in the TMPD lupus model. Interestingly, consis-
tent with the increased number of peritoneal granulocytes in
TMPD-treated TLR7 ? / ? mice ( Fig. 3 A ), the neutrophil
chemoattractant CXCL5 was up-regulated in the absence of
TLR7, whereas the expression of other infl ammatory media-
tors was comparable between the groups (Table S1).
Several studies have demonstrated that self-RNA present
in ICs may act as an endogenous TLR7 ligand causing the
production of IFN-I ( 18, 19 ). Fc ? Rs have been reported to
play an essential role in this process by enhancing the inter-
nalization of ICs, thereby allowing RNA to interact with
TLR7 in endosomes ( 32 ). Defi ciency of either TLR7 or Fc ? R
? chain, an integral component of Fc ? RI and Fc ? RIII, ren-
ders mouse DCs unable to produce IFN-I in response to lu-
pus ICs ( 33 ). Because TMPD induces IFN-I production long
before the onset of lupus autoantibodies and ICs ( 27 ), we ex-
amined the potential role of Fc ? R in the IFN-I response to
TMPD. Surface expression of Fc ? RI (CD64) and Fc ? RII/III
(CD32/CD16) in TMPD-induced PECs was prominent on
Ly6C hi monocytes ( Fig. 4 A ). Fc ? Rs were also expressed by
a fraction of granulocytes, whereas lymphocytes and DCs in
the peritoneal cavity displayed little surface expression of these
receptors ( Fig. 4 A ).
We next analyzed the eff ects of TMPD on Fc ? R ? chain –
defi cient (Fc ? R ? / ? ) mice. The accumulation of Ly6C hi mono-
cytes and up-regulation of ISG expression were comparable
in Fc ? R ? / ? and wild-type mice ( Fig. 4, B and C ). Elevated
surface expression of Sca-1 on peripheral blood lympho-
cytes was also similar between the groups (unpublished data).
Collectively, these fi ndings suggest that TMPD elicits IFN-I
production through a TLR7-dependent but Fc ? R-indepen-
Ly6C hi monocytes express high levels of TLR7
Next, we examined the distribution of TLR7 expression in
the infl ammatory infi ltrate induced by TMPD. PECs from mice
treated with TMPD 2 wk earlier were sorted into four dis-
tinct populations based on surface marker phenotype: Ly6C hi
monocytes (CD11b + Ly6C hi ; ? 30% of PECs), granulocytes
(CD11b + Ly6G + ; ? 30% of PECs), DCs (CD11c + ; ? 2% of
PECs), and a negative fraction containing mainly B and T
lymphocytes. As reported previously ( 27 ), the DC fraction
consisted of > 80% CD11b + myeloid DCs, and few PDCs
(CD11c + CD11b ? B220 + ) were present.
Quantitative PCR revealed that Ly6C hi monocytes ex-
pressed higher levels of TLR7 than other peritoneal cell subsets
( Fig. 5 A ). Prominent expression of the chemokine receptor
CCR2 is consistent with their immature monocytic pheno-
type, as reported previously ( 34 ). In striking contrast, elevated
expression of TLR7 was not a feature of Ly6C hi monocytes in
the spleen or bone marrow. Although TLR7 expression also
was found on other PEC subsets, DCs displayed greater ex-
pression of TLR3 and TLR9 , whereas TLR4 transcripts were
predominantly found in granulocytes ( Fig. 5 A ).
In line with these fi ndings, when peritoneal Ly6C hi mono-
cytes were depleted by i.p. injection of clodronate-containing
expression of several IFN-stimulated chemokines, including
CCL2 , CCL12 , CCL7 , and CXCL10 , in comparison with
TLR7 ? / ? mice (Table S1, available at http://www.jem.org/
cgi/content/full/jem.20080462/DC1). This pattern of che-
moattractant production is similar to the chemokine signa-
ture recently described in SLE patients ( 31 ). These observations
support the role of TLR7 as the primary mediator of IFN-I
Figure 3. IFN-I production induced by TMPD is TLR7 dependent.
(A) Comparison of the number of total PECs, Ly6C hi monocytes, and gran-
ulocytes 2 wk after TMPD treatment in wild-type ( n = 5), TLR7 ? / ? ( n = 5),
and TLR9 ? / ? ( n = 5) mice. (B) Flow cytometry analysis of peritoneal cells
(box indicates Ly6C hi monocytes and dashed oval indicates granulocytes).
(C) RT-PCR analysis of Mx1 and IRF7 expression in PECs (normalized to
peritoneal cells from an untreated wild-type animal) and ELISA quantifi ca-
tion of MCP-1 in the peritoneal lavage fl uid. (D) Flow cytometry of Sca-1
surface expression on peripheral blood mononuclear cells. MFI of Sca-1 on
B220 + cells is shown. Each bar in A and C represents the mean ( n > 4 per
group), and error bars indicate SE. Data are representative of two indepen-
dent experiments. *, P < 0.05 using the Student ’ s t test.
JEM VOL. 205, December 22, 2008
to the peritoneal cavity after TMPD treatment expressed high
levels of TLR7 and actively responded to TLR7 ligands.
The Y-linked autoimmune accelerating (Yaa) locus amplifi es
the effects of TMPD
The Yaa locus is essential for the spontaneous development
of autoantibodies and glomerulonephritis in the BXSB model
of mouse lupus ( 35 ). Yaa also accelerates disease onset in other
lupus-prone strains ( 36, 37 ). Interestingly, TLR7 is among the
17 genes found in the Yaa locus ( 38, 39 ). Because TLR7 is
normally located on the X chromosome in both humans and
mice, males possess one copy of the gene, whereas a similar
gene dosage is achieved in females through X inactivation.
Male mice with the Yaa locus, however, have two functional
copies of the gene ( 38, 39 ). A recent study showed that the
TLR7 gene duplication alone was responsible for the autoim-
mune features associated with the Yaa mutation ( 40 ).
Because TMPD induces IFN-I production via TLR7, we
asked whether the eff ects of the adjuvant oil are more pro-
nounced in the presence of the Yaa locus. Compared with fe-
male controls (designated TLR7 +/+ ), BXSB × B6 male mice
carrying the Yaa mutation (TLR7 +/Yaa ) exhibited greater ac-
cumulation of Ly6C hi monocytes in the peritoneal cavity 2 wk
after TMPD treatment ( Fig. 6 A ). Importantly, increasing the
gene dosage of TLR7 was associated with signifi cantly higher
production of IFN-I, assessed by measuring ISG expression
( Fig. 6 B ). In contrast, the IFN-I response to TMPD was simi-
lar between males and females in wild-type strains, including
C57BL/6, BALB/c, and 129Sv (unpublished data).
We further examined the long-term eff ect of TMPD
treatment in the BXSB model. Consistent with previous
studies ( 35 ), BXSB males died prematurely beginning at 5 mo
of age ( Fig. 6 C ). Mortality was signifi cantly accelerated when
a single dose of TMPD was administered i.p. at 8 – 10 wk of
age. 60% of TMPD-treated animals succumbed by 5 mo of
age compared with 20% in the control group. Although 5 out
of 10 PBS-treated animals survived until 7 mo, only 1 out of
10 in the TMPD-treated group remained. Thus, not only was
the induction of IFN-I accentuated by the Yaa mutation, TMPD
treatment also hastened disease progression in the BXSB
model of lupus.
TLR7 is essential for the development of autoantibodies
against RNA-associated antigens
A recent study using MRL- lpr mice showed that TLR7 is re-
quired for the development of anti-Sm antibodies ( 41 ). To
assess whether TLR7 is also involved in autoantibody produc-
tion in the TMPD model of lupus, we compared the long-term
response to TMPD in wild-type BALB/c and BALB/c.
TLR7 ? / ? mice. No mortality was found in either group and
only mild proteinuria was detected by 24 wk after treatment
(Fig. S1, available at http://www.jem.org/cgi/content/full/
jem.20080462/DC1). Comparable to previous observations
( 42 ), BALB/c mice displayed signifi cant hypergammaglobu-
linemia 24 wk after TMPD treatment ( Fig. 7 A ). The in-
crease in serum IgG was reduced by 50% in TLR7 ? / ? mice,
liposomes (clo-lip), the expression of TLR7 by PECs was
greatly reduced, whereas the levels of TLR9 transcripts re-
mained unaff ected ( Fig. 5 B ). We further analyzed the re-
sponse of Ly6C hi monocytes to various TLR ligands in vitro.
Sorted Ly6C hi monocytes secreted large amounts of MCP-1
and IL-6 when co-cultured with the synthetic TLR7 ligand
R848 ( Fig. 5 C ). They also responded to the TLR4 ligand
LPS, albeit less strongly even at the highest dose of LPS tested
(10 μ g/ml). Consistent with their low levels of TLR3 and
TLR9 expression, Ly6C hi monocytes exhibited weak re-
sponses to poly I:C and CpG DNA ( Fig. 5 C ). In contrast,
isolated granulocytes did not produce measurable amounts of
MCP-1 or IL-6 in response to any TLR ligands used in this
study (unpublished data). Hence, Ly6C hi monocytes recruited
Figure 4. Fc ? RI and Fc ? RIII are dispensable for IFN-I induction
by TMPD. (A) Flow cytometry analysis of Fc ? RI (CD64) and Fc ? RII/III
(CD32/CD16) in PEC populations in TMPD-treated wild-type mice (open
histograms). Shaded histograms represent staining with isotype control
antibodies. (B) Peritoneal cell infl ux and (C) ISG expression in wild-type
mice and Fc ? RI/III ? / ? ( ? chain – defi cient) mice ( n = 3 per group) 2 wk
after TPMD treatment. Dashed boxes in B indicate Ly6C hi monocytes.
Each bar in C represents the mean, and error bars indicate SE. Data are
representative of two independent experiments.
MECHANISM OF INTERFERON PRODUCTION IN EXPERIMENTAL LUPUS | Lee et al.
mice ( 26 ), were not induced in TLR7 ? / ? mice ( Fig. 8 A ).
A recent study identifi ed the Su antigen as an RNA-binding
component of the microRNA pathway known as argonaute
2 (ago2) ( 44 ). ELISA using recombinant ago2 confi rmed that
the development of autoantibodies against Su/ago2 was TLR7
dependent ( Fig. 8 B ), suggesting that the autoimmune re-
sponse to microRNA-associated antigens is also mediated by
TLR7. Collectively, in addition to its role in mediating IFN-I
production, TLR7 is essential for the generation of autoan-
tibodies against RNA-associated antigens (nRNP/Sm and
Su/ago2) in TMPD-induced lupus.
TMPD enhances TLR7 stimulation in vitro
To further investigate the link between TMPD treatment
and TLR7 activation, we studied the eff ect of TMPD in vitro.
Although TMPD has been used for decades, mechanistic
studies on its cellular eff ects have been limited by the hydro-
carbon ’ s poor immiscibility in aqueous solutions. We found
that this problem could be circumvented by fi rst mixing TMPD
with fetal bovine serum before the addition of culture medium
(unpublished data). Unlike stimulation with R848, a TLR7
ligand that elicits IL-6 production and co-stimulatory mole-
cule up-regulation in mouse J774 macrophages, the addition
of TMPD in vitro did not induce these responses ( Fig. 9 A
and not depicted). TMPD solubilized in nonphysiological
solvents such as ethanol, DMSO, mannide monooleate, or
whereas IgM levels were similar between the groups. Consistent
with the prominent role of IFN-I in IgG2a isotype switch ( 43 ),
a profound reduction of IgG2a was found in TLR7 ? / ? mice
( Fig. 7 B ). IgG1 and IgG2b levels were also mildly reduced in
the absence of TLR7, whereas IgG3 was slightly increased.
As early as 12 wk after TMPD treatment, 8 out of 12 wild-
type mice developed detectable serum levels of antinuclear anti-
bodies (ANAs) and anti-nRNP/Sm autoantibodies ( Fig. 7,
C and D ). In contrast, only one animal in the TLR7 ? / ? group
showed a low titer ANA and none developed autoantibodies
to nRNP/Sm ( Fig. 7, C and D ). Similar to IFNAR ? / ? ani-
mals ( 22 ), most TLR7 ? / ? mice exhibited low levels of ANAs of
unknown specifi city by 24 wk after treatment, but their titers
remained signifi cantly lower than BALB/c controls ( Fig. 7 C ).
A single TLR7 ? / ? animal with a high ANA titer (1:1,280)
produced autoantibodies against DNA/chromatin (unpublished
data). In contrast, autoantibodies against nRNP-Sm remained
undetectable in all TLR7 ? / ? mice at this time point ( Fig. 7 D ).
We further confi rmed the autoantibody profi le by immuno-
precipitation using nuclear extracts from 35 S-labeled K562
cells. Consistent with the fi ndings by ELISA, autoantibodies
against various components of nRNP/Sm (A-G) were found
in wild-type but not TLR7 ? / ? mice ( Fig. 7 E ).
Immunoprecipitation studies also revealed that autoanti-
bodies against the Su antigen, which develops in ? 20% of
lupus patients ( 26 ) and ? 50% of TMPD-treated BALB/c
Figure 5. Ly6C hi monocytes express high levels of TLR7. (A) RT-PCR analysis of TLR expression in sorted PEC populations, splenic Ly6C hi monocytes,
and bone marrow monocyte precursors from wild-type TMPD-treated mice. (B) RT-PCR analysis of TLR7 and TLR9 expression in PECs from TMPD-treated
mice 48 h after i.p. injection of PBS or clo-lip. Each bar represents the mean, and error bars indicate SE. (C) ELISA for MCP-1 and IL-6 produced by sorted
peritoneal Ly6C hi monocytes (5 × 10 4 cells/well) 24 h after TLR ligand stimulation. Wedges denote increasing concentrations of LPS, R848, and CpG DNA
(100 ng/ml, 1 μ g/ml, and 10 μ g/ml), and poly I:C (200 ng/ml, 2 μ g/ml, and 20 μ g/ml). Data are representative of two independent experiments.
JEM VOL. 205, December 22, 2008
inability to reach the endosomal compartment where TLR7
and TLR9 are localized. When they form ICs with lupus au-
toantibodies (anti-Sm/RNP or anti-dsDNA), endogenous nu-
cleic acids may be delivered more effi ciently to endosomes
because of uptake by Fc ? Rs, stimulating IFN-I production
by PDCs ( 17, 47 ). This model for IFN-I induction in human
SLE is supported by numerous in vitro studies ( 19, 32, 48 ).
Although Fc ? RIIa mediates the activation of human PDCs,
ICs trigger IFN-I production by mouse PDCs in a TLR7-
and Fc ? RI/III-dependent manner ( 33 ).
However, it is not known whether the development of
antiribonucleoprotein autoantibodies is a cause of IFN-I dys-
regulation or a consequence of it. Therapeutic use of IFN- ?
can induce many features of SLE, including anti-dsDNA an-
tibodies, suggesting that IFN-I dysregulation occurs upstream
of IC formation. Consistent with that view, IFN-I up-regula-
tion in the TMPD model occurs within the fi rst 2 wk of treat-
ment, more than 2 mo before the onset of lupus autoantibodies
( 27 ). Fc ? RI and Fc ? RIII were not required for the IFN-I
? -cyclodextrin was also ineff ective in triggering TLR7 acti-
vation ( Fig. 9 A ), suggesting that TMPD itself is not a ligand
However, exposure to TMPD dramatically enhanced the
response to subsequent stimulation with TLR7 ligands. R848-
induced IL-6 production and co-stimulatory molecule up-
regulation were augmented in J774 cells pretreated overnight
with TMPD ( Fig. 9 B ). Similar enhancement of chemokine
and cytokine production was found in bone marrow – derived
macrophages stimulated with R848 but not the TLR9 ligand
ODN 2395 ( Fig. 9 C ). Importantly, these observations were
specifi c to TMPD, as treatment with other hydrocarbon oils
that do not induce lupus, such as medicinal mineral oil and
squalene, did not enhance stimulation by R848 ( Fig. 9 D ).
We further examined whether TMPD augments the response
to TLR7 ligands by altering the expression or location of
TLR7. TLR7 remained exclusively intracellular regardless of
TMPD treatment, and its expression levels were not aff ected
at the protein or mRNA level ( Fig. 9 E ). Moreover, TMPD
treatment did not enhance endocytosis of FITC-dextran or
phagocytosis of latex beads or apoptotic cells (Fig. S2, available
suggesting that accelerated uptake of ligands is also unlikely
to explain our fi ndings. Collectively, these data indicate that
TMPD is not a direct ligand for TLR7 but instead acts to
enhance the response to TLR7 stimulation.
Recent studies strongly suggest a link between elevated
IFN-I production and the pathogenesis of SLE. More than
half of SLE patients display increased expression of ISGs, of-
ten in association with active disease and autoantibodies against
snRNPs and DNA, as well as renal involvement and endo-
thelial dysfunction ( 2 – 6, 45 ). However, the exact cause of IFN-I
dysregulation in lupus remains controversial, and it is un-
clear whether IFN-I overproduction promotes autoantibody
production or vice versa.
The TMPD model of lupus recapitulates many features of
human SLE, including glomerulonephritis, arthritis, and au-
toantibodies against dsDNA and snRNPs ( 25, 26 ). Moreover,
like SLE, TMPD-induced lupus is more severe in females
than males ( 46 ). We recently found that TMPD-treated mice
exhibit the IFN signature and that their lupus is dependent
on IFN-I signaling ( 22 ). The major IFN-I – producing cells in
TMPD lupus are Ly6C hi monocytes rather than PDCs ( 27 ).
In this study, we show that TMPD triggers IFN-I production
via the TLR7 – MyD88 pathway. Our data also exclude a major
role of other pathways of IFN-I production, including TLR9,
TLR3 – TLR4 – TRIF, RIG-I – Mda5 – IPS-1, and DAI – TBK1.
Although there was a strict requirement for TLR7 and MyD88,
expression of ISGs and recruitment of Ly6C hi monocytes in
response to TMPD was unexpectedly independent of Fc ? Rs.
The innate sensors TLR7 and TLR9 have been impli-
cated in SLE because of their ability to recognize endogenous
nucleic acids and trigger IFN-I production ( 47 ). Mammalian
nucleic acids are generally weak TLR ligands because of their
Figure 6. Yaa mutation amplifi es the effects of TMPD. (A) Flow cy-
tometry of peritoneal cells and (B) RT-PCR analysis of ISG expression in
BXSB × B6 female (TLR7 +/+ ) and male (TLR7 +/ Yaa ) mice. Dashed boxes in A
indicate Ly6C hi monocytes. Each bar in B represents the mean, and error
bars indicate SE. Data are representative of two independent experiments.
*, P < 0.05 using the Student ’ s t test. (C) Survival curve for male BXSB mice
after PBS or TMPD treatment (arrow denotes treatment at 8 – 10 wk of age).
MECHANISM OF INTERFERON PRODUCTION IN EXPERIMENTAL LUPUS | Lee et al.
toantibodies against ssRNA in 564Igi transgenic mice ( 53, 54 ).
The connection between TLR7 and the generation of RNA-
associated autoantibodies is further illustrated by the recent
demonstration of a duplication of the TLR7 gene in Yaa mice.
The presence of the Yaa cluster was suffi cient to induce produc-
tion of RNA-associated autoantibodies in C57BL/6 Fc ? IIB ? / ?
and C57BL6.Sle1 mice, two autoimmune strains that nor-
mally lack these antibody specifi cities ( 38, 39 ). TLR7, and not
the other 16 genes aff ected by the Yaa mutation, is responsible
for the autoimmune pathology ( 40 ). However, increased IFN-I
production has not been reported in these models. Our fi nd-
ings indicate that TLR7 also plays an essential role in TMPD
lupus. Similar to the MRL- lpr model ( 41 ), TLR7 is required
for the generation of anti-nRNP/Sm autoantibodies in TMPD-
treated mice. Importantly, the IFN signature in TMPD-treated
mice, which is established within 2 wk of treatment (long be-
fore the appearance of anti-nRNP autoantibodies), was abol-
ished in the absence of TLR7. In contrast, the eff ects of TMPD
were amplifi ed in the presence of the Yaa locus. Therefore,
this study provides evidence for direct in vivo involvement of
TLR7 in the induction of IFN-I, even in the absence of auto-
antibodies and ICs.
We have previously shown that Ly6C hi monocytes are a
major source of IFN-I in the TMPD model ( 27 ). Depletion
of monocytes but not DCs reduced IFN-I production and
ISG expression. In this study, we found that Ly6C hi mono-
cytes also express higher levels of TLR7 and display a greater
response in vitro to R848 than to other TLR ligands. Al-
though TLR7 is normally found on monocytes and macro-
phages, its expression on peritoneal Ly6C hi monocytes in
TMPD-treated mice was several fold higher than on splenic
response to TMPD because it was unaff ected in ? chain – de-
fi cient mice. Moreover, a previous study also showed that the
absence of Fc ? RI/III or Fc ? RIIb does not aff ect anti-Sm/
RNP autoantibody production in TMPD-treated mice ( 49 ).
Although IC formation and Fc ? Rs are not required to initiate
IFN-I production, we cannot exclude the possibility that they
amplify IFN-I secretion and accelerate disease progression
subsequent to the development of autoantibodies.
A pathogenic role of TLR7 has been described in several
mouse models of SLE. In MRL- lpr mice, TLR7 ligands ac-
celerate the onset of glomerulonephritis, whereas deletion of
TLR7 abrogates the development of anti-Sm autoantibodies
and lessens the severity of kidney disease ( 41, 50 ). Lupus in
MRL- lpr mice has been reported to be ameliorated, not ex-
acerbated, by IFN-I ( 51 ), and the lpr defect prevents induc-
tion of TMPD lupus ( 52 ).
Dual engagement of TLR7 and the B cell receptor can di-
rectly activate autoreactive B cells in the AM14 model, and
TLR7 is also required for the spontaneous production of au-
Figure 8. TLR7 is required for the development of anti-Su/ago2
autoantibodies. (A) Immunoprecipitation of serum autoantibodies 24 wk
after TMPD treatment (8% polyacrylamide gel; n = 6 per group). Arrows
indicate the 100-kD Su antigen, and numerical values denote the molecu-
lar mass (kD). (B) Anti-Su/ago levels at baseline and 24 wk after TMPD
treatment measured by ELISA using recombinant ago2 protein. Horizontal
lines indicate medians. *, P < 0.05 using the Mann-Whitney U test.
Figure 7. TLR7 promotes hypergammaglobulinemia and mediates
the development of anti-nRNP/Sm autoantibodies. (A) Total IgM and
IgG and (B) IgG subclass levels in BALB/c.TLR7 ? / ? ( n = 8) and wild-type
BALB/c ( n = 12) mice before and 24 wk after TMPD treatment. Bars repre-
sent the mean, and error bars indicate SE. *, P < 0.05; and **, P < 0.001
using the unpaired t test. (C) Fluorescent ANA titers (titration emulation)
and (D) anti-nRNP/Sm IgG levels (antigen-capture ELISA) at 12 and 24 wk
after TMPD treatment. Horizontal lines indicate medians. *, P < 0.05 using
the Mann-Whitney U test. (E) Immunoprecipitation of serum autoanti-
bodies ( n = 6 per group) using nuclear extracts from 35 S-labeled K562
cells (12.5% polyacrylamide gel). Arrows indicate components of nRNP/Sm,
and numerical values denote the molecular mass (kD).
JEM VOL. 205, December 22, 2008
It is noteworthy that besides activating IFN-I production
via TLR7, TMPD also induced the recruitment of granulocytes
via an MyD88-dependent but TLR7-independent pathway.
The number of peritoneal granulocytes actually increased in
the absence of IFN-I production, as seen in TLR7 ? / ? and
IFNAR ? / ? mice. MyD88 is used in the signaling pathways
of other cytokines (IL-1 and IL-18) and TLRs (except TLR3),
which are potential mediators of granulocyte recruitment in
Finally, our fi ndings may shed light on other pathology
induced by TMPD. The development of plasmacytomas after
i.p. injection of TMPD in BALB/cAnPt mice was fi rst de-
scribed more than three decades ago ( 61 ). Subsequently TMPD
was used to enhance monoclonal antibody production by hy-
bridomas ( 62 ). How TMPD elicits these eff ects is incompletely
understood, although IL-6 has been implicated. Interestingly,
or bone marrow monocytes. In contrast, DCs in the perito-
neal exudate displayed lower levels of TLR7 and more prom-
inent TLR3 and TLR9 expression. The high expression level
of TLR7 by Ly6C hi monocytes may be of critical importance
in the pathogenesis of TMPD lupus, as a recent study demon-
strated that increased gene dosage of TLR7 is suffi cient to
trigger anti-RNA antibodies and glomerulonephritis in C57BL/6
mice ( 40 ). Interestingly, the recruitment of Ly6C hi mono-
cytes to the peritoneum seems to be partially dependent on
IFN-I, as seen in TLR7 ? / ? , MyD88 ? / ? , and IFNAR ? / ?
mice. TLR7 signaling also induces the expression of several
IFN-stimulated chemokines ( CCL2 , CCL7 , and CCL12 ),
suggesting that the mechanism may involve enhanced pro-
duction of monocyte chemoattractants, creating an amplifi -
cation loop of Ly6C hi monocyte recruitment and IFN-I
production. The recruitment of DCs and granulocytes, on
the other hand, was not dependent on IFN-I or TLR7.
The mechanism linking TMPD to the activation of TLR7
has been partially elucidated by our studies. The hydrocarbon
structure of TMPD is distinct from known TLR7 ligands,
including ssRNA, R848, loxoribine, and other guanosine
analogues. Indeed, our in vitro studies showed that TMPD
did not activate TLR7 directly but instead augmented the in-
fl ammatory response to TLR7 ligands such as R848. The
ability of hydrocarbon oils to enhance TLR7 stimulation in
vitro seems related to their ability to induce lupus-like disease
in vivo. Unlike TMPD, squalene and medicinal mineral oil
were ineff ective in augmenting the response to R848. Mice
treated with squalene and mineral oil do not display the IFN
signature and few develop lupus autoantibodies ( 27, 55 ).
TMPD appears to enhance activation via the TLR7 pathway
in at least two ways: (a) by augmenting the recruitment of
Ly6C hi monocytes, which express high levels of TLR7, and
(b) by enhancing the intrinsic responsiveness of TLR7 to its
ligands. Additional studies will be needed to elucidate whether
TMPD causes increased uptake of apoptotic/necrotic mate-
rial, enhancing the recognition of TLR7 ligands, or if TMPD
interacts with components of the TLR7 signaling pathway,
augmenting the response to receptor – ligand interactions.
Although the underlying mechanisms are distinct, the
pathological consequences of excess TLR7 activation are
shared by TMPD-induced lupus and the Yaa model. An im-
portant unanswered question that encompasses both models
is the nature of the exogenous or endogenous ligands re-
sponsible for activating the TLR7 pathway. It is possible that
chronic TMPD-stimulated infl ammation provides a persis-
tent source of autoantigens from apoptotic cells and that en-
dogenous TLR7 ligands such as the U1 RNA component of
the Sm/RNP antigen ( 56 – 58 ) trigger the fi rst wave of IFN-I
production. Downstream signaling events may elicit further
IFN-I production ( 59 ) and TLR7 expression ( 60 ), culminat-
ing in a positive feedback cycle that promotes autoimmunity
by persistently activating TLR7. It remains to be verifi ed
experimentally whether or not RNA-associated autoanti-
gens from apoptotic cells are key mediators of Yaa- and TMPD-
induced lupus in vivo.
Figure 9. TMPD enhances TLR7 stimulation in vitro. (A) ELISA for IL-6
production in J774 cells cultured in the presence of 1 μ g/ml R848, 1 μ g/ml
TMPD incorporated in serum, or 300 μ M TMPD solubilized in ethanol,
DMSO, mannide monooleate (MM), or ? -cyclodextrin ( ? -CyD). ND, not
detectable. (B) ELISA (IL-6 and MCP-1) and fl ow cytometric analysis (CD80
and CD86) in J774 cells or (C) bone marrow-derived macrophages cultured
for 20 h with or without TMPD and stimulated with PBS, 1 μ g/ml R848, or
2 μ g/ml ODN 2395 for 24 h. MFI values are provided. Shaded histograms
represent J774 cells cultured in medium alone, whereas open histograms
represent cells treated with TMPD. (D) Comparison of IL-6 production and
CD80 expression (MFI) in J774 cells cultured with various hydrocarbon oils
and stimulated with PBS or R848. (E) Flow cytometry and RT-PCR analysis
of TLR7 expression in J774 cells cultured with or without TMPD for 20 h.
Each bar represents the mean, and error bars indicate SE. Data are represen-
tative of three or more independent experiments.
MECHANISM OF INTERFERON PRODUCTION IN EXPERIMENTAL LUPUS | Lee et al.
plus 10 U/ml heparin) were seeded on 96-well cell-culture plates (5 × 10 4
cells/well). Cells were stimulated with the doses indicated in the fi gures of
peptidoglycan, poly I:C, R848, CpG ODN2395 (InvivoGen), or LPS (from
Salmonella typhimurium ; Sigma-Aldrich) and were incubated at 37 ° C in a 5%
CO 2 atmosphere for 24 h before collecting the supernatant. MCP-1 and IL-6
ELISAs (BD) were performed according to the manufacturer ’ s instructions.
Optical density was converted to concentration using standard curves based
on recombinant cytokines analyzed by a four-parameter logistic equation
(Softmax Pro 3.1 software; MDS Analytical Technologies).
Cell culture with TMPD. 1 ml TMPD, mineral oil or squalene was added
to 9 ml of fetal bovine serum in a 15-ml polypropylene tube and was rotated
for 48 h at 4 ° C. The surface layer of unincorporated hydrocarbon oil was re-
moved by aspiration at the end of the incubation. The amount of TMPD
incorporated using this method was ? 1 μ g/ml, as determined by gas chroma-
tography/mass spectroscopy (not depicted; Analytical Toxicology Core, Uni-
versity of Florida). J774 cells or bone marrow – derived macrophages were
seeded on 24-well plates (5 × 10 5 cells/well) and cultured overnight in com-
plete DMEM containing 10% FCS with or without hydrocarbon oils. For sub-
sequent stimulation, cells were washed with PBS, and fresh complete medium
was added before the addition of TLR ligands. Incorporation of TMPD in
DMSO and ? -cyclodextrin (Sigma-Aldrich) has been described previously
( 68 ). TMPD (10% vol/vol) also was added to ethanol or mannide monooleate
(5% in PBS; Sigma-Aldrich). Solvent alone was used as a control, and a range
of TMPD concentrations (3 – 300 μ M) was tested. Endocytosis was quantifi ed
by uptake of 5 μ g/ml FITC-dextran (Sigma-Aldrich), and phagocytosis by in-
ternalization of FITC-labeled microbeads (10:1 beads/cells ratio; Invitrogen) or
tetramethylindodicarbocyanine perchlorate (DiD) – labeled apoptotic BW5147
cells (10:1 apoptotic cell/ target cell ratio) after overnight incubation of J774
cells in complete medium with or without TMPD. Apoptosis of BW5147 cells
was induced by heat shock in a 45 ° C water bath for 10 min. After 4 h of incu-
bation at 37 ° C, apoptotic cells ( > 80% annexin V positive; not depicted) were
labeled with the fl uorescent dye DiD (Invitrogen). J774 Cells were washed and
incubated with the fl uorescent substrates for 30 min at 37 ° C (in PBS with 0.5%
BSA), washed three times, and analyzed by fl ow cytometry. ELISA, fl ow cy-
tometry, and RT-PCR were performed as described. Bone marrow – derived
macrophages were generated from BALB/c mice as previously described ( 8 ).
Autoantibody analysis. Serum ANAs in BALB/c.TLR7 ? / ? and wild-
type BALB/c mice were determined 12 and 24 wk after TMPD by indi-
rect immunofl uorescence using HEp-2 cells (Innova). Sera were diluted
1:40, and titers were determined using a titration emulation system (Image
Titer; Rhigene, Inc.). Immunoprecipitation and antigen-capture ELISA to
detect serum autoantibodies against nRNP/Sm were performed as previ-
ously described ( 26, 69 ). Determination of anti-Su/ago2 by ELISA has also
been previously described ( 44 ). Recombinant ago2 protein was a gift from
E. Chan and K. Ikeda (University of Florida, Gainesville, FL).
Statistical analysis. For quantitative variables, diff erences between groups
were analyzed by the unpaired Student ’ s t test. Survival curves were analyzed
using the log-rank test. ANA titers and autoantibody levels were compared
using the Mann-Whitney U test. Data are presented as means ± SD. All tests
were two-sided, and P < 0.05 was considered signifi cant. Statistical analyses
were performed using Prism 4.0 software (GraphPad Software, Inc.).
Online supplemental material. Table S1 provides PCR array analysis of
cytokine/chemokine expression in PECs from wild-type and TLR7 ? / ?
mice. Table S2 provides the sequence of all PCR primers used in this study.
Fig. S1 shows the levels of proteinuria in BALB/c and TLR7 ? / ? mice 24 wk
after TMPD treatment. Fig. S2 shows the eff ect of TMPD on endocytosis of
FITC-dextran and phagocytosis of FITC-coated latex beads or apoptotic
lymphocytes in J774 cells. Online supplemental material is available at
We thank Dr. E. Sobel for helpful discussion, M. Xu for assistance with manuscript
preparation, Drs. E. Chan and K. Ikeda for providing recombinant ago2 protein, and
although TLR7 can trigger B cell activation and antibody
production ( 53 ), IFN-I plays an important role in antibody
class switching and promotes plasma cell diff erentiation in the
presence of IL-6 ( 63 ). Whether TLR7 activation and IFN-I
production are involved in the pathogenesis of plasmacyto-
mas and enhancement of antibody production by hybridomas
warrants further investigation.
MATERIALS AND METHODS
Mice. MyD88 ? / ? , TRIF ? / ? , TLR7 ? / ? , TLR9 ? / ? , and IFNAR ? / ? mice
(backcrossed > 7 generations to the C57BL/6 background), and IPS-1 ? / ? ,
TNF ? / ? , TNF ? / ? TBK1 ? / ? mice (on a mixed 129Sv/B6 background) have
all been described previously ( 7, 8, 29, 64 – 66 ). Wild-type C57BL/6 and
heterozygous littermates were used as controls. BALB/c.TLR7 ? / ? (back-
crossed > 8 generations to the BALB/c background) and wild-type BALB/c
mice were used for long-terms studies of autoantibody production. Animals
were bred and maintained in a specifi c pathogen-free facility of the Re-
search Institute for Microbial Diseases, Osaka University. C57BL/6 wild-
type and Fc ? RI/III ? / ? mice (Taconic) and BXSB mice (The Jackson
Laboratory) were maintained in a specifi c pathogen-free facility at the Uni-
versity of Florida. BXSB × B6 F1 mice were generated by breeding BXSB
males with C57BL/6 females. 12 – 16-wk-old animals received a single i.p.
injection of 0.5 ml TMPD (Sigma-Aldrich). Blood samples were obtained
before TMPD treatment and weekly thereafter. Peritoneal cells, spleen, and
blood were harvested 2 wk after treatment. Monocyte depletion was per-
formed by i.p. injection of 200 μ l clo-lip, as previously described ( 67 ).
These studies were approved by the University of Florida Institutional Ani-
mal Care and Use Committee and the Osaka University Animal Care and
Real-time quantitative PCR (RT-PCR). RT-PCR was performed as
previously described ( 24 ). In brief, total RNA was extracted from 10 6 peri-
toneal cells using TRI zol reagent (Invitrogen), and cDNA was synthesized
using the Superscript II First-Strand Synthesis kit (Invitrogen) according to
the manufacturer ’ s protocol. SYBR green RT-PCR analysis was performed
using a thermocycler (Opticon II; MJ Research). Amplifi cation conditions
were as follows: 95 ° C for 10 min, followed by 45 cycles of 94 ° C for 15 s,
60 ° C for 25 s, and 72 ° C for 25 s. After the fi nal extension (72 ° C for 10 min),
a melting-curve analysis was performed to ensure specifi city of the products.
Primers used in this study are listed in Table S2 (available at http://www
.jem.org/cgi/content/full/jem.20080462/DC1). Cytokine/chemokine PCR
array (Superarray) analysis was performed using a sequence detector (ABI
7700; Applied Biosystems) according to the manufacturer ’ s protocols.
Flow cytometry and cell sorting. The following conjugated antibodies
were used: anti – CD11b-PE, anti – CD8-allophycocyanin (APC), anti – CD4-
FITC, anti – CD11c-PE, anti – B220-PerCPCy5.5, anti – Sca-1 – PE, anti – CD64-
PE, anti – CD32/16-PE (all from BD), anti – Ly6C-FITC, anti – Ly6C-biotin,
and avidin-APC (all from eBioscience). Before surface staining, peritoneal or
peripheral blood cells were incubated with anti – mouse CD16/32 (Fc block;
BD) for 10 min. Cells were then stained with an optimized amount of primary
antibody or the appropriate isotype control for 10 min at room temperature
before washing and resuspending in PBS supplemented with 0.1% BSA. Intra-
cellular staining for TLR7 was performed as previously described ( 50 ) using
rabbit anti – mouse TLR7 or rabbit IgG isotype control (eBioscience) and goat
anti – rabbit IgG-FITC (SouthernBiotech). 50,000 events per sample were ac-
quired using a FACSCalibur (BD) and analyzed with FCS Express 3 software
(De Novo Software). Cell sorting was performed using a fl ow cytometer
(FACSDiva; BD). Peritoneal, splenic, and bone marrow Ly6C hi monocytes
(CD11b + Ly6C hi ), peritoneal DCs (CD11c + ), and granulocytes (CD11b + Ly6G + )
were sorted to > 90% purity for cell culture or RNA isolation.
TLR stimulation. Sorted cells resuspended in complete DMEM (contain-
ing 10% FCS, 10 mmol/liter Hepes, glutamine, and penicillin/streptomycin
JEM VOL. 205, December 22, 2008
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Dr. N.S. Szabo for gas chromatography/mass spectroscopy analysis of hydrocarbon
oil mixed with FCS. The work was supported with resources and the use of facilities
at the Malcolm Randall Veterans Administration Medical Center.
This work was supported by research grants AR44731, AR51766, and
AR050661 from the United States Public Health Service, and by generous gifts from
Lupus Link, Inc. and Mr. L.M. Schott to the University of Florida Center for
Autoimmune Disease. P.Y. Lee and J.S. Weinstein are National Institutes of Health
T32 trainees (DK07518 and AR007603). D.C. Nacionales is the recipient of an
Arthritis Foundation Postdoctoral Fellowship.
The authors have no confl icting fi nancial interests.
Submitted: 5 March 2008
Accepted: 3 November 2008
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