Rheumatology 2008;47:437–441
Advance Access publication 23 February 2008
doi:10.1093/rheumatology/ken013
Is Inhibitor of differentiation 3 involved in human primary
Sjögren’s syndrome?
J. Sellam1,*, C. Miceli-Richard1,*, J.-E. Gottenberg1, A. Proust2, M. Ittah1, F. Lavie1, P. Loiseau3
and X. Mariette1
KEY WORDS: Sjögren’s syndrome, Inhibitor of differentiation 3, Mouse model, T cells, Genetic polymorphism, Anti-SSA/SSB, Salivary gland
epithelial cell.
in serum [9]. Autoimmune manifestations are explained by Id3
deficiency in T cells, which could be responsible for disturbed
thymopoiesis leading to the generation and accumulation of
autoreactive T cells. Moreover, Id3 deficiency could also be
involved in intrinsic abnormalities in the exocrine glands, as was
observed in non-obese diabetic (NOD) mice [5].
To date, the implications of Id3 in human pSS have not been
investigated. From the phenotype of the Id3/ mouse and the cell
types involved in the symptoms in this model, we supposed that
impaired Id3 expression could have a role in pSS pathogenesis and
investigated the level of Id3 mRNA in blood T cells, in cultured
salivary gland epithelial cells (SGECs) and in total minor salivary
glands, the target organ of this autoimmune disease. Moreover,
because this single genetic deletion of Id3 leads to a Sjögren-like
syndrome in mouse, we aimed to assess the genetic contribution
of Id3 in human pSS. Id3 was sequenced, and single nucleotide
polymorphisms (SNPs) with potential functional relevance were
genotyped in a cohort of French Caucasian patients with pSS and
in controls.
Introduction
Primary Sjögren’s syndrome (pSS) is a frequently occurring
chronic autoimmune disorder characterized by lymphocyte
infiltration of glandular tissue and the presence of autoantibodies
(anti-Ro/SSA and anti-La/SSB). Salivary and lachrymal glands
are primarily affected. Oral and ocular dryness due to insufficient
secretion is the most predominant clinical manifestation.
Lymphocytic infiltrates of exocrine glands consist mainly of
activated CD4-positive T cells (60–70%), but the target cells,
epithelial cells, have an intrinsically activated status, acting as a
non-professional antigen presenting cell-producing cytokines and
expressing MHC-I HLA D-related (HLA-DR) and functional costimulatory molecules [1–3].
The aetiology of pSS is still unknown. Animal models are
powerful tools to aid in understanding the pathogenesis of human
pSS. Several animal models of SS based on the histopathological
findings of focal lymphocytic infiltrates in the lachrymal and
salivary glands have been proposed [4]. However, few demonstrate
a close resemblance solely to pSS, because they always share
symptoms of other autoimmune diseases and rarely secrete antiRo/SSA or anti-La/SSB antibodies [4, 5].
Inhibitor of differentiation 3 (Id3) is a nuclear protein inhibitor
of the basic-helix-loop-helix (bHLH) protein transcription factor
involved in cell proliferation and differentiation of a wide range of
cell types such as immune system cells and various somatic cells,
including epithelial cells [6–8]. To date, the Id3-deficient (Id3/)
mouse represents the best animal model for human pSS because it
displays lymphocytic infiltration almost restricted to exocrine
glands and positive anti-Ro/SSA and anti-La/SSB antibodies
Patients and methods
Subjects
Fresh peripheral blood was collected from four patients with pSS
fulfilling the European American Consensus Group criteria [10]
(three females, mean age 52 yrs, two with anti-Ro/SSA and anti-La/
SSB antibodies, three with focus score 1 on labial salivary gland
testing) and four healthy controls (all female, mean age 62 yrs).
For SGECs culture, biopsy specimens of minor salivary glands
were obtained from seven female patients with pSS (mean age
52 yrs, three with positive anti-SSA antibodies alone, one with
positive anti-SSA and anti-SSB antibodies and four with positive
lip biopsy results) and from 10 control subjects (nine women
and one man, mean age 54 yrs) with sicca symptoms but not
autoantibodies or lymphoid infiltrates on lip biopsy.
For ex vivo Id3 expression in exocrine glands, minor salivary
gland biopsy were obtained from 10 pSS patients fulfilling
European American consensus group criteria (mean age
57 17 yrs, range 40–80) and 10 sicca controls without signs
1
Rhumatologie and 2Hématologie, INSERM U802, Hôpital Bicêtre, Assistance
Publique des Hôpitaux de Paris (AP-HP), Université Paris-Sud, Le Kremlin Bicêtre
and 3Immunologie et Histocompatibilité, INSERM U396, Hôpital Saint-Louis,
AP-HP, Paris, France.
Submitted 17 August 2007; revised version accepted 7 January 2008.
Correspondence to: X. Mariette, Service de Rhumatologie, Hôpital de Bicêtre,
78 rue du Général Leclerc, 94275 Le Kremlin Bicêtre.
E-mail: xavier.mariette@bct.aphp.fr
J. Sellam and C. Miceli-Richard equally contributed to this work.
437
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Objectives. Inhibitor of differentiation 3 (Id3)-deficient mice show sicca symptoms, lymphocyte infiltration of exocrine glands and positive
anti-Ro/SSA and anti-La/SSB antibodies, all hallmarks of primary Sjögren’s syndrome (pSS). The impairment of Id3 in T cells and, possibly, in
salivary glandular epithelial cells (SGECs) seems to be involved. This animal model prompted us to investigate the role of Id3 in human pSS.
Methods. Quantitative Id3 expression in peripheral T cells, cultured SGECs and in total minor salivary glands was assessed by RT-PCR in
pSS patients and controls. After Id3 sequencing, we investigated two single nucleotide polymorphisms (SNPs) (c.313G>A and g.-156A>G)
in a case–control study of 212 Caucasian pSS patients and 168 controls.
Results. Quantitative Id3 expression was not decreased in pSS patients nor in SGECs, in T cells or in minor salivary glands. As well, patients
and controls did not differ in allele and genotype frequencies of Id3 SNPs (P ¼ 0.67 and P ¼ 0.71 for the c.313G>A and the g.-156A>G,
respectively). Neither SNP was associated with a pattern of autoantibody secretion.
Conclusion. Although the Id3-deficient mouse model represents an attractive model for human pSS, Id3 expression is not impaired in
SGECs, peripheral T cells and in labial salivary glands in pSS patients and Id3-relevant SNPs do not give evidence of genetic predisposition
in Caucasian pSS patients.
438
J. Sellam et al.
of autoimmunity (mean age 56 10 yrs, range 37–70) already
described elsewhere [11]. Among the 10 pSS patients, 9 of them
had a focus score >1, 7 had anti-SSA antibodies and 4 had antiSSB autoantibodies.
For Id3 genetic study, we included a cohort of 209 unrelated
patients with pSS according to the European American consensus
group criteria (40% without autoantibodies, 28% with anti-SSA
antibodies only and 32% with both anti-SSA and anti-SSB
antibodies) and 168 healthy blood donors. All patients and
controls were Caucasians. The study received approval from the
local ethics committee, and informed consent was obtained from
all subjects.
Blood T-cell isolation
SGECs culture and characterization
Primary cultures of SGECs were established from minor salivary
glands as previously described [12]. In brief, each lobule was cut
into small fragments and set in six 75-cm2 flasks with basal
epithelial medium (a 3 : 1 mixture of Ham’s F-12 and DMEM)
supplemented with 2.5% fetal calf serum, epidermal growth factor
(10 ng/ml), hydrocortisone (0.4 g/ml), insulin (0.5 g/ml), penicillin (100 IU/ml) and streptomycin (100 g/ml) and incubated
at 378C under 5% CO2. After 4–5 weeks’ culture at 70–80%
confluence, cells were dissociated with a 0.125% trypsin–EDTA
solution for real-time quantitative RT-PCR. To exclude cell
dedifferentiation during primary culture or contamination by
fibroblastic cells, morphological characteristics and cytokeratin-7
staining for ductal SGECs were evaluated. As reported previously
[12], all tested samples were 95–100% positive for cytokeratin-7,
-19 and -903 but not for cytokeratin-20, which confirm the ductal
epithelial origin of these cells and exclude the fibroblastic nature.
Moreover, complementary staining with MPO, CD20, CD3,
CD45 and smooth muscle actin excluded the possibility of
contamination with myeloid cells, B cells, T cells or myoepithelial
cells.
RNA isolation from minor salivary glands
After minor labial salivary glands were dissected from the lower
lip of the subjects, RNA extraction, cRNA production and cDNA
synthesis and amplification were performed as described
previously [11].
Id3 mRNA quantitation
Total RNA was isolated from isolated T cells and cultured SGECs
by use of the RNeasy Mini kit (Qiagen, Courtaboeuf, France).
cDNA synthesis involved use of Enhanced Avian HS RT-PCR
(Sigma-Aldrich, Saint Quentin Fallavier, France). Id3 and -actin
cDNA levels were determined by use of Light Cycler-based kinetic
quantitative PCR (Roche Diagnostics, Meylan, France). Id3 and
-actin PCR products were detected by use of LightCycler
FastStart DNA Master SYBR Green I (Roche Diagnostics). To
correct for variations in mRNA recovery and reverse transcription
yield, the amount of Id3 cDNA was normalized to that of -actin.
Amplification primers for the human genes were as follows: Id3,
forward 50 -CTGAGCTTGCTGGACGACA-30 and reverse
30 -ATGTAGTCGATGACGCGCTGTA-50 ; and -actin, forward
Sequencing analysis of Id3
Because Id3 polymorphisms have never been studied in Caucasian
patients, Id3 was sequenced with genomic DNA isolated from
PBMCs of six patients with pSS and six healthy controls.
Polymorphism screening included the 3 exons, the intron–exon
junction boundaries and the 50 flanking region, thus including
the putative promoter region of Id3 (2200 bp upstream of the
transcription initiation site). Putative functional consequences of
the identified polymorphisms in the promoter region were assessed
using AliBaba 2.1, a program for predicting transcription factorbinding sites [13].
Case–control study of SNPs
Among the four SNPs identified, two with potential functional
relevance were genotyped. The c.313G>A SNP was genotyped by
the PCR restriction fragment-length polymorphism method in 209
patients with pSS (126 with positive autoantibodies, including 58
with anti-Ro/SSA only and 68 with anti-Ro/SSA and anti-La/SSB
antibodies and 83 without autoantibodies) and 168 healthy
French blood donors. PCR was performed in a 20-ml final
reaction volume with PTC 200 (Peltier Thermal Cycler) with use
of 100 ng DNA, 1.25 U AmpliTaq Gold (Applied Biosystems, CA,
USA), the appropriate buffer supplied by the manufacturer
(Tampon GeneAmp 1) and MgCl2 (1.5 mM). Cycle conditions
were 958C for 12 min, then 30 cycles of 958C for 30 s, 588C for 30 s
and 728C for 30 s, then a final extension at 728C for 7 min.
The g.-156A>G SNP was genotyped by competitive allelespecific PCR by use of fluorescence resonance energy transfer
(FRET) technology.
Statistical analysis
Quantitative results are expressed as means S.E.M. For quantitative comparison of results between patients and controls,
Mann–Whitney U-test was used. All genotyped SNPs were in
Hardy–Weinberg equilibrium. Comparisons of allelic and genotypic frequencies of c.313G>A and g.-156A>G polymorphisms
between patients and controls involved two-sided chi-square test.
A Bonferroni correction was applied for two tested SNPs. Both
unadjusted and adjusted (denoted by Pa) P-values are reported.
A P < 0.05 was considered significant.
Results
Quantitative Id3 mRNA expression in human pSS
Because total Id3 deficiency in the mouse model leading to a
Sjögren-like syndrome is related to a specific Id3 impairment in
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Peripheral blood mononuclear cells (PBMCs) were obtained by
centrifugation with Ficoll gradient (PAA Laboratories, Pasching,
Austria). T cells were negatively separated from other PBMCs by
use of a Pan T-Cell Isolation Kit II and magnetic-activated cellsorting columns (Miltenyi Biotec, Bergish Gladbach, Germany).
T-cell purity was assessed by flow cytometry performed with use
of an EPICS XL device (Beckman Coulter), showing <0.2%
CD14þ cells and <5% CD22þ cells by use of anti-CD14 FITC,
anti-CD22 PC5 antibodies or appropriate isotype-matched
control (Becton Dickinson).
50 -GCTGTGCTACGTCGCCCT-30 and reverse 50 -AAGGTAGT
TTCGTGGATGCC-30 . Each sample was processed in duplicate,
with initial incubation at 968C for 10 min, then 40 cycles of 958C
for 10 s, 608C for 15 s and 728C for 20 s. For each run, serially
diluted cDNA of human B cells infected with EBV (B EBV cells)
were used for quantitative standards. We determined the cell
equivalence (CE) number of Id3 and -actin mRNA in each
sample according to the standard curve generated from values
obtained with B EBV cells. The unit number showing relative Id3
mRNA level in each sample was determined as a value of Id3 CE
normalized to -actin CE. Melting-curve analysis was performed
to assess the specificity of PCR product.
For ex vivo Id3 expression in total exocrine glands, quantitative
RT-PCR was performed as described elsewhere [11] using the Id3
primer sequences described above. Normalization of amount of
Id3 cDNA was performed using the amount of cDNA hypoxanthine phosphoribosyltransferase (HPRT) sequences. HPRT
PCR primers were: 50 -TGACACTGGCAAAACAATGCA-30 and
reverse, 50 -GGTCCTTTTCACCAGCAAGCT-30 .
Id3 and primary Sjögren’s syndrome
T cells, we investigated the mRNA expression of Id3 in peripheral
T cells of patients with pSS and healthy donors but found no
difference in Id3 expression between the groups (ratio Id3/-actin
1.2 0.09 in pSS patients and 1.1 0.01 in controls; P ¼ 0.38)
(Fig. 1A).
Also, because the abnormal phenotype of SGECs in pSS could
be related to an intrinsic Id3 impairment in these cells, we further
investigated the expression of Id3 mRNA in cultured SGECs of 7
patients with pSS and 10 with sicca symptoms without autoimmunity. Id3 expression in SGECs was not decreased in pSS
NS
Id3 gene sequencing
1.2
1.0
0.8
0.6
0.4
Id3 gene polymorphism analysis
0.2
The allele and genotype frequency of c.313G>A and g.-156A>G
in patients and controls are reported in Tables 2 and 3. All
genotyped SNPs were in Hardy–Weinberg equilibrium. pSS
patients and controls did not differ in allele and genotype
frequencies of polymorphisms. For the c.313G>A, G and A
allelic frequency were 79 and 21%, respectively, in pSS patients
vs 81 and 19%, respectively, in controls (P ¼ 0.67). For the
g.-156A>G, A and G allelic frequency were 52 and 48%,
respectively, in pSS patients vs 53 and 47%, respectively, in
controls (P ¼ 0.71). Allelic and genotypic distributions of
c.313G>A and g.-156A>G according to the profile of antibody
secretion are reported in Tables 2 and 3. Both SNPs were not
associated with a specific pattern of autoantibody secretion:
adjusted P-value (Pa) ¼ 0.34 and Pa ¼ 0.10 for c.313G>A and
Pa ¼ 0.09 and Pa ¼ 0.14 for g.-156A>G (for allelic and genotypic
frequencies, respectively).
0
Controls
n =4
pSS
n =4
NS
B 1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
Controls
n =10
pSS
n =7
Discussion
FIG. 1. RT-PCR results of quantitative Id3 mRNA expression in pure cell
populations from pSS patients and controls. Results are expressed as mean
(solid histograms) and S.E.M (vertical lines). (A) Id3 expression in blood T cells.
(B) Id3 expression in SGECs. NS, non significant.
Since the Id3-knockout mouse was described as an animal model
of pSS, we aimed to investigate the role of Id3 in human pSS.
Here, we demonstrate that the mRNA expression of Id3 is not
TABLE 1. Sequence variations of human Id3 gene with the corresponding minor allele frequencies
Sequence variations
c.313G>A
c.331T>G
g.-156A>G
g.-234G>A
g.-386_-387insG
g.-1962T>C
g.-2085(GAA)5-6
0.16
0.055
0.42
0.08
0.18
0.46
0.045
Minor allele frequency
The genotyped SNPs are represented in bold. The reference sequence is provided by Ensembl database (http://www.ensembl.org) (OTTHUMG00000003229).
TABLE 2. Allelic and genotypic frequencies of Id3 gene c.313G/A polymorphism in pSS patients and controls and according to the presence of autoantibodies
c.313G/A
SS (n¼209)
Allele frequenciesa
G
332 (79)
A
86 (21)
Genotype frequencies
GG
131 (63)
GA or AAb
78 (37)
pSS without
auto-Ab (n ¼ 83)
pSS with
anti-SSA only (n ¼ 58)
pSS with anti-SSA and
anti-SSB (n ¼ 68)
Controls (n ¼ 168)
OR (95% CI)
pSS vs controls
P-value
129 (78)
37 (22)
99 (85)
17 (15)
104 (76)
32 (24)
271 (81)
65 (19)
0.93 (0.65,1.33)
1.08 (0.75,1.55)
0.67
0.67
47 (57)
36 (43)
44 (76)
14 (24)
40 (59)
28 (41)
111 (66)
57 (34)
0.86 (0.56, 1.32)
1.16 (0.76, 1.77)
0.49
0.49
a
The allelic frequencies are calculated on 418 chromosomes for patients and 336 chromosomes for controls. bDue to the low number of AA genotype carriers, AA and AG genotypes were analysed
together. Results are expressed as number of patients (%). pSS, primary Sjögren’s syndrome; auto-Ab, auto-antibody; NA, not applicable; OR, odds ratio.
Downloaded from http://rheumatology.oxfordjournals.org/ at Pennsylvania State University on February 27, 2014
1.4
Id3/β-actin
patients as compared with control subjects (ratio Id3/-actin
1.4 0.07 vs 1.5 0.05; P ¼ 0.5) (Fig. 1B).
As culture procedure could change the expression of Id3 in
SGECs, we performed Id3 RNA quantification in vivo from total
labial salivary glands biopsy in 10 patients and 10 sicca controls
subjects without signs of autoimmunity. Id3 expression was
increased in pSS patients compared with controls (ratio Id3/
HPRT 2.8 2.3 in pSS patients vs 1.0 0.8 in controls; P ¼ 0.03).
Using genomic DNA of six healthy controls and six patients, five
SNPs were identified as well as one insertion and a variability of a
short sequence repeats (Table 1). We genotyped two SNPs with
minor allele frequency higher than 10% and potential functional
relevance: one located in the promoter region (g.-156A>G)
modifying putative Sp1 transcription factor-binding sites and
the other (c.313G>A), a non-synonymous SNP (A105T) located
in the second exon. Using a program for predicting transcriptionbinding site, the other identified polymorphisms were not
functionally relevant. Among the genotyped SNPs, c.313G>A
was already reported in public databases (http://www.ncbi.nlm.
nih.gov/projects/SNP).
A 1.6
Id3/β-actin
439
J. Sellam et al.
440
TABLE 3. Allelic and genotypic frequencies of Id3 gene g.-156A>G polymorphism in pSS patients and controls and according to the presence of autoantibodies
g.-156A>G
pSS (n ¼ 212)
Allele frequenciesa
A
220 (52)
G
204 (48)
Genotype frequencies
AA
55 (26)
AG
110 (52)
GG
47 (22)
pSS without
auto-Ab (n ¼ 77)
pSS with
anti-SSA only (n ¼ 63)
pSS with anti-SSA and
anti-SSB (n ¼ 72)
Controls (n ¼ 154)
Odds ratio (95% CI)
pSS vs controls
P-value
70 (45)
84 (55)
64 (51)
62 (49)
86 (60)
58 (40)
164 (53)
144 (47)
0.94 (0.71, 1.27)
1.06 (0.79, 1.42)
0.71
0.71
14 (18)
42 (55)
21 (27)
18 (29)
28 (44)
17 (27)
23 (32)
40 (56)
9 (12)
43 (28)
78 (51)
33 (21)
0.90 (0.57, 1.44) AA vs AG or GG
0.67
1.04 (0.63, 1.73) GG vs AA or AG
0.86
a
The allelic frequencies are calculated on 424 chromosomes for patients and 308 chromosomes for controls. Results are expressed as number of patients (%); pSS, primary Sjögren’s syndrome;
auto-Ab, auto-antibody; NA, not applicable; OR, odds ratio.
human pSS [20] probably through collaboration between T and B
cells [21].
All these results prompted us to investigate the presence of
impaired expression of Id3 in human pSS. Since adoptive transfer
of T cells is responsible for the development of the disease
and Id3/ mice with T cell deficiency show no infiltrates, we
quantified Id3 expression in blood T cells in pSS patients and
healthy controls but found no difference in mRNA expression
between the two groups. However, we cannot eliminate that Id3
expression is disturbed only in a subgroup of T cells such as tissueinfiltrating T cells, autoreactive T cells or regulatory T cells. In
pSS, the target cells SGECs are primarily affected and could drive
the immune response in exocrine tissue [1, 22]. Id3 deficiency could
be involved in this functional impairment, thus facilitating the
autoantigen presentation [5]. However, we found no difference
between patients and controls in Id3 expression in SGECs.
Nevertheless, the level of expression of Id3 in SGECs could be
modified by the culture conditions and time, and we could not
eliminate a dysregulation of Id3 in vivo. Thus, we performed Id3
mRNA quantification using cDNA from total labial salivary
glands in 10 pSS patients and 10 controls. Interestingly, we have
found a significant higher expression of Id3 in patients compared
with controls. But, it could be only related to the greater number
of inflammatory cells present in biopsies from patients who could
express more Id3. Finally, our study still has some limitations.
First, quantification of Id3 was performed on mRNA and the
possibility of a defect of the protein in pSS patients remains
possible but not assessed here. Lastly, we cannot exclude an Id3
defect during organogenesis, which could disappear during the
life. Whatever it is, Id3 expression does not seem to be
quantitatively decreased in human pSS.
However, although the Id3 mRNA level was not impaired in
peripheral T cells, SGECs and exocrine glands, defective function
of Id3 could relate to Id3 polymorphisms. Since Id3 gene
polymorphisms have not been extensively studied in humans, we
first carried out Id3 gene sequencing in 12 subjects and identified 2
SNPs with potential functional relevance. Interestingly, no
significant association was found between these two SNPs and
pSS. Moreover, since most of the genetic predisposition to pSS is
related to the pattern of autoantibody secretion [23] and since the
Id3 knockout mouse has anti-Ro/SSA and anti-La/SSB antibodies, we studied the association between Id3 polymorphisms
and autoantibody secretion but found no significant association
with pattern of autoantibody secretion.
In conclusion, although the Id3/ mouse shows clinical and
biological symptoms very close to those observed in human pSS,
Id3 is not down-regulated in blood T cells and SGECs of patients
with pSS, the target cells of the disease. Moreover, the two
relevant polymorphisms of Id3 are not involved in genetic
predisposition to human pSS in a Caucasian population. Thus,
Id3 seems to be not involved in the pathogenesis of human pSS.
These results illustrate the difference between disease in animal
models and in humans.
Downloaded from http://rheumatology.oxfordjournals.org/ at Pennsylvania State University on February 27, 2014
decreased in blood T cells, cultured SGECs and in minor salivary
glands in patients with pSS as compared with healthy controls.
Moreover, Id3 is not associated with a genetic predisposition to
the disease or to a specific pattern of autoantibody secretion.
Human pSS is considered as a multigenic and multifactorial
autoimmune disease of unknown origin. Mouse models are of
great value for studying the pathogenesis of SS, especially because
they allow for investigating the initiation phase of the autoimmune process, which is not possible in humans. Among such
models, NOD, MRL/lpr, NFS/sld and B-cell activating factor
transgenic mice have been extensively studied as models of SS
[4, 14]. However, the models may differ from human pSS and
imperfectly reflect the manifestations observed in humans. Indeed,
these mice are not models of pSS, because they also show
characteristic features of other autoimmune diseases such as
diabetes mellitus, RA and SLE. Moreover, secretory function is
not always altered, as in the MRL/lpr mouse, and the autoantibody profile can differ from human disease, as in the NOD mouse,
in which no anti-La/SSB antibodies are detected [4].
Interestingly, Li et al. [9] reported that the unique deletion of
one gene, Id3, in mouse resulted in symptoms very similar to those
observed in human pSS. Id3 is a member of the inhibitor of
differentiation family of transcription factors, up-regulated in
a broad range of cell types to regulate cell proliferation and
differentiation [15]. The primary function of the Id3 protein is to
inhibit bHLH transcription factors, thus preventing the DNA
binding of bHLH and activating the transcription of target genes
[16, 17]. The interaction between Id3 and bHLH proteins could be
a key regulatory event leading to cellular proliferation and
inhibition of differentiation in somatic cells. In general, the
expression of Id genes is high in proliferating cells and low in
differentiating and quiescent cells. The authors first reporting on
the Id3-deficient mouse described impaired T-cell-dependent and
-independent immune response and disturbed cell proliferation
after B-cell antigen receptor (BCR) stimulation, thus revealing a
specific role for Id3 in mediating signals from BCR to cell cycle
progression during the humoral immune response [18, 19].
However, this mouse, at 10 weeks of age, exhibited no particular
abnormalities in appearance, general behaviour, body and organ
size or mortality rate. The same group reported that at 6–8
months of age, mice showed symptoms mimicking human pSS
(sialadenitis, keratitis, sicca syndrome, salivary gland infiltrates
and anti-Ro/SSA and anti-La/SSB antibodies) [9]. Notably,
symptoms occurred when the mice reached an age comparable
with middle age in humans, which is the usual time of
development of human pSS. Id3/ mice show no significant
elevated urine protein level, no hyperglycaemia and the lymphocyte infiltration is mainly observed in exocrine glands, with
occasional immune cells in lung or kidney. These data
are consistent with this mouse model being exclusively a model
of SS not associated with another autoimmune disease.
Moreover, Id3/ mice respond to treatment with anti-CD20
monoclonal antibody, which also suggests a role of B cells like in
Id3 and primary Sjögren’s syndrome
Rheumatology key messages
Although Id3/ mouse represents the best animal model for
human pSS, Id3 mRNA is not quantitatively decreased in the
human pSS in blood T cells and SGECs.
Genetic polymorphisms of Id3 do not predispose to pSS in
Caucasian population.
Id3 seems to be not involved in human pSS pathogenesis,
illustrating the difference between autoimmune disease in animal
models and in humans.
Acknowledgements
We thank Xavier Puéchal, Le Mans, France and Eric Hachulla,
Lille, France, who helped collect DNA from patients.
Disclosure statement: The authors have declared no conflicts of
interest.
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Downloaded from http://rheumatology.oxfordjournals.org/ at Pennsylvania State University on February 27, 2014
Funding: The authors received a grant from Fondation pour la
Recherche Médicale, Agence Nationale pour la Recherche to
carry out the study.
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