ARTICLE
Auteur(s) : Amalia Lamana1, Ana M Ortiz1, José M Alvaro-Gracia1, Belén
Díaz-Sánchez1, Jesús Novalbos2, Rosario
García-Vicuña1, Isidoro
González-Álvaro1
1Rheumatology Service, Hospital Universitario La
Princesa, IIS La Princesa
2Clinical Pharmacology Service, Hospital Universitario
La Princesa, IIS La Princesa, Madrid, Spain
Interleukin-15 (IL-15) is a cytokine that shares certain
biological functions with IL-2, and which plays a very relevant
role in the innate immune response. IL-15 mRNA is expressed in a
variety of tissues and cells, including the placenta, skeletal
muscle, kidney, lung, heart, fibroblasts, epithelial cells and
activated monocytes. However, it is difficult to measure meaningful
quantities of IL-15 in the supernatants of many of these cells,
suggesting that post-transcriptional regulatory events critically
affect IL-15 expression [1, 2].
Interestingly, IL-15 has been implicated in the pathophysiology
of rheumatoid arthritis (RA), and indeed, this cytokine can be
detected in the synovial fluid of patients with RA, but not in
patients with osteoarthritis or other inflammatory joint diseases
[3-5]. In addition, increased levels of IL-15 have been found in
the serum of patients with RA, but not in healthy controls [6-9].
On the other hand, IL-15-activated lymphocytes induce macrophages
to produce tumour necrosis factor (TNF) in vitro [10-13], and the
neutralization of IL-15 activity improves arthritis in animal
models and in patients with RA [14, 15].
Identifying reliable biomarkers that can predict disease
severity and the response to treatment is of particular interest
for patients with early arthritis (EA). The aforementioned role of
IL-15 in RA and the fact that we previously found that only a
subpopulation of RA patients display increased serum (s)IL-15
levels [9], supports the hypothesis that sIL-15 might be useful as
a biomarker for patients with EA. However, little is known about
the behaviour of sIL-15 in the general population, a crucial step
prior to defining what may be considered to be an elevation in the
levels of sIL-15. Hence, the main purpose of this study was to
analyze the levels of sIL-15 levels in healthy individuals, and to
determine whether any variations are associated with age, gender or
circadian rhythm. In addition, the sIL-15 levels were studied in EA
patients, along with their variation with disease activity and
other parameters.
DONORS AND Methods
Patients
Serum was obtained from three groups of individuals that had
previously offered their verbal or written consent to be included
in the register, and their written, informed consent to participate
in the study: a) a group of 18 healthy volunteers, nine men
and nine women, aged between 20 and 24 years, who
participated in a pharmacokinetic study of an iron compound, and in
whom the circadian effect on IL-15 production was assessed; b) a
group of 153 patients, 67 men and 86 women, aged
between 25 and 90 years (median 58.5 years) scheduled for
surgery at the Orthopaedic Surgery and Traumatology Service of our
institution, where blood samples were routinely obtained during the
preoperative period (none of these patients presented inflammatory
disorders or other co-morbid conditions and thus they served as
healthy controls); and c) the group of early arthritis patients.
The group of early arthritis patients (group c) included
174 patients from the Early Arthritis Registry of the Hospital
Universitario de La Princesa. There were 40 men and
134 women in this group, and while the median age was 50.8
years (IQR: 38.9-64.1), the men were significantly older than the
women (table 1). At the end of the
follow-up period, 121 (69.5%) patients fulfilled the ACR
classification criteria for RA [16], and the remaining
53 patients were diagnosed with undifferentiated arthritis
(UA). The distribution of men and women in both diagnostic groups
was similar (table 1), although the
patients who met the ACR criteria were significantly older than
those patients with undifferentiated arthritis (table 1). A more detailed description of
this population is shown in table 1.
During the two-year follow-up period, patients at the EA clinic
(EAC) attended four, structured visits. At each visit, the
following data were collected and entered into an electronic
database: clinical and demographic information; disease duration at
the beginning of the follow-up; 28 tender and swollen joint
counts (TJC and SJC, respectively); global disease activity on a
100 mm visual analogue scale assessed both by the patient
(GDAP) and by the physician; the Spanish version of the Health
Assessment Questionnaire [17]; and laboratory tests including
erythrocyte sedimentation rate (ESR), the levels of C-reactive
protein (CRP), and the rheumatoid factor (RF) assessed by
nephelometry. In addition, we obtained serum samples that were
frozen at - 80°C until sIL-15 was measured. The study protocol
was reviewed and approved by the Local Research Ethics
Committee.
Table 1 Characteristics of patients with early
arthritis at the baseline visit
|
Data
|
All patients (n = 174)
|
Rheumatoid arthritis (n = 121)
|
Undifferentiated arthritis (n = 53)
|
P value
|
|
Female gender
|
134 (77)
|
94 (77.7)
|
40 (75.5)
|
NS
|
|
Age, years, median (IQR)
|
50.8 (38.9-64.1)
|
54.4 (43.2-67.3)
|
49.4 (35.3-59.9)
|
0.03
|
|
Positive rheumatoid factor
|
75 (43)
|
65 (53.8)
|
9 (17)
|
< 0.001
|
|
Anti-CCP
|
67 (38.5)
|
62 (51.2)
|
5 (9.4)
|
< 0.001
|
|
IL-15 > 20 pg/mL
|
50 (29)
|
42 (35%)
|
8 (15%)
|
0.008
|
|
IL-15 pg/mL, median (IQR)
|
8.05 (2.6-23.8)
|
10.6 (4-30)
|
5.4 (1-15.1)
|
0.006
|
|
DAS28, median (IQR)
|
4.5 (3.3-5.7)
|
4.9 (3.8-5.9)
|
4.7 (2.8-4.7)
|
< 0.001
|
|
HAQ, median (IQR)
|
1 (0.5-1.625)
|
1.125 (0.5-1.75)
|
0.75 (0.375-1.25)
|
0.005
|
Measurement of serum IL-15
The concentration of sIL-15 was measured using a sandwich enzyme
immune assay (EIA). Briefly, 96-well, high binding EIA plates
(Costar, Cambridge, MA, USA) were coated overnight at 4°C with
the MAB647 MAb (anti-IL-15, 50 μL/well: R&D Systems Europe
Ltd., Abingdon, UK), diluted to 4 μg/mL in PBS (pH 7.4). Each well
was then washed twice with 200 μL of wash buffer [0.05% Tween
20 in PBS (pH 7.4)] and blocked for 1 hour at 37°C by
adding 200 μL of PBS containing 2% BSA. Between each step, the
wells were washed three times with 200 μL of wash buffer.
Subsequently, 50 μL/well of diluent buffer [0.1% BSA, 0.05%
Tween20, 1 mg/mL normal mouse immunoglobulin (Calbiochem, San
Diego, CA, USA], 20 mM Trizma base, 150 mM NaCl (pH 7.3)],
plus 50 μL of each sample and standard dilutions of recombinant
human IL-15 (500 to 6.2 pg/mL; R&D Systems) were added to the
respective wells (in duplicate) and incubated at room temperature
for 2 h. The bound IL-15 was detected with BAM247
(biotinylated anti-IL-15 MAb, 50 μL/well; R&D Systems), and
diluted at 200 ng/mL in diluent buffer for 1 h at room
temperature. After washing, streptavidin HRP (100 μL/well, 1/5,000
in diluent buffer; Calbiochem) was added to the wells for
20 min at room temperature, and the antibody binding was
visualised with 3,3′,5,5′-tetramethylbenzidine (100 μL/well,
Chemicon International Inc., Temecula, CA, USA). The optical
density of each well was determined using a microtitre plate reader
LP400 (Sanofi Diagnostics Pasteur, Marnes la Coquette, France) set
to 450 nm, with a wavelength correction set to 550 nm.
Cytokine values were calculated from the standard curve and samples
that generated values higher than the highest standard were diluted
(1:1) in diluent buffer and assayed again.
As described previously [9], this protocol excluded the possible
interference of rheumatoid factor in the immune assay, and although
we previously failed to observe significant differences in sIL-15
levels between samples processed in the presence or absence of
murine immunoglobulins, we maintained this supplement in the
diluent buffer. In fact, increased IL-15 levels were observed in
patients positive and negative for rheumatoid factor (data not
shown). For this procedure, the intra-assay variability (mean ±
standard deviation, SD) was 15.4 ± 21.7% and the inter-assay
variability was 21.9 ± 33.4%.
Quantitative analysis of IL-15 mRNA using RT-PCR
To analyse the possible correlation between the expression of the
two IL-15 mRNA isoforms and the sIL-15 levels, we studied eleven
samples from patients with IL-15 serum levels below the limit of
the detection of our EIA (see above). They were compared with
samples from four patients with serum IL-15 levels higher than
60 pg/mL. This limit was chosen since it corresponds to the
90th percentile of the distribution of sIL-15 levels in the group
of patients with early arthritis (table 2).
Total cellular RNA from PBLs was isolated with the Ultraspec RNA
reagent (Biotecx, Houston, Texas, USA), according to the
manufacturer's protocol. Blood samples were taken at the patients’
first visit, prior to the onset of treatment. The RNA was
re-suspended in 0.02 mL of water and stored at - 70°C.
Total RNA was converted into cDNA. The reverse transcriptase (RT)
reaction was carried out using 2 μg of DNaseI-treated RNA and the
ImProm-II Reverse Transcriptase (Promega GmbH, Mannheim, Germany),
and gene expression was quantified by SYBR Green real-time PCR
(Roche Diagnostics GmbH, Penzberg, Germany) in a DNA Lightcycler
rapid thermal cycler system (Roche, Mannheim, Germany). The
sequences of the cytokine specific 5′ and 3′ primer pairs were as
follows: GAPDH forward: 5′ GAA GGT GAA GGT CGG AGT C 3′; GAPDH
reverse: 5′ GAA GAT GGT GAT GGG ATT TC 3′; IL15 forward b: 5′ GGA
TTT ACC GTG GCT TTG AGT AAT GAG 3′; IL15 forward a: 5′ GCC TTC ATG
GTA TTG GGA AC3′; IL15 reverse: 5′ GAA TCA ATT GCA ATC AAG AAG TG
3′. The results for each IL-15 isoform were normalized to the GAPDH
expression and measured in parallel in each sample. The PCR
products were resolved in a 2% agarose gel and visualized with
GelStat Nucleic Acid Gel Stain (Lonza, Basel, Switzerland).
Table 2 Changes in serum IL-15 levels
in patients with RA during a 2-year follow-up period
|
Study subjects
|
Serum levels of IL-15 (pg/mL)
|
|
Median
|
25th-75th percentile
|
90th percentile
|
P value when compared with visit 1
|
|
All EA patients
|
|
|
|
|
|
Visit 1 (baseline)
|
8.05*
|
2.6-23.8
|
57.7
|
-
|
|
Visit 2
|
8.4
|
3.0-35.1
|
54.9
|
0.936
|
|
Visit 3
|
8.4
|
3.0-23.2
|
41.6
|
0.026
|
|
Visit 4
|
6.4
|
0-17.9
|
50.3
|
0.031
|
|
RA patients
|
|
|
|
|
|
Visit 1 (baseline)
|
10.8
|
4.4-32.6
|
61.0
|
-
|
|
Visit 2
|
11.4
|
3.1-37.0
|
68.0
|
0.808
|
|
Visit 3
|
8.8
|
3.5-31.7
|
45.0
|
0.007
|
|
Visit 4
|
7.0
|
1.0-18.5
|
65.4
|
0.101
|
|
UA patients
|
|
|
|
|
|
Visit 1 (baseline)
|
6.2
|
1.1-16.3
|
35.0
|
-
|
|
Visit 2
|
4.8
|
2.4-17.5
|
39.2
|
0.501
|
|
Visit 3
|
4.5
|
1.1-19.0
|
31.0
|
0.82
|
|
Visit 4
|
6.7
|
0-15.0
|
29.5
|
0.151
|
Statistical analysis
Categorical variables were compared with the chi-squared test
(χ2) or the Mann-Whitney U test. The correlation between
age and sIL-15 levels in the group of healthy controls was assessed
using the Pearson's product-moment correlation coefficient. The
Wilcoxon signed-rank test was used to compare the sIL-15 levels at
follow-up visits in the group of patients with RA. The data are
expressed as the median and interquartile range
(25th-75th percentile, IQR). All the
statistical analyses were performed with Stata, version 9.2 for
Windows (StataCorp LP, College Station, TX, USA), and unless
otherwise specified, statistical significance was set at p <
0.05.
Results
Serum IL-15 levels in healthy controls
The sIL-15 levels in the healthy subjects did not follow
a normal distribution, but rather, there was a higher
frequency of values close to zero and a long tail to the right,
with a median sIL-15 value of 0.83 (IQR 0-8.68) pg/mL (figure 1A). There
were no significant differences in sIL-15 values according to
gender (figure 1B) as the
median value in men was 1.99 (0-8.68) pg/mL compared with 0.50
(0-8.25) pg/mL in women (p = 0.821). In addition, the sIL-15
levels did not correlate with age (r = 0.033, p = 0.685, figure 1C).
Taking into account these findings, we established a cut-off point
of 20 pg/mL to consider sIL-15 levels as elevated, since this
value corresponded to the 90th percentile for this healthy
population (figure 1A).
Lack of circadian effect on serum IL-15 levels
Some cytokines, such as IL-6 and TNF, show circadian fluctuations
in their production, [18]. Hence, we assessed whether the
differences in the aforementioned data could be due to the
collection of samples during a particular period of the circadian
cycle that naturally corresponds to low cytokine production.
Accordingly, we measured sIL-15 in samples obtained over a 24-hour
period in 18 healthy volunteers. In all cases there was no
clear-cut circadian rhythm associated with the sIL-15 values, and
the median values of sIL-15 were close to zero at all times (figure 2).
However, increasing sIL-15 values were observed in two subjects
during the study period (figure 2), although
the pattern of sIL-15 production in these cases still failed to
follow a circadian cycle.
Serum IL-15 levels in early arthritis patients
In the EA group, 30% of patients had sIL-15 values above
20 pg/mL, the cut-off point that corresponded to the
90th percentile of the healthy population (figure 3A). The
proportion of patients with increased sIL-15 was greater in
patients fulfilling the ACR criteria for RA than in those with UA
(34.7% versus 15.1%; table 1 and
figure 4).
In addition, sIL-15 levels in the early arthritis group were higher
than those in healthy controls whose sIL-15 concentrations were
above the cut-off point of 20 pg/mL (figure 3A). This was
also the case in both the RA and UA subgroups, although the
difference was greater in those fulfilling the ACR criteria
for RA (figure 4).
Serum IL-15 levels did not correlate with disease duration from
the beginning of symptoms to the first visit to the EAC (figure 3B). In
addition, sIL15 levels did not fluctuate as the disease activity
changed as a result of treatment during the follow-up period (figure 3C).The
variations in sIL-15 levels during the two-year follow-up of EA
patients are shown in table 2.
A slight trend towards a decrease over time was observed in
the whole early arthritis group, although it was not statistically
significant (table 2).
On average, this decrease was less than 3 pg/mL over the
follow-up period, and it was only significant in the RA subgroup of
patients at the 3rd visit (table 2).
Expression of IL15 mRNA variants in peripheral blood
lymphocytes of patients with early arthritis
We assessed whether the alternative splicing of IL-15 mRNA could
explain the differences in sIL-15 levels in patients with EA. Two
different variants of human IL-15 mRNA exist, and the precursor
protein encoded by each variant differs in the signal peptide
sequence. The authentic IL-15 mRNA encodes a precursor protein with
a 48-amino acid signal peptide (long signal peptide, LSP), while
the alternatively spliced form of IL-15 mRNA, generated by
retention of exon “A” (figure 5A), has a
premature termination codon that provides an alternative initiation
codon. The new signal peptide generated is only 21 amino acids
long (short signal peptide, SSP), and the associated IL-15 produced
from this SSP isoform is not secreted, but rather it is stored
intracellularly, accumulating in the nucleus and cytoplasm [19-21].
To measure the levels of the two IL-15 mRNA variants, we
performed RT-PCR using specific primers (figure 5A).
Accordingly, we found that expression of the two IL-15 mRNA
variants appeared to be higher in patients with increased sIL-15
than in those in which this cytokine was not detected (figure 5B). However,
these differences were only significant for the SSP IL-15 mRNA
variant. Since both variants were increased in patients with higher
sIL-15, we investigated whether the ratio between both IL-15 mRNA
variants was weighted towards the LSP precursor protein in patients
with high sIL-15. In most of the EA samples tested, both cDNA
variants were amplified by RT-PCR, although they were
differentially expressed in each sample (figure 5C). However,
the ratio between the two amplification products obtained by RT-PCR
(643 bp/524 bp) was very similar in both groups of patients (figure 5C).
Discussion
The present study provides two relevant findings: about 30% of
patients with EA have sIL-15 levels higher than the cut-off point
that can be considered normal in the general population; the
behaviour of this cytokine suggests that it may be a reliable
biomarker for this subpopulation of patients.
Our data indicate that the presence of sIL-15 in the general
population is extremely rare, since in 70% of the healthy controls,
the sIL-15 levels were below the threshold for detection of our
assay (6.5 pg/mL). Indeed, in only 10% of healthy subjects were the
sIL-15 values above 20 pg/mL, which led us to select
arbitrarily this 90th percentile as the upper limit for
normal sIL-15 values. Considering this cut-off value, 30% of the
patients with early arthritis had high sIL-15 levels, and although
this finding was more frequent in patients that fulfilled the ACR
classification criteria for RA, the sIL15 levels do not seem to be
useful for the diagnosis of early RA. Nevertheless, the detection
of this cytokine had many characteristics that suggest it may be a
reliable biomarker. Firstly, in contrast to other cytokines, it did
not suffer circadian variations and thus, it can be measured at any
time of the day. Secondly, no important differences in sIL-15
levels were found according to age, gender or disease duration.
Thirdly, variations in sIL-15 according to disease activity were
not evident and treatment did not seem to induce any relevant
changes in the serum levels of this cytokine, such that sIL-15 can
be measured both in naïve and treated patients. Therefore, sIL-15
seems to be useful as a biomarker of a subpopulation of patients
with EA rather than as an acute phase reactant.
In this regard, we previously observed a significant correlation
between sIL15 and the number of disease-modifying antirheumatic
drugs (DMARDs) prescribed to patients [9]. If we accept that the
number of DMARDs used in one patient can be considered as a
surrogate variable of disease severity, it is possible that those
patients with EA and increased sIL15 may correspond to a more
aggressive phenotype of the disease. This hypothesis seems
reasonable since IL-15 appears to be involved in some of the
mechanisms underlying the perpetuation of TNF production [10-12],
the survival of human Th17 cells [22], and the production of IL-17
[6], as well as in the proliferation of B lymphocytes and the
promotion of osteoclast differentiation [23]. All these events
contribute significantly to the persistence of synovitis and
osteoclast formation that leads to bone destruction in RA.
On the other hand, as regards the factors involved in the
modulation of sIL-15 levels, it is well known that both IFN-γ and
TNF induce the expression of membrane-anchored IL-15 [11, 12].
Indeed, we have shown that treatment with TNF antagonists can
moderately decrease sIL-15 levels [24]. However, it is very
difficult to trigger the production of soluble IL-15 in vitro and
it has been proposed that its induction is under strict,
post-transcriptional control [1]. Here, we have shown that the
presence of high sIL-15 levels is not related to a switch in IL-15
mRNA transcription towards the LSP IL-15 mRNA variant. By contrast,
we found that our patients expressed both mRNA variants more
strongly than patients with no detectable sIL-15. It is possible
that genetic variations at the promotor level may be involved,
although no association has been observed between genetic
variations in the IL-15 gene and the risk of developing RA
[25].
As occurs in other conditions such as cancer, the value of
biomarkers is not restricted to diagnostic accuracy, but might also
be relevant in assessing therapeutic response or detection of
severe disease. Our findings suggest that the measurement of sIL15
may be useful for early identification of a subpopulation of
patients with recent-onset arthritis with a putative,
characteristic RA clinical course. However, further studies are
necessary to determine whether this subset of patients behaves
differently in terms of their clinical evolution or response to
treatment.
Acknowledgments
We thank Marta Pulido, MD, for her editorial assistance with the
manuscript.
Financial support. This work was partially supported by
the RETICS Programme (RD08/0075 - RIER) and an FIS grant (05/2044)
from the Instituto de Salud Carlos III (ISCIII). Amalia Lamana is
the recipient of a DIB-SER grant from the Spanish Foundation of
Rheumatology. The work of Isidoro González-Álvaro was, in part,
supported by a grant from the Research Intensification Programme in
the National Health Care System, Instituto Carlos III, Madrid,
Spain.
Disclosure. Dr I. González-Alvaro has received
unrestricted research grants from Abbott Laboratories,
Sanofi-Aventis and Bristol-Myers Squibb during the past five years
for research projects that bear no relationship to the present
study.
The remaining authors have no conflicts of interest to
disclose.
References
1 Tagaya Y, Bamford RN, DeFilippis AP,
Waldmann TA. IL-15: a pleiotropic cytokine with diverse
receptor/signaling pathways whose expression is controlled at
multiple levels. Immunity 1996; 4: 329.
2 Fehniger TA, Caligiuri MA. Interleukin 15: biology
and relevance to human disease. Blood 2001; 97: 14.
3 McInnes IB, al-Mughales J, Field M, et al.
The role of interleukin-15 in T-cell migration and activation in
rheumatoid arthritis. Nat Med 1996; 2: 175; [see comments].
4 Thurkow EW, van der Heijden IM, Breedveld FC,
et al. Increased expression of IL-15 in the synovium of
patients with rheumatoid arthritis compared with patients with
Yersinia-induced arthritis and osteoarthritis. J Pathol 1997; 181:
444.
5 Ortiz AM, Laffon A, Gonzalez-Alvaro I. CD69
expression on lymphocytes and interleukin-15 levels in synovial
fluids from different inflammatory arthropathies. Rheumatol Int
2002; 21: 182.
6 Ziolkowska M, Koc A, Luszczykiewicz G,
et al. High levels of IL-17 in rheumatoid arthritis patients:
IL-15 triggers in vitro IL-17 production via cyclosporin
A-sensitive mechanism. J Immunol 2000; 164: 2832.
7 Cordero OJ, Salgado FJ, Mera-Varela A,
Nogueira M. Serum interleukin-12, interleukin-15, soluble
CD26, and adenosine deaminase in patients with rheumatoid
arthritis. Rheumatol Int 2001; 21: 69.
8 Suzuki J, Morimoto S, Amano H, Tokano Y,
Takasaki Y, Hashimoto H. Serum levels of interleukin
15 in patients with rheumatic diseases. J Rheumatol 2001; 28:
2389.
9 Gonzalez-Alvaro I, Ortiz AM, Garcia-Vicuna R,
Balsa A, Pascual-Salcedo D, Laffon A. Increased
serum levels of interleukin-15 in rheumatoid arthritis with long-
term disease. Clin Exp Rheumatol 2003; 21: 639.
10 McInnes IB, Leung BP, Sturrock RD,
Field M, Liew FY. Interleukin-15 mediates T
cell-dependent regulation of tumor necrosis factor-alpha production
in rheumatoid arthritis. Nat Med 1997; 3: 189.
11 Miranda-Carus ME, Balsa A, Benito-Miguel M,
Perez de Ayala C, Martin-Mola E. IL-15 and the initiation
of cell contact-dependent synovial fibroblast-T lymphocyte
cross-talk in rheumatoid arthritis: effect of methotrexate. J
Immunol 2004; 173: 1463.
12 Gonzalez-Alvaro I, Dominguez-Jimenez C,
Ortiz AM, et al. Interleukin-15 and interferon-gamma
participate in the cross-talk between natural killer and monocytic
cells required for tumour necrosis factor production. Arthritis Res
Ther 2006; 8: R88.
13 Gonzalez-Alvaro I, Ortiz AM, Romero FI,
Laffon A, Sanchez-Madrid F. CD69 expression on
lymphocytes is a key event in the TNF-alpha production mediated by
intercellular contacts between macrophages and IL-15-activated
lymphocytes. Rheumatology (Oxford) 2002; 41: S26.
14 Ruchatz H, Leung BP, Wei XQ, McInnes IB,
Liew FY. Soluble IL-15 receptor alpha-chain administration
prevents murine collagen-induced arthritis: a role for IL-15 in
development of antigen- induced immunopathology. J Immunol 1998;
160: 5654.
15 Baslund B, Tvede N, Danneskiold-Samsoe B,
et al. Targeting interleukin-15 in patients with rheumatoid
arthritis: A proof-of-concept study. Arthritis Rheum 2005; 52:
2686.
16 Arnett FC, Edworthy SM, Bloch DA, et al.
The American Rheumatism Association 1987 revised criteria for the
classification of rheumatoid arthritis. Arthritis Rheum 1988; 31:
315.
17 Esteve-Vives J, Batlle-Gualda E, Reig A.
Spanish version of the Health Assessment Questionnaire:
reliability, validity and transcultural equivalency. Grupo para la
Adaptacion del HAQ a la Poblacion Espanola. J Rheumatol 1993; 20:
2116.
18 Cutolo M, Straub RH. Circadian rhythms in
arthritis: Hormonal effects on the immune/inflammatory reaction.
Autoimmun Rev 2008; 7: 223.
19 Onu A, Pohl T, Krause H, Bulfone-Paus S.
Regulation of IL-15 secretion via the leader peptide of two IL-15
isoforms. J Immunol 1997; 158: 255.
20 Tagaya Y, Kurys G, Thies TA, et al.
Generation of secretable and nonsecretable interleukin
15 isoforms through alternate usage of signal peptides. Proc
Natl Acad Sci USA 1997; 94: 14444.
21 Meazza R, Gaggero A, Neglia F, et al.
Expression of two interleukin-15 mRNA isoforms in human tumors does
not correlate with secretion: role of different signal peptides.
Eur J Immunol 1997; 27: 1049.
22 Annunziato F, Cosmi L, Santarlasci V,
et al. Phenotypic and functional features of human Th17 cells.
J Exp Med 2007; 204: 1849.
23 Miranda-Carus ME, Benito-Miguel M, Balsa A,
et al. Peripheral blood T lymphocytes from patients with early
rheumatoid arthritis express RANKL and interleukin-15 on the cell
surface and promote osteoclastogenesis in autologous monocytes.
Arthritis Rheum 2006; 54: 1151.
24 Gonzalez-Alvaro I, Ortiz A, Tomero E,
et al. El bloqueo terapéutico del factor de necrosis tumoral
disminuye la concentración sérica de interleucina 15 en
pacientes con artritis reumatoide. Rheumatol Clin 2009; 5: 23.
25 Rueda B, Lopez-Nevot MA, Gonzalez-Gay MA,
et al. Molecular screening and association study of IL15 gene
polymorphisms in rheumatoid arthritis. Cytokine 2007; 38: 84.
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