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Complementactivationinpatientswith
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ARTHRITIS & RHEUMATISM
Vol. 44, No. 5, May 2001, pp 997–1002
© 2001, American College of Rheumatology
Published by Wiley-Liss, Inc.
Complement Activation in Patients With Rheumatoid Arthritis
Mediated in Part by C-Reactive Protein
Esmeralda T. H. Molenaar,1 Alexandre E. Voskuyl,1 Atoosa Familian,2 Gerard J. van Mierlo,2
Ben A. C. Dijkmans,3 and C. Erik Hack4
Objective. Complement activation in patients with
rheumatoid arthritis (RA) is considered to be triggered
by immune complexes. Recently, it was shown that
C-reactive protein (CRP) can activate the complement
system in vivo. We therefore hypothesized that part of
the complement activation in RA is due to CRP. The aim
of this study was to investigate CRP-mediated complement activation in RA, and to assess its correlation with
disease activity.
Methods. Complexes between CRP and the activated complement components C3d (C3d–CRP) and
C4d (C4d–CRP), which reflect CRP-mediated complement activation, as well as the overall levels of activated
C3 and C4 were measured in the plasma of 107 patients
with active RA and 177 patients with inactive RA.
Inactive RA was defined according to the American
College of Rheumatology criteria for clinical remission.
Disease activity was assessed by the modified Disease
Activity Score (DAS28).
Results. Plasma levels of C3d–CRP and C4d–CRP
were increased in the majority of the patients, and were
significantly higher in patients with active disease versus those with inactive RA (P < 0.001). In patients with
active RA, the plasma concentrations of C3d–CRP and
C4d–CRP correlated significantly with the DAS28
(Spearman’s rho 0.61 and 0.55, respectively; P < 0.001),
whereas these correlations were less pronounced in
patients with inactive RA (Spearman’s rho 0.28 [P <
0.001] and 0.25 [P ⴝ 0.001], respectively). Levels of
activated C3 and C4 were also increased in the majority
of the patients, particularly in patients with active RA.
Conclusion. Part of the activation of complement
in RA is mediated by CRP and is correlated with disease
activity. We suggest that this activation is involved in
the pathogenesis of RA.
Rheumatoid arthritis (RA) is a chronic disease of
unknown cause, characterized by inflammation of the
joints. The pathogenesis of RA is incompletely understood, although there is compelling evidence that cytokines such as tumor necrosis factor ␣ and interleukin-1
are involved (1). Furthermore, there is substantial evidence that the complement system is also involved in the
pathogenesis of RA (2–6). Increased levels of complement products and immune complexes have been found
in the serum and synovial fluid of RA patients (4,5) and
correlate with disease activity (6). Moreover, studies in
animals have demonstrated that the complement system
contributes to the inflammatory damage in arthritis;
inhibition of the complement cascade ameliorates experimental arthritis (7,8).
Complement is traditionally considered to be
mainly activated by bacteria or immune complexes.
Indeed, the latter have been implicated as the trigger for
complement activation in RA (9). However, circulating
immune complexes from patients with RA appear to
have very little effect on activation of the complement
system (10). Since there is no conclusive evidence that
immune complexes are the main trigger for complement
activation in RA, other potential triggers for complement activation in RA should be considered. One of
these triggers may be C-reactive protein (CRP), since
this acute-phase protein can activate complement both
in vitro (11) and in vivo (12–14).
1
Esmeralda T. H. Molenaar, MD, Alexandre E. Voskuyl, MD,
PhD: Vrije Universiteit Medical Center, Amsterdam, The Netherlands; 2Atoosa Familian, MD, Gerard J. van Mierlo: Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, Amsterdam, The Netherlands; 3Ben A. C. Dijkmans, MD, PhD: Academic
Hospital Vrije Universiteit and Jan van Breemen Instituut, Amsterdam, The Netherlands; 4C. Erik Hack, MD, PhD: Academic Hospital
Vrije Universiteit and Central Laboratory of the Netherlands Red
Cross Blood Transfusion Service, Amsterdam, The Netherlands.
Address correspondence and reprint requests to Alexandre E.
Voskuyl, MD, PhD, Department of Rheumatology, Vrije Universiteit
Medical Center, P.O. Box 7057, 1007 MB Amsterdam, The Netherlands.
Submitted for publication July 25, 2000; accepted in revised
form February 6, 2001.
997
998
MOLENAAR ET AL
CRP–complement complexes (12) serve as one
parameter of CRP-mediated complement activation.
These complexes have been detected in the circulation
of renal allograft recipients (12) and in patients with
sepsis (13). Notably, circulating levels of CRP are associated with the disease activity of RA (15). CRP has
been found to be localized in inflamed joints in a rabbit
model of arthritis (16), suggesting a possible role in local
inflammatory reactions. Yet the association between
CRP and the activity of RA is generally considered to be
indirect in that the levels of CRP reflect the production
of inflammatory cytokines, and the association has never
been considered to result from a direct pathogenic effect
of CRP.
The present study was performed on the assumption that CRP is involved in the activation of complement in RA. Therefore, plasma levels of complexes
between CRP and complement, as well as complement
activation products (C3b/c [denotes C3b, C3bi, and/or
C3c] and C4b/c) were determined in patients with active
and inactive RA. In addition, we assessed the association
of these parameters with disease activity.
PATIENTS AND METHODS
Patients. Clinical data and blood samples were collected from 284 RA patients who were recruited from an outpatient clinic. Of those patients, 177 were classified as having
inactive RA and 107 were classified as having active RA.
Inactive RA was defined by the American College of
Rheumatology (ACR) criteria for clinical remission (17).
Accordingly, clinical remission is present when 5 of the following 6 criteria are fulfilled: 1) duration of morning stiffness not
exceeding 15 minutes; 2) no fatigue; 3) no joint pain; 4) no
joint tenderness or pain on motion; 5) no soft tissue swelling in
joints or tendon sheets; and 6) erythrocyte sedimentation rate
(ESR) ⬍30 mm/hour for a female patient or ⬍20 mm/hour for
a male patient. For this study, these criteria were modified by
omitting the “no fatigue” criterion so that a patient was
classified as having inactive RA when fulfilling 4 of the 5
remaining criteria. The criteria for joint pain and joint tenderness on motion were modified by allowing the consideration of
mild arthralgia if local synovitis was absent and anatomic
changes in the joint could be demonstrated radiologically, as
previously described (18).
Patients with active RA included 55 patients with a
disease duration of ⬎1 year. In addition, 52 consecutive
patients with early RA with a disease duration of ⬍1 year were
also included. Patients were classified with active disease when
not fulfilling the criteria for clinical remission (17).
In order to assess disease activity, the modified Disease
Activity Score (DAS28) was calculated. This composite index
consists of the swollen and tender joint counts (each from a
possible total of 28 joints), the ESR, and a visual analog scale
for general health (19).
All RA patients fulfilled the 1987 ACR (formerly, the
American Rheumatism Association) criteria for RA (20). The
protocol was approved by the local institutional ethics review
committee.
Collection of blood samples. Blood samples from
patients were collected in vacutainer tubes containing EDTA.
Plasma was obtained by centrifugation of blood and stored in
aliquots at ⫺70°C until tested.
Measurement of activated complement, CRP, and
CRP–complement complexes. Activation of C3 and C4 was
assessed with an enzyme-linked immunosorbent assay
(ELISA), as described elsewhere in detail (21). In brief,
monoclonal antibodies recognizing neoepitopes on C4b/c and
C3b/c were used as catching antibodies. Biotinylated polyclonal rabbit anti-human C4 and C3c antibodies were used as
detecting antibodies. Levels of C3b/c and C4b/c above the
upper limits of the normal values in healthy controls, i.e., 57
nmoles/liter and 5 nmoles/liter, respectively, were considered
to be increased.
CRP was measured with a sandwich-type ELISA as
described by Wolbink et al (12). Levels of CRP above the
upper limit of normal (i.e., 5 mg/liter) were considered to be
increased.
Complexes between CRP and the degradation products of the activated complement components C3d (C3d–
CRP) and C4d (C4d–CRP) were measured by ELISAs, as
previously described (12). Levels of C3d–CRP and C4d–CRP
above the detectable level in healthy controls (i.e., 4 pmoles/
liter) were considered to be increased.
Statistical methods. Comparisons between patients
with active RA and patients with inactive RA were made using
the Mann-Whitney U test or the chi-square test. Correlations
between the CRP–complement complexes and parameters of
disease activity in active and inactive RA patients were analyzed using Spearman’s rank correlation coefficients. Twosided P values less than 0.05 were considered statistically
significant.
RESULTS
Demographic and clinical characteristics. The
characteristics of the 2 patient groups (active and inactive RA) are presented in Table 1. The disease duration
and the presence of radiologic erosions were significantly lower in the patients with active RA when compared with those with inactive RA. Furthermore, parameters of disease activity and the frequency of treatment
with disease-modifying antirheumatic drugs were, as
expected, significantly higher in the patients with active
RA when compared with those with inactive RA.
Plasma levels of activated complement, CRP, and
CRP–complement complexes. Increased C3b/c levels
were found in 99% of the 107 active RA patients and in
98% of the 177 inactive RA patients. The median level
of C3b/c in active RA patients was significantly higher
compared with that in inactive RA patients (Table 2).
Increased C4b/c levels were found in 98% of the active
RA patients and in 98% of the inactive RA patients. The
COMPLEMENT ACTIVATION BY CRP
999
Table 1. Demographic and clinical characteristics of patients with
active and inactive rheumatoid arthritis (RA)*
Age, years
Female, no. (%)
Disease duration, years
RF positive, no. (%)
Erosions on radiographs,
no. (%)
Currently taking DMARDs,
no. (%)
28–swollen joint count
28–tender joint count
ESR, mm/hour
DAS28
CRP, mg/liter
Active RA
(n ⫽ 107)
Inactive RA
(n ⫽ 177)
59 (18–91)
83 (78)
1 (0–50)
70 (65)
61 (57)
59 (24–86)
114 (64)
7 (1–47)
121 (68)
135 (76)
0.98
0.02
⬍0.001
0.50
0.001
96 (90)
124 (70)
⬍0.001
7 (0–25)
4 (0–28)
29 (1–113)
4.7 (1.0–8.1)
12 (1–112)
0 (0–9)
0 (0–6)
10 (1–40)
1.9 (0.1–3.5)
3 (0.07–47)
⬍0.001
⬍0.001
⬍0.001
⬍0.001
⬍0.001
P
* Except where otherwise indicated, values are the median (range).
RF ⫽ rheumatoid factor; DMARDs ⫽ disease-modifying antirheumatic drugs; ESR ⫽ erythrocyte sedimentation rate; DAS28 ⫽ modified Disease Activity Score (19); CRP ⫽ C-reactive protein.
median level of C4b/c in active RA patients was not
significantly different from that in the inactive RA
patients (Table 2).
The proportion of patients with an increased
CRP level was significantly higher among those with
active RA (72%) compared with those with inactive RA
(33%). Also, the median level of CRP was significantly
higher in patients with active RA when compared
with that in patients with inactive RA (Table 1 and
Figure 1A).
The proportion of patients with an increased
plasma level of C3d–CRP tended to be higher among
active RA patients (91%) when compared with that
among inactive RA patients (66%). Moreover, the median level of C3d–CRP was significantly elevated in
patients with active RA when compared with that in
patients with inactive RA (Table 2 and Figure 1B).
Increased plasma levels of C4d–CRP were found
in the same percentage of patients (93%) from both
Table 2. Plasma levels of activated C3 and C4 and C3d–CRP and
C4d–CRP complexes in patients with active and inactive RA*
C3b/c, nmoles/liter
C4b/c, nmoles/liter
C3d–CRP, pmoles/liter
C4d–CRP, pmoles/liter
C3d–CRP:C3b/c
C4d–CRP:C4b/c
Active RA
(n ⫽ 107)
Inactive RA
(n ⫽ 177)
P
135 (46–374)
32 (5.7–212)
89 (9–1,214)
290 (1–3,000)
0.16 (0.03–3.12)
1.5 (0.04–22.1)
112 (23–279)
27 (6.1–300)
18 (7–384)
46 (1–1,502)
0.6 (0.04–11.4)
8.5 (0.01–150)
0.002
0.93
⬍0.001
⬍0.001
⬍0.001
⬍0.001
* Except where otherwise indicated, values are the median (range).
See Table 1 for definitions.
Figure 1. Plasma levels of C-reactive protein (CRP) (A), C3d–CRP
(B), and C4d–CRP (C) in patients with inactive and active rheumatoid
arthritis (RA). Bold lines indicate the median value. Dotted lines
indicate the upper limit of normal.
patient groups. The median level of C4d–CRP was
significantly elevated in active RA patients when compared with that in inactive RA patients (Table 2 and
Figure 1C).
1000
MOLENAAR ET AL
Table 3. Correlation between activated C3 and C4, CRP, CRP–
complement complexes, and parameters of disease activity in patients
with active and inactive RA*
Active RA
DAS28
CRP
C3b/c
C4b/c
Inactive RA
DAS28
CRP
C3b/c
C4b/c
CRP
C3d–CRP
C4d–CRP
C3b/c
C4b/c
0.68†
–
0.13
0.12
0.62†
0.89†
0.18
0.18
0.56†
0.83†
0.26§
0.26‡
0.14
0.13
–
0.11
0.22‡
0.12
0.11
–
0.22§
–
0.05
0.09
0.28†
0.92†
0.14
0.10
0.25§
0.79†
⫺0.04
0.28§
0.26§
0.05
–
0.05
0.22§
0.09
0.05
–
* Values are the Spearman’s rank correlation coefficients. See Table 1
for definitions.
† P ⬍ 0.001.
‡ P ⬍ 0.05.
§ P ⬍ 0.01.
Because of the skewed distribution of activated
complement components, we also assessed differences
in the C3d–CRP and C4d–CRP levels in the total group
of patients (n ⫽ 284). Patients were classified in subgroups based on whether the plasma concentration of
C3b/c was below or above the median value in the total
group of patients. Levels of C3d–CRP were significantly
higher in the group of patients with a C3b/c concentration above the median when compared with the levels in
patients with a C3b/c concentration below the median
(P ⫽ 0.004). Conversely, levels of C4d–CRP were not
significantly different between patients with C3b/c concentrations above or below the median. When patients
were classified in subgroups based on the plasma concentration of C4b/c, the group of patients with a C4b/c
concentration below the median value was found to have
significantly lower levels of the C4d–CRP complex compared with the levels in patients with a C4b/c concentration above the median (P ⫽ 0.005). In contrast, levels of
C3d–CRP were not significantly different between patients with a C4b/c concentration above or below the
median.
Correlations of activated complement and CRP–
complement complexes with parameters of disease activity. In patients with active and inactive RA, significant
correlations were found between the levels of CRP–
complement complexes, levels of CRP, and the DAS28.
The strength of these correlations was less pronounced
in patients with inactive RA (Table 3). No significant
correlations were found between the levels of activated
complement components and the CRP levels. The levels
of both C3b/c and C4b/c correlated significantly with the
DAS28 (except in patients with active RA) and with the
levels of C4d–CRP, but not with the levels of C3d–CRP
(Table 3).
Because of the skewed distribution of activated
complement components, correlation coefficients were
also calculated in all patients (n ⫽ 284). Patients were
classified in 2 subgroups based on whether the plasma
concentration of the activated complement components
was above or below the median value. In the subgroup of
patients with levels of C3b/c above the median, the
C3b/c levels correlated significantly (P ⬍ 0.01) with the
levels of C3d–CRP (r ⫽ 0.30), C4d–CRP (r ⫽ 0.26), and
CRP (r ⫽ 0.28). In patients with levels of C3b/c below
the median, no such correlations were found. In patients
with levels of C4b/c above the median, a weak, but not
significant, correlation between the C4b/c and C4d–CRP
complex levels was found, whereas in patients with C4b/c
levels below the median, no correlations were found.
DISCUSSION
The main conclusion from this study is that the
plasma levels of activated complement and CRP–
complement complexes are increased in the majority of
patients with RA and that these levels are correlated
with parameters of disease activity. The observation of
increased levels of CRP–complement complexes in this
study points to the involvement of CRP in complement
activation and a possible role of CRP-mediated complement activation in the pathogenesis of RA.
The presence of increased levels of activated
complement components in RA patients has been reported before (6) and is confirmed by the results of the
present study. In general, these levels are much higher in
synovial fluid than in plasma (4), suggesting that spillover from the joints contributes to the increased plasma
levels. Such a spillover would explain the higher levels of
circulating C3b/c and C4b/c in the patients with active
disease, since these patients may have more intense
activation of complement in their joints. Complement is
a potent inflammatory system, and therefore activation
of this system is likely to contribute to local inflammatory reactions in the inflamed joints. Indeed, complement has been shown to enhance tissue damage in
animal models of arthritis (7,8).
Although circulating levels of activated complement components were higher in patients with active
disease, the overall correlation between complement
activation and disease activity was weak. Several explanations may account for this. First, circulating levels of
activation products may not adequately reflect local
activation in the joints. Second, the clearance rate of the
fragments measured may be too high to allow a precise
appreciation of the extent of complement activation in a
chronic disease. Although there are no data regarding
COMPLEMENT ACTIVATION BY CRP
the clearance of activated C3 or C4 in vivo, we have
observed that the half-life of clearance of these products
is within 1 hour, and presumably in the range of 10–30
minutes (22). Finally, although we took care that the
blood specimens were handled and stored appropriately,
some in vitro activation of samples may have blurred the
results to some extent.
Complement activation has been previously demonstrated in patients with RA, as has been reported
here. Circulating immune complexes have been held
responsible for the complement activation in RA patients. However, there is little evidence that immune
complexes from RA patients are indeed a main trigger
for this complement activation (10). CRP–complement
complexes are specific markers for CRP-mediated activation of the complement system, since these complexes
are only generated during CRP-induced activation of
complement (12). Thus, our data point to a contribution
of CRP to the activation of complement. The weak
correlations between the levels of C4b/c and C3b/c,
which reflect overall activation independent of the nature of the activator, and the levels of the CRP–
complement complexes suggest that this contribution
may be limited and that other activators, such as immune complexes, may be involved as well. This has been
shown previously by others and is based on observations
from experimental and human studies, particularly on
Felty’s syndrome and rheumatoid vasculitis (23,24). In
addition to the role of CRP, it is clear that rheumatoid
factor also plays an important role as a trigger for
complement activation through the formation of immune complexes (25,26)
It is now generally accepted that cytokines play a
dominant role in the pathogenesis of RA. These cytokines induce their detrimental effects by stimulating
various effector mechanisms, such as the release of
metalloproteinases and the infiltration of inflammatory
cells. Studies in patients with cancer receiving high doses
of interleukin-2 have shown that cytokines may induce
complement activation (27). Therefore, another effector
mechanism of cytokines in inflammatory conditions may
be activation of complement. We have found increasing
levels of complement–CRP complexes in patients receiving interleukin-2 (Wolbink GJ, Hack CE: unpublished
observations), thus pointing to CRP as the link between
complement activation and cytokines. Indeed, the synthesis of CRP by the liver during inflammatory conditions is stimulated by cytokines such as interleukin-6.
The results of the study reported here support the
concept that, in RA, CRP-mediated complement activation can be one of the effector mechanisms triggered by
cytokines.
1001
A model explaining the mechanism of CRPmediated complement activation has been described
previously (28). In this model, secretory phospholipase
A2 (sPLA2) hydrolyzes cell membrane phospholipids to
yield lysophospholipids and free fatty acids. In normal
cells, there is an asymmetric distribution of phospholipids in the 2 leaflets of the lipid bilayer of the cell
membrane. During apoptosis of the cell, phospholipids
of both the inner and outer leaflet exchange (flip-flop
phenomenon). The sPLA2 cannot hydrolyze the phospholipids in the cell membranes of normal cells, but it
does hydrolyze those of flip-flopped cells (28). The
presence of lysophospholipids together with that of the
negatively charged phosphatidylserine in the outer leaflet of the cell membrane causes some disruption of the
tight package of the phospholipids, making phosphorylcholine groups accessible for interaction with CRP.
Cell-bound CRP is, in turn, able to activate the complement system. This activation may enhance inflammation
and contribute to tissue damage. Notably, levels of
sPLA2 are elevated in plasma, and in particular in the
synovial fluid of RA patients (29,30). Increased levels of
sPLA2 were also found in our patients (31), which
supports previous observations and is consistent with the
hypothesis on the role of sPLA2 in CRP-mediated
complement activation. Currently, we are investigating
the validity of this concept by analyzing the binding of
CRP in cells and phospholipid microparticles obtained
from RA joints.
Circulating CRP–complement complexes have
been previously demonstrated in patients with infections
of varying severity and were significantly higher in
patients with shock and in patients with a fatal outcome
(13). Furthermore, depositions of CRP together with C3
and C4 activation fragments have been found in tissue
specimens from patients who died after a myocardial
infarction. These CRP and complement depositions
were localized only in infarcted tissue, but not in normalappearing areas of the myocardium (14), suggesting an
association between CRP, complement activation, and
tissue damage. Such an association was demonstrated by
Griselli et al, who showed that injection of human CRP
in rats enhanced infarct size by 40% after ligation of the
coronary artery, the effect of which was dependent on
complement (32). One could thus speculate that, in RA,
CRP may have a similar detrimental effect. Whether this
explains the relationship between CRP levels and progressive radiologic evidence of joint damage (15,33)
remains to be established.
In conclusion, the results of this study demonstrate that CRP can activate complement in RA. There-
1002
MOLENAAR ET AL
fore, this acute-phase protein should be considered an
inflammatory mediator in this disease.
REFERENCES
1. Fox DA. Cytokine blockade as a new strategy to treat rheumatoid
arthritis: inhibition of tumor necrosis factor. Arch Intern Med
2000;160:437–44.
2. Brodeur JP, Ruddy S, Schwartz LB, Moxley G. Synovial fluid
levels of complement SC5b–9 and fragment Bb are elevated in
patients with rheumatoid arthritis. Arthritis Rheum 1991;34:
1531–7.
3. Abbink JJ, Kamp AM, Nuijens JH, Eerenberg AJM, Swaak AJG,
Hack CE. Relative contribution of contact and complement
activation to inflammatory reactions in arthritic joints. Ann
Rheum Dis 1992;51:1122–8.
4. Swaak AJG, van Rooijen A, Planten O, Han H, Hattink O, Hack
E. An analysis of the levels of complement components in the
synovial fluid in rheumatic diseases. Clin Rheumatol 1987;22:350–7.
5. Shingu M, Watanabe Y, Tomooka K, Yoshioka K, Ohtsuka E,
Nobunaga M. Complement degradation products in rheumatoid
arthritis. Br J Rheumatol 1994;33:299–300.
6. Makinde VA, Senaldi G, Jaward AS, Berry H, Vergani D.
Reflection of disease activity in rheumatoid arthritis by indices of
activation of the classical complement pathway. Ann Rheum Dis
1989;48:302–6.
7. Goodfellow RM, Williams AS, Levin JL, Williams BD, Morgan
BP. Local therapy with soluble complement receptor 1 (sCR1)
suppresses inflammation in mono-articular arthritis. Clin Exp
Immunol 1997;110:45–52.
8. Wang Y, Rollins SA, Madri JA, Matis LA. Anti-C5 monoclonal
antibody therapy prevents collagen-induced arthritis and ameliorates established disease. Proc Natl Acad Sci U S A 1995;92:
8955–9.
9. Sato Y, Sato R, Watanabe H, Kogure A, Watanabe K, Nishimaki
T, et al. Complement activating properties of monoreactive and
polyreactive IgM rheumatoid factors. Ann Rheum Dis 1993;52:
795–800.
10. Hack CE, Eerenberg-Belmer AJM, Lim UG, Haverman J, Aalberse RC. Lack of activation of C1, despite circulating immune
complexes detected by two C1q methods, in patients with rheumatoid arthritis. Arthritis Rheum 1984;27:40–8.
11. Volonakis JE. Complement activation by C-reactive protein complexes. Ann N Y Acad Sci 1982;389:235–49.
12. Wolbink GJ, Brouwer MC, Buysman S, ten Berge IJM, Hack CE.
CRP-mediated activation of complement in vivo: assessment by
measuring circulating complement-C-reactive protein complexes.
J Immunol 1996;157:473–9.
13. Wolbink GJ, Bossink AWJ, Groeneveld ABJ, de Groot MCM,
Thijs LG, Hack CE. Complement activation in patients with sepsis
is in part mediated by C-reactive protein. J Infect Dis 1998;177:
81–7.
14. Lagrand WK, Niessen HWM, Wolbink GJ, Jaspers LH, Visser
CA, Verheugt FWA, et al. C-reactive protein co-localizes with
complement in human hearts during acute myocardial infarction.
Circulation 1997;95:97–103.
15. Van Leeuwen MA, van Rijswijk MH, van der Heijde DMFM, te
Meerman GT, van Riel PLCM, Houtman PM, et al. The acute
phase response in relation to radiographic progression in early
rheumatoid arthritis: a prospective study during the first three
years of the disease. Br J Rheumatol 1993;23:9–13.
16. Kushner I, Kaplan MH. Studies of acute phase protein. I. An
immunohistochemical method for the localization of C-reactive
protein in rabbits: association with necrosis in local inflammatory
lesions. J Exp Med 1961;114:961–74.
17. Pinals RS, Masi AT, Larsen RA, and The Subcommittee for
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
Criteria of Remission in Rheumatoid Arthritis of the American
Rheumatism Association Diagnostic and Therapeutic Criteria
Committee. Preliminary criteria for clinical remission in rheumatoid arthritis. Arthritis Rheum 1981;24:1308–15.
Ten Wolde S, Breedveld FC, Hermans J, Vandenbroucke JP, van
der Laar MAFJ, Markusse HM, et al. Randomised placebo
controlled study of stopping secondline drugs in rheumatoid
arthritis. Lancet 1996;347:347–52.
Prevoo MLL, van ’t Hof MA, Kuper HH, van Leeuwen MA, van
de Putte LBA, van Riel PLCM. Modified disease activity scores
that include twenty-eight–joint counts: development and validation in a prospective longitudinal study of patients with rheumatoid arthritis. Arthritis Rheum 1995;38:44–8.
Arnett FC, Edworthy SM, Bloch DA, McShane DJ, Fries JF,
Cooper NS, et al. The American Rheumatism Association 1987
revised criteria for the classification of rheumatoid arthritis.
Arthritis Rheum 1988;31:315–24.
Wolbink GJ, Bollen J, Baars JW, ten Berge RJM, Swaak AJG,
Paardekooper J, et al. Application of a monoclonal antibody
against a neoepitope on activated C4 in an ELISA for the
quantification of complement activation via the classical pathway.
J Immunol Methods 1993;163:67–76.
Buysmann S, Hack CE, van Diepen FN, Surachno J, ten Berge
IJM. Administration of OKT3 as a two-hour infusion attenuates
for dose side effects. Transplantation 1997;64:1620–3.
Breedveld FC, Lafeber GJ, de Vries E, van Krieken JH, Cats A.
Immune complexes and the pathogenesis of neutropenia in Felty’s
syndrome. Ann Rheum Dis 1986;45:696–702.
Westedt ML, Daha MR, de Vries E, Valentijn RM, Cats A. IgA
containing immune complexes in rheumatoid arthritis and in
active rheumatoid disease. J Rheumatol 1985;12:449–55.
Pope RM, Yoshinoya S, McDuffy S. Detection of immune complexes and their relationship to rheumatoid factor in a variety of
autoimmune disorders. Clin Exp Immunol 1981;46:256–67.
Elson CJ, Scott DGI, Blake DR, Bacon PA, Holt PDJ. Complement-activating rheumatoid factor containing complexes in patients with rheumatoid vasculitis. Ann Rheum Dis 1983;42:147–50.
Thijs LG, Hack CE, Strack van Schijndel RJM, Nuijens JH,
Wolbink GJ, Eerenberg-Belmer AJM, et al. Complement activation and high dose of interleukin-2 [letter]. Lancet 1989;2:395.
Hack CE, Wolbink GJ, Schalkwijk C, Seijer H, Hermens WT, van
de Bosch H. A role for secretory phospholipase A2 and C-reactive
protein in the removal of injured cells. Immunol Today 1997;187:
111–5.
Koo Sin Lin M, Farewell V, Vadas P, Bookman AAM, Keystone
EC, Pruzanski W. Secretory phospholipase A2 as an index of
disease activity in rheumatoid arthritis: prospective double blind
study of 212 patients. J Rheumatol 1996;23:1162–6.
Loeser RF, Smith DM, Turner RA. Phospholipase activity in
synovial fluid from patients with rheumatoid arthritis, osteoarthritis and crystal-associated arthritis. Clin Exp Rheumatol 1990;8:
379–86.
Molenaar ETH, Voskuyl AE, Hack CE, Dijkmans BAC. Levels of
secretory phospholipase A2 are elevated in patients with active
rheumatoid arthritis when compared to patients with inactive
rheumatoid arthritis [abstract]. Ann Rheum Dis 2000;59 Suppl
1:105.
Griselli M, Herbert J, Hutchinson WL, Taylor KM, Sohail M,
Krausz T, et al. C-reactive protein and complement are important
mediators of tissue damage in acute myocardial infarction. J Exp
Med 1999;190:1733–9.
Van Leeuwen MA, van Rijswijk MH, Sluiter WJ, van Riel PLCM,
Kuper IH, van de Putte LBA, et al. Individual relationship
between progression of radiological damage and the acute phase
response in early rheumatoid arthritis: towards development of a
decision support system. J Rheumatol 1997;24:20–7.