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Regular Article |
RI and Fc
RIII and Inhibitory Fc
RII in Inflammation and Cartilage Destruction during Experimental Antigen-Induced Arthritis

From the Department of Rheumatology,*
University Medical
Centre, Nijmegen; and the Department of Human and Clinical
Genetics,
University Medical Centre, Leiden,
The Netherlands
| Abstract |
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RI, -II, -III). In a
previous study we found that if a chronic T-cell-mediated
antigen-induced arthritis (AIA) was elicited in knee joints of FcR
-chain-deficient mice that lack functional Fc
RI and
Fc
RIII, joint inflammation was comparable but severe
cartilage destruction was absent. We now examined the individual role
of the stimulatory Fc
RI and Fc
RIII and inhibitory Fc
RII in
inflammation and functional cartilage damage in knee joints with AIA
using Fc
RI-, Fc
RII-, and Fc
RIII-deficient
mice. Three weeks after immunization with the antigen-methylated bovine
serum albumin (BSA), cellular (T-cell responses as
measured by lymphocyte proliferation) immunity raised against mBSA was
comparable in all groups examined. Humoral (total IgG,
IgG1, IgG2a, and IgG2b levels) immunity against mBSA
was comparable in Fc
RI-/- and Fc
RIII-/- but higher in
Fc
RII-/- if compared to controls. Joint swelling as measured by
99mTc uptake at days 1, 3, and 7 was
similar in Fc
RI-/- and Fc
RIII-/- mice and significantly
higher in Fc
RII-/-. Chronic inflammation and cartilage damage
(depletion of proteoglycans, metalloproteinase (MMP)-induced
neoepitopes, and matrix erosion) was studied histologically in
total knee joint sections stained with hematoxylin or safranin-O.
Histologically, at day 7 after AIA induction, exudate
and infiltrate in the knee joint was similar in Fc
RI-/- and
Fc
RIII-/- and significantly higher (230% and 340%) in
Fc
RII-/- mice if compared to controls. Aggrecan breakdown in
cartilage caused by MMPs and, which is related to severe
irreversible cartilage erosion, was further studied by
immunolocalization of MMP-mediated neoepitopes (VDIPEN) and image
analysis. MMP-induced neoepitopes determined in various cartilage
layers (tibia and femur) were primarily inhibited in Fc
RI-/- (79
to 87% and 87 to 88%, respectively) and comparable in
Fc
RIII-/-. VDIPEN neoepitopes were much higher (82 to 122% and
200 to 250%, respectively) in Fc
RII-/- mice. Initial
depletion of proteoglycans was similar (60 to 100%) in all groups. In
the chronic phase, cartilage matrix erosion in the lateral and
medial tibia was significantly elevated in Fc
RII-/- (222% and
186%, respectively) but not in Fc
RI-/- or Fc
RIII-/-
mice. These results suggest that during T-cell-mediated AIA,
Fc
RI and Fc
RIII act in concert in acute and chronic inflammation
whereas Fc
RI is the dominant FcR involved in severe cartilage
destruction. Fc
RII is a crucial inhibiting factor in acute and
chronic inflammation and cartilage erosion.
| Introduction |
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Immune complexes containing IgG, the dominant immunoglobulin in the
circulation, communicate with synovial cells via cellular receptors for
IgG that belong to the IgG superfamily.5-7
Murine
phagocytic effector cells express three different classes of IgG
receptors (Fc
RI, -II, -III).8,9
Fc
RI and Fc
RIII
are hetero-oligomeric complexes in which ligand-binding
chains are
associated with the signal-transducing
-chain. This
-chain is
required for their assembly and triggering of various effector
functions including phagocytosis,10
antigen-presenting
function,11
antibody-dependent
cytotoxicity,12
and the release of inflammatory
mediators.13
These effector functions are regulated by an
immunoreceptor tyrosine-based activation motif within the
-chain.14
The third receptor class for IgG, Fc
RII is a single
-chain
receptor and contains an immunoreceptor tyrosine-based inhibitory
motif-containing cytoplasmic domain that by co-ligation of the
immunoreceptor tyrosine-based activation motif receptor, inhibits
cellular activation signals through the recruitment of the inositol
phosphatase SHIP.15
Fc
RII has been shown to be a
negative regulator of Fc
RIII in IgG IC-triggered
inflammation.16
Recently we found that activating Fc
R (Fc
RI and Fc
RIII) were
crucial in severe cartilage destruction during antigen-induced
arthritis (AIA).17
Irreversible cartilage destruction
within this model occurs through enzymatic cleavage by
metalloproteinases (MMPs) of cartilage constituents. These Zn-dependent
endopeptidases are capable of cleaving aggrecan and collagen type II,
the main components of cartilage, which leads to severe cartilage
erosion.18-20
Various MMPs (MMP-1, -2, -3, -7, -8, -9,
-13) have been found to cleave aggrecan between amino residues
Asn341-Phe342 resulting in the neoepitope FVDIPEN that remains in the
cartilage.21
AIA elicited in knee joints of FcR
-chain -/- lacking functional
Fc
RI and Fc
III showed similar synovial inflammation if compared
to controls at day 7 after arthritis induction. Nevertheless, severe
cartilage destruction as MMP-mediated matrix destruction and erosion
was fully absent in arthritic FcR
-chain -/- knee joints. These
results suggest that Fc
RI and/or Fc
RIII are of crucial importance
in severe cartilage destruction within this model. Fc
RIII has been
suggested as the most likely candidate in IC-mediated joint
inflammation.22
We now investigated the involvement of
activating Fc
RI and Fc
RIII and the inhibitory Fc
RII in severe
cartilage destruction seen during AIA. Expression of MMP-induced
aggrecan neoepitopes and erosion of the cartilage matrix was
investigated in the knee joints of arthritic mice by histology and
immunolocalization. Our findings indicate that Fc
RI and not
Fc
RIII is the dominant activatory Fc receptor involved in severe
cartilage destruction in a model in which T cells play a dominant role.
In contrast, Fc
RII is involved in inhibition of severe cartilage
destruction within this model and may be a new therapeutic target to
combat severe cartilage destruction.
| Materials and Methods |
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Fc
RIII-/- mice were made deficient for the
ligand-binding
-chain of Fc
RIII (Dr. Verbeek) and were
backcrossed to the C57BL/6 background for 12
generations.23
Fc
RI-/- were made deficient for the
ligand-binding
-chain of Fc
RI (Dr. Verbeek) and were backcrossed
to BALB/c for six generations.24
Fc
RII-/- were
developed by Dr. Takai (Sendai, Japan)25
in the 129
SV (H-2b) and C57BL6 (H-2b) background. Control C57BL/6 and
129SV/C57BL/6 hybrids were derived from Jackson Laboratories (Bar
Harbor, ME) and bred in our own facilities. Homozygous mutants and
their wild-type controls, 10 to 12 weeks old, were used in the
experiments.
Antibody Determination in Serum
Methylated BSA-specific antibodies of various isotypes (total IgG,
IgG1, IgG2a, IgG2b, IgG3) were measured in sera of individual mice with
an enzyme-linked immunosorbent assay (ELISA). Antigen was coated on
microtiter plates (Greiner, Alphen a/d Rijn, The Netherlands) at a
concentration of 100 µg/ml. Antibody titers were assessed by twofold
serial dilution of the sera followed by detection of bound mouse Ig
with 1:500 diluted peroxidase-conjugated rabbit anti-mouse Ig (Miles
Laboratories Inc., Elkhart, IN, USA). O-Phenylenediamine (1 mg/ml;
Sigma, Zwijndrecht, The Netherlands) was used as substrate for
peroxidase, and the antibody titer was determined by using 50% of the
maximal extinction as an end point. Sera of Fc
RI-/-,
Fc
RII-/-, and Fc
RIII-/- mice were compared to sera of their
wild-type controls. In each group at least 10 mice were tested.
T-Cell Proliferation
Mouse spleen cells were isolated and washed in RPMI supplemented with 10% fetal calf serum, glutamine (2 mmol/L), and pyruvate (1 mmol/L). Erythrocytes were lysed by treatment of the cells with a 0.16 mol/L NH4CL solution in 0.17 mol/L Tris, pH 7.2, for 5 minutes. After two washes in RPMI, the cells were plated on plastic T flasks (75 mm2) from Falcon Plastics, Oxnard, CA. After 60 minutes of incubation at 37°C, the nonadherent cells were harvested by aspiration and two 4- to 5-ml RPMI washes of the adherent cells. One hundred µl of RPMI containing 1 x 105 T-cell-enriched spleen cells were placed in each well of a sterile, U-bottomed polystyrene microculture plate (Costar, Cambridge, MA). Antigens or mitogens were added in another 100 µl to give a total volume of 200 µl, and final concentrations of antigen of 25, 12.5, and 6.25 µg/ml. Cultures were maintained at 37°C in a humidified atmosphere of 2% CO2 and 98% air for 4 days. Sixteen hours before harvesting, 1 µCi of [3H]-thymidine (6.7 Ci/mmol; New England Nuclear, Boston, MA) was added in 25 µl of RPMI. Cultures were harvested with a cell harvester (Tomtec) and [3H]-thymidine incorporation was determined.
Induction of Experimental Arthritis
Mice were immunized with 100 µg of methylated BSA (mBSA, Sigma)
emulsified in 100 µl of Freunds complete adjuvant. Injections were
divided over both flanks and footpath of the forelegs. Heat-killed
Bordetella pertussis (RIVM, Bilthoven, The Netherlands) was
administered intraperitoneally as an additional adjuvant. Two
subcutaneous booster injections with 50 µg of mBSA/CFA were given in
the neck region 1 week after the initial
immunization.26
Two weeks after these injections,
arthritis was induced by intra-articular injection of either 15 µg
(Fc
RII-/-) or 60 µg (Fc
RII-/-, Fc
RI-/-, and
Fc
RIII-/-) of mBSA in 6 µl of saline into the right knee joint,
resulting in chronic arthritis. The approval to induce arthritis in
mice was given by the local ethical committee.
99mTc Uptake Measurements
Joint inflammation was measured by 99mTc
pertechnetate uptake in the knee joint. This method has earlier been
shown to correlate well with histological findings.27
Briefly, mice were injected intraperitoneally with 12 µCi of
99mTc and subsequently sedated with
chloralhydrate. Thirty minutes thereafter,
-radiation was assessed
by use of a collimated Na-I-scintillation crystal and the knee in a
fixed position. Arthritis was scored as the ratio of the
99mTc uptake in the right (R) and the left (L)
knee joint. R:L ratios >1.1 were taken to indicate inflammation of the
right knee joint.
Histology
Total knee joints were dissected, fixed in phosphate-buffered formalin (pH 7.4), decalcified in 5% buffered formic acid, and subsequently embedded in paraffin wax. Semiserial frontal whole knee joint sections (7 µm) were stained with hematoxylin and eosin (H&E) or Safranin-O and Fastgreen. Histological parameters (joint inflammation, proteoglycan depletion, and erosion) were scored by two independent observers in a blinded manner.
Determination of Proteoglycan Depletion
Total knee joint sections were stained with Safranin-O and Fastgreen. Loss of red staining from various cartilage layers (femur and tibia), which is related to loss of proteoglycans, was determined using an arbitrary scale from 0 to 3. Normal cartilage and cartilage fully depleted of proteoglycans was taken as a 0 and 3 value, respectively.
Immunolocalization of MMP-Induced Neoepitope
For immunohistochemical analysis, sections were deparaffinized, rehydrated, and digested with chondroitinase ABC (0.25 U/ml, 0.1 mol/L Tris-HCL, pH 8.0; Sigma) for 1 hour at 37°C, to remove chondroitin sulfate from the proteoglycans. Sections were then treated with 1% H2O2 in methanol for 20 minutes and subsequently 5 minutes with 0.1% (v/v) Triton X-100 in phosphate-buffered saline (PBS). After incubation with 1.5% (v/v) normal goat serum for 20 minutes, sections were incubated with affinity-purified anti-VDIPEN IgG overnight at 4°C. These antibodies were kindly given by Irwin Singer and Ellen Bayne (Merck Research Laboratories, Rahway, NJ) and have been extensively characterized before.28,29 In addition, sections were incubated with biotinylated goat anti-rabbit IgG and binding detected using avidin-peroxidase staining (Elite kit; Vector Laboratories, Inc., Burlingame, CA). Development of the peroxidase product was done using nickel enhancement and counterstaining was done with orange G (2%) for 5 minutes.
Immunolocalization of Aggrecanase-Induced Epitopes
Undecalcified cryosections were digested with proteinase-free chondroitinase ABC (0.25 U/ml Tris-HCl, pH 8.0) for 1 hour at 37°C to remove chondroitin sulfate from the PG. Subsequently, sections were fixed with periodate-lysine-paraformaldehyde fixative for 20 minutes. Sections were then treated with 1% H2O2 for 20 minutes followed by 5 minutes with 0.1% Triton X-100 in PBS. After incubation with 1.5% normal goat serum for 20 minutes, sections were incubated for 18 hours with the primary antibody recognizing the sequence NITEGE.30 Then sections were incubated with biotinylated goat anti-rabbit IgG and were detected using avidin-peroxidase staining. Development of the peroxidase product was done using nickel enhancement. Counterstaining was done with orange G.
Immunolocalization of IgG
Paraffin-embedded total knee joint sections were pretreated with chondroitinase ABC and additionally stained with goat anti-mouse IgG peroxidase overnight. Development of the peroxidase product was done using diaminobenzidine (0.5 mg/ml). Sections were counterstained with H&E.
Measurement and Characterization of Cartilage Erosion
Erosion and chondrocyte death was determined in total knee joint sections stained with H&E. Erosion was detected as ruffling of the cartilage surface and was only mild at day 7 after AIA induction. Ruffling of the cartilage surface was determined using an arbitrary scale of 0 to 3. Normal cartilage surface and maximal ruffling within this experiment was taken as a 0 and 3 value, respectively.
| Results |
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RIII and Inhibitory Fc
RII in Acute
and Chronic Joint Inflammation during AIA
As the absence of a particular Fc
R may alter the immunological
response against methylated BSA during immunization, thereby impairing
the onset and course of arthritis, we first tested cellular and humoral
immunity to mBSA, 3 weeks after immunization. Cellular immunity as
measured by spleen lymphocyte proliferation against mBSA showed no
significant differences between knockouts and their controls (Figure 1
; B, D, and F). In addition, humoral
immunity was measured by ELISA. Total IgG, IgG1, IgG2a, IgG2b, and IgG3
anti-mBSA levels were high but not significantly different in immunized
Fc
RI-/- and Fc
RIII-/- if compared to their controls (Figure 1, A and C)
. In sera of Fc
RII-/- immunized mice however, total
IgG, IgG2a, and IgG3 anti-mBSA were fourfold higher and IgG1 was
even eightfold higher. IgG2b anti-mBSA was not significantly different
(Figure 1E)
.
|
R in joint inflammation,
AIA was elicited by injection of 60 µg of mBSA directly into the knee
joints of immunized Fc
RI-, Fc
RIII-, and Fc
RII-deficient mice
and their wild-type controls. Because Fc
RIII-/- has been described
as a main regulator of IC diseases, we expected a down-regulation of
swelling in Fc
RIII-/- mice but knee swelling was not significantly
different from controls at all time points measured (Figure 2B)
|
RI-/- was also
comparable (Figure 2A)
RI and Fc
III are
redundant with respect to joint inflammation. Subsequently we
investigated the role of Fc
RII in joint inflammation. Because
Fc
RII-/- mice have been shown to be highly vulnerable to ICs,
injection of 60 µg of mBSA into the knee joint may be too high and
for that reason we also injected a lower (15 µg) mBSA dose. Injection
of 15 µg of mBSA into knee joints of Fc
RII-/- mice resulted in a
significantly higher knee joint swelling if compared to controls (2.4
versus 1.7) at day 1 but no difference was found anymore at
day 4 or day 7 after AIA induction (Figure 2C)
In addition, cellular infiltration and exudate in the knee joint was
studied by histology. At day 7 after induction of AIA, total knee joint
sections were made and stained with H&E. In Fc
RI-/- and
Fc
RIII-/- arthritic knees, similar exudate and infiltrate was
measured in all animals studied (Figure 3, A and B)
. In arthritic knees of
Fc
RII-deficient mice, both exudate and infiltrate were found to be
significantly elevated (180% and 242% in the 60-µg group,
respectively) (Figure 3D)
. This reached significance only in mice
injected with the high dose of mBSA (Figure 3
; D, E, and F).
|
RI-/- and Fc
RIII-/-
and higher in Fc
RII-/- mice, we further investigated whether the
absence of a particular Fc receptor might influence the type of
inflammatory cell present in the joint. The polymorphonuclear
leukocyte/macrophage ratio was determined by immunolocalization using
NIMP-R14 that stains polymorphonuclear leukocyte specifically. In
arthritic knee joints of Fc
RI-/-, Fc
RIII-/-, and
Fc
RII-/- mice and their controls, no differences were found in the
polymorphonuclear leukocyte/macrophage ratio that was 40:60 in the
exudate and 25:75 in the infiltrate (data not shown).
As Fc receptors have been shown to be involved in removal
of ICs from various body compartments, the presence of IgG ICs
localized in the arthritic joints at day 7 AIA was determined using
rabbit anti-murine IgG antibodies. No significant differences in IC
deposition was found in the knee joints of Fc
RI-/-,
Fc
RIII-/-, and Fc
RII-/- mice and their controls (data not
shown).
Activatory Fc
RI and Fc
RIII and Inhibitory Fc
RII Are Not
Involved or Redundant in Loss of Proteoglycans from Cartilage Layers in
Knee Joints with AIA
Subsequently, we studied the role of Fc
RI, Fc
RIII, and
Fc
RII in cartilage damage. The earliest cartilage damage seen during
experimental arthritis is loss of proteoglycans from the cartilage
matrix that is evident between 24 and 48 hours after AIA induction.
Proteoglycan breakdown was measured by determining the loss of red
staining in safranin O-stained knee joint sections using an arbitrary
scale from 0 to 3. At day 7 after induction of AIA, loss of red
staining in the cartilage layers of femur and tibia in control mice
injected with 60 µg of mBSA reached almost maximal values (Figure 4
; A, B, and D). In arthritic knee joints
of Fc
RI-/- (Figure 4A)
, Fc
RIII-/- (Figure 4B)
, and
Fc
RII-/- (Figure 4D)
mice, proteoglycan depletion was not
significantly different from their arthritic control groups. Injection
of the 15-µg mBSA dose showed lower PG depletion (Figure 4C)
.
Although proteoglycan depletion was slightly higher in the
Fc
RII-/- mice, this difference did not reach significance.
|
RI Activates Whereas Fc
RII Inhibits the Induction
of MMP Cleavage Site Neoepitope VDIPEN during AIA. No Effect of
Fc
RIII on VDIPEN ExpressionWithin AIA, MMPs have been shown to be involved in degradation of aggrecan31,32 and collagen33 leading to irreversible cartilage destruction. MMPs degrade aggrecan leaving the C terminal ending with the amino acid sequence VDIPEN that can be detected by specific antibodies around day 5 after induction of AIA.32 For this reason, AIA day 7 was taken to detect VDIPEN expression in the cartilage matrix.
The amount of VDIPEN was measured by determining the area of cartilage
expressing VDIPEN using automated image analysis. In all investigated
knee joints of wild-type mice injected with 60 µg of mBSA, prominent
VDIPEN staining was found in the cartilage layers of tibia and femur
(Figure 5
; A to D). Strikingly, in
arthritic knees of Fc
RI-/-, VDIPEN expression was significantly
lower in medial and lateral femur (88% and 87%, respectively) and in
medial and lateral tibia (79% and 87%, respectively) (Figure 5A
and
micrographs in Figure 5, E and F
). In arthritic knees of
Fc
RIII-/-, VDIPEN expression was comparable to controls (Figure 5B)
. In contrast, in Fc
RII-/- arthritic joints, VDIPEN was
significantly higher in lateral and medial femur and lateral tibia
(250%, 200%, and 122% higher, respectively), indicating that
Fc
RII is involved in MMP-mediated cartilage destruction (Figure 5, C and D
and micrographs in Figure 5, G and H
). VDIPEN expression was much
lower (between 56 to 76%) when 15 µg of mBSA was injected if
compared to the 60-µg group but still significantly higher in lateral
and medial tibia of Fc
RII-/- if compared to their wild-type
controls (Figure 5C)
.
|
RII Is Involved in Inhibition of Erosion of the
Cartilage Matrix
To examine the role of Fc
RI, Fc
RIII, and Fc
RII in severe
irreversible cartilage destruction, we also analyzed erosion of the
cartilage matrix in paraffin sections. Erosion of the cartilage matrix
that is only mild at day 7 after AIA was determined as ruffling of the
cartilage surface. No significant differences in matrix erosion were
found in knees of Fc
RI-/- and Fc
RIII-/- mice if compared to
their wild-type controls (Figure 6, A and B)
. In contrast, in knee joints of Fc
RII-/- mice, erosion was
enhanced in the 60-µg mBSA group and this difference reached
significance in the lateral and medial tibia (222% and 186% higher,
respectively) (Figure 6D
and micrographs in Figure 6, E and F
). In the
15-µg mBSA group, although erosion was somewhat higher, differences
did not reach significance (Figure 6C)
.
|
| Discussion |
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RI
and Fc
RIII is related to acute and sustained inflammation and is
also a major determinant of severe destruction of cartilage in AIA. In
the present study we show that both Fc
RI and Fc
RIII are important
in synovial inflammation whereas Fc
RI is the dominant activatory
receptor involved in severe cartilage destruction within this model. In
contrast, Fc
RII is crucial in negative regulation of both acute and
chronic inflammation and late severe cartilage destruction.
Because the absence of a particular Fc
R may impair the T- and
B-cell-mediated immunological response against the arthritogen mBSA,
cellular and humoral immunity against mBSA was determined. T-cell
responses against mBSA were however not different in immunized
FC
RI-/-, Fc
RIII-/- and Fc
RII-/- mice and
their controls and is in line with earlier studies showing that loss of
functional Fc
RI and Fc
RIII did not perturb T-cell
maturation.34
Fc
RIII is also expressed on mast cells,
and Fc
RIII-deficient mice lack IgG-mediated mast cell
degranulation.35
However, earlier studies by our
laboratory showed that the course of AIA elicited in knee joints of
mast cell-deficient (WBB6F1-W/Wv) mice was not
significantly different from control littermates, suggesting that mast
cells do not play an important role in joint inflammation within this
model.36
Measuring humoral immunity, isotype-specific antibody responses against
mBSA were not different in Fc
RI-/- and Fc
RIII-/-, which is in
line with earlier studies.37
In immunized Fc
RII-/-
however, all anti-mBSA isotype antibody titers (with the exception of
IgG2b) were fourfold to eightfold elevated if compared to controls. In
the present study, we investigated Fc
RII-/- on a hybrid
SV129/C57BL6 background because this background does not display
abnormalities in the immunological status. Fc
RII-/- on other
backgrounds (eg, C57BL/6) develop autoantibodies of multiple IgG
subclasses38
that might enhance the arthritis induced by
mBSA immunization. Differences in autoimmune development however
suggest that Fc
RII in combination with genetic loci may be important
in breaking the tolerance not only against an autoantigen such as
collagen type IV39
but also against an exogenous antigen
such as mBSA. Fc
RII may function to maintain tolerance in the
periphery and together with genetic loci, gate B-cell activation
against various antigens.
As the adaptive immunity in Fc
RI-/- and Fc
RIII-/- is not
altered, local expression of both activating Fc
R in the joint may
drive synovial inflammation and cartilage destruction. Immune complex
mediated activation is predominantly regulated by synovial macrophages
that have been shown to drive onset,40,41
elongation,42
and flare-up43
during AIA. In a
previous study we found that mice that express nonfunctional Fc
RI
and Fc
RIII and developing comparable adaptive immunity with controls
showed a significantly lower knee joint swelling. In this study, both
Fc
RI-/- and Fc
RIII-/- mice showed however comparable swelling
with controls. These results suggest that Fc
RI and Fc
RIII present
on macrophages act in concert with respect to swelling. In the absence
of one receptor its function may be fully compensated by the other FcR.
These receptors that are expressed on mononuclear cells44
are involved in the respiratory burst on cross-linking by IgG ICs. As a
result these cells release vasoactive products such as oxygen and
nitrogen radicals and histamine that are highly involved in vascular
leakage leading to enhanced 99 mTc uptake in the
joint.
In humans, Fc
RIIIA has been suggested to play a role in the
pathogenesis of RA and a close correlation was found between Fc
RIIIA
expression and the location of both synovitis and extracellular
features.45
A recent study suggests a dominant role for
Fc
RIIIA in the induction of both tumor necrosis factor-
and
interleukin-1
production by human macrophages in RA after receptor
ligation by small ICs.46
Furthermore many animal studies
have shown that Fc
RIII is crucial in IC-dependent diseases raised in
skin,47
kidney,48
or lung.49
A
reverse passive arthus reaction is inhibited within Fc
RIII-/-
mice.23
Recently, we also found that arthritis elicited by
ICs only is also very strongly Fc
RIII-dependent (Nabbe K, Van Lent
P, Blom AB, Holthuysen A, Verbeek S, Vandenberg W, manuscript
in preparation). The reason why Fc
RIII does not play an
important role within AIA may be that apart from ICs T cells also play
an important role in chronicity within this model. During AIA,
mBSA-specific Th1 cells accumulate in the arthritic joint thereby
releasing interferon-
. Interferon-
is one of the most potent
cytokines involved in up-regulation of Fc
RI on
macrophages.50
Local interferon-
production may cause a
shift in Fc
R expression from Fc
RIII to Fc
RI and may explain
the redundancy found within this study.
The inhibiting Fc
RII seems to be of utmost importance in
both the acute and chronic phase of synovial inflammation and absence
leads to significantly higher inflammation. Fc
RII is expressed on
various hematopoietic cells and is a negative regulator of Fc
RIII
receptor on B cells and macrophages51
and probably also of
Fc
RI.52
Fc
RII may act as a negative regulator of
antibody production and/or local IC triggered activation. As most of
the anti-mBSA isotype titers were elevated, this may be responsible for
a higher IC load within the knee joint.
Although we did not find differences in the IC load in the knee joints
of Fc
RII-/- and controls at day 7 after AIA using
immunolocalization, differences may have been present at earlier time
points of this arthritis. Local IC-triggered activation in the joint
may further be different. Absence of the Fc
RII on macrophages has
been shown to enhance the release of inflammatory mediators such as
interleukin-1 and tumor necrosis factor-
53
that are
highly involved in synovial inflammation. Comparing two doses of mBSA
we found that only the high dose (60 µg) of mBSA was
Fc
RII-dependent during the complete 7-day course of arthritis.
Immune complexes drive inflammation by both activating Fc receptors and
complement and the two systems seemed to be co-dominant in the early
arthus reaction.54
Our results suggest that after the
arthus, in the developing phase of chronicity of experimental
arthritis, higher IC doses may be more FcR-dependent if compared to
lower IC doses.
Earlier studies have shown that macrophages are crucial in cartilage
destruction seen during AIA.38-41
Macrophages may
function either indirectly by attracting inflammatory cells or directly
as important producers of cytokines55
and
enzymes56
and in RA, activation of macrophages may be
T-cell-dependent.57,58
During AIA, two phases of cartilage
destruction are observed. The first early phase, which is characterized
by proteoglycan loss, is mediated by aggrecanase, a member of the ADAMS
(a desintegrin and metalloproteinase) family. The second phase that
starts at approximately day 5 after AIA induction, is characterized by
MMP-mediated matrix destruction resulting in irreversible cartilage
erosion.32
Because no difference was found in PG breakdown
nor NITEGE staining in cartilage surfaces of arthritic knee joints of
Fc
R-, Fc
RIII-, or Fc
RII-deficient mice and their wild-type
controls (data not shown), this suggests that these receptors are not
important or redundant in aggrecanase-induced cartilage damage.
In contrast, MMP-mediated cartilage destruction as measured by VDIPEN
staining was significantly lower in Fc
RI-/- but not in
Fc
RIII-/- arthritic knee joints. The latter indicates that Fc
RI
rather than Fc
RIII is involved in late severe cartilage destruction.
This type of cartilage destruction only occurs in experimental models,
containing an IC component.32
Other arthritis models
induced by bacterial or yeast cell walls never resulted in severe
cartilage destruction and also expression of VDIPEN neoepitopes was
fully absent.32
As we showed earlier, the activatory FcR
are probably involved in activation of latent MMPs present in the
cartilage matrix of arthritic knees, binding of FcRI may lead to
activation of synovial macrophages leading to selective production of
pro-MMP-activating factors. Although erosion was still mild at day 7
after AIA induction, there was a tendency that erosion was lower in
cartilage layers of arthritic knees of Fc
RI-/- mice. Differences
may diverge more at later time points when erosion becomes more severe
within this model.
In contrast in the absence of Fc
RII, significantly higher
MMP-mediated destruction was found within the cartilage layers of the
arthritic joints. First, this may be because of an elevated load of IC
within the joint as a result of higher anti-mBSA titers and may explain
the higher VDIPEN expression in the 60-µg mBSA group. Furthermore,
macrophages deficient for Fc
RII produce higher interleukin-1
concentrations on activation with ICs.39
As interleukin-1
is the dominant cytokine involved in VDIPEN expression during
AIA59
this also may contribute to the higher VDIPEN
expression in the cartilage. Moreover the absence of Fc
RII may
elevate mechanisms involved in activation of pro-MMPs into their active
form. A higher concentration of enzymes released by macrophages and/or
polymorphonuclear leukocytes such as elastase may be responsible for
more efficient activation of pro-MMPs.60
Whether Fc
RII
contributes to higher joint inflammation and severe cartilage
destruction either by elevation of anti-mBSA antibodies and subsequent
raise of ICs and/or by elevation of local hypersensitivity of
macrophages to ICs is momentarily under investigation by blocking
Fc
RII at the onset of AIA using anti-Fc
RII antibodies.
The above results suggest that expression of the activatory Fc
RI on
the surface of local cells present in the knee joint during
T-cell-dependent AIA is the dominant activatory Fc receptor involved in
cartilage destruction whereas the inhibiting Fc
RII-/- may be an
important regulating receptor of severe cartilage destruction. During
late phases of human arthritis, monocytes/macrophages are the dominant
hematopoietic cells present in the RA joint and a strong correlation
between the number of macrophages and erosion of the cartilage matrix
was found during RA.61
Disturbance in the balance between
activating Fc
RI and Fc
RIII receptors and the inhibiting Fc
RII
receptor on synovial macrophages may have important implications for
cartilage destruction during arthritis and the inhibiting Fc
RII may
form a new target for therapeutic intervention of cartilage destruction
within this destructive disease.
| Footnotes |
|---|
Supported by the Foundation against Rheumatism.
Accepted for publication August 29, 2001.
| References |
|---|
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