The Long Pentraxin Ptx3 Is Synthesized in IgA Glomerulonephritis

The Long Pentraxin Ptx3 Is Synthesized in
IgA Glomerulonephritis and Activates
Mesangial Cells
This information is current as
of January 20, 2017.
Benedetta Bussolati, Giuseppe Peri, Gennaro Salvidio,
Daniela Verzola, Alberto Mantovani and Giovanni Camussi
J Immunol 2003; 170:1466-1472; ;
doi: 10.4049/jimmunol.170.3.1466
http://www.jimmunol.org/content/170/3/1466
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References
The Journal of Immunology
The Long Pentraxin Ptx3 Is Synthesized in IgA
Glomerulonephritis and Activates Mesangial Cells1
Benedetta Bussolati,* Giuseppe Peri,† Gennaro Salvidio,‡ Daniela Verzola,‡
Alberto Mantovani,† and Giovanni Camussi2*
P
rimary IgA nephropathy is the most common type of glomerulonephritis (GN)3 and is a principal cause of renal
failure worldwide. Typical clinical features include hematuria and proteinuria. IgA GN is defined by granular deposition of
IgA and C3 in the glomerular mesangial areas, and it is considered
an immune complex-mediated GN. IgA GN is characterized by
proliferative changes in the glomerular mesangial cells (MC) and
increases in the mesangial matrices. The activation of MC by IgA
immune complexes or Abs is considered the initiating event in the
pathogenesis of IgA GN (1). In vitro, IgA immune complexes
stimulate MC production of proinflammatory mediators, such as
chemokines, cytokines, and platelet-activating factor (PAF) (2).
These mediators may, in turn, affect MC functions by stimulating
cell contraction, proliferation, or matrix production (3), leading to
glomerular injury.
*Cattedra di Nefrologia, Dipartimento di Medicina Interna, Università di Torino and
Centro Ricerca Medicina Sperimentale, Ospedale S. Giovanni Battista, Torino, Italy;
†
Dipartimento di Immunologia e Biologia Cellulare, Istituto di Ricerche Farmacologiche Mario Negri, Milan, Italy; and ‡Cattedra di Nefrologia, Dipartimento di Medicina Interna, Università di Genova, Genova, Italy
Received for publication July 31, 2002. Accepted for publication November 19, 2002.
The costs of publication of this article were defrayed in part by the payment of page
charges. This article must therefore be hereby marked advertisement in accordance
with 18 U.S.C. Section 1734 solely to indicate this fact.
1
This work was supported by the National Research Council (Target Project Biotechnology), Istituto Superiore di Sanità (Target Project AIDS), and MURST Cofin
(2001 and ex60%).
2
Address correspondence and reprint requests to Dr. Giovanni Camussi, Cattedra di Nefrologia, Dipartimento di Medicina Interna, Ospedale Maggiore S. Giovanni Battista,
Corso Dogliotti 14, 10126, Torino, Italy. E-mail address: [email protected]
3
Abbreviations used in this paper: GN, glomerulonephritis; FSGS, focal segmental
glomerular sclerosis; MC, mesangial cell; MPGN, membranoproliferative GN; PAF,
platelet-activating factor; PTX3, long pentraxin.
Copyright © 2003 by The American Association of Immunologists, Inc.
Pentraxins are a family of proteins considered to be markers of
the acute phase of inflammation, usually characterized by cyclic
pentameric structure (4 – 6). Short pentraxins are produced in the
liver in response to inflammatory mediators (7), and their function
includes amplification of innate resistance against microbes, regulation of inflammation, and complement activation (6). PTX3 is
the first cloned long pentraxin, structurally related to, but distinct
from, C-reactive protein and serum amyloid P component. PTX3
was cloned as an IL-1-inducible gene in endothelial cells and as a
TNF-inducible gene in fibroblasts (8). Inflammatory cytokines induce PTX3 expression in a variety of cell types, mainly endothelial
cells and mononuclear phagocytes (8 –12). Studies in transgenic
mice and gene-targeted mice suggest an important role for PTX3
in the regulation of inflammatory reactions and innate immunity
(13–15) (A. Mantovani, unpublished observations). This is supported by studies showing the ability of PTX3 to bind to the C1q
component of the complement cascade (12) and to participate in
the clearance of apoptotic cells (16). Moreover, PTX3 is elevated
in critically ill patients, with a gradient from systemic inflammatory response syndrome to septic shock (17), and in several other
diseases, such as myocardial infarction (18), rheumatoid arthritis
(19), atherosclerosis (20), and small vessel vasculitis (21).
The aim of the present study was to investigate whether PTX3
is involved in glomerular inflammation. In particular, we investigated PTX3 expression in two different conditions: GN characterized by inflammatory and proliferative lesions driven by resident
MC and/or by infiltrating leukocytes, such as IgA GN, membranoproliferative GN (MPGN), and diffuse proliferative lupus GN, and
nonproliferative GN without signs of glomerular inflammation,
such as membranous GN and focal segmental glomerular sclerosis
(FSGS). Moreover, we investigated the possible effects of recombinant PTX3 on the function of cultured human MC with particular
0022-1767/03/$02.00
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The long pentraxin PTX3 has been recently involved in amplification of the inflammatory reactions and regulation of innate
immunity. In the present study we evaluated the expression and role of PTX3 in glomerular inflammation. PTX3 expression was
investigated in the IgA, type I membranoproliferative, and diffuse proliferative lupus glomerulonephritis, which are characterized
by inflammatory and proliferative lesions mainly driven by resident mesangial cells, and in the membranous glomerulonephritis
and the focal segmental glomerular sclerosis, where signs of glomerular inflammation are usually absent. We found an intense
staining for PTX3 in the expanded mesangial areas of renal biopsies obtained from patients with IgA glomerulonephritis. The
pattern of staining was on glomerular mesangial and endothelial cells. Scattered PTX3-positive cells were also detected in glomeruli of type I membranoproliferative glomerulonephritis. The concomitant expression of CD14 suggests an inflammatory origin
of these cells. Normal renal tissue and biopsies from patients with the other glomerular nephropathies studied were mainly
negative for PTX3 expression in glomeruli. However, PTX3-positive cells were detected in the interstitium of nephropathies
showing inflammatory interstitial injury. In vitro, cultured human mesangial cells synthesized PTX3 when stimulated with TNF-␣
and IgA and exhibited specific binding for recombinant PTX3. Moreover, stimulation with exogenous PTX3 promoted mesangial
cell contraction and synthesis of the proinflammatory lipid mediator platelet-activating factor. In conclusion, we provide the first
evidence that mesangial cells may both produce and be a target for PTX3. The detection of this long pentraxin in the renal tissue
of patients with glomerulonephritis suggests its potential role in the modulation of glomerular and tubular injury. The Journal
of Immunology, 2003, 170: 1466 –1472.
The Journal of Immunology
regard to cell contraction, proliferation and synthesis of the proinflammatory lipid mediator PAF.
Materials and Methods
Materials
Polymyxin B and BSA fraction V (tested for ⬍1 ng of endotoxin/mg),
human factor VIII antiserum, anti-smooth muscle cell myosin mAb, anticytokeratin mAb, anti-desmin, and anti-actin mAb were purchased from
Sigma-Aldrich (St. Louis, MO). Anti-CD14 IOM2 and Leu M3 mAb were,
respectively, from Immunotech (Marseilles, France) and BD Biosciences
(Mountain View, CA). Human recombinant TNF-␣, IL-10, IL-1␤, human
monomeric IgA, and LPS from Escherichia coli (0111:B4) were purchased
from Sigma-Aldrich. IL-12 was a gift from G. Trinchieri. Synthetic PAF
(1-hexadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine) was obtained from
Bachem Feinchemikalien (Bubendorf, Switzerland). Human PTX3 was purified from CHO cells stably and constitutively expressing the protein as previously described (12).
Subjects
Immunofluorescence studies
Immunofluorescence studies were performed on kidney biopsies from the
patients described above. The tissues were rapidly frozen in liquid nitrogen, and 2-␮m-thick cryostat sections were fixed in 3.5% paraformaldehyde for 15 min and washed in PBS. To block the nonspecific binding,
sections were preincubated with human serum (1/10 dilution) for 30 min.
The sections were then incubated with anti-PTX3 rat mAbs (MNB4 and
MNB6) at a concentration of 1 ␮g/ml or with the irrelevant rat control
serum for 2 h at room temperature, washed in PBS, and incubated with
FITC-conjugated sheep anti-rat IgG. The slides were washed, mounted
with Vectashield mounting medium (Vector Laboratories, Burlingame,
CA), and examined. Control experiments included incubation of sections
with nonimmune control Abs or the omission of primary Abs followed by
the appropriate labeled secondary Abs. The specificity of anti-PTX Ab was
tested by preadsorption of the Ab (10 ␮g/ml) with purified recombinant
PTX3 (30 ␮g/ml). The number of glomeruli available on each section for
analysis of PTX3 expression ranged from three to seven. Three nonsequential sections were examined for each specimen. Fluorescence intensity was
evaluated in nonsequential sections to observe at least six glomeruli, and
the amount and extent of fluorescence were graded on a scale from 0 –3.
Culture of human MC
Human glomeruli were isolated from surgical specimens of kidneys using
the method described by Striker et al. (22). The separated cortex was sliced
and forced through a graded series of stainless steel meshes, and isolated
uncapsulated glomeruli were recovered. MC were obtained from collagenase-treated isolated glomeruli to remove the epithelial cell component.
The cells used were characterized by the following criteria (22): 1) morphologic appearance of stellate cells growing in interwoven bundles, 2)
uniform fluorescence with FITC-labeled phalloidin specific for filamentous
actin, 3) immunofluorescence staining for smooth muscle-type myosin, 4)
immunofluorescence staining of extracellular matrix for type IV collagen
and fibronectin using monospecific antisera, and 5) negative immunofluorescence staining for HLA-DR and leukocyte common Ag (CD-45) and
human factor VIII Ags. In parallel experiments cell viability was monitored
by trypan blue and ranged between 88 and 95%. Cells were used between
the second and fourth culture passages.
PTX3 assay
Recombinant PTX3 was purified from stably transfected CHO cells as
previously described (12). The levels of PTX3 in plasma or culture supernatant were measured by ELISA, based on mAb MNB4 and rabbit antiserum, as previously described (18). For cell culture experiments cells were
grown to confluence in 24-well plates, serum-starved overnight, and then
stimulated using DMEM containing 0.25% BSA. After 24 h cell supernatants were centrifuged and immediately frozen at ⫺20°C.
Binding of PTX3 to MC
The binding of biotinylated PTX3 to MC was evaluated by cytofluorometric analysis as previously described (16). Cells were challenged with biotinylated PTX3 (range tested, 0.1–500 ␮g/ml) for 30 min at room temperature. The procedure of biotinylation did not influence the structural or
functional integrity of the molecule (16). Cell-bound PTX3 was revealed
by flow cytometry after addition of PE-conjugated streptavidin (Pierce,
Rockford, IL). The fluorescence background was calculated with PE-conjugated streptavidin only. The specificity of the binding was verified incubating apoptotic cells with biotinylated PTX3 (1 ␮g/ml) in the presence
of the native protein (10- to 1000-fold the biotinylated PTX3).
Purification and quantification of PAF
The effect of PTX3 on PAF production from MC was studied. Cells were
equilibrated for 15 min in Tris-buffered Tyrode containing 0.25% delipidized BSA (fraction V) as previously described (23) and then were incubated at 37°C for the indicated time with PTX3 (100 ng/ml). The supernatants and cell pellets were extracted according to a modification of the
Bligh and Dyer procedure (24), with formic acid added to lower the pH of
the aqueous phase to 3.0. PAF was quantified after extraction and purification by TLC (silica gel plates 60 F254, Merck, Darmstadt, Germany) and
HPLC (␮Porasil column; Millipore Chromatographic Division, Waters
Corp., Milford, MA) by aggregation of washed rabbit platelets as previously reported (23, 25).
Shape change of MC
MC, seeded in small petri dishes (35 mm in diameter) coated with dimethylpolyxiloxane at subconfluent density, in DMEM with 0.25% BSA were
kept in an attached, hermetically sealed, NP-2 incubator (Nikon, Melville, NY)
at 37°C. Cells were stimulated with PTX3 (100 ng/ml), and cell shape change
was studied over a 2-h period under a Nikon Diaphot inverted microscope with
a ⫻20 phase-contrast objective as previously described (25). Cell shape
change was recorded using a JVC-1CCD video camera. Image analysis was
performed with a MicroImage analysis system (Cast Imaging, Venice Italy)
and an IBM-compatible system equipped with a video card (Targa 2000; Truevision, Santa Clara, CA). Image analysis was performed by digital saving and
comparing of the images before stimulation and then at 5-min intervals for 2 h.
The cell planar surface was calculated using MicroImage software (Cast Imaging, Venice, Italy). A reduction of the planar cell surface by ⬎15% was used
as a parameter of cell shape change compatible with a cell contraction. Both
the number of contracted cells and the mean cell contraction were indicated.
Between 10 and 25 cells were analyzed for each experimental condition, and
each experiment was repeated at least four times. Values are given as the
mean ⫾ SE.
Results
Glomerular expression of PTX3
PTX3 expression was investigated by immunofluorescence using
two different rat anti-human PTX3 Abs on renal biopsies from
patients with IgA (n ⫽ 25), type I MPGN (n ⫽ 6), diffuse proliferative lupus GN (n ⫽ 9), and membranous (n ⫽ 15) and FSGS
(n ⫽ 8) GN. Five normal human renal tissues obtained from kidney nephrectomized for polar renal carcinoma were used as controls. PTX3 was detected (Table I and Fig. 1, A and B) in the
mesangium of 22 of 25 IgA GN patients. In some glomeruli the
pattern of PTX3 staining was concomitantly endothelial and mesangial (Fig. 1A). In others, a typical intracytoplasmatic mesangial
pattern was observed (Fig. 1B). Moreover, PTX3 was expressed on
inflammatory cells infiltrating the renal interstitium and on peritubular capillaries (Fig. 1, C and D). Double immunofluorescence
staining with anti-CD14 Ab indicated that several of the PTX3positive cells present in the interstitium were monocytes/macrophages (Fig. 1D, inset), whereas glomerular PTX3-positive cells
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The study included 25 patients presenting IgA GN, 15 patients presenting
membranous GN, 8 patients with FSGS. None of the patients had evidence
of systemic disease on a clinical or laboratory basis. In addition, biopsies
from nine patients with proliferative diffuse GN due to systemic lupus
erythematosus (World Health Organization classes IVa and IVb) and from
six patients with type I MPGN were studied. The presence of these diseases
was confirmed by pathologic evaluation of renal biopsy specimens, such as
light microscopy, electron microscopy, and immunofluorescence staining.
No patients received steroids or immunosuppressive drugs before renal
biopsy. In each instance informed consent was obtained from the donors
for the use of tissue samples for experimental purposes. Normal kidney
tissue was obtained from an intact pole of kidney removed for a circumscribed tumor (n ⫽ 5). These patients were selected for absence of proteinuria and lack of glomerular abnormalities detected by light and immunofluorescence microscopy. For all patients the protein content of 24-h
urinary samples was measured by the Pyrogallol Red method. The creatinine concentration in plasma was analyzed by the kinetic Jaffé method
with a Synchron CX3 (Beckman, Palo Alto, CA).
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PTX3 IN IgA GLOMERULONEPHRITIS
Table I. PTX3 expression in normal renal tissue (n ⫽ 5) and in renal biopsies derived from patients with IgA GN (n ⫽ 25), membranous GN
(n ⫽ 15), FSGS (n ⫽ 8), diffuse proliferative lupus GN (n ⫽ 9), and type I MPGN (n ⫽ 6)a
Glomeruli
Normal tissue
IgA GN
Diffuse proliferative lupus GN
Type I MPGN
Membranous GN
FSGS
Peritubular Vessels
Interstitium
Inc.
Int.
Inc.
Int.
Inc.
Int.
0/5
23/25
0/9
4/6
0/15
0/8
0
1.84 ⫾ 1.1
0
0.8 ⫾ 0.3
0
0
0/5
6/25
7/9
4/6
1/15
0/8
0
0.28 ⫾ 0.6
1.75 ⫾ 0.5
1.16 ⫾ 0.5
0.13 ⫾ 0.1
0
0/5
9/25
8/9
4/6
5/15
5/8
0
0.36 ⫾ 0.4
2.22 ⫾ 0.4
1.5 ⫾ 0.5
0.46 ⫾ 0.3
1 ⫾ 0.3
a
PTX3 was evaluated by immunofluorescence using two different rat anti-PTX3 Ab. The amount and extent of fluorescence were assessed and were graded on a scale from
0 to 3. Results are expressed as the incidence of positive biopsies (Inc.) and as the mean ⫾ SEM fluorescence intensity (Int.).
were negative. In contrast, absence of staining was observed on
tubular cells (Fig. 1). The staining pattern obtained with the two
different rat anti-PTX3 mAbs used, MNB4 and MNB6, was superimposable. Control normal renal tissue showed only scattered
FIGURE 2. Micrographs showing PTX3 and CD14 coexpression in
type I MPGN. A, Detection of PTX3 in some cells within a glomerulus and
interstitium by FITC-labeled anti-PTX3 Ab. B, Staining of the same section with PE-labeled anti-CD14 Ab. Magnification, ⫻150.
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FIGURE 1. Micrographs showing PTX3 expression in renal biopsies. A
and B, PTX3 staining is detectable in the glomerular mesangium of IgA
GN. Both endothelial (A, arrows) and mesangial (B) patterns of staining
were observed. C and D, Inflammatory cells infiltrating the interstitium (C)
and peritubular capillaries (D, arrows) were positive for PTX3 in IgA GN,
whereas the tubular epithelial cells were negative. Double immunofluorescence staining with PE-labeled anti-CD14 Ab (inset) and with FITC-labeled anti-PTX3 Ab (D, arrowheads) shows cells positive for both CD14
and PTX3. E, Glomerular and tubular structures of normal tissue showed
only rare PTX3-positive cells. F, Intense positive staining for PTX3 in the
interstitium of a FSGS with tubulo-interstitial damage. The glomerulus was
negative. G and H, Preadsorption of the anti-PTX3 Abs with the recombinant protein abolished glomerular (G) and peritubular (H) staining in IgA
GN. Magnification: A–D, G, and H, ⫻400; E and F, ⫻150.
positive cells in glomeruli and negative interstitium (Fig. 1E). In
four of six MPGN, several PTX3-positive cells were detected in
glomeruli (Table I and Fig. 2A). The majority of these cells were
also positive for CD14 staining (Fig. 2B), suggesting their inflammatory origin. In diffuse proliferative lupus GN, PTX3-positive
cells were mainly absent in glomeruli despite the intense proliferative and inflammatory reaction. In contrast, both MPGN and diffuse proliferative lupus GN showed an intense infiltration of
PTX3-positive cells in the interstitium (Table I). In membranous
GN and FSGS, glomeruli were mainly negative, with only rare
positive cells detected in the mesangial areas of some glomeruli
(Table I). The membranous GN and, in particular, FSGS that exhibited a chronic tubulo-interstitial injury showed intense infiltration of PTX3-positive cells (Table I and Fig. 1F). In contrast,
membranous GN and FSGS that did not exhibit tubulo-interstitial
damage showed only a few scattered PTX3-positive cells in the
interstitium (Table I). Replacement of the primary Ab with an
The Journal of Immunology
irrelevant rat Ab or preabsorption of the anti-PTX3 Abs with recombinant PTX3 (1 ␮g/ml) abrogated the staining observed on
both glomeruli and interstitium in IgA GN (Fig. 1, G and H).
PTX3 release by MC
PTX3 binding to MC
To verify the possible role of PTX3 on MC, PTX3 was purified
from CHO cells stably and constitutively expressing the protein,
and binding to MC was revealed by flow cytometry. Biotinylated
PTX3 efficiently bound MC (Fig. 4, A and C). The preincubation
of MC with the native molecule (100-fold) inhibited the binding
(Fig. 4B), demonstrating its specificity. A linear increase in binding was observed when increasing concentrations of biotinylated
PTX3 were used, reaching a plateau at ⬃100 ␮g/ml (Fig. 4C).
Since other pentraxins, such as C-reactive protein, bind to the
FcR (5), we evaluated whether the binding of PTX3 on MC was
inhibited by preincubation with IgA or IgG (30 min at 4°C). No
difference in PTX3 binding to MC was observed (data not shown).
PAF production by PTX3-stimulated MC
PTX3 induced the production of PAF from MC (Fig. 4). Heat
inactivation of PTX3 significantly reduced the effect on PAF synthesis, indicating its specificity (Fig. 5). PAF production peaked 30
min after stimulation with 100 ng/ml of PTX3 and was mainly
associated to the cell fraction (Fig. 5). Cell viability tested at the
end of each experiment by trypan blue dye exclusion test was
⬎90%.
Shape change of MC
Shape change of MC, compatible with cell contraction, was evaluated as changes in planar surface area in response to different
stimuli. PTX3 induced a reduction of the cell planar surface of
⬎15% in 84% of MC (Fig. 6). Fig. 7 is representative of the MC
shape change observed after stimulation with PTX3. The change in
shape of individual cells occurred at different times (Fig. 7). Heat
inactivation of PTX3 abolished its effect on cell shape, indicating
its specific effect. The changes in cell shape of MC were reversed
by replacement of the stimuli with fresh medium. No significant
cell shape change was observed in MC stimulated with vehicle
alone.
Discussion
FIGURE 3. A, PTX3 release in the supernatant of cultured human MC
stimulated for 24 h with vehicle alone (DMEM ⫹ 0.25% BSA), TNF-␣
(TNF; 10 ng/ml), IgA (1 ␮g/ml), LPS (100 ng/ml), IL-1 (40 ng/ml), angiotensin II (AT-II; 10 U/ml), IL-10 (20 ng/ml), and IL-12 (20 ng/ml). Data
represent the mean ⫾ SEM of at least three individual experiments performed in triplicate. B, PTX3 release in the supernatant of MC stimulated
for 24 h with increasing doses of IgA. Data represent the mean ⫾ SEM of
three individual experiments performed in triplicate. ANOVA with Dunnett’s multicomparison test was performed between vehicle and treatment
(ⴱ, p ⬍ 0.05).
PTX3 has recently been involved in amplification of inflammatory
reactions and regulation of innate immunity. In the present study
we evaluated the expression and role of PTX3 in glomerular pathology. We found intense staining for PTX3 in the expanded mesangial areas of renal biopsies obtained from patients with IgA GN.
Moreover, cultured human MC synthesized PTX3 when stimulated
with TNF-␣ and IgA and exhibited specific binding of recombinant PTX3. Furthermore, stimulation with exogenous PTX3 promoted MC contraction and synthesis of the proinflammatory lipid
mediator PAF.
PTX3, a recently cloned member of the pentraxin family, has
been reported to be mainly expressed by activated endothelial cells
and monocytes (8, 10). In vivo, PTX3 expression has been observed in diseased human vessels during small vessel vasculitis
(21) and advanced atherosclerosis (20). In the present study we
found intense staining of PTX3 in the mesangium of patients with
IgA GN. PTX3 was expressed by both glomerular mesangial and
endothelial cells. In patients with type I MPGN, several PTX3positive cells were also detected in glomeruli. At variance with
IgA GN, PTX3-positive cells coexpressed CD14, indicating their
inflammatory origin. Normal renal tissue and biopsies from patients with other glomerular nephropathies, such as diffuse proliferative lupus GN, membranous GN, and FSGS, were mainly negative for PTX3 expression in glomeruli. These data indicate that
mesangial and endothelial glomerular cells are activated to synthesize PTX3 in IgA GN. An increased level of acute phase proteins and, in particular, of C-reactive protein, has recently been
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The expression of PTX3 by MC in IgA GN prompted us to evaluate whether human cultured MC could release PTX3 in their supernatant. Basal PTX3 production, evaluated by ELISA in 12 different primary cell lines, showed a high variability among cell
lines, with PTX3 levels ranging from ⬍0.2 to 13.4 ng/5 ⫻ 105
cells (mean ⫾ SE, 2.1 ⫾ 1.3; n ⫽ 12). No differences among cell
passages were observed. TNF-␣ (10 ng/ml) significantly increased
PTX3 release (Fig. 3A) after 24-h incubation. Moreover, stimulation with IgA induced a dose-dependent PTX3 release from MC
(Fig. 3, A and B). Other stimuli known to induce PTX3 in monocytes, such as LPS and IL-1 (11), were ineffective in inducing
PTX3 from MC. Moreover, stimuli specific for MC activation,
such as IL-10, IL-12, and angiotensin II (3), did not stimulate
PTX3 synthesis (Fig. 3A).
1469
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PTX3 IN IgA GLOMERULONEPHRITIS
reported in IgA GN (26). Indeed, it has been proposed that PTX3
may play the same function in the periphery as C-reactive protein
does in the circulation (12, 21). We also found the expression of
FIGURE 4. PTX3 binding to MC. A, MC were incubated with PTX3 (1
␮g/ml) as described in Materials and Methods, and binding was revealed
by addition of PE-streptavidin (dark line). The background fluorescence is
indicated by the filled line. B, PTX3 (1 ␮g/ml) binding to MC (dark line)
is significantly reduced by competitive experiments with recombinant
PTX3 (1 mg/ml; filled line). Two experiments were carried out with similar
results. In each individual experiment the Kolmogorov-Smirnov statistic
analysis between biotinylated PTX3 and biotinylated PTX3 plus recombinant PTX3 was significant (p ⬍ 0.05). C, Increasing concentrations of
biotinylated PTX3 were added to MC. Results are expressed as the mean
fluorescence intensity. Data are representative of one experiment of three
with comparable results.
FIGURE 6. Kinetics of change of MC shape after stimulation with 100
ng/ml of PTX3 evaluated using a video-recording system as described in
Materials and Methods. Cell retraction is expressed as the reduction of the
planar surface evaluated before stimulation. Between 10 and 25 cells were
analyzed for each experimental condition, and each experiment was repeated at least four times. Values are given as the mean ⫾ SEM. ANOVA
with Dunnett’s multicomparison test was performed between vehicle and
PTX3 (ⴱ, p ⬍ 0.05).
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FIGURE 5. A, PAF production from 1 ⫻ 106 MC stimulated with recombinant PTX3 (100 ng/ml) or heat-inactivated PTX3 (H-I PTX3; 100
ng/ml) for 30 min. ANOVA with Dunnett’s multicomparison test was performed between PTX3 and inactivated PTX3 (ⴱ, p ⬍ 0.05). B, Time course
of PAF synthesis from 1 ⫻ 106 MC stimulated with 100 ng/ml PTX3. PAF
was detected as cell associated (F) and released in the supernatant (䡺).
Data are the mean ⫾ SEM of three individual experiments.
The Journal of Immunology
1471
FIGURE 7. Micrographs representative of MC,
seeded in petri dishes coated with dimethylpolyxiloxane
at subconfluent density, in DMEM with 0.25% BSA
stimulated with PTX3. Cell shape change was studied
over a 2-h period under a Nikon Diaphot inverted microscope with a ⫻20 phase-contrast objective using a
JVC-1CCD video camera. The figure shows the morphological changes in MC, consistent with a progressive cell
contraction, observed every 30 min after stimulation with
PTX3 (magnification, ⫻200).
may improve renal injury and vascular inflammatory lesions (32–
34). In humans, reduced PAF inactivation due to PAF acetylhydrolase gene mutation has been shown to worsen the course of IgA
nephropathy (35).
Recently, PTX3 was shown to enhance tissue factor expression
by endothelial cells, suggesting a role in thrombogenesis and ischemic vascular disease (36). Therefore, PTX3 in IgA GN could
participate in the activation of both endothelial and MC , and contribute to glomerular inflammation by inducing the production of
secondary mediators. A similar mechanism may be involved in
tubular interstitial injury associated with different GN. In conclusion, we provide the first evidence that MC may both produce and
be a target of PTX3. The detection of this long pentraxin in the
renal tissue of patients with GN suggests its potential role in the
modulation of glomerular and tubular injury.
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PTX3 in endothelial cells and in CD14-positive monocytes infiltrating the renal interstitium in IgA GN with tubulo-interstitial injury, indicating that the cells involved in the inflammatory process
were activated to synthesize PTX3. However, a double immunofluorescence study suggests that cells other than monocytes and
vascular endothelium may contribute to the interstitial expression
of PTX3. As it has been shown that PTX3 is a TNF-inducible gene
in fibroblasts (8), one can speculate that renal interstitial fibroblasts
may synthesize PTX3 in the injured interstitium. The expression
by inflammatory interstitial cells and peritubular capillaries was
not specifically linked to IgA GN, as it was also detectable in all
GN with tubulo-interstitial injury. Of interest is the absence of
glomerular PTX3 expression in diffuse proliferative lupus GN despite the presence of inflammatory cells and of IgA-containing
immune deposits in glomeruli.
The mesangial detection of PTX3 in IgA GN suggest that MC
may contribute, after an appropriate stimulation, to the synthesis of
this pentraxin. We therefore investigated the ability of MC to synthesize PTX3 in vitro and the stimuli involved in its production.
Human cultured MC synthesized PTX3 in basal conditions and
increased PTX3 synthesis when stimulated with IgA or TNF-␣, a
cytokine implicated in IgA GN. Other stimuli known to induce
PTX3 synthesis in monocytes, such as IL-1 and LPS (11), as well
as other mediators known to activate MC (3) were ineffective,
indicating a specific stimulatory pathway for PTX3 synthesis by
MC that could be relevant for the pathogenesis of IgA GN.
To further investigate the role of PTX3 in IgA GN, we studied
whether PTX3 could bind and activate MC. In particular, we evaluated some cell functions relevant for mesangial physiopathology,
such as contraction and synthesis of the proinflammatory mediator
PAF. We found that PTX3 bound to MC in a dose-dependent and
saturable way. Although we could not identify the receptor involved in PTX3 binding, its specificity was demonstrated by the
displacement of biotinylated PTX3 by recombinant PTX3. The
exact role of PTX3 in glomerulonephritis remains to be determined. Indeed, to date there has been little functional information
about PTX3. We here demonstrated the PTX3 is involved in MC
activation. In a time-lapse analysis, the microscopic observation of
MC stimulated with PTX3 showed morphological changes in cell
shape compatible with cell contraction. The alterations in MC
shape observed are similar to those induced by PAF (27) and
TNF-␣ (28). The contraction of mesangium is relevant in glomerulonephritides, as it is responsible for a reduction in the glomerular
filtration area and may therefore affect the coefficient of filtration
(29). In addition, PTX3 enhanced the synthesis by MC of PAF, a
mediator of glomerular inflammation and injury (30). PAF favors
immune complex deposition in glomeruli and affects glomerular
filtration and permeability in several experimental models (31).
Indeed, several studies suggested that blockade of PAF receptor
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PTX3 IN IgA GLOMERULONEPHRITIS