are antineutrophil cytoplasmic antibody-associated vasculitides pauci-immune?

VASCULITIS 0889-857X/Ol $15.00 + .OO

ARE ANTINEUTROPHIL CYTOPLASMIC

ANTIBODY-ASSOCIATED VASCULITIDES PAUCI-IMMUNE?

Raoul H. Brons, MSc, Cees G. M. Kallenberg, MD, PhD, and Jan Willem Cohen Tervaert, MD, PhD

Vasculitis, or inflammation of blood vessels,So can be encountered in a variety of diseases with diverse clinical manifestations. Virtually all blood vessels of any size and type can be involved in vasculitis, resulting in a wide range of clinical symptoms.', 50 Vasculitis can present as the major manifestation of a primary disease or as a relatively minor compo- nent of another underlying disease. It can be infectious or noninfectious and either systemic or limited to one or only a few organs.lS

Classification of the vasculitides is based primarily on the type and size of the blood vessels involved. In 1990, the American College of Rheumatology published classification criteria for the major vasculitic syndromes.68 Names and definitions for many forms of vasculitis were adopted at a consensus conference in Chapel Hill in 1994.61

PATHOPHYSIOLOGIC CHARACTERISTICS

In many forms of vasculitis, antigen-antibody complexes participate in the pathogenesis of the vascular inflammation?*, Evidence for the involvement of immune complexes (ICs) in vasculitis stems from vasculi-

From the Department of Clinical Immunology, University Hospital Groningen, Groningen (RHB, CGMK), and the Department of Clinical and Experimental Immunology, Uni- versity Hospital Maastricht, Maastricht (JWCT), The Netherlands

RHEUMATIC DISEASE CLINICS OF NORTH AMERICA

VOLUME 27 - NUMBER 4 * NOVEMBER 2001 a33

834 BRONS et a1

tic lesions resembling those found in experimental immune complex- mediated conditions such as the local Arthus reaction phenomenon and serum sickness." For serum sickness, animal models have been developed with vasculitis as a prominent feature. In these experimental models, intravenous injection of an antigen leads to the presence of ICs once the animal develops an immune response to the antigen. These ICs are formed intravascularly and can deposit in several vascular beds4* such as the glomerulus, thereby causing immune complex-mediated glomerulonephritis.

Not only does evidence exist that ICs are formed in animal models, but immunoglobulins and complement components have also been detected in vascular lesions of patients with vasc~litis.~~, 55, 82, 83, 94 DNA- anti-DNA complexes have, for instance, been demonstrated in vascular lesions of systemic lupus erythematosus-associated vasculitis.' Whether these ICs accumulate in the blood vessel by deposition from the circula- tion, in situ formation, or a combination of these two mechanisms is not known. ICs also play an important role in other vasculitic diseases.44 In Henoch-Schonlein purpura, IgA deposits are found in the skin, intestine, and kidneys99; in mixed cryoglobulinemic vasculitis, IgM and IgG deposits are detected'Ol; and in cutaneous leukocytoclastic vasculitis, circulating ICs and IgG and IgM deposits are found.5

In addition to classic IC-mediated vasculitis, other types of immunopathogenic mechanisms may be involved in vascular damage in vasculitis. One of these is cell-mediated immune reactivity in which antigens trigger T lymphocytes to release a variety of cytokines, causing an influx and accumulation of monocytes in and around blood vessels. These monocytes may release lysosomal enzymes, causing vessel wall damage similar to neutrophil-mediated vessel damage.38

Another immunopathogenic mechanism is the Shwartzman reaction. After a first injection (either local or systemic) with endotoxin (lipopolysaccharide [LPS]), a secondary exposure to LPS 24 hours later results in vasculitis and hemorrhagic necrosis at the site of the first exposure. Endothelial cells are critical for the initiation of local Shwartz- man reactions. Interleukin (1L)-1 and tumor necrosis factor (TNF) can substitute for the primary injection of LPS in inducing a local Shwartz- man reaction. LPS, IL-1, and TNF induce endothelial cells to become thrombogenic and can induce the expression of cell adhesion molecules on endothelial cells, making endothelial cells adhere to leukocytes more ea~i1y.l~ Leukocytes get activated intravascularly because of the LPS injection, resulting in upregulation of CDllb/CD18 expression,4 followed by degranulation and production of oxygen radicals once these cells adhere to activated endothelium.

Another immunopathogenic mechanism is vascular injury mediated by an antibody with specificity for components of the blood vessel itself. Examples of these antibodies are anti-endothelial cell antibodies (AECAS)~* and anti-glomerular basement membrane antibodies (anti- GBMs). The latter bind to the major autoantigenic target on the GBM, which is the NC1 domain of the cxj chain of type IV collagen.63, lo4 This

PAUCI-IMMUNE VASCULITIDES 835

leads to the in situ formation of ICs. Neutrophils bind to these ICs with Fcy receptors, and their ensuing activation results in damage to the glomerulus.1o2 AECAs, on the other hand, are probably not directly cytotoxic but may affect the endothelium by modifying some of its complex functional processes.6, It has been suggested that immunoglobulin deposition on the endothelial membrane results in endothelial activation.” In particular, AECA IgG from patients suffering from primary vasculitides such as Wegener ’s granulomatosis (WG) can induce dramatic upregulation of adhesion molecules and increased secretion of proinflammatory cytokines (IL-lp, IL-6) and chemoattractants (IL-8, monocyte chemoattractant protein-1).28 This results in attraction and activation of leukocytes to the inflammatory site, facilitating not only their adhesion but also extravascular migration and granuloma formation.”

Within the group of small vessel vasculitides, the anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides stand out because of the presence of a possible pathogenic autoantibody. In these forms of vasculitis, ANCAs are found almost invariably in the sera of patients suffering from these conditions. The immunopathogenic mechanisms of ANCA-associated vasculitides are still unknown. In contrast to secondary forms of vasculitis, however, the lesions in ANCA-associated vasculitides show a paucity or absence of vascular immune deposits.5l Immune pathogenic mechanisms other than immune complex-mediated mechanisms have been sought in these forms of vasculitis.

ANTI-NEUTROPHIL CYTOPLASMIC ANTIBODIES

Davies et al.27 first described ANCAs in a few patients with necrotizing glomerulonephritis in 1982. ANCAs are autoantibodies directed against constituents of neutrophil and mononuclear cell *06

and they can be detected by indirect immunofluorescence microscopy using ethanol-fixed neutrophils as a Three types of staining can be observed: a cytoplasmic staining with accentuation of the fluo- rescence intensity in the area within the nuclear lobes (cytoplasmic [C] ANCA), a perinuclear-staining [PI ANCA, or a more diffuse cytoplasmic staining (atypical ANCA).18 Numerous studies have characterized these autoantibodies with respect to their antigenic specificity and pathogenic potential. The main antigen producing a C-ANCA pattern in ANCA- associated vasculitis is proteinase 3 (PR3), and the main antigen producing a P-ANCA pattern is myeloperoxidase (MPO).% Antibodies directed against other proteins such as leukocyte elastase, lactoferrin, lysozyme, bactericidal permeability protein, catalase, a-enolase, cathepsin G, and p- glucuronidase can produce a P-ANCA pattern as well. These antibodies, however, are not specific for vasculitis.22,45, The third pattern, atypical ANCA, has not been linked to a particular antigen thus far.18

836 BRONS et a1

ANTINEUTROPHIL CYTOPLASMIC ANTIBODY-ASSOCIATED VASCULITIDES

The ANCA-associated vasculitides consist of four different diseases: WG, microscopic polyangiitis (MPA), Churg-Strauss syndrome (CSS), and idiopathic necrotizing crescentic glomerulonephritis (NCGN).

WG is a form of small vessel vasculitis that is characterized by chronic inflammation of the upper and lower respiratory tract, systemic necrotizing vasculitis, and necrotizing crescentic glomerulonephritis.61 Locoregional or limited WG is a more limited form of this disease in which the lesions are limited to the upper and lower respiratory tract. PR3-ANCAs are found in 80% to 90% of WG patients.l9,

MPA is another form of ANCA-associated small vessel vasculitis in which the lungs and kidneys are frequently inv0lved.5~. 90 In the lungs, alveolar capillaritis is common, but contrary to WG, granulomatous inflammation of the respiratory tract is not found. ANCAs, found in approximately 80% to 90% of MPA patients, are directed primarily against MPO in this disease.48* 67

CSS, also known as allergic granulomatous angiitis, is characterized by asthma or a history of allergy, eosinophilia of blood and tissue, and systemic necrotizing vasculitis.66 Renal involvement is common, although often less severe than that associated with WG or MPA. ANCAs are found in approximately 50%32 to 75%21 of CSS patients, and their specificity is antiMPO in most cases.

The last of the ANCA-associated vasculitides is pauci-immune NCGN. This form of vasculitis is restricted to the kidneys and is often (but not always) associated with ANCAS.~O* 36, 51, 57 The disease is characterized by NCGN lacking glomerular immunoglobulin deposits. The ANCA specificity is predominantly antiMP0.46, 58

PATHOPHYSIOLOGIC RELEVANCE OF ANTINEUTROPHIL CYTOPLASMIC ANTIBODIES

The pathophysiologic relevance of ANCAs has been studied exten- sively (reviewed by Muller Kobold et aP6). Falk et a135 demonstrated that IgG fractions from ANCA-positive sera (PR3-ANCA or MPO-ANCA) or F(ab’), fragments of the autoantibodies were capable of inducing TNF- primed neutrophils to release lysosomal enzymes and produce reactive oxygen species. This could conceivably occur in vivo in a patient with ANCA-associated vasculitis when a (chronic) infection primes leukocytes, resulting in the expression of ANCA antigens on the surface of neutrophils and monocytes.”, 75, The ANCA antigens are then available for interaction with ANCAs, resulting in the release of reactive oxygen species and lytic enzymes causing vascular injury. Leukocyte activation, resulting from ANCA binding to surface-expressed ANCA antigens, is not only dependent on the F(ab’), fragments of the autoantibodies but also on the interaction between the Fc fragment and Fcy receptor 1174 and possibly the Fcy receptor IIIb on neutrophils as well.65


PR3-ANCAs can also exert their pathophysiologic role by interfering with the irreversible interaction between PR3 and its natural inhibitor, al-antitrypsin.25, 30, It does so by obstructing the binding of a,-antitrypsin to PR3, causing the enzyme to be active for a longer period of time, which results in excessive protein breakdown and possible vascular injury. A similar interference is observed between MPO, its natural inhibitor ceruloplasmin, and MPO-ANCAs, whereby binding of MPO- ANCAs to MPO prevents the inactivation of MP0.43

Another pathophysiologic role of ANCAs is shown by studies using cultured human umbilical cord endothelial cells (HUVECs). These studies show that ANCAs promote adhesion of neutrophils to monolayers of endothelial cells and may cause vascular injury by activating primed neutrophils, resulting in lysis of activated endothelial cells.33, 89 A contro- versial point in the interaction of ANCAs with endothelial cells is the alleged production of PR3 by HUVECs. According to Mayet et al,71 activated HUVECs are able to express PR3. Treating endothelial cells with cytokines such as TNF, IL-1, or interferon-y induced PR3 expression on the cell membrane71,95; thus, the antigen may be available for interaction with ANCAs at sites of cytokine production such as inflammatory foci. Other groups, however, have not been able to reproduce these results.",80 It has also been shown that ANCAs were able to bind to endothelial cells that were incubated with exogenous PR3 or MP0.91 Recently, Taekema-Roelvink et allo3 demonstrated that PR3 binds to a Ill-kd membrane molecule present on HUVECs. Taken together, these findings suggest that the interaction between ANCAs and endothelium is an interesting focus in the pathophysiologic findings of WG, especially in light of possible in situ IC formation.

PAUCI-IMMUNE LESIONS IN ANTINEUTROPHIL CYTOPLASMIC ANTIBODY-ASSOCIATED VASCULITIDES

As noted, the ANCA-associated vasculitides are described as being pauci-immune vasculitides.61 This suggests that all vascular lesions in ANCA-associated vasculitides (e.g., in the kidneys, lungs, gut, muscle, and skin) are characterized by necrotizing inflammation but a paucity of immune deposits.5°, 58, 6o Pauci-immune crescentic glomerulonephritis was first described by Stilmant et alloo in 16 patients. Since then, several groups have described this form of glomerulonephritis in relation to systemic vasculitis or as an idiopathic f ~ r m . ~ ~ , ~ The discovery of ANCAs and the widespread use of ANCA testing revealed that most pauci- immune g%omerulonephritides are associated with serologic positivity for ANCAS.~~, 50 The paucity of immunoglobulin deposits distinguishes ANCA-associated glomerulonephritis from IC vasculitis and anti-GBM- mediated glomerulonephritis in which granular and linear immune deposits, respectively, are found. Paucity of immune deposits cannot only be detected in the kidneys but in other organs as well. Pauci-immune capillaritis, for instance, has been observed in the lungs of patients with

838 BRONS et a1

ANCA-associated vas~ulitides.~, The finding that almost all kidney biopsies of patients with ANCA-associated vasculitis exhibit pauci-immune glomerulonephritis led scientists and clinicians to believe that ICs do not play a role in ANCA-associated vasculitides. Attention was shifted away from the possibility that ICs may be involved in initiating vasculitic lesions.

Recently, however, data obtained from our animal model of ANCA-associated NCGN have redirected attention to the role of ICs in ANCA-associated vasculitis. In this model, Brown-Norway rats were immunized with human MPO. The rats developed antihuman MPO antibodies, which partly cross-react with rat MPO and. also showed delayed-type hypersensitivity to human MP0.13, 53 Five weeks after im- munization, the left kidney was perfused with a lysosomal extract containing MPO (and lytic enzymes such as PR3) followed by hydrogen peroxide (H202), the substrate of MPO. Twenty-four hours after perfusion, IgG and C3 deposits were observed along the GBM. When kidney tissue was obtained 4 days or 10 days after perfusion, no intraglomerular immune deposits were found, however.13 These findings suggest that the initial step in the development of NCGN is focal IC formation, followed by a rapid clearance of these immunoreactants, leading to a pathologic picture of pauci-immune NCGN. Lytic enzymes in the lyso- soma1 extract used for perfusion are, at least in part, responsible for the degradation of the immune deposits that are detected in the early stages of the lesion^.'^

IMMUNE COMPLEXES IN ANTINEUTROPHIL CYTOPLASMIC ANTIBODY-ASSOCIATED VASCULITIDES

There are indications that ICs may play a role in the initiation of vascular lesions in these diseases. First, as mentioned previously, other forms of small vessel vasculitides (not belonging to the ANCA-associated vasculitides) such as Henoch-Schonlein purpura and cryoglobulinemic vasculitis are associated with immune deposits. Second, circulating ICs (CICs) can be detected in patients with active ANCA-associated vasculitis (Table 1). Determination of CICs by Clq binding assays, polyethylene precipitation, or Raji cell assays performed in sera obtained from patients with active WG showed positive results in a number of

55, 83, 94, 96 In one study, 17 patients were tested for the presence of CICs using a Clq binding assay during periods of disease activity, and 11 patients were found to be positive. Within a few days after starting treatment, CICs became undetectable and remained negative during remission. Nevertheless, the Clq binding assay became positive during relapses that were provoked by infections (5 of 9 relapses) and reverted back to normal after treatment.82 CICs have not only been detected in WG but also in patients with CSS (see Table l).66,69,86Third, immune deposits can sometimes be found in lesions of patients with ANCA-associated vasculitides. In 1982, Shasby et a194 described the presence of immune deposits in pulmonary lesions of a patient with


Table 1. THE PRESENCE OF CIRCULATING IMMUNE COMPLEXES IN SERA FROM

SYNDROME PATIENTS WEGENER'S GRANULOMATOSIS PATIENTS AND CHURG-STRAUSS

Sera Sera Author Tested Positive Test Used

Wegener 's granulomatosis Howell and E p ~ t e i n ~ ~ 2 2 Clq precipitin reaction Shasby et a194 2 1 Raji cell assay Fauci et aP9 36 16 Raji cell assay and Clq binding

s011ing96 3 3 Clq binding assay and assay

polyethylene glycol precipitation

Ronco et a1= 7 6 Clq binding assay

Pinching et als2 17 11 Clq binding assay

Sale et alS6 1 1 Raji cell assay Lanham et alffi 14 2 Clq binding assay Manger et aP9 5 5* Polyethylene glycol precipitation

9 2 Raji cell assay

Churg-Strauss syndrome

'No IgG-containing complexes, but all sera tested contained IgE complexes.

WG. Not only pulmonary lesions but renal lesions can sometimes dis- play immune deposits (Table 2)!7, 55,

Studying renal biopsies of WG patients, we found scanty IgG deposits in most of the 28 biopsies examined but never in a linear or granular

83

Table 2. IMMUNE DEPOSITIONS IN PULMONARY, RENAL OR SKIN BIOPSIES OF

OR NECROTIZING CRESCENTIC GLOMERULONEPHRITIS PATIENTS WITH WEGENER'S GRANULOMATOSIS, CHURG-STRAUSS SYNDROME,

Type of Biopsies Authors Biopsy Tested Biopsies Positive Disease

Shasby et a P Pulmonary 2 2 (2 G and 2 C3) WG Pmchmg et alS2 Renal 13 8 (8 G or M and 8 C3) WG Hu et a1% Renal 1 1 (G, A, M, and C3) WG Ronco et a P Renal 11 2 (1 G, 2 M, and 1 A) WG Grotz et a147 Renal 11 10 (10 M, G, or A and 10 C3) WG Brouwer et all4 Renal 20 (7 M and 10 C3) wc Andrassy et a13 Renal 2 2 (2 A) WG

WG WG

Vrtovsnik et allo8 Renal 1 1 (A) Hu et a1% Skin 4 1 (M and C3) Hansen et aY9 SkLn 1 1 (6, 2.1, A, and 63) WG Patten and TomeckP Slap 4 3 (all G, M, A, C3, and C3cl Wd; Daoud et 31'6 Skin 14 II (not speaheld~ WG grons Et a19 ShIl 32 11 (7 G, 8 hi, 3 A, and 10 C3c) WG Lanham et ale Renal 5 4 (3 M, 1 A, and 3 C3) css Neumann et a P Renal 37 8 (not specified) NCGN

G = IgG, M = IgM, A = IgA, C3(c) = complement factor 3(c), WG = Wegener's granulomatosis, CSS = Churg-Strauss syndrome, NCGN = necrotmng crescenhc glomerulonephritis

840 BRONS et a1

pattern.14 By using double-staining techniques, it was found that the presence of IgG corresponded with the extracellular presence of PR3, MPO, and elastase. We postulate that this finding is suggestive of IC deposition in the kidneys. Other groups have found immune deposits containing IgA in renal lesions of patients with WG.2, 3, lo8 Recently, Neumann et a178 detected immune deposits in kidney sections of 8 of 37 patients with ANCA-associated NCGN. These 8 patients had signifi- cantly higher proteinuria compared with NCGN patients without immune deposits.

In addition, immune deposits in skin biopsies of patients with WG have been described.z6, 49, 56, 79 One study compared immunofluorescence data from the skin of two patients with immunofluorescence data found in concomitant renal biopsies.56 Immune deposits were detected in one patient in skin and renal biopsies, whereas the other patient showed no immune deposits in the skin biopsy but showed IgG and IgA deposits in the renal biopsy.

To test the hypothesis that ICs may be involved in initial lesion development, we recently performed a study to determine whether immune deposits could be found in skin biopsies of patients with WG.l2 These biopsies were taken from newly developing lesions. We demonstrated that immune deposits were present in the blood vessel walls of 4 of 11 skin biopsies obtained from patients with newly diagnosed WG and in 4 of 21 biopsies obtained from patients with relapses of WG. In contrast to this, renal biopsies taken at the same time as the skin biopsies showed a paucity of immune deposits.

The reason why ICs are scarcely detected in lesional biopsies is not known. We postulate that this is a result of the exaggerated inflammatory response found in these patients. Binding of ICs by neutrophils and monocytes stimulates these cells to release oxygen radicals and lytic enzymes such as PR3 and MPO. Additionally, ANCA antigens are expressed at the cell surface of these cells, which, in the presence of ANCA, may result in an exaggerated activation of these cells.35 This exaggerated activation of neutrophils may result in the excessive release of lytic enzymes such as human neutrophil elastase and PR3, both of which are capable of proteolysis of immunoglobulins.31 This excessive proteolysis causes the ICs to be degraded more rapidly and may explain the absence of immune deposits in renal lesions of patients with ANCA-associated vasculitides (Fig. 1). Similar mechanisms have been described in an Arthus-reaction animal model of va~culitis.’~~ 23 In this animal model, neutrophils degrade the immune deposits within 18 to 48 hours after deposition.

ANTIGENS POSSIBLY INVOLVED IN IMMUNE COMPLEX FORMATION

Antineutrophil Cytoplasmic Antibody Antigens

The presence of immune deposits in tissues and the presence of CICs in serum of patients with ANCA-associated vasculitides imply that

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vasculitides (Fig. 1). Similar mechanisms have been described in an antigens in these ICs is not known but may include ANCA antigens, because MPO and PR3 are released extracellularly in inflammatory conditions. Circulating PR3 is present in sera of patients with active WG,54 whereas circulating MPO is present in sera of patients with NCGN,% possibly forming CICs in the presence of PR3-ANCAs and MPO- ANCAs, respectively.

The presence of extracellular PR3 and MPO have also been detected in renal lesions of patients with WG.14 By double-staining techniques, it has been shown that the presence of IgG corresponded with the presence of extracellular PR3 and MPO. PR3 and MPO do not seem to be present in endothelial cells,m but as a result of the cationic nature of PR3 and MPO, both can bind to these cells after being released from activated neutrophils or monocytes.gO The presence of PR3-ANCAs or MPO- ANCAs could then result in the in situ formation of I C S . ~ ~ Another indication that this may occur comes from a recent study identifying MPO-ANCAs in guanidine extracts of glomerular immune deposits of an MPO-ANCA-positive patient with systemic lupus erythematos~s.~~

AntiEndothelial Cell Antibody Antigens

AECAs can be detected in approximately 80% of patients with WG and MPA4O, 91 and in 70% of patients with CSS.93 AECA antigens could be a source of IC formation. AECAs are a group of antibodies directed against a variety of endothelial structures.6 AECAs usually recognize multiple antigenic determinants. These determinants could be constitutively expressed antigens, constitutively expressed antigens that are con- sequently modulated by c y t ~ k i n e s ~ , ~ ~ , ~ ~ ~ ; cryptic antigens modulated by cytokines; or molecules that adhere to endothelial cells such as DNA, MPO, or p2-glycoproteins.6,16,29,73,89 The binding of AECAs to these antigens induces IC formation that could initiate the vasculitic process.

Bacterial Antigens

Bacterial antigens may also be a source of IC formation. In 1936, Friedrich Wegener was the first to suggest that WG was triggered by an infection of the airways and that all its clinical manifestations were a result of an “allergic reaction to this infection.”lo9 Pinching et alsl showed that in 9 of 20 patients with WG, relapses were preceded by a bacterial or viral infectious episode. Furthermore, 10 of 18 patients had a history of chronic infection of the respiratory tract before the onset of WG. Several bacteria have been implicated in the induction of vasculitis or have been implicated as being responsible for relapses of the disease (e.g., Klebsiella aerogenes, Staphylococcus aureus, Haemophilus influenza, Ba- cill us subtilis) .81

In 1994, our group reported that 67% of patients with WG were


chronic nasal carriers of S. aureus and that this carriage was a substantial risk factor for the development of relapses of this disease.” Furthermore, we demonstrated that prophylactic treatment with cotrimoxazole, an antibiotic that potentially eliminates staphylococcal nasal carriage, re- duced the relapse freq~ency?~ suggesting a role for S. uureus carriage in the pathophysiologic characteristics of WG. Yousif et alllo isolated several cationic proteins of S. aureus and discovered that a number of these proteins bound to glomerular structures. These cationic proteins could act as planted antigens, resulting in the in situ formation of ICs. To test this hypothesis, animal models were developed and showed that at least two of these staphylococcal antigens were capable of inducing glomerulonephritis in rats.4l. ll1

Recently, we also reported that a cationic protein of S. aureus, staphylococcal acid phosphatase (SAcP), is capable of binding to HUVECs and human glomerular endothelial cells in vitro by way of charge- interactionP Because we also found antibodies directed against SAcP in patients with WG,9 we hypothesized that in WG patients who carry S. uureus chronically, SAcP may enter the bloodstream and subsequently bind to endothelial cells. In the presence of antibodies directed against SAcP, ICs are formed. To confirm that SAcP could induce a glomerulonephritis by binding to glomerular endothelium, we developed an animal model in which SAcP was locally perfused into the left kidney of SAcP-immunized Brown-Norway rats.1° Ten days after perfusion, the immunized animals developed a severe crescentic glomerulonephritis similar to what can be seen in patients with WG.

Because SAcP is capable of causing glomerulonephritis in an animal model, we postulated that this antigen may be present in renal biopsies of patients with WG. Using a polyclonal antibody directed against SAcP, we detected the presence of SAcP in 3 of 19 renal biopsies of patients with WG. A monoclonal antibody directed against SAcP confirmed this finding in 2 of these 3 biopsies. Ten control biopsies of patients with other forms of glomerulonephritis did not show any staining using either the polyclonal or monoclonal antibody.” As a result, SAcP is a candidate for initiating glomerulonephritis in patients with WG.

SUMMARY

The role of ICs in ANCA-associated vasculitides remains controver- sial. The ANCA-associated vasculitides are described as being pauci- imrnurie. We hypothesize that the absence of ICs is a result of an exaggerated inflammatory response caused by the presence of ANCAs. We present evidence indicating that ICs may play a role in the initiation or relapses of the disease. The nature of the involved antigen(s) is not yet known. Possible candidates are reviewed and include ANCA antigens, AECA antigens, and staphylococcal antigens.

844 BRONS et a1

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are antineutrophil cytoplasmic antibody-associated vasculitides pauci-immune?

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