Autoimmunity is triggered by cPR-3(105-201), a protein complementary to human autoantigen proteinase-3

Bacterial DNA motifs trigger ANCA production in ANCA-associated vasculitis in remission

OBJECTIVES

CpG motifs, which are highly prevalent in bacterial DNA, have been shown to trigger the production of ANCA in vitro by B lymphocytes from patients with active ANCA-associated vasculitis (AAV). Staphylococcus aureus is associated with relapses in AAV, and CpG motifs from staphylococcal DNA may trigger ANCA production in AAV patients in remission. We investigated the presence of ANCA-producing B lymphocytes during quiescent disease and tested the capacity of these cells to produce ANCA in response to CpG.

METHODS

Expression of Toll-like receptor 9 (TLR9) by B lymphocytes from AAV patients and controls was assessed. Peripheral blood mononuclear cells were isolated from 23 PR3-ANCA and 15 MPO-ANCA patients (33 quiescent, 5 active disease) and 14 healthy controls, and cultured for 12 days in the presence of cytosine-phosphate-guanine oligodeoxynucleotide (CpG-ODN) and IL-2. B-lymphocyte activation, differentiation, immunoglobulin production and in vitro ANCA production were studied.

RESULTS

TLR9 expression by B lymphocytes was comparable in AAV patients and controls. B lymphocytes were activated and differentiated towards a plasma cell phenotype in response to CpG-ODN and IL-2. ANCA were produced in vitro by 13 out of 23 PR3-ANCA patients and 3 out of 15 MPO-ANCA patients.

CONCLUSIONS

We conclude that ANCA-producing B lymphocytes can be present in the peripheral blood of AAV patients during remission. These autoreactive B lymphocytes are triggered by CpG-ODN and IL-2 to produce ANCA in vitro. CpG motifs may trigger the production of ANCA in vivo, contributing to the development of relapses in AAV.

ANCA-associated vasculitides--advances in pathogenesis and treatment

Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV) include Wegener granulomatosis, microscopic polyangiitis, Churg-Strauss syndrome and renal-limited vasculitis. This Review highlights the progress that has been made in our understanding of AAV pathogenesis and discusses new developments in the treatment of these diseases. Evidence from clinical studies, and both in vitro and in vivo experiments, supports a pathogenic role for ANCAs in the development of AAV; evidence is stronger for myeloperoxidase-ANCAs than for proteinase-3-ANCAs. Neutrophils, complement and effector T cells are also involved in AAV pathogenesis. With respect to treatment of AAV, glucocorticoids, cyclophosphamide and other conventional therapies are commonly used to induce remission in generalized disease. Pulse intravenous cyclophosphamide is equivalent in efficacy to oral cyclophosphamide but seems to be associated with less adverse effects. Nevertheless, alternatives to cyclophosphamide therapy have been investigated, such as the use of methotrexate as a less-toxic alternative to cyclophosphamide to induce remission in non-organ-threatening or non-life-threatening AAV. Furthermore, rituximab is equally as effective as cyclophosphamide for induction of remission in AAV and might become the standard of therapy in the near future. Controlled trials in which specific immune effector cells and molecules are being therapeutically targeted have been initiated or are currently being planned.

Temporal association of Streptococcus, Staphylococcus, and parainfluenza pediatric hospitalizations and hospitalized cases of Henoch-Schönlein purpura

OBJECTIVE

To determine if hospitalizations for specific infectious exposures are associated with hospital admissions for Henoch-Schönlein purpura (HSP).

METHODS

We conducted a retrospective cohort study using administrative data of children admitted to 40 children's hospitals between January 1, 2002, and December 31, 2008. We examined the association of standardized rates of group A ß-hemolytic Streptococcus (GABS), Staphylococcus aureus, parainfluenza, influenza, adenovirus, and respiratory syncytial virus (RSV)-associated hospital admissions with standardized rates of HSP hospital admissions on a month by month basis using autoregressive moving average process models to account for temporal autocorrelation and clustering by hospital.

RESULTS

Among the 3,132 admissions for HSP observed over the 7-year study period, hospital admissions were most frequent September through April, but with substantial variability between hospitals for each month. Accounting for these month by month differences within each hospital, the rate of HSP admissions in a given month increased significantly as the standardized rates of GABS (p = 0.01), S. aureus (p < 0.01), and parainfluenza (p = 0.03) admissions increased.

CONCLUSION

Our results demonstrate a local month by month temporal association between hospitalization for GABS, S. aureus, and parainfluenza and hospitalization for HSP. Future investigations will be required to determine causality.

Longitudinal studies of patients with ANCA vasculitis demonstrate concurrent reactivity to complementary PR3 protein segments cPR3m and cPR3C and with no reactivity to cPR3N

Antibodies recognizing the complement of the middle of PR3 (cPR3m) occur in ∼30% of PR3-anti-neutrophil cytoplasmic autoantibodies (ANCA)-vasculitis patients and immunization of animals with a peptide complementary to the middle of PR3 (cPR3m) induces not only anti-complementary PR3 antibodies, but also anti-PR3 antibodies derived through an anti-idiotypic response. PR3 epitopes recognized by patient ANCA, however, are not restricted to the middle of PR3. This prompted us to test for antibodies that react with proteins complementary to the terminal regions of PR3 (cPR3C and cPR3N) in PR3-ANCA patients. Anti-cPR3C reactivity was detected in 28% of patients but anti-cPR3N reactivity in only 15%. Ranked anti-cPR3C and anti-cPR3m reactivity correlated in the cohort, whereas there was no significant relationship between cPR3C and cPR3N reactivity. Serial samples from 3 patients' revealed that anti-cPR3C and anti-cPR3m reactivity followed a similar pattern over time. Serial samples from a fourth patient demonstrated an anti-cPR3N response without concurrent cPR3m or cPR3C reactivity. Epitope determination by mass spectrometry identified a 13-amino acid sequence on cPR3C that contained a common binding site recognized by antibodies from three patients. This peptide sequence contains a "PHQ" motif which was reported to be the basis for cross-reactivity of anti-cPR3m antibodies with plasminogen. Why these antibodies are detected in only ∼30% of the patients remains unclear. The data reveal that it is not due to lack of inclusion of flanking regions of complementary PR3 during screening. Instead, quite unexpectedly, the data demonstrate that patients' antibodies react with a restricted epitope that exists in both cPR3m and cPR3C.

The neonatal Fc receptor as therapeutic target in IgG-mediated autoimmune diseases

Therapy approaches based on lowering levels of pathogenic autoantibodies represent rational, effective, and safe treatment modalities of autoimmune diseases. The neonatal Fc receptor (FcRn) is a major factor regulating the serum levels of IgG antibodies. While FcRn-mediated half-life extension is beneficial for IgG antibody responses against pathogens, it also prolongs the serum half-life of IgG autoantibodies and thus promotes tissue damage in autoimmune diseases. In the present review article, we examine current evidence on the relevance of FcRn in maintaining high autoantibody levels and discuss FcRn-targeted therapeutic approaches. Further investigation of the FcRn-IgG interaction will not only provide mechanistic insights into the receptor function, but should also greatly facilitate the design of therapeutics combining optimal pharmacokinetic properties with the appropriate antibody effector functions in autoimmune diseases.

Natural autoantibodies to myeloperoxidase, proteinase 3, and the glomerular basement membrane are present in normal individuals

Anti-neutrophil cytoplasmic antibodies (ANCAs) have a pathogenic role in ANCA-associated vasculitis. The origin of ANCAs and anti-glomerular basement membrane (GBM) antibodies, however, is unknown. In this study, we determined whether natural autoantibodies against myeloperoxidase (MPO), proteinase 3 (PR3), and GBM were present in each of 10 healthy Chinese and Swedish individuals, negative for all three antigens by routine ELISA. Antibodies were purified from isolated IgG by antigen-specific affinity columns. Natural anti-GBM autoantibodies gave a linear staining pattern along the GBM of human renal sections. On ethanol-fixed granulocytes, both natural anti-MPO and anti-PR3 autoantibodies gave cytoplasmic staining. The titers of natural anti-MPO/PR3 autoantibodies were significantly lower than those from patients with vasculitis. In competition ELISA, the binding of natural anti-MPO autoantibodies could be inhibited by MPO, but not by PR3 or noncollagenous domains from type IV collagen. The same specificity results were found for natural anti-PR3 and anti-GBM autoantibodies. Overall, individuals of the Chinese origin had more natural autoantibodies than did those of the Swedish origin, but no other differences were found. Hence, our study shows that healthy individuals have masked circulating, noncross-reactive, antigen-specific natural autoantibodies against MPO, PR3, and GBM in their serum and IgG fractions. Further studies are needed to determine their role if any in the etiology of ANCA-associated vasculitis and anti-GBM disease.

Management of ANCA-associated vasculitis: Current trends and future prospects

The antineutrophil cytoplasm antibody (ANCA)-associated vasculitides are a spectrum of heterogeneous autoimmune diseases characterized by necrotizing small vessel vasculitis and the presence of ANCA. These chronic multisystem disorders may be life-threatening if there is major organ involvement, such as acute renal failure or pulmonary hemorrhage, and require significant initial immunosuppression and long-term maintenance treatment. Long-established protocols using cyclophosphamide and prednisolone have resulted in dramatically improved outcomes for patients since the 1970s. Subsequently, international collaboration has contributed to a growing evidence base and consensus in the management of these rare disorders. Modifications to traditional treatment protocols by the use of azathioprine or methotrexate rather than cyclophosphamide, and the introduction of newer agents, such as rituximab, has maintained outcomes whilst decreasing toxicity. However, the treatment limitations of incomplete efficacy, infection, and cumulative toxicity persist. These issues have continued to drive the search for safer and more effective modulation of the immune system using targeted immunotherapy. This review will explore the current evidence base for management of ANCA-associated vasculitis and future treatment prospects.

Pathogenesis of ANCA-associated vasculitis

Antineutrophil cytoplasm antibody (ANCA)-associated vasculitis (AAV) comprises a group of systemic inflammatory vasculitides associated with circulating autoantibodies directed against the neutrophil granule components proteinase 3 and myeloperoxidase. ANCA interact with their target antigens on cytokine primed neutrophils, causing neutrophil activation via several signaling pathways that culminates in endothelial interaction, degranulation, cytokine production, and endothelial and tissue damage. The presence of autoantibodies implies the assistance of autoreactive T-helper cells and B cells, and a failure of regulatory mechanisms. This article reviews the current evidence for the pathogenic mechanisms culminating in autoantibody production, the effects of ANCA-neutrophil and neutrophil-endothelial interactions, and the mechanisms of tissue damage.

Idiotype, anti-idiotype network of autoantibodies: pathogenetic considerations and clinical application

A common serologic finding in autoimmune diseases is the presence of autoantibodies against intracellular autoantigens. Recent data suggest that an anti-idiotypic network exists in these diseases, regulating the production of autoantibodies (idiotypic response). The anti-idiotypic antibodies can be monitored using complementary epitopes, designed according to the “molecular recognition” theory. The role of antiidiotypic antibodies in neonatal lupus and type 1 diabetes are discussed. In neonatal lupus, mothers with high anti-idiotypic antibody activity against anti-La autoantibodies are at lower risk of giving birth to an un-healthy child, as compared with mothers without anti-idiotypic antibodies. Similarly,the lack of particular anti-idiotypic antibodies against anti-GAD65 autoantibodies predispose in type 1 diabetes. These findings imply that antiidiotypic antibodies may confer protection from the harmful effect of autoantibodies in certain autoimmune diseases [corrected].

Prolonged infections associated with antineutrophil cytoplasmic antibodies specific to proteinase 3 and myeloperoxidase: diagnostic and therapeutic challenge

Chronic infections may mimic antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV). We investigated which markers may help in the diagnosis and the prognosis of infections associated with proteinase 3 (PR3) and myeloperoxidase (MPO)-ANCA. In this study (1993-2008)--with an average follow-up of 5.1 years--we compared 66 AAV patients with 17 PR3 and/or MPO-ANCA-positive patients with protracted bacterial (11/17) or viral (6/17) infections. Seven of 17 patients had subacute bacterial endocarditis (SBE), while six of 17 patients had various autoimmune manifestations of chronic hepatitis C virus (HCV) infection. We determined ANCA, antinuclear antibodies, anti-PR3, anti-MPO, anticardiolipin (aCL), antibeta 2 glycoprotein I (beta2-GP I), cryoglobulins, C3, and C4. Patients with infections were younger than AAV patients (p < 0.01). There was no difference in frequency of renal and skin lesions. AAV patients more frequently had pulmonary and nervous system manifestations (p < 0.01). Patients with infections more frequently had dual ANCA (high PR3, low MPO), aCL, anti-beta2-GP I, cryoglobulins, and hypocomplementemia (p < 0.001). Immunosuppressive therapy (IST) was used in five 17 patients who had persistently high ANCA, cryoglobulinemia, and hypocomplementemia. There was no difference in frequency of lethality and renal failure in the two study groups. In patients who are PR3- and/or MPO-ANCA positive, SBE and HCV infection should be excluded. Although similar in renal and skin manifestations in comparison to AAV, only patients with infections developed multiple serological abnormalities. In patients with infections, concomitant presence of ANCA, cryoglobulins, and hypocomplementemia was associated with severe glomerulonephritis. The serological profile should be repeated after specific antimicrobial or surgical therapy, since some cases might require IST.

The contribution of genetic variation and infection to the pathogenesis of ANCA-associated systemic vasculitis

The aetiology of anti-neutrophil cytoplasmic antibody (ANCA)-associated systemic vasculitis has not been well defined. Here we review two factors which may play a role in the pathogenesis of the disease: genetics and infection. In particular, we discuss the role of autoantibodies to LAMP-2, which may arise following infection with Gram-negative bacteria, and may contribute to the development of ANCA-associated systemic vasculitis in genetically susceptible individuals.

The cellular mechanism by which complementary Id+ and anti-Id antibodies communicate: T cells integrated into idiotypic regulation

The V region antigenic determinants (idiotopes (Ids)) of antibodies (Abs) have been suggested to be involved in regulating the immune system. Certain diseases such as diabetes mellitus have recently been associated with a disequilibrium between Id(+) and anti-Id Abs. However, it is unknown how Abs carrying complementary idiotypes (that is, Id(+) and anti-Id Abs) regulate each other at the level of B and T cells. In this study, we show that B lymphoma cells genetically equipped with anti-Id BCR V regions receive a signal when exposed to Id(+)Ig. Moreover, they become x 10(4) more efficient at presenting exogenous Id(+) Ab to CD4(+) T cells in vitro. Activated Id-specific T cells in turn regulated the Id-specific B lymphoma cells. Similar results were obtained in vivo in a surrogate model in which an Id-peptide was incorporated genetically into the C-region of a recombinant Ab that targeted IgD on B cells. The findings suggest that conventional T-B collaboration can explain communication between complementary Id(+) and anti-Id Ab at the cellular level. A model is suggested that integrates present and previous data on B-cell regulation by Id-specific T cells.

Mechanisms and markers of vascular damage in ANCA-associated vasculitis

Much progress has been made in understanding the pathogenesis of anti-neutrophil cytoplasmic antibodies (ANCA)-associated small-vessel vasculitis and interaction between ANCA and micro-vascular endothelial cells are centre stage. The interactions of these key players culminate in respiratory burst of the neutrophil with release of radicals and proteases and subsequent endothelial cell and tissue damage. During the last decade, markers have become available to assess the extent and/or acuity of vascular damage in a clinical setting. First, circulating endothelial cells (CEC) have emerged as reliable surrogate markers of endothelial damage in vasculitis. More recently, endothelial microparticles have been used and appear to reflect damage and activation of the cells. Data on endothelial progenitor cells in vasculitis are sparse but intriguing while a genuine progenitor cell deficiency remains controversial. The severely damaged phenotype of CEC in vasculitis led to the hypothesis that such circulating apoptotic and/or necrotic debris may itself be a mediator of disease and first data from experimental studies have added proof to this assumption. Such effects may well contribute to a pro-inflammatory environment in ANCA-associated small-vessel vasculitis and in vascular disease in general. Here, we review mechanisms and markers of endothelial damage and repair in ANCA-associated vasculitis and put these findings into perspective.

T cells and dendritic cells in glomerular disease: the new glomerulotubular feedback loop

A newly described glomerulotubular feedback loop may explain the relationship between glomerular damage, epitope spreading, tubulointerstitial nephritis, proteinuria as a progression factor, and the importance of the local milieu in kidney damage. It also opens the horizons for exciting innovative approaches to therapy of both acute and chronic kidney diseases.

Anti-PR3 immune responses induce segmental and necrotizing glomerulonephritis

Wegener's granulomatosis (WG) is a life-threatening autoimmune vasculitis that affects lungs, kidneys and other organs. A hallmark of WG is the presence of classic anti-neutrophil cytoplasmic antibodies (c-ANCA) against self-proteinase 3 (PR3). Little is known about the role of these antibodies and PR3-specific immune responses in disease development. In this study, we demonstrate that PR3-specific autoimmune responses are pathogenic in non-obese diabetic (NOD) mice with an impaired regulatory arm of the immune response. Immunization of autoimmunity prone NOD mice with rmPR3 (recombinant mouse PR3) in complete Freund's adjuvant (CFA) resulted in high levels of c-ANCA, without detectable disease development. However, when splenocytes from these immunized mice were transferred into immunodeficient NOD-severe combined immunodeficiency (SCID) mice, the recipient mice developed vasculitis and severe segmental and necrotizing glomerulonephritis. No disease developed in NOD-SCID mice that received splenocytes from the CFA-alone-immunized donors (controls), indicating that disease development depends upon PR3-specific immune responses. In contrast to the pathology observed in NOD-SCID mice, no disease was observed when splenocytes from rmPR3-immunized C57BL/6 mice were transferred into immunodeficient C57BL/6-RAG-1(-/-) mice, suggesting that complex and probably multi-genetic factors play a role in the regulation of disease development.

Anti-neutrophil cytoplasmic antibody pathogenesis in small-vessel vasculitis: an update

Vasculitides associated with serum positivity for anti-neutrophil cytoplasmic antibodies (ANCAs) that affect small- to medium-sized vessels are commonly known as ANCA-associated vasculitis (AAV) and include Wegener's granulomatosis, microscopic polyangiitis, and Churg-Strauss syndrome. Evidence derived from both in vitro studies and recent animal models points to a pathogenic role of ANCAs in AAV. In 2002, the first in vivo breakthrough in the pathogenesis of ANCAs showed that mouse ANCAs against myeloperoxidase (MPO) led to intrinsic pauci-immune renal vasculitis in mice. In 2004, a report using both in vitro and in vivo studies proposed that proteinase 3 (PR3)-directed autoimmunity involved the complementary peptide of PR3 (cPR3), which is encoded by the antisense strand of the PR3 gene. The last breakthrough came in October 2008 with a previously undescribed molecular explanation for the origin and development of injury in pauci-immune renal vasculitis, with potential clinical implications. This report showed that infection by fimbriated bacteria may trigger cross-reactive autoimmunity to a previously characterized ANCA antigen, lysosomal membrane protein-2, which is contained in the same vesicles that harbor MPO and PR3. Infection by fimbriated bacteria resulted in the production of autoantibodies, which activated neutrophils and killed human microvascular endothelium in vitro and caused renal vasculitis in rats. Although the evidence for a pathogenic role of ANCAs, mainly MPO-ANCAs, is striking, various questions remain unanswered. Understanding the key pathogenic mechanisms of AAV may provide a safer, more rational therapeutic approach than the traditional (ie, corticosteroids and immunosuppressants) treatment strategy.

[Wegener's granulomatosis and microscopic polyangiitis]

Wegener's granulomatosis (WG) and microscopic polyangiitis (MPA) are primary systemic small vessel vasculitides, associated with a positive C/PR3-ANCA in WG and P/MPO-ANCA in MPA. The most prominently involved organs are the upper (only in WG) and lower respiratory tract and the kidneys. The diagnostic work-up is an interdisciplinary approach assessing disease stage and extent. Treatment is adapted to disease stage and extent and relies on a combination of a cytotoxic plus a tapering regimen of corticosteroids. Induction of remission in "early systemic" disease can be achieved with low-dose methotrexate. In severe generalized vasculitis cyclophosphamide (CYC) is the mainstay of therapy, in rapidly progressive glomerulonephritis in combination with plasmapheresis. After 3-6 months of induction CYC is switched to a maintenance treatment with azathioprine. Alternatives are leflunomide, mycophenolate or methotrexate (creatinine < 150 micromol/l). Age > or = 50 at diagnosis, renal dysfunction and pulmonary involvement are associated with higher mortality rates. The relapse rate is approximately 50% within 5 years, being higher in WG than MPA.

Microscopic polyangiitis triggered by recurrent methicillin-resistant Staphylococcus aureus bacteremia

Most of the purported links between microbial agents and primary small-vessel anti-neutrophilic antibody-positive (ANCA) vasculitides remain speculative. There is strong circumstantial evidence for the role of Staphylococcus aureus in the development of Wegener's granulomatosis, but its role in other ANCA-positive vasculitis syndromes is less clear. We describe a patient who developed a non-granulomatous, necrotizing small-vessel vasculitis with a positive anti-neutrophil cytoplasmic antibody of a perinuclear type (p-ANCA), along with anti-myeloperoxidase antibodies after recurrent episodes of methicillin-resistant Staphylococcus aureus bacteremia.

Autoreactive T-cell receptor (Vbeta/D/Jbeta) sequences in diabetes are homologous to insulin, glucagon, the insulin receptor, and the glucagon receptor

The hypervariable (Vbeta/D/Jbeta) regions of T-cell receptors (TCR) have been sequenced in a variety of autoimmune diseases by various investigators. An analysis of some of these sequences shows that TCR from both human diabetics and NOD mice mimic insulin, glucagon, the insulin receptor, and the glucagon receptor. Such similarities are not found in the TCR produced in other human autoimmune diseases. These data may explain how insulin, glucagon, and their receptors are targets of autoimmunity in diabetes and also suggest that TCR mimicking insulin and its receptor may be targets of anti-insulin autoantibodies. Such intra-systemic mimicry of self-proteins also raises complex questions about how "self" and "nonself" are regulated during TCR production, especially in light of the complementarity of insulin for its receptor and glucagon for its receptor. The data presented here suggest that some TCR may be complementary to other TCR in autoimmune diseases, a possibility that is experimentally testable. Such complementarity, if it exists, could either serve to down-regulate the clones bearing such TCR or, alternatively, trigger an intra-immune system civil war between them.

Wegener's granulomatosis: a model of auto-antibodies in mucosal autoimmunity

Wegener's granulomatosis (WG) is an autoimmune condition marked by vasculitis of small and medium sized vessels particularly affecting the upper respiratory tract and kidneys. There is a strong mucosal component similar to other autoimmune conditions such as systemic lupus erythematosus and Behçet's disease. While the pathogenesis of WG is not completely known, auto-antibodies such as IgG ANCAs have been implicated in endovascular damage and modulation of neutrophil/monocyte responses by Fc receptor (FcR) signaling. Due to the substantial mucosal involvement in WG (oral, nasal, and upper respiratory tract involvement), it is probable that IgA antibodies (perhaps IgA ANCAs) play a role in disease. Given discrepancies in associating ANCA levels with disease activity, future work should determine if IgA ANCAs are present in WG patients and examine the biology underlying the ANCAs' signaling partners--the FcRs.

Vasculitis syndromes: LAMP-2 illuminates pathogenesis of ANCA glomerulonephritis

The discovery that antibodies to a bacterial antigen can cross-react with a mammalian protein to cause pauci-immune necrotizing and crescentic glomerulonephritis opens up new possibilities for the diagnosis and treatment of this condition.

Antigenic complementarity between coxsackie virus and streptococcus in the induction of rheumatic heart disease and autoimmune myocarditis

A variety of clinical, epidemiological, and experimental data suggest that rheumatic heart disease and autoimmune myocarditis are not only similar in their pathogenesis, but may often be due to combined infections with coxsackie virus (CX) and streptococcus A bacteria (SA). This paper reviews the evidence for this hypothesis, provides some new experimental data supporting the hypothesis, and suggests specific experiments for testing it. While, it is well-established that the M protein of SA mimics myosin, we demonstrate using homology search tools that various CX proteins mimic actin. We further demonstrate that antibody against CX recognizes actin as an antigen, and that anti-actin antibodies recognize CX antigen. Thus, anti-CX antibodies may also target muscle. Moreover, since myosin and actin are molecularly complementary, it follows that some SA and CX proteins may be molecularly complementary. Some antibodies against these complementary proteins in SA and CX should therefore act like idiotype-antiidiotype antibodies. We show that, indeed, CX and SA antibodies precipitate each other. Thus, it is possible that combined CX-SA infections produce more severe disease by producing pairs of idiotypic antibodies that act like antiidiotypic antibodies as well, thereby, disregulating immune control and triggering an autoimmune reaction against both myosin and actin simultaneously. We predict that combinations of the appropriate actin- and myosin-like antigens from CX and SA will, therefore, be much more autoimmunogenic than antigens from CX or SA alone, and that the combination will not require use of adjuvants or self-proteins that many current protocols require. It is possible that co-infections involving CX or SA with other infectious agents may produce similarly enhanced disease.

Antineutrophil cytoplasmic autoantibodies: how should the biologist manage them?

Antineutrophil cytoplasmic antibodies (ANCA) are directed against enzymes found in the granules of the polymorphonuclear (PMN) leukocytes. They are detected by indirect immunofluorescence microscopy assays on human ethanol fixed neutrophils. Three different fluorescence patterns can be distinguished: a cytoplasmic pattern (cANCA), a perinuclear pattern (pANCA), and an atypical pattern (aANCA). The use of other fixatives, e.g., formalin and methanol, allows differentiation between the pANCA and the antinuclear antibodies. ANCA specificity is determined by solid phase assays (ELISA, immunodot, and multiplex assay). ANCA with high titres and defined specificities (antiproteinase 3 [PR 3] or antimyeloperoxidase [MPO]) are proven to be good serological markers of active primary systemic vasculitis: c/PR 3-ANCA for Wegener's granulomatosis and p/MPO-ANCA for microscopic polyangiitis. The former have higher sensitivity and specificity for Wegener's granulomatosis than the latter for microscopic polyangiitis. ANCA with low titres and unknown specificity have been detected in a wide range of inflammatory and infectious diseases leading to a critical reappraisal of the diagnostic significance of ANCA testing. Physicians must keep in mind the possible occurrence of infectious diseases like subacute endocarditis that could be dramatically worsened by irrelevant immunosuppressive therapy. ANCA findings in certain manifestations, such as the pulmonary-renal syndrome in which massive pulmonary hemorrhage can quickly be life-threatening, warrant ANCA testing as an emergency test for patient care.

Pathways to ANCA production: from differentiation of dendritic cells by proteinase 3 to B lymphocyte maturation in Wegener's granuloma

Wegener's granulomatosis, microscopic polyangiitis, and Churg-Strauss syndrome are idiopathic systemic vasculitides in which circulating anti-neutrophil cytoplasmic antibodies (ANCA) directed against proteinase 3 (PR3) or myeloperoxidase (MPO) are commonly found. Within the last 25 years, these antibodies were subject of intensive studies, and a growing body of evidence arose for a distinct role of ANCA in the pathogenesis of the ANCA-associated vasculitides (AAV). Yet, the evidence derived from clinical observations and in vitro studies remains circumstantial. The various animal models have provided substantial support for a pathogenic role of MPO-ANCA in vivo, but the debate if ANCA play a primary role in the pathogenesis of these diseases is still open. The aim of this review was to update current basic and clinical research on ANCA in the pathophysiology of AAV and to point out and discuss limitations and inconsistencies of the clinical and experimental evidence.

Molecular mimicry in pauci-immune focal necrotizing glomerulonephritis

Pauci-immune focal necrotizing glomerulonephritis (FNGN) is a severe inflammatory disease associated with autoantibodies to neutrophil cytoplasmic antigens (ANCA). Here we characterize autoantibodies to lysosomal membrane protein-2 (LAMP-2) and show that they are a new ANCA subtype present in almost all individuals with FNGN. Consequently, its prevalence is nearly twice that of the classical ANCAs that recognize myeloperoxidase or proteinase-3. Furthermore, antibodies to LAMP-2 cause pauci-immune FNGN when injected into rats, and a monoclonal antibody to human LAMP-2 (H4B4) induces apoptosis of human microvascular endothelium in vitro. The autoantibodies in individuals with pauci-immune FNGN commonly recognize a human LAMP-2 epitope (designated P(41-49)) with 100% homology to the bacterial adhesin FimH, with which they cross-react. Rats immunized with FimH develop pauci-immune FNGN and also develop antibodies to rat and human LAMP-2. Finally, we show that infections with fimbriated pathogens are common before the onset of FNGN. Thus, FimH-triggered autoimmunity to LAMP-2 provides a previously undescribed clinically relevant molecular mechanism for the development of pauci-immune FNGN.

Evolutionarily conserved antigens in autoimmune disease: implications for an infective aetiology

The immune system has evolved to eliminate or inactivate infectious organisms. An inappropriate response against self-components (autoantigens) can result in autoimmune disease. Here we examine the hypothesis that some evolutionarily conserved proteins, present in pathogenic and commensal organisms and their hosts, provide the stimulus that initiates autoimmune disease in susceptible individuals. We focus on seven autoantigens, of which at least four, glutamate decarboxylase, pyruvate dehydrogenase, histidyl-tRNA synthetase and alpha enolase, have orthologs in bacteria. Citrullinated alpha-enolase, a target for autoantibodies in 40% of patients with rheumatoid arthritis, is our main example. The major epitope is highly conserved, with over 90% identity to human in some bacteria. We propose that this reactivity of autoantibodies to shared sequences provides a model of autoimmunity in rheumatoid arthritis, which may well extend to other autoimmune disease in humans.

Antibodies with dual reactivity to plasminogen and complementary PR3 in PR3-ANCA vasculitis

Patients with inflammatory vascular disease caused by anti-neutrophil cytoplasmic autoantibodies (ANCA) can harbor antibodies not only to the autoantigen proteinase 3 (PR3) but also to complementary PR3 (cPR3(105-201)), a recombinant protein translated from the antisense strand of PR3 cDNA. The purpose of this study was to identify potential endogenous targets of anti-cPR3(105-201) antibodies. Patients' plasmapheresis material was tested for the presence of antigens reactive with affinity-purified rabbit and chicken anti-cPR3(105-201) polyclonal antibodies. Antigen-containing fractions were tested with patients' anti-cPR3(105-201) affinity-purified IgG, and putative protein targets were sequenced by mass spectrometry. Unexpectedly, plasminogen was identified as a target of anti-cPR3(105-201). Reactivity of affinity-purified antibodies from two patients was lost when plasminogen was converted to plasmin, indicating restricted specificity. Antiplasminogen antibodies from five patients bound plasminogen at a surface-exposed loop structure within the protease domain. This loop contains an amino acid motif that is also found in a portion of recombinant cPR3(105-201); site-directed mutagenesis of this sequence decreased antibody reactivity by 30%. Functionally, antiplasminogen antibodies delayed the conversion of plasminogen to plasmin and increased the dissolution time of fibrin clots. Serologically, antiplasminogen antibody levels were higher in PR3-ANCA patients (n = 72) than healthy control subjects (n = 63), myeloperoxidase-ANCA patients (n = 34), and patients with idiopathic thrombosis (n = 57; P = 0.001). Of the patients with PR3-ANCA, nine had documented deep venous thrombosis events, five of whom were positive for antiplasminogen antibodies. In summary, capitalizing on interactions with complementary proteins, specifically complementary PR3, this study identified plasminogen as a previously undescribed autoantigen in PR3-ANCA vasculitis.

Vasculitis and infections: contribution to the issue of autoimmunity reviews devoted to "autoimmunity and infection"

Infections are associated with secondary forms of vasculitis. However, there is increasing evidence that microbial agents play a role also in primary systemic vasculitides. For a long time it has been noted that Hepatitis B virus (HBV) is involved in polyarteritis nodosa (PAN) although the incidence of HBV-associated PAN seems to decline. Cryoglobulinemic vasculitis has been shown to be strongly associated with Hepatitis C Virus (HCV) infection, but this is most striking in Southern Europe and less in Northern Europe. Different microbial agents have been suggested to influence disease expression in other primary vasculitides but no specific association has been established. In Wegener’s Granulomatosis (WG) chronic carriage of Staphylococcus aureus (S. aureus) is associated with a strongly increased risk for relapsing disease. Various pathogenic pathways for this association have been suggested by clinical and experimental observations. Recent studies even suggest that S. aureus derived peptides, amongst others, may induce proteinase 3-ANCA via idiotypic–anti-idiotypic interactions. Treatment with co-trimoxazole in WG localized to the upper airways may result in (temporary) remission of the disease.

CpG oligodeoxynucleotide stimulates production of anti-neutrophil cytoplasmic antibodies in ANCA associated vasculitis

BACKGROUND

Wegener's Granulomatosis and Microscopic Polyangiitis are life-threatening systemic necrotizing vasculitides of unknown aetiology. The appearance of circulating antibodies to neutrophil cytoplasmic antigens (ANCA) is strongly associated with the development of the disease. A link between infection and disease has long been suspected, and the appearance of ANCA antibodies has been reported following bacterial and viral infections. The depletion of circulating B cells with monoclonal antibody therapy can induce remission, and this observation suggests a pathogenic role for B cells in this disease. As bacterial DNA is known to induce B cell proliferation and antibody production via TLR-9 stimulation, we have explored the possibility that unmethylated CpG oligodeoxynucleotide, as found in bacterial and viral DNA, may play a role in stimulating circulating autoreactive B cells to produce ANCA in patients with vasculitis.

RESULTS

We have confirmed that unmethylated CpG oligonucleotide is a potent stimulator of antibody production by PBMC in vitro. The stimulation of PBMC with CpG oligonucleutides resulted in the production of similar amounts of IgG in both ANCA+ patients and normal controls. In spite of this, PR3 ANCA+ patients synthesised significantly higher amount of IgG ANCA than normal controls. In MPO ANCA+ patients, there was a tendency for patients to produce higher amount of ANCA than controls, however, the difference did not reach significance. Furthermore, we were able to detect circulating MPO-reactive B cells by ELISpot assay from the peripheral blood of 2 MPO+ ANCA vasculitis patients. Together, this indicates that circulating anti-neutrophil autoreactive B cells are present in ANCA+ vasculitis patients, and they are capable of producing antibodies in response to CpG stimulation. Of note, CpG also induced the production of the relevant autoantibodies in patients with other types of autoimmune diseases.

CONCLUSION

Circulating ANCA autoreactive B cells are present in patients with ANCA+ vasculitis. The production of ANCA from these cells in response to unmethylated CpG stimulation lead us to propose that stimulation of these cells by immunostimulatory DNA sequences such as CpG oligodeoxynucleotide during infection may provide a link between infection and ANCA associated vasculitis. This phenomenon may also apply to other antibody mediated autoimmune diseases.

ANCA patients have T cells responsive to complementary PR-3 antigen

Some patients with proteinase 3 specific anti-neutrophil cytoplasmic autoantibodies (PR3-ANCA) also have antibodies that react to complementary-PR3 (cPR3), a protein encoded by the antisense RNA of the PR3 gene. To study whether patients with anti-cPR3 antibodies have cPR3-responsive memory T cells we selected conditions that allowed cultivation of memory cells but not naïve cells. About half of the patients were found to have CD4+TH1 memory cells responsive to the cPR3(138-169)-peptide; while only a third of the patients had HI-PR3 protein responsive T cells. A significant number of T cells from patients responded to cPR3(138-169) peptide and to HI-PR3 protein by proliferation and/or secretion of IFN-gamma, compared to healthy controls while there was no response to scrambled peptide. Cells responsive to cPR3(138-169)-peptide were not detected in MPO-ANCA patients suggesting that this response is specific. The HLADRB1(*) 15 allele was significantly overrepresented in our patient group and is predicted to bind cPR3(138-169) peptide with high affinity. Regression analysis showed a significant likelihood that anti-cPR3 antibodies and cPR3-specific T cells coexist in individuals, consistent with an immunological history of encounter with a PR3-complementary protein. We suggest that the presence of cells reacting to potential complementary protein pairs might provide an alternative mechanism for auto-immune diseases.

[Progress in pathogenesis and therapy of vasculitis syndrome]

Since antineutrophil cytoplasmic autoantibody (ANCA) was found, the researches in the pathogenesis of vasculitis syndrome have been developing. Proinflammatory cytokines including tumor necrosis factor-alpha are induced by certain infections, by which ANCA that binds to granule components of cytoplasm adhesions to endothelial cells. These endothelial cells produce proteolytic enzymes and oxygen radicals, which leads to vasculitis. It might be contributed in the production of ANCA that bacterial organisms are mimicry to the peptide sequences of granule components. The multicentric randomized clinical trials undertaken by the European Vasculitis Study Group (EUVAS) optimized that cyclophosphamide-corticosteroid combination therapy was useful to ANCA-associated vasculitis. It is increasing evidences that biologics are useful to ANCA-associated vasculitis, although it is necessary to take care of severe adverse effects.

Pathogenesis of PR3-ANCA associated vasculitis

Wegener's Granulomatosis (WG) is closely associated with antineutrophil cytoplasmic autoantibodies (ANCA), particularly those directed to proteinase 3 (PR3). ANCA directed to myeloperoxidase (MPO) are associated with microscopic polyangiitis (MPA) and the Churg Strauss syndrome. PR3-ANCA associated vasculitis differs from MPO-ANCA associated vasculitis particularly in the occurrence of granulomatous inflammation and more widespread disease in the former condition. Studies in experimental animals strongly suggest a pathogenic role for MPO-ANCA, but this is less clear for PR3-ANCA. Here, we review pathogenic pathways in PR3-ANCA associated vasculitis focussing on unique patterns of PR3 expression on the neutrophil membrane in WG, as surface expression of PR3 is a prerequisite for stimulation by PR3-ANCA; (PR3-specific) cellular immunity in WG; and the role of Staphylococcus aureus carriage in this disease. These factors, together, may explain, at least in part, differences in clinical expression between MPO-ANCA and PR3-ANCA associated vasculitis.

Hypotheses on the etiology of antineutrophil cytoplasmic autoantibody associated vasculitis: the cause is hidden, but the result is known

The first description of what is now known as antineutrophil cytoplasmic autoantibody-associated necrotizing vasculitis appeared more than 140 yr ago. Since then, many aspects of the pathogenic pathway have been elucidated, indicating the involvement of antineutrophil cytoplasmic autoantibodies, but why antineutrophil cytoplasmic autoantibodies are produced in the first place remains unknown. Over the years, many hypotheses have emerged addressing the etiology of antineutrophil cytoplasmic antibody production, but no exclusive factor or set of factors can so far be held responsible. Herein is reviewed the most influential hypotheses regarding the causes of antineutrophil cytoplasmic antibody-associated vasculitis with the aim of placing in an epidemiologic background the different hypotheses that are centered on environmental and genetic influences.

Neutrophil elastase, proteinase 3 and cathepsin G: physicochemical properties, activity and physiopathological functions

Polymorphonuclear neutrophils form a primary line of defense against bacterial infections using complementary oxidative and non-oxidative pathways to destroy phagocytized pathogens. The three serine proteases elastase, proteinase 3 and cathepsin G, are major components of the neutrophil primary granules that participate in the non-oxidative pathway of intracellular pathogen destruction. Neutrophil activation and degranulation results in the release of these proteases into the extracellular medium as proteolytically active enzymes, part of them remaining exposed at the cell surface. Extracellular neutrophil serine proteases also help kill bacteria and are involved in the degradation of extracellular matrix components during acute and chronic inflammation. But they are also important as specific regulators of the immune response, controlling cellular signaling through the processing of chemokines, modulating the cytokine network, and activating specific cell surface receptors. Neutrophil serine proteases are also involved in the pathogenicity of a variety of human diseases. This review focuses on the structural and functional properties of these proteases that may explain their specific biological roles, and facilitate their use as molecular targets for new therapeutic strategies.

Atypical p-ANCA is not a poor prognostic marker in Postinfectious Glomerulonephritis

Postinfectious glomerulonephritis (PIGN) most commonly follows streptococcal infection. Antineutrophil cytoplasmic antibodies (ANCA) are characteristically negative in PIGN. We report on five cases who had positive atypical pANCA at presentation. The outcome was typical of other cases of PIGN with complete resolution of the glomerulonephritis in all five patients. Atypical pANCA occurs in a number of inflammatory conditions and antigenic targets may include proteins other than myeloperoxidase or proteinase 3. The presence of atypical p-ANCA does not indicate a poor prognosis.