Anti-proteinase 3 antibodies, their characterization and disease associations

Rare Overlap of Granulomatosis With Polyangiitis in a Patient With Rheumatoid Arthritis

Granulomatosis with polyangiitis (GPA) is a systemic small/medium-sized vessel vasculitis, which is a member of the family of antineutrophil cytoplasmic auto-antibody-associated vasculitides. This disorder affects multiple organs as it is a systemic disease, but overlapping with rheumatoid arthritis is extremely rare, with few cases reported in the medical literature. We report a case of a 55-year-old female with a history of rheumatoid arthritis who presented with recurrent upper/lower respiratory tract symptoms that responded poorly to antibiotics. The patient had elevated antiproteinase antibodies, ANCA IgG titer with a cytoplasmic staining pattern, proteinuria, hematuria, chest imaging showing cavitating and non-cavitating masses, and biopsies of lung and nasal tissue confirming the diagnosis of GPA. Our patient was given immunosuppressant therapy and improvement in lab work and clinical symptoms were seen throughout the course of treatment. This case report is unique as GPA usually rarely presents with rheumatoid arthritis (RA), but in this case, the patient had a history of rheumatoid arthritis with a new biopsy-proven GPA. This case report will help future physicians to better diagnose similar cases and help to facilitate clinical recognition and treatment for the same.

Spontaneous hematoma of the thigh associated with antiproteinase-3 antibody in a patient with metastatic squamous cell carcinoma treated with nivolumab

We report an unusual case of spontaneous intramuscular hematoma associated with antiproteinase 3 antibody in a patient with metastatic squamous cell carcinoma receiving nivolumab and the medical literature is reviewed.

Immunoglobulin (Ig)M antibodies to proteinase 3 in granulomatosis with polyangiitis and microscopic polyangiitis

Anti-neutrophil cytoplasmic antibodies (ANCA) appear to play an important role in the pathogenesis of ANCA-associated vasculitis (AAV). However, ANCA alone are not sufficient to generate disease, and some evidence suggests that infectious triggers may serve as inciting events for AAV disease activity. Antibodies of the immunoglobulin (Ig)M isotype often serve as markers of recent infection, and IgM ANCA have been identified previously in patients with AAV, although the frequency and clinical relevance of IgM ANCA is not well established. We sought to characterize IgM ANCA more clearly by creating a novel enzyme-linked immunosorbent assay (ELISA) for IgM antibodies to proteinase 3 [IgM proteinase 3 (PR3)-ANCA], which we applied to two large, clinically well-characterized trial cohorts of patients with granulomatosis with polyangiitis and microscopic polyangiitis. In the first cohort, IgM PR3-ANCA occurred with a frequency of 15·0%, and were associated with a higher degree of disease severity and a trend towards a higher rate of alveolar haemorrhage (29·6 versus 15·7%, P = 0·10). Analysis of follow-up samples in this cohort showed that the presence of IgM PR3-ANCA was transient, but could recur. In the second cohort, IgM PR3-ANCA occurred with a frequency of 41·1%, and were also associated with a higher degree of disease severity. A higher rate of alveolar haemorrhage was observed among those with IgM PR3-ANCA (45·3 versus 15·8%; P < 0·001). The association of transient IgM PR3-ANCA with an acute respiratory manifestation of AAV suggests a possible link between an infectious trigger and AAV disease activity.

IgA and IgG antineutrophil cytoplasmic antibody engagement of Fc receptor genetic variants influences granulomatosis with polyangiitis

Granulomatosis with polyangiitis (Wegener's) is a rare autoimmune neutrophil-mediated vasculitis that can cause renal disease and mucosal manifestations. Antineutrophil cytoplasmic antibodies (ANCA) are present in many patients, vary in level over time, and induce neutrophil activation through engagement with Fc receptors (FcRs). Given roles for FcRs in ANCA-mediated neutrophil activation and IgA antibodies in mucosal immunity, we hypothesized that FcR genetics and previously unappreciated IgA ANCA affect clinical presentation. We assembled a total of 673 patients and 413 controls from two multicenter cohorts, performed ELISA and immunofluorescence assays to determine IgA and IgG ANCA positivity, and used Illumina, TaqMan, or Pyrosequencing to genotype eight haplotype-tagging SNPs in the IgA FcR (FCAR) and to determine NA1/NA2 genotype of FCGR3B, the most prevalent neutrophil IgG FcR. We evaluated neutrophil activation by measuring degranulation marker CD11b with flow cytometry or neutrophil extracellcular trap formation with confocal microscopy. Functional polymorphisms in FCGR3B and FCAR differed between patient groups stratified by renal involvement. IgA ANCA were found in ∼30% of patients and were less common in patients with severe renal disease. Neutrophil stimulation by IgA or IgG ANCA led to degranulation and neutrophil extracellcular trap formation in a FcR allele-specific manner (IgA:FCAR P = 0.008; IgG:FCGR3B P = 0.003). When stimulated with IgA and IgG ANCA together, IgG ANCA induced neutrophil activation was reduced (P = 0.0001). FcR genotypes, IgA ANCA, and IgG ANCA are potential prognostic and therapeutic targets for understanding the pathogenesis and presentation of granulomatosis with polyangiitis (Wegener's).

Anti-neutrophil cytoplasmic antibodies target sequential functional proteinase 3 epitopes in the sera of patients with Wegener’s granulomatosis

Many patients with Wegener’s granulomatosis (WG) have anti-neutrophil cytoplasmic antibodies (c-ANCA). Aside from being a diagnostic marker, these autoantibodies may play roles in disease pathogenesis. Proteinase 3 (PR3) is the primary target of c-ANCA in WG patient sera. Of 60 c-ANCA-positive patients, 10 patients were selected for detailed humoral epitope analysis, contingent upon serum availability, using samples with positive levels of anti-PR3 by enzyme-linked immunosorbent assay (ELISA). Sequential epitope specificities of anti-PR3 antibodies detected by screening the maximally overlapping solid-phase octapeptides of PR3 showed seven major common antigenic targets bound by WG patient sera. These include novel and previously identified sequential PR3 epitopes bound by c-ANCA. B cell epitope prediction algorithms identified all or part of the seven defined epitopes. Several epitopes share sequence and structural proximity with functional sites, including the catalytic triad and proposed binding sites of other potential proteins [PR3 complementary peptide and soluble endothelial protein C receptor (sEPCR)]. Epitope 4 (VVLGAHNVRTQ) had the highest binding prevalence (90%) and epitope 2 (AQPHSRPYMAS) has the highest average reactivity of the antigenic regions. Epitope 4 includes the interaction site between sEPCR and PR3 which may serve as an important interaction to down-regulate inflammation. Epitopes 3, 5 and 7 are in direct proximity to amino acids that form the catalytic triad of the protein. c-ANCA targets both unique and previously known sequential PR3 peptides. This information may prove useful in understanding anti-PR3-mediated disease pathogenesis in systemic vasculitides.

Uveitis Seroreactivity to Candidate pANCA Antigens: Mycobacterial HupB and Histone H1(69-171)

PURPOSE

Certain uveitis patients express the disease-marker antibody pANCA. Histone H1 (H1) and mycobacterial HupB (HupB) are recently identified candidate pANCA antigens. This study addresses the hypothesis that H1 and HupB are targets of disease-associated seroreactivity in pANCA+ uveitis.

METHODS

Sera from 293 uveitis patients were categorized for pANCA activity. H1(69-171) and HupB recombinant proteins were used as antigenic targets in ELISA studies. Selected sera were analyzed for reactivity by Western blot.

RESULTS

Seroreactivities to ANCA, H1(69-171), and HupB were frequently detected in uveitis patients. No significant relationship existed between the level of ANCA antibody and reactivity to either recombinant antigen. There was, however, a significant, positive correlation between H1(69-171) and HupB seroreactivities.

CONCLUSIONS

Correlation between H1(69-171) and HupB reactivities suggests the presence of a shared dominant epitope, which is recognized by antibodies in a substantial number of uveitis patients. Seroreactivities to ANCA and HupB/H1 are independent immunologic markers that may identify biologically distinctive subsets of uveitis.

Use of immunofluorescence and confocal laser scanning microscopy in identifying rare cases of anti-neutrophil cytoplasmic antibodies (ANCA) showing dual specificities to myeloperoxidase and proteinase3

Anti-neutrophil cytoplasmic antibodies (ANCA) are the immunodiagnostic markers for idiopathic necrotizing crescentic glomerulonephritis affecting mainly medium to small sized blood vessels. The diagnosis of ANCA associated vasculitis (AAV) is mainly based on clinical and histopathological characteristics along with the serological evidence. Immunofluorescence microscopy (IIF) is considered as the "gold standard" for ANCA detection, and ANCA showing two major patterns ie, cytoplasmic (c-ANCA) and perinuclear (p-ANCA) react with different antigenic targets of neutrophils like Proteinase3 (PR3) and Myeloperoxidase (MPO). A third unusual and rare immunofluorescence pattern called as "X- ANCA" or atypical ANCA is also sometimes seen. The difficulty in identification of ANCA immunofluorescence patterns is mainly seen due to the rare dual patterns seen in the same sera and also the additional nuclear immunofluorescence seen due to presence of anti-nuclear antibodies. ANCA testing by immunofluorescence and Confocal Laser scanning microscopy, as well as by specific ELISAs for detection of anti-PR3 and anti-MPO antibodies have helped in improving the diagnosis. Patients having dual specificities to MPO and PR3 in a patient is a rare finding. Among 425 clinically and histopathologically proven cases of AAV, eight patients (1.9%) had dual specificities, of which five patients showed mixed immunofluorescence pattern and 3 patients showed X-ANCA pattern which was confirmed by both immunofluorescence and Confocal Laser scanning microscopy and the dual specificities to MPO and PR3 were detected by individual ELISAs.

The binding of proteinase 3 antineutrophil cytoplasmic antibodies (PR3-ANCA) varies in different ELISAs

BACKGROUND

The demonstration of proteinase 3 specific antineutrophil cytoplasmic antibodies (PR3-ANCA), and the estimation of antibody values are useful in the diagnosis and management of patients with Wegener's granulomatosis (WG). However, external quality assessment programmes suggest that PR3-ANCA binding varies in different assays.

AIM

To demonstrate variations in PR3-ANCA binding in different commercial and in house enzyme linked immunosorbent assays (ELISAs).

METHOD

Binding of a PR3-ANCA standard and 19 sera from patients with WG was compared in eight commercial and in house assays. Binding was expressed in different units depending on the kit.

RESULTS

One commercial assay performed unsatisfactorily. Three commercial kits produced PR3-ANCA binding (70, 102, and 84 U/ml) close to the expected value for the standard (100 U/ml). Serial dilutions of this standard were linear in only one commercial assay and the in house assay. Sera from patients with WG with borderline binding in the in house assay bound in the eight commercial kits at 0-148 kit units; low binding sera ranged from 0 to 273 units; moderately strong sera bound at 7-260 units; and strongly binding sera bound at 13-336 units. In four assays, at least one strongly positive serum bound at levels greater than the provided range.

CONCLUSIONS

Levels of antibody binding and units of binding have not been standardised in commercially available PR3-ANCA ELISAs. This may affect the diagnosis and management of patients with WG, in addition to the implementation of international guidelines for treatment.

Wegener's granulomatosis diagnosed by testicular biopsy

Urogenital involvement, other than the kidneys, is extremely rare in Wegener's granulomatosis (WG) and occurs in less than 1% of the cases. When encountered it is confined to prostate, bladder, urethra, cervix, and vagina. Granulomatous infiltration of the testis from WG has not been cited in the medical literature. We report a case of WG in a Hispanic male who presented with sensorineural hearing loss and hemoptysis. He had a pulmonary lesion and a painless right testicular mass, which was found to have necrotizing granulomas on excisional biopsy. This may be the first reported case of WG diagnosed by testicular biopsy as testicular involvement is rare in WG. We believe that the actual incidence of testicular involvement in WG may be higher as genital examination may be ignored during routine physical examinations.

Atypical C-ANCA following high dose intravenous immunoglobulin

AIMS

(1) To assess a range of intravenous immunoglobulin products for atypical classical antineutrophil cytoplasmic antibody (C-ANCA) staining and to determine if this is present in patients treated with high dose intravenous immunoglobulin (2 g/kg/month) and replacement doses (200 mg/kg fortnightly); (2) using the United Kingdom national external quality assessment scheme (NEQAS), to determine if laboratories could differentiate this pattern from classical ANCA.

METHODS

ANCA testing was performed on 30 batches of intravenous immunoglobulin from several manufacturers. Six patients treated with high dose intravenous immunoglobulin and 11 receiving replacement doses of immunoglobulin for hypogammaglobulinaemia were tested for ANCA by indirect immunofluorescence on cytospin preparations of ethanol fixed neutrophils and by enzyme linked immunosorbent assay (ELISA). One of the positive immunoglobulin batches was tested blindly by 125 laboratories involved in NEQAS by indirect immunofluorescence and by ELISA in some laboratories.

RESULTS

16 of 31 batches of intravenous immunoglobulin from six different manufacturers were atypical C-ANCA positive. Three of six patients receiving high dose intravenous immunoglobulin and none of 11 patients on replacement doses were atypical C-ANCA positive. The results of the NEQAS assessment by indirect immunofluorescence were 68% C-ANCA positive, 17% negative, 9% atypical C-ANCA, and 6% P-ANCA.

CONCLUSIONS

Some but not all intravenous immunoglobulin products yield a positive atypical cANCA by indirect immunofluorescence. An identical pattern may be observed in patients receiving high dose intravenous immunoglobulin but not in those on replacement doses. Of laboratories participating in NEQAS, 68% reported this pattern as cANCA. This reinforces the importance of reporting only "classical ANCA," defined by international ANCA workshops, to maintain the specificity of ANCA immunofluorescence and its close disease associations.

Diagnostic value of classical and atypical antineutrophil cytoplasmic antibody (ANCA) immunofluorescence patterns

BACKGROUND

The "classical" antineutrophil cytoplasmic antibody (C-ANCA) pattern seen on indirect immunofluorescence (IIF) is characterised by granular cytoplasmic staining showing central or interlobular accentuation, and is strongly associated with antiproteinase-3 antibodies (PR3-ANCA) and Wegener's granulomatosis. However, many laboratories report C-ANCA in the presence of any cytoplasmic IIF staining, regardless of pattern, which risks reducing the diagnostic value of this pattern.

AIMS

To classify different cytoplasmic ANCA patterns and thus determine whether stringent application of the classical criteria for C-ANCA would produce better correlation between C-ANCA and (1) PR3-ANCA enzyme linked immunosorbent assay (ELISA) results; (2) a diagnosis of systemic vasculitis (including Wegener's granulomatosis).

METHODS

72 sera with cytoplasmic IIF collected over a two year period were analysed by IIF and a commercial PR3-ANCA ELISA kit.

RESULTS

Three IIF patterns were defined: "classical/true" C-ANCA as described above (n = 27 (37.5%)); "flat" ANCA with homogeneous cytoplasmic staining (n = 21 (29%)); and "atypical" ANCA which included all other cytoplasmic patterns (n = 24 (33.5%)). Twenty five of the 27 true C-ANCA sera (92.5%) contained PR3-ANCA (p < 0.0001), but none of the 21 with flat ANCA and only one of the 24 with atypical ANCA. From clinical data on 23 of the 27 true C-ANCA positive patients, 20 (87%) had evidence of Wegener's granulomatosis or systemic vasculitis (p < 0.0001 v the other two patterns). However, none of 19 sera with flat ANCA and clinical data had evidence of systemic vasculitis.

CONCLUSIONS

Restricting the term "c-ANCA" to the "classical" description of central/interlobular accentuation on IIF, will improve its correlation with PR3-ANCA positivity and a diagnosis of systemic vasculitis.

Pulmonary vasculitis

Pulmonary vascular inflammation may be seen in a variety of primary lung diseases and in the setting of numerous systemic illnesses. This article reviews those entities in which pulmonary vasculitis represents a central feature of the pathologic process (Wegener's granulomatosis, Churg-Strauss syndrome, and pulmonary capillaritis). In addition, features of pulmonary involvement in other systemic vasculitides (Giant Cell Arteritis, Takayasu's Arteritis, and Behçet's disease) are described. Finally, general principles for the treatment of vasculitis are reviewed.

pANCA antibodies in patients with anterior uveitis: identification of a marker antibody usually associated with ulcerative colitis

A pANCA autoantibody (antineutrophil cytoplasmic antibody, perinuclear pattern) has been described in uveitis patients, but its correlation with systemic illnesses and the specific type of pANCA has not been defined. The goals of this study were to determine the (1) frequency of pANCA autoantibodies in uveitis, (2) systemic associations in the pANCA + uveitis patients, and (3) type of pANCA antigen recognized by the uveitis-associated autoantibody. Serum was obtained from 59 patients with anterior uveitis or panuveitis and from nonuveitis controls. A detailed medical and family history was obtained from each subject at the time of phlebotomy. Sera were screened by neutrophil ELISA to determine the frequency of ANCA positivity. Immunofluorescence assays were then used to differentiate cANCA from pANCA. The specificity of the pANCA + antibodies was further characterized by DNase 1 sensitivity and granule antigen ELISAs. ANCA antibodies were detected in 29% of all patients with panuveitis or anterior uveitis. In 41% of these ANCA + patients, serum antibody detected a perinuclear antigen that was sensitive in all cases to DNase 1. The majority of pANCA + uveitis patients were either HLA-B27 positive or had systemic evidence of immune-mediated diseases. Two pANCA + patients had no medical or family history of other immune-mediated diseases. This study identifies a subset of uveitis patients distinguished by expression of a specific pANCA marker antibody. The characteristics of this antibody are similar to the pANCA antibody present in most patients with ulcerative colitis. Expression of the pANCA autoantibody in uveitis patients is a susceptibility marker for other immune-mediated diseases.

Antineutrophil cytoplasmic antibody (ANCA)-positive cutaneous leucocytoclastic vasculitis associated with antithyroid therapy in Graves' disease

Presented is a case of a 27-year-old male with Graves' disease on long-term propylthiouracil treatment who, when changed to carbimazole, rapidly developed a petechial and purpuric eruption on the legs, which subsequently flared on treatment with radioiodine. The clinical diagnosis of leucocytoclastic vasculitis was confirmed on skin biopsy. High-titre antineutrophil cytoplasmic antibodies in a perinuclear pattern (P-ANCA) were identified. No anti-myeloperoxidase activity was noted; therefore, the P-ANCA were classified in the atypical group. The target antigens, as determined by enzyme-linked immunosorbent assay, were lysozyme, lactoferrin and bactericidal/permeability increasing protein. Propylthiouracil and carbimazole are chemically related antithyroid drugs. There are reports of typical and atypical P-ANCA-positive cutaneous vasculitis due to propylthiouracil. Cutaneous vasculitis associated with atypical P-ANCA has not been noted previously to be temporally related to carbimazole use. The consideration of thionamides as possible aetiological agents in cases of P-ANCA-positive drug-induced vasculitis is suggested.

Anticytokeratins are a potential source of false-positive indirect immunofluorescence assays for C-ANCA

Antibodies to neutrophil cytoplasmic antigens (ANCA) targeted toward granule enzymes have been recognized as a valuable diagnostic tool in the detection of Wegener's granulomatosis and systemic vasculitides. However, the most commonly used method of detection, the indirect immunofluorescence assay, is prone to false-positive results due to antibodies of different pathological significance either targeted to, or cross-reacting with, similarly distributed epitopes. Using double immunofluorescence, the present study demonstrates that anticytokeratin antibodies are able to produce false-positive C-ANCA immunofluorescence assays. In addition, a case of natural appearance of cytokeratin-reactive antibodies causing a false-positive "pseudo-ANCA" staining pattern in a patient presenting with sepsis is reported. Since the expression of cytokeratins is almost exclusively confined to epithelial cells, the most plausible explanation for both phenomena is a crossreaction of anticytokeratin antibodies with granule associated epitopes. Due to the natural appearance of anticytokeratin antibodies in association with a variety of other pathologic entities, it is of crucial importance for the diagnostic significance of the C-ANCA immunofluorescence assay to exclude anticytokeratin caused false-positive results. It is shown that supplementary indirect immunofluorescence tests performed on cultured human epithelial cells readily distinguish anticytokeratin caused "pseudo-ANCA" from true C-ANCA.

Induction of interleukin-1 and subsequent tissue factor expression by anti-proteinase 3 antibodies in human umbilical vein endothelial cells

OBJECTIVE

To assess the ability of anti-proteinase 3 (anti-PR3) classic antineutrophil cytoplasmic antibodies (cANCA) to stimulate endothelial expression of tissue factor (TF), which is the main initiator of the coagulation cascade that can lead to endothelial injury and thrombosis in patients with Wegener's granulomatosis.

METHODS

Human umbilical vein endothelial cells (HUVEC) were grown to confluence and stimulated with affinity-purified anti-PR3 antibodies, Igs from healthy subjects, and endotoxin (lipopolysaccharide) as positive control.

RESULTS

TF activity was generated in anti-PR3-stimulated cells, as shown by a chromogenic test. This activity was inhibited by specific anti-TF antibodies. TF messenger RNA (mRNA) was found in anti-PR3-stimulated cells, as detected by reverse transcriptase-polymerase chain reaction, but not in cells stimulated with irrelevant human Igs or Igs from normal control sera. TF expression reached maximum levels 12 hours after exposure to the anti-PR3 cANCA, and did not require complement. TF mRNA expression was inhibited by cycloheximide, suggesting a requirement for protein synthesis. When added to the incubation medium, interleukin-1 (IL-1) receptor antagonist inhibited the induced TF mRNA expression, suggesting that cANCA-stimulated cells initiate IL-1 synthesis. Moreover, cANCA induced IL-1alpha mRNA before TF mRNA.

CONCLUSION

This study showed that anti-PR3 treatment of HUVEC induces sequential expression of IL-1alpha mRNA and TF mRNA, as well as their corresponding proteins. Both proteins could have pathogenic roles in the vasculitic process, since TF is the main initiator of the coagulation cascade.

Autoantibodies and target antigens in antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides

In this study of antineutrophil cytoplasmic antibody (ANCA)-associated diseases, we determined the prevalence of other autoantibodies and the antigen specificities of ANCA. ANA were common, occurring in 7 of 36 (19%) patients with Wegener's granulomatosis, in 16 of 34 (47%) patients with microscopic polyarteritis, in 6 of 11 (55%) patients with segmental necrotising glomerulonephritis and in 8 of 18 (44%) of those with ANCA-associated systemic vasculitis without renal involvement. ANA were associated more often with pANCA and microscopic polyarteritis than with cANCA (P < 0.05). Patterns were speckled (n = 23), homogeneous (n = 10) or nucleolar (n = 4). Anticardiolipin antibodies were also common, occurring in 10 of 25 (40%) patients with Wegener's granulomatosis, in 8 of 14 (57%) patients with microscopic polyarteritis and in 6 of 18 (33%) of those with a systemic vasculitis. However, anticardiolipin antibodies did not correlate with the presence of ANCA in any of the disease groups. Anti-GBM antibodies were demonstrated in only 2 of 25 (8%) patients with Wegener's granulomatosis, in 1 patient with microscopic polyarteritis (1/14, 7%) and in 1 with segmental necrotising glomerulonephritis (1/11, 9%). All four patients with anti-GBM antibodies had either cANCA or pANCA. In the second part of the study, the target antigens of ANCA were determined in Wegener's granulomatosis, microscopic polyarteritis, systemic vasculitis, inflammatory bowel disease, rheumatoid arthritis and systemic lupus erythematosus (SLE). Of the 19 sera with cANCA, 13 (68%) were directed against proteinase 3; other antigens were myeloperoxidase (1/19, 5%), elastase and lactoferrin together (1/19, 5%), lysozyme (1/19, 5%) or unknown (3/19, 16%). Of the 12 (58%) sera from patients with Wegener's granulomatosis who had cANCA, 7 bound to proteinase 3. Antimyeloperoxidase antibodies were present in 14 of 45 (31%) sera with pANCA; other antigens were proteinase 3 (5/45, 11%), elastase (3/45, 78%), lactoferrin (1/45, 2%), cathepsin G (5/45, 11%) or unknown (17/45, 38%). Antimyeloperoxidase antibodies were common in microscopic polyarteritis (6/14, 43%) and systemic vasculitis (5/16, 31%). However, the majority of target antigens in systemic vasculitis and rheumatoid arthritis with pANCA were not determined. "Atypical" ANCA were present in four patients, one with inflammatory bowel disease (1/8, 13%) and three with SLE (3/15, 20%). The specificities were cathepsin G, cathepsin G plus lactoferrin, or unknown in two sera. A recent report has suggested that bactericidal/permeability-increasing protein may be the target in patients with inflammatory bowel disease.

Antineutrophil cytoplasmic antibodies: major autoantigens, pathophysiology, and disease associations

Antineutrophil cytoplasmic antibodies (ANCA) are important serological markers for the primary systemic vasculitides, including microscopic polyarteritis and necrotizing crescentic glomerulonephritis. Numerous reports have established the clinical utility of ANCA titer in monitoring disease activity, relapses, and response to treatment. ANCA, detected by indirect immunofluorescence (IIF) assays using patient's serum and ethanol-fixed human neutrophils, produce two common fluorescent staining patterns: cytoplasmic (C-ANCA), involving a 29-kD neutral serine protease termed proteinase 3 (PR3), and perinuclear (P-ANCA), the result mainly of myeloperoxidase (MPO), but occasionally by other components of the azurophilic granules including lysozyme, elastase, cathepsins, and lactoferrin. Some sera contain granulocyte-specific antinuclear antibodies (GS-ANA), which require formaldehyde fixation of neutrophils to cross link cytoplasmic antigens for distinguishing between ANCA and the GS-ANA by IIF. Positive IIF is confirmed by Western blot analysis or specific enzyme-linked immunosorbent assay for PR3, MPO, and other neutrophil granule antigens. The C-ANCA pattern is highly specific for Wegener's granulomatosis, a disease characterized by granulomatous inflammation, necrotizing and crescentic glomerulonephritis, and vasculitis; P-ANCA is found in sera of individuals with vasculitis, glomerulonephritis, and several other diseases. ANCA are predominantly immunoglobulin (Ig)G isotype, but may be IgM and IgA. Various pathophysiologic mechanisms have been proposed involving ANCA-mediated neutrophil activation in a hypothetical model of vasculitic diseases: positive signals via the FcgammaRII (CD32) receptor after IgG-ANCA binding to membrane-associated PR3, relevant cytokines, production of adhesion molecules on both activated neutrophils and endothelial cells, and the release of neutrophil reactive oxygen species and degranulation causing endothelial cell damage. Interference of C-ANCA with PR3 proteolysis and PR3 inhibition physiologically by the alpha1-proteinase inhibitor may have a pathogenic role. No convincing data have been reported for the existence of autoreactive T lymphocytes reactive to any degree with the neutrophil azurophilic enzymes. Studies of various drug- and infectious agent-related diseases and ANCA may contribute to understanding the mechanism(s) involved in some vasculitides.

Autoantibodies in the diagnosis of systemic rheumatic diseases

Distinct profiles of autoantibodies directed to intracellular antigens can be detected in the systemic connective tissue diseases. They aid in establishing the correct diagnosis and are included in many sets of diagnostic criteria, such as the ones developed for systemic lupus erythematosus (anti-Smith antigen and anti-double-strand DNA antibodies), mixed connective tissue disease (anti-U1-nuclear ribonucleoprotein antibodies), and Sjögren's syndrome (SS) (anti-SS-A/Ro and anti-SS-B/La antibodies). They are useful prognostic markers in some situations and facilitate clinical and treatment follow-up. Autoantibodies have also been used as probes to gain insights into cell biology, helping to isolate and purify intracellular proteins involved in key cellular functions. We give detailed information on two of the most useful techniques for the detection of autoantibodies in the clinical and research laboratory settings, indirect immunofluorescence and immunoblotting. We also discuss several of the antigen-autoantibody systems found in systemic lupus erythematosus (Smith antigen, U1-nuclear ribonucleoprotein, SS-A/Ro, SS-B/La, proliferating cell nuclear antigen ribosomal ribonucleoprotein, double-strand DNA, histones, antiphospholipids, Ku, Ki/SL), systemic sclerosis (centromere, topo I, RNA polymerases, fibrillarin, polymyositis-Scl, Th/To), polymyositis/dermatomyositis (transferRNA synthetases, signal recognition particle, and others), and SS (SS-A/Ro, SS-B/La, nucleolar organizing region-90, p80-coilin), addressing their clinical significance, common detection methods, immunogenetic associations, and the molecular and cellular biology of the cognate antigens.

Antineutrophil cytoplasmic autoantibodies, autoantigens, and systemic vasculitis

Antineutrophil cytoplasmic antibodies (ANCA) encompass a heterogeneous group of autoantibodies targeting antigens in neutrophils (PMN), monocytes, and endothelial cells. ANCA are routinely detected by the indirect immunofluorescence technique (IFT) and at least three different patterns of fluorescence can be distinguished which have been assigned the acronyms cANCA, pANCA and aANCA. cANCA is mostly induced by proteinase 3 (PR3) antibodies (PR3-ANCA), and pANCA by myeloperoxidase (MPO) antibodies (MPO-ANCA), while aANCA has unidentified subspecificity. Over the past decade, ANCA have been the subject of extensive investigation. They have proved to be of significant value both as diagnostic tools and for follow-up in several forms of systemic vasculitis (e.g. Wegener's granulomatosis, WG; microscopic polyarteritis, MPA; Churg-Strauss syndrome, CSS) which are now termed 'ANCA-associated vasculitides'. Furthermore, it is suspected that the presence of ANCA is an important factor in the pathogenesis of these disease groups. Data regarding the detection of ANCA and their diagnostic value and role in the pathogenesis of vasculitic disorders will be discussed in this review. Growing evidence points to a pathophysiological and diagnostic relevance of the distribution of the ANCA target antigens PR3 and MPO (presence in the circulation, on cell membranes, and in tissue extracellularly). An autoimmune process has been implicated in the pathogenesis of ANCA-associated vasculitis, but it is uncertain which mechanism underlies the induction of the ANCA-related immunoresponse. In this paper mechanisms such as antigenic cross-reactivity between human PMN proteins and extrinsic antigens by molecular mimicry, idiotypic immunoglobulin regulation, and T-cell reactivity to PR3 and MPO will be discussed.