Taking anti-neutrophil cytoplasmic antibody (ANCA) testing beyond the limits.

The application of anti-neutrophil cytoplasmic antibody (ANCA)testing has received much interest since ANCA were discovered[1] and since they were reported to be useful in both the diagnosisand monitoring of disease activity in Wegener's granulomatosis(WG) [2]. Although there is little doubt that the recognitionof the association between the presence of ANCA and active vasculitishas had a very positive influence on research on the pathogenesisand treatment of ANCA-associated diseases (reviewed by Savage[3]), there are reasons to worry about the application of thisrecently gained knowledge in clinical practice. In this commentthe problems with the clinical application of ANCA tests arecategorized for the sake of clarity as (i) standardization problems,(ii) difficulties with application of the test in the appropriate     

IgA class antineutrophil cytoplasmic antibodies in primary sclerosing cholangitis and autoimmune hepatitis

Antineutrophil cytoplasmic antibodies (ANCA) of IgG class have been described at high prevalence in autoimmune hepatitis (AIH) and primary sclerosing cholangitis (PSC). Data on IgA class ANCA in these diseases are limited. The aim of this study was to determine the prevalence and fluorescence patterns of IgA class ANCA in AIH and PSC and to examine a relationship between the presence of IgA ANCA and clinical characteristics in these patients. Sera from 35 patients with PSC (21 with concomitant inflammatory bowel disease), 40 patients with AIH and 10 healthy controls were studied. ANCA were detected on ethanol-fixed neutrophils using an indirect immunofluorescence technique. ANCA of the IgA class were found in 20% of sera from patients with PSC and in 50% of AIH sera. The majority of AIH patients with IgA class ANCA showed a 'classical' perinuclear staining pattern, whereas the 'classical' and 'atypical' perinuclear fluorescence patterns were distributed equally in PSC. In sera containing IgG and IgA class ANCA simultaneously, IgG class ANCA showed an 'atypical' pANCA fluorescence pattern whereas IgA class ANCA produced a 'classical' perinuclear staining. The presence of IgA class ANCA was not associated with disease-specific clinical characteristics. IgA class ANCA are more frequently detected in sera of patients with AIH than PSC. The diversity of fluorescence patterns points to different target antigens of IgA class ANCA with distinct subcellular localizations.     

Inhibition of CD4+ T lymphocyte binding to fibronectin and immune-cell accumulation in inflammatory sites by non-peptidic mimetics of Arg-Gly-Asp.

The Arg-Gly-Asp (RGD) cell adhesion motif has been demonstrated in various studies to play a pivotal role in leucocyte and platelet interactions with plasma and extracellular matrix (ECM) glycoproteins. The recognition of the RGD sequence is mediated by heterodimeric receptors designated integrins of the beta 1 subfamily, expressed on distinct cell types, including T lymphocytes. We have recently shown that flexible non-peptidic mimetics of RGD, in which the two ionic side groups were separated by a linear spacer of 11 atoms, bound specifically to the platelet integrin alpha 11b beta 3, and inhibited T cell-mediated immune responses. The present study was designed to (i) further characterize the structural requirements for RGD interactions with CD4+ T cells, and (ii) examine the mechanisms by which the RGD mimetics interfere with immune cell reactivity in vivo. We now report that freezing the conformational degrees of freedom in the spacer chain, which fixes the relative orientation of the guanidinium and carboxylate side groups in a favourable manner, results in a higher level of inhibition of T cell binding to immobilized fibronectin, an RGD-containing ECM glycoprotein. In vivo, treatment of mice with relatively low doses of the RGD mimetics, but not the RGD peptide, inhibited the elicitation of an adoptively transferred DTH reaction. This inhibition was achieved by direct impairment of the ability of antigen-primed lymph node cells to migrate and accumulate in inflammatory sites. Hence, we suggest that the design and production of non-peptidic mimetics of RGD offers a novel approach to study defined parameters related to the structure-function requirements of small adhesion epitopes. Furthermore, this approach could be used therapeutically to inhibit pathological processes which depend on RGD recognition.     

Alpha 1-antitrypsin deficiency and anti-proteinase 3 antibodies in anti-neutrophil cytoplasmic antibody (ANCA)-associated systemic vasculitis.

alpha 1-antitrypsin (alpha 1-AT) is a naturally occurring inhibitor of proteinase 3 (PR3) and elastase, two of the target antigens of anti-neutrophil cytoplasmic antibodies (ANCA). An increased incidence of alpha 1-AT phenotypes associated with dysfunctional alpha 1-AT or low serum levels has been reported in patients with anti-PR3 antibodies. We have studied the relationship between ANCA, and phenotypes and serum levels of alpha 1-AT. Phenotypes usually associated with a moderate or severe reduction in alpha 1-AT serum levels or in dysfunctional activity were found more often in individuals with anti-PR3 antibodies than in the general population: four of the 31 patients (13%) with anti-PR3 antibodies had phenotypes MZ (n = 2), S (n = 1) or Z (n = 1) (P < 0.05). However, the corresponding alpha 1-AT serum levels were normal (n = 3) or elevated (n = 1). None of the 31 sera with anti-PR3 antibodies had low levels of alpha 1-AT. No abnormal alpha 1-AT phenotype was demonstrated in seven patients with anti-elastase antibodies, despite a low level of alpha 1-AT in one serum. Anti-myeloperoxidase antibodies are common in patients with ANCA, but no abnormal phenotype or low serum alpha 1-AT level was demonstrated in any of 29 sera containing these antibodies. Finally anti-glomerular basement membrane (GBM) antibodies occur occasionally in patients with ANCA-associated diseases, but again none of 10 sera had an abnormal alpha 1-AT phenotype or low serum level. ANCA were not demonstrated by indirect immunofluorescence in any serum from 73 patients with abnormal alpha 1-AT phenotypes. These results confirm that patients with anti-PR3 antibodies often have alpha 1-AT phenotypes that are usually associated with low serum levels of alpha 1-AT or with dysfunctional protein. Nevertheless, the incidence of anti-PR3 antibodies in patients with abnormal alpha 1-AT phenotypes is very low. This probably reflects the rarity of Wegener's granulomatosis, the major disease associated with anti-PR3 antibodies, and the relative frequency of abnormal alpha 1-AT phenotypes. The mechanism for the development of anti-PR3 antibodies in patients with abnormal alpha 1-AT phenotypes is not clear, but may relate to the increased propensity of unbound and uninhibited PR3 to stimulate autoantibody production.     

Induction of biologically active antineutrophil cytoplasmic antibodies by immunization with human apoptotic polymorphonuclear leukocytes

Translocation of intracellular components to the cell surface during the priming or apoptosis of polymorphonuclear leukocytes (PMN) is an important mechanism for interaction of antineutrophil cytoplasmic antibodies (ANCA) with these antigens. To test the capacity of apoptotic PMN to trigger production of ANCA, six groups of mice were immunized with either live or apoptotic lymphocytes, or with live, apoptotic, formalin-fixed, or lysed PMN. Mice immunized with both live and apoptotic neutrophils developed high titers of antibodies which gave a granular cytoplasmic immunofluorescent pattern. These antibodies were specific for lactoferrin and myeloperoxidase. Following a second intravenous infusion of apoptotic PMNs, mice developed anti-PR3 antibodies. Vasculitis lesions were not found in mice which developed ANCA. The ANCA-containing IgG fraction induced superoxide production by human PMNs. These results support the hypothesis that neutrophil-specific antigens presented on the cell membranes of apoptotic PMN may induce ANCA in the proper conditions.     

Dendritic cells and tolerance induction

We isolated a 27-kD protein using cation exchange chromatography from an acid extract of neutrophil granules. N-terminal amino acid sequence analysis of the first 10 residues showed that this protein is azurocidin, a member of the family of neutral serine proteinase found in the neutrophil, which shares amino acid sequence homology with the three other neutral serine proteinases, elastase, proteinase 3 (PR3) and cathepsin G, but unlike them is without proteolytic activity. To test whether, in addition to these proteases, azurocidin might be a target for the humoral autoimmune responses associated with human vasculitis, 185 indirect immunofluorescence (IIF)-positive ANCA sera, made up of four groups of sera with specificities for PR3 (n = 37), myeloperoxidase (MPO; n = 50), bactericidal/permeability-increasing protein (BPI; n = 41) and sera that recognized none of them (triple negative, n = 57), and 46 normal sera were screened for IgG anti-azurocidin antibodies using an ELISA incorporating purified azurocidin. Twenty of the 185 IIF-positive sera and 2/46 normal sera displayed reactivity with azurocidin. Positive sera could blot the 27-kD band by Western blot analysis. Further study of the 20 positive sera revealed that: (i) 10 also had autoreactivity for MPO, of which six additionally recognized lactoferrin; (ii) two had reactivity with BPI; (iii) the remaining eight sera were positive only for azurocidin. All 20 sera were from patients with systemic vasculitis, and four of the six sera with triple reactivity (for azurocidin, MPO and lactoferrin) were from patients with hydralazine-induced vasculitis. We concluded that: (i) azurocidin is a novel ANCA antigen; (ii) anti-azurocidin antibodies from a subgroup of patients might represent the consequence of a drug-induced multi-clone activation.     

Anti-myeloperoxidase IgG subclass distribution and avidity in sera from patients with propylthiouracil-induced antineutrophil cytoplasmic antibodies associated vasculitis

OBJECTIVE: Propylthiouracil (PTU) could induce MPO-ANCA-positive vasculitis. The aim of this study was to compare the IgG subclass distribution and avidity of MPO-ANCA in sera from patients with primary ANCA-associated vasculitis (AASV) and PTU-induced vasculitis. METHODS: Nineteen patients with primary AASV with MPO-ANCA and thirteen patients with PTU-induced vasculitis were enrolled in the current study. Sera in both active phase and remission were collected. Anti-MPO IgG subclasses were detected by antigen specific ELISAs using specific monoclonal antibodies as second antibodies, and MPO-ANCA avidity was assessed by antigen-inhibition ELISAs. RESULTS: In primary AASV, all four anti-MPO IgG subclasses could be detected in active phase with IgG1 (100%), IgG2 (73.7%), IgG3 (63.2%) and IgG4 (94.7%), and in remission, IgG1 and IgG4 subclasses in most patients remained positive. However, in PTU-induced vasculitis, anti-MPO IgG3 subclass could not be detected, the anti-MPO IgG subclasses in active phase were IgG1 (100%), IgG2 (61.5%) and IgG4 (46.2%). Furthermore, five out of the six patients (88.8%) with PTU-induced vasculitis with positive IgG4 subclass in active phase turned to negative in remission, however, only eight out of the fourteen patients (57.1%) with primary AASV turned to negative. The median avidity constant of MPO-ANCA was 56 (8.96 to >140) x 10(7) mol/l for patients with primary AASV and 0.7 (<0.28 to >140) x 10(7) mol/l for patients with PTU-induced vasculitis respectively. Furthermore, the relative levels of MPO-ANCA avidity were associated with elevation of ESR in primary AASV and were associated with BVAS scores in patients with PTU-induced vasculitis, respectively. CONCLUSION: MPO-ANCA IgG subclass distribution and avidity were different between patients with primary AASV and PTU-induced vasculitis. It was suggested that the mechanism of ANCA production in PTU-induced vasculitis was different from that in primary AASV, and the avidity of MPO-ANCA might be associated with disease activity.     

Anti-neutrophil cytoplasmic antibodies (ANCA) directed against bactericidal/permeability increasing protein (BPI): a new seromarker for inflammatory bowel disease and associated disorders

It was our purpose to determine the immunodiagnostic value of ANCA directed against BPI in diseases known to be associated with ANCA, such as ANCA-associated vasculitides, inflammatory bowel disease (IBD) and the associated condition primary sclerosing cholangitis. The immunoreactivity of recombinant BPI (rBPI) was established in order to develop an ELISA specific for rBPI. By means of this assay, BPI-ANCA were assessed in sera of 178 patients with IBD or the associated disorder primary sclerosing cholangitis, 112 patients with ANCA-associated vasculitides, and in sera of 182 disease and 140 healthy controls. BPI-ANCA were found to be closely associated with IBD and primary sclerosing cholangitis (34% and 44% of ANCA-positive sera, respectively). By contrast, BPI-ANCA positivity was low (<10%) in the double-negative sera of patients with ANCA-associated vasculitides and in disease and healthy controls. BPI-ANCA appear to constitute an important marker for IBD and primary sclerosing cholangitis, but not for the ANCA-associated vasculitides.     

C-antineutrophil cytoplasmic antibody positivity in vasculitis patients is associated with the Z allele of alpha-1-antitrypsin, and P-antineutrophil cytoplasmic antibody positivity with the S allele

BACKGROUND.: Antineutrophil cytoplasmic antibodies (ANCA) in vasculitis haveeither cANCA or pANCA patterns as defined by immunofluorescence.The target autoantigen of cANCA is usually proteinase 3 (PR3),whereas that of pANCA is usually myeloperoxidase (MPO). Alpha-1-antitrypsin(1AT) is the major physiological inhibitor of PR3, while MPOis an inhibitor of 1AT. METHODS.: To determine whether there was an association between ANCA positivevasculitis, ANCA pattern, and 1AT deficiency alleles, we studied1AT phenotypes of 99 cANCA and 99 pANCA positive vasculitispatients by isoelectric focusing and immunoblotting, and comparedthem with 2310 controls from the same geographical area. RESULTS.: C-ANCA patients showed an increased frequency of the Z allele(0.055 versus 0.018 in controls), conferring a relative riskof 3. They showed no increase in frequency of the S allele.P-ANCA patients showed an increased frequency of the S allele(0.091 versus 0.046 in controls) conferring a relative riskof 2. The frequency of the Z allele also appeared to be increased(0.030 versus 0.018 in controls), but this was not statisticallysignificant. CONCLUSIONS.: These findings demonstrate an association between ANCA-positivevasculitis and deficiency phenotypes of 1AT, and suggest a rolefor 1AT in the development of systemic vasculitis.     

抗嗜中性粒细胞胞浆抗体与狼疮性肾炎的关系

目的探讨抗嗜中性粒细胞胞浆抗体（ANCA）与狼疮性肾炎（LN）临床相关表现和发病机制的关系。方法分别应用间接免疫荧光法和酶联免疫吸附分析的方法,检测81例LN患者血清中的ANCA,并分析ANCA与LN临床表现和其它实验室检查结果之间的关系。结果单用间接免疫荧光法检测时,ANCA在LN中的阳性率是30.9％（25／81）。对间接免疫荧光法检测为阳性的血清,用酶联免疫吸附分析法进行验证,结果仅有72.0％（18／25）仍为阳性,全部是核周型ANCA（p-ANCA）,未见中央型ANCA（c-ANCA）出现。ANCA阳性组LN患者合并浆膜炎、神经系统累及、贫血、抗ds-DNA抗体阳性和低补体的频率均显著高于ANCA阴性组LN患者。结论ANCA在LN中的阳性率为30.9％,并与LN特定的临床表现相关,提示ANCA可能参与了LN的发病过程。