Anti-myeloperoxidase antibodies in sera from patients with propylthiouracil-induced vasculitis might recognize restricted epitopes on myeloperoxidase molecule

Myeloperoxidase (MPO) is one of the major target antigens of antineutrophil cytoplasmic antibodies (ANCA) in primary systemic vasculitis. It is known that propylthiouracil (PTU) could induce MPO-ANCA-positive vasculitis. The production of anti-MPO antibodies in patients with PTU-induced vasculitis may be different from that in patients with primary microscopic polyangiitis (MPA). One possible reason for this may be differences in epitope recognition. The aim of this study is to compare the epitopes of antibodies to MPO in sera from patients with PTU-induced vasculitis (n = 10) and MPA (n = 10). The sera were collected and used to inhibit monoclonal antibodies against human MPO (3D8 and 6B9) and affinity purified, horseradish peroxidase conjugated human anti-MPO antibodies (Pab1-HRP, Pab2-HRP) in a competitive inhibition enzyme-linked immunosorbent assay (ELISA) system using soluble human MPO as solid phase ligand. The Pab1-HRP and Pab2-HRP were affinity purified from plasma exchanges of a patient with PTU-induced vasculitis and a patient with MPA, respectively. The inhibition rates were evaluated and compared between the PTU and primary MPA groups. In the PTU group all 10 sera could inhibit 3D8: the average inhibition rate was 44.7% +/- 5.0%; 9/10 sera could inhibit 6B9: the average inhibition rate was 35.6% +/- 6.0%. However, in the MPA group all 10 sera could inhibit 3D8 and 6B9; the average inhibition rates were 68.4% +/- 16.1% (P < 0.01) and 62.2% +/- 17.2% (P < 0.01), respectively. Sera in both the PTU and MPA groups could inhibit Pab1-HRP and the inhibition rates were 81.4% +/- 9.4%versus 86.6% +/- 17.2% (P > 0.05). However, the average inhibition rate for Pab2-HRP in the MPA group was significantly higher than that in the PTU group (76.3% +/- 7.8%versus 58.9% +/- 15.5%, P < 0.01). We conclude that anti-MPO antibodies from patients with PTU-induced vasculitis and from patients with primary MPA could recognize more than one epitope on the native MPO molecule. Although the epitopes overlapped between the two groups, the epitopes of anti-MPO antibodies from patients with PTU-induced vasculitis might be more restricted.     

Follow-up of avidity and titer of anti-myeloperoxidase antibodies in sera from patients with primary ANCA-associated vasculitis

Antineutrophil cytoplasmic antibodies (ANCA) are important serologic markers for ANCA-associated vasculitis (AAV). Our previous studies in propylthiouracil (PTU)-induced AAV demonstrated that withdrawal of PTU resulted in clinical remission and significant decrease of avidity of PTU-induced myeloperoxidase (MPO)-ANCA. This study investigated the changes in avidity and titer of MPO-ANCA in sequential sera from some patients with primary AAV with different disease activities. Sequential sera samples of seven patients with MPO-ANCA-positive vasculitis at their initial onset, remission and relapse were collected. The avidity of MPO-ANCA was assessed by antigen-inhibition enzyme-linked immunosorbent assay (ELISA). The titer of MPO-ANCA was determined by a two-fold dilution of sera in MPO specific ELISA. The titer of MPO-ANCA was not significantly different between initial onset and remission. The avidity constant (aK) of MPO-ANCA in active phase is not significantly different from that in remission (724.9 ± 828.4 l/mol vs. 353.4 ± 551.7 l/mol, p = 0.303). No significant correlation could be found between aK and the level of Birmingham Vasculitis Activity Score, times of relapse, the number of organ involvement, serum creatinine, or CRP. Avidity and titer of MPO-ANCA did not decreased significantly during remission in AAV, indicating the chronic repeated antigen stimulation was not removed, which might be the reason for recurrent relapses.     

A comparison of the characteristics of circulating anti-myeloperoxidase autoantibodies in vasculitis with those in non-vasculitic conditions

Although circulating anti-neutrophil cytoplasmic antibodies (ANCA) specific for myeloperoxidase (MPO) are strongly associated with the presence of vasculitis, they have been described in sera from patients with other conditions. High levels of anti-MPO antibodies can also persist in sera from patients with vasculitis despite the achievement of clinical remission. One possible interpretation is that a potentially pathogenic subset of anti-MPO antibodies exists, which is only present in patients with active vasculitis. We therefore compared the characteristics of anti-MPO antibodies in sera from patients with active vasculitis (n = 18) with those present in remission (n = 9) and in a disease control group (n = 10) without clinical evidence of vasculitis. The class, subclass and ability of anti-MPO antibodies from the three groups of patients to recognize three different conformational epitopes were analysed using ELISA-based techniques. The expression of an idiotope, designated 9G4, was also examined. Epitope recognition by anti-MPO antibodies from all patients tested was found to be similar. Sera from patients with active vasculitis showed an over-representation of IgG4 subclass anti-MPO antibodies and a more frequent presence of IgM class anti-MPO antibodies. In disease controls, IgG1 anti-MPO antibodies were predominant. In vitro, neutrophil activation by ANCA has been shown to be dependent on engagement of neutrophil FcγRIIa receptors following binding of these autoantibodies to surface-expressed ANCA antigens. We found that active vasculitis may be associated with the presence of circulating anti-MPO antibodies which do not significantly bind this receptor, suggesting that mechanisms other than those dependent on FcγRIIa binding should be explored. In addition, the expression of the 9G4 idiotope on anti-MPO antibodies in 60% (12/18) of patients with active vasculitis and 20% (2/10) of disease control patients may indicate a common origin for anti-MPO antibodies in different individuals.     

Detection of anti-myeloperoxidase and anti-elastase antibodies in vasculitides and infections.

Autoantibodies that produce a perinuclear pattern on indirect immunofluorescent examination of ethanol-fixed neutrophils (pANCA) are found in about half of all cases of microscopic polyarteritis. These antibodies are often directed against myeloperoxidase or elastase and we have developed sensitive reproducible ELISAs for their detection and study. Seven sera from 19 patients with microscopic polyarteritis or segmental necrotizing glomerulonephritis contained anti-myeloperoxidase or anti-elastase antibodies or both. In contrast, only one of 18 sera from patients with Wegener's granulomatosis, where the pattern of immunofluorescence is predominantly cytoplasmic, had anti-myeloperoxidase antibodies and no anti-elastase antibodies were detected. Using sera from patients with microscopic polyarteritis, both anti-myeloperoxidase and anti-elastase antibodies were demonstrated to be of high affinity. There was no immunoglobulin class, subclass or light chain restriction noted. Anti-myeloperoxidase and anti-elastase antibodies were also found occasionally in anti-glomerular basement membrane disease, mixed connective tissue disease, systemic lupus erythematosus, post-streptococcal glomerulonephritis and atypical pneumonia. In further studies these antibodies were not associated with other lung infections, although anti-elastase antibodies were noted in one of 14 sera positive for ASOT that were tested. Anti-myeloperoxidase antibodies were found more frequently than anti-elastase antibodies and these antibodies were occasionally present together. In addition some sera with pANCA had neither anti-myeloperoxidase nor anti-elastase antibodies. The target molecules in these cases remain unclear.     

丙基硫氧嘧啶诱发的小血管炎和原发性小血管炎抗髓过氧化物酶抗体亲和力的比较

目的　比较丙基硫氧嘧啶(PTU)相关性小血管炎和原发性小血管炎抗髓过氧化物酶(MPO)抗体亲和力的大小及其与临床表现的关系。方法　以纯化的人MPO为抗原,采用抗原抑制性酶联免疫吸附法对我院确诊的13例PTU相关性小血管炎和19例原发性显微镜下多血管炎(MPA)的患者血清中抗MPO抗体的亲和力进行检测,分析其与临床表现的关系,并对两组抗体的亲和力大小进行比较。亲和常数(aK)的值以使血清抗MPO抗体百分结合率下降5 0 %所需的抑制抗原的摩尔浓度的倒数表示。结果　PTU组不同患者血清抗MPO抗体百分结合率下降5 0 %所需的抑制抗原量差异较大,从<0 .1μg ml到>5 0 μg ml不等。亲和常数的范围为<0 .2 8×10 7mol L到>14 0×10 7mol L ,其中位数为0 .75×10 7mol L。血清中抗 MPO抗体的亲和常数与伯明翰小血管炎活动性评分(BVAS)呈正相关(r=0 .5 83,P =0 .0 37) ,与抗体滴度、受累器官数、血红蛋白(Hb)、血沉(ESR)、C反应蛋白(CRP)、血肌酐(Scr)浓度均没有相关性(P >0 .0 5 )。MPA组不同患者血清抗MPO抗体百分结合率下降5 0 %所需的抑制抗原量差异较PTU组小,从<0 .1μg ml到1.5 6 μg ml不等,亲和常数的范围为8.97×10 7mol L到大于14 0×10 7mol L ,其中位数为5 6 .0×10 7mol L。血清中抗MPO抗体的亲和常数与血     

Anti-endothelial cell antibodies (AECA) in patients with propylthiouracil (PTU)-induced ANCA positive vasculitis are associated with disease activity

Increasing evidence has demonstrated that propylthiouracil (PTU) could induce ANCA positive vasculitis. However, our previous work has suggested that only one-fifth of the PTU-induced ANCA positive patients had clinical vasculitis and so the mechanism is not clear. Anti-endothelial cell antibodies (AECA) have been implicated in the pathogenesis of various vasculitides, including primary ANCA positive systemic vasculitis. The purpose of this study is to investigate the prevalence of AECA and their possible role in the pathogenesis of patients with PTU-induced ANCA positive vasculitis. Sera from 11 patients with PTU-induced ANCA positive vasculitis at both active and quiescent phases, and sera from 10 patients with PTU-induced ANCA but without clinical vasculitis, were studied. Sera from 30 healthy blood donors were collected as normal controls. Soluble proteins from 1% Triton-100 extracted in vitro cultured human umbilical vein endothelial cells were used as antigens and an immunoblotting technique was performed to determine the presence of AECA, and their specific target antigens were identified. In patients with PTU-induced ANCA positive vasculitis, 10 of the 11 patients in an active phase of disease were serum IgG-AECA positive and six protein bands of endothelial antigens could be blotted (61 kD, 69 kD, 77 kD, 85 kD, 91 kD and 97 kD). However, in the quiescent phase, seven of the 10 positive sera turned negative. None of the ANCA positive but vasculitis negative patients or normal controls were AECA positive. In conclusion, AECA could be found in sera from patients with PTU-induced ANCA positive vasculitis and were associated more closely with vasculitic disease activity.     

-463 G/A myeloperoxidase promoter polymorphism is associated with clinical manifestations and the course of disease in MPO-ANCA-associated vasculitis

Wegener's granulomatosis, microscopic polyangiitis, and Churg Strauss syndrome are forms of systemic vasculitides in which neutrophils and monocyte macrophages infiltrate the walls of small blood vessels, leading to destruction and occlusion. These diseases are associated with autoantibodies directed against granular components of neutrophils and monocytes, i.e., antineutrophil cytoplasmic antibodies (ANCA). The most common target antigens of ANCA in these vasculitides are myeloperoxidase (MPO) and proteinase 3 (PR3). ANCA-stimulated neutrophils injure endothelial cells, a process that is dependent upon the production of reactive oxygen radicals and the release of granular components such as MPO and PR3. Here we investigate whether a common functional MPO promoter polymorphism (-463 G/A) is associated with increased incidence and clinical aspects of ANCA-associated small vessel vasculitis. Genotyping was carried out for 142 patients with ANCA-associated small vessel vasculitis and 129 ethnically matched controls. The GG genotype was found to be associated with an increased risk for MPO-ANCA-associated vasculitis in females (86% GG, P = 0.045), but not males (64% GG, P = 1.0). Interestingly, the MPO A allele is associated with an increased incidence of relapses (P = 0.012) and an earlier age at diagnosis (P = 0.03) of MPO-ANCA-associated vasculitis. Both these associations are specific for MPO-ANCA and are not observed in patients with PR3-ANCA-associated vasculitis. These findings suggest that MPO expression levels influence the disease course of MPO-ANCA-associated vasculitis and further support the view that genetic factors are involved in the pathophysiology of this autoimmune disease.     

用硫氰酸盐洗脱法筛选高亲和力噬菌体抗体

目的 :建立一种从抗体库中筛选高亲和力噬菌体抗体的方法。方法 :选择已知亲和力高低不同的噬菌体抗体以不同的比例组成模拟抗体库 ,在常规筛选程序的基础上 ,用不同浓度的硫氰酸盐进行洗脱 ,选择性去除低亲和力抗体 ,保留高亲和力体 ,对最后获得的噬菌体抗体制备质粒DNA进行内切酶谱分析 ,判断其中高亲和力抗体的比例。结果 :实验证明工作浓度硫氰酸盐的孵育不影响噬菌体颗粒的感染活性 ;抗体库筛选过程中用硫氰酸盐进行洗脱 ,发现随着硫氰酸盐浓度的增加 ,洗脱回收的噬菌体抗体中高亲和力克隆的比例逐渐升高。结论 :硫氰酸盐洗脱法用于噬菌体抗体的筛选有助于成功获得期望的高亲和力抗体。     

Measurement of high affinity antibodies on antigen-immunoblots

We describe a semi-quantitative method for measuring the relative affinity of antigen-specific oligoclonal IgG bands separated by isoelectric focusing followed by blotting onto antigen-coated membrane and incubation with sodium thiocyanate. When the developed blot is digitised in greyscale, densitograms can be made and peak areas calculated using ImageJ freeware. By expressing peak area as a percentage of the total area under the curve we have shown that there is a statistically significant rise in percentage of peak area for a given band which persists with increasing molarities of sodium thiocyanate.     

抗中性粒细胞胞浆抗体在ANCA相关血管炎患者中的临床意义

目的抗中性粒细胞胞浆抗体(anti-neutrophil cytoplasmic antibody,ANCA)两种类型,核周型(p-ANCA)及胞浆型(c-ANCA),比较p-ANCA阳性与c-ANCA阳性的ANCA相关血管炎(ANCA-associated vasculitis,AAV)患者临床特征、实验室指标及器官受累的差异。方法选取50例AAV患者,血清ANCA的检测采用间接免疫荧光法。根据ANCA血清分型分为p-ANCA阳性组与c-ANCA阳性组,同时检测两组患者血生化、尿常规、炎症指标、免疫指标;高分辨CT(high resolution CT,HRCT)评估AAV患者肺脏受累情况;AAV患者疾病活动度采用疾病累及范围指数(disease extent index,DEI)评分。结果 p-ANCA阳性组患者易伴发红细胞减少及肺间质疾病;c-ANCA阳性的患者年龄更小,病程更短,更易伴发镜下血尿、听力下降、鼻窦炎。两组的DEI评分无显著差异。结论 c-ANCA阳性患者临床表现重于p-ANCA阳性组患者,器官受累更重,预后更差。     

Practical considerations of the ability of monoclonal antibodies to detect antigenic differences between closely related variants

This report describes an investigation of the abilities of different immunoassays to detect differences in affinities between related antigens for particular monoclonal antibodies. Nine different monoclonal antibodies were used and 6 strains of influenza virus represented closely related antigens. Parameters defining assay sensitivity were estimated experimentally for each antibody in 4 different immunoassays. Predicted failures of particular assays to detect differences in antigen affinities, based on these parameters, were demonstrated. One assay method failed to detect heteroclitic activity of 1 antibody which was clearly evident in the other 3 assays. As well as supporting theoretical models of assay sensitivity derived in the preceding paper the experiments demonstrated a significant effect of antibody subclass.     

The effect of epitope density and antibody affinity on the ELISA as analysed by monoclonal antibodies

The antibody titre and the optical density values in an ELISA are influenced by the epitope density of the antigen and the affinity of the antibody tested. This has major implications in the interpretation of ELISA results.     

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.     

A rapid method for the determination of antibody affinity

A rapid method for estimating antibody affinity is described. To perform the assay fixed amounts of radiolabeled antigen and antibody are mixed in different total reaction volumes. The fraction of antigen bound to antibody is measured in aliquots from each reaction volume by the ammonium sulfate precipitation technique. Affinity constants can be estimated from these data graphically or by means of a microcomputer. This method is much quicker and easier to perform than traditional techniques for estimating antibody affinity.     

Theoretical considerations of the ability of monoclonal antibodies to detect antigenic differences between closely related variants, with particular reference to heterospecific reactions

In theory monoclonal antibodies can be used to analyse antigenic determinants in great detail by correlating differences in antibody affinity for variant antigens with their amino acid differences. In particular, heteroclitic antibodies should be detected, which would normally be masked in a polyclonal antiserum. Recognition of such antibodies may be important for our understanding of the scope of antibody repertoires particularly when the immunogen is closely related to a component of the immunised animal. In practice the immunoassays commonly used to measure affinity differences between different antigens fall short of these capabilities. Mathematical studies were carried out to identify factors controlling the sensitivity of 4 types of assay to differences in affinities for different antigens. The most important factors controlling assay sensitivity were found to be the ratio of antibody affinity (K) to epitope density in direct binding assays, the ratio of K to antibody concentration in liquid phase competition assays, and the ratio of solid phase to liquid phase values of K for solid-phase competition assays. It is predicted that a combination of solid-phase competition assay with high epitope density and direct binding assay with low epitope density would result in optimal detection of heteroclitic antibodies and small differences in antibody affinity for cross-reactive antigens.     

Vascular thrombosis and vasculitis in the gastrointestinal tract are associated with poor prognosis in patients with COVID-19

Aim: To report pathologic findings in the gastrointestinal (GI) tract of coronavirus disease 2019 (COVID-19) patients. Material and Methods: we evaluated clinical and GI tract histologic findings in six COVID-19 patients that presented with GI symptoms like diarrhea, and abdominal pain. This study includes surgical resection specimens from five patients and two sets of biopsy specimens from one patient. Results: Idiopathic inflammatory bowel disease was considered in three of six cases based on clinical, radiologic, and endoscopic presentation. Histologically, the enteric mucosa had a spectrum of histologic changes, including active enteritis, chronic active enteritis, and transmural necrosis. Extensive thrombi in vessels and/or vasculitis were identified in three out of the six cases. The presence of extensive vascular thrombi is associated with poor prognosis, and the three patients deceased in a short period of time (ranges from 7-67 days, median 14 days) after admission for GI symptoms. Severe acute respiratory syndrome coronavirus 2 (SARS-Cov-2) RNA was detected in bowel tissue of one case. The other three patients recovered and were discharged and free of GI symptoms (follow-up period ranges from 235 days to 270 days, median 237 days). Conclusion: COVID-19 associated enteritis may mimic Crohn’s disease clinically, radiologically and endoscopically, and these two entities can be differentiated by pathologic findings. COVID-19 patients with GI symptoms may warrant a workup to evaluate for pathologic changes, as the presence of vasculitis and microthrombi may predict poor clinical outcome.     

硫氰酸盐洗脱法测定噬菌体抗体的相对亲和力

目的　建立一种测定噬菌体抗体相对亲和力的方法。方法　参照硫氰酸盐洗脱法测定完整抗体分子和Fab段相对亲和力的方法 ,在ELISA实验中以酶标抗M13为二抗检测 5个单克隆噬菌体抗体的相对亲和力 ,并与可溶性Fab段的相对亲和力进行比较。结果　噬菌体抗体可以耐受硫氰酸盐的洗脱 ,用硫氰酸盐洗脱法测定 5个噬菌体抗体所得亲和力排序与测定其相应可溶性抗体分子片段所得结果一致。结论　硫氰酸盐洗脱法可用于噬菌体抗体相对亲和力的测定。     

IgG subclass distribution and relative functional affinity of anti-myeloperoxidase antibodies in systemic vasculitis at presentation and during follow-up.

Circulating IgG autoantibodies to myeloperoxidase (MPO) are associated with renal vasculitis and have been implicated in its pathogenesis. However, raised levels of these autoantibodies may persist during clinical remission. We tested whether this paradox could be explained by immunoglobulin subclass switching during disease evolution, since different subclasses have different immunological and biochemical properties. Sera with anti-myeloperoxidase (anti-MPO) activity from 33 patients with active disease and 20 anti-MPO positive follow-up sera were studied by an ELISA using a panel of anti-human IgG subclass monoclonal reagents previously calibrated on human myeloma proteins. Anti-MPO subclass distribution in initial sera was: IgG1, 31 (94%); IgG2, 10 (30%); IgG3, 24 (73%); and IgG4, 22 (67%). IgG3 anti-MPO decreased during follow-up (P less than 0.02), with no change in IgG1 and IgG4. Relative functional affinity of anti-MPO antibodies in purified IgG subclasses was studied by the diethylamine method. IgG3 fractions consistently had a greater affinity for MPO than the other subclasses. Sequential studies in four patients demonstrated an affinity maturation for IgG1 and IgG4 anti-MPO as IgG3 anti-MPO disappeared. We conclude that dynamic changes of subclass distribution and affinity may explain discrepancies between anti-MPO antibody titre and disease expression.     

The affinity of anti-HBc antibodies in acute and chronic hepatitis B infection.

Antibodies to hepatitis B core antigen (anti-HBc) are found in the sera of all individuals infected with hepatitis B virus. A role for these antibodies has been suggested in determining the outcome of infection. In this study, the affinity of anti-HBc antibodies in asymptomatic virus carriers was compared with that of antibodies present in the sera of patients with chronic liver disease. Persistently infected individuals with no evidence of clinical disease were found to have anti-HBc antibodies of greater affinity, compared with the chronic liver disease group. Sera from patients with chronic hepatitis contained high levels of low-affinity antibody whereas antibody levels in asymptomatic carriers were significantly lower. These findings are discussed in relation to the predicted role of anti-HBc antibodies in mediating hepatitis B virus-related hepatocellular injury.     

Neutrophil extracellular trap formation is associated with autophagy‐related signalling in ANCA‐associated vasculitis

Increasing evidence indicates that aberrant neutrophil extracellular trap (NET) formation could contribute to the pathogenesis of anti‐neutrophil cytoplasmic antibody (ANCA)‐associated vasculitis (AAV). Recent research has provided evidence that a novel type of ANCA autoantibody, anti‐lysosomal membrane protein‐2 (LAMP‐2) antibody, may have a pathogenic role in AAV. We have shown previously that anti‐LAMP‐2 antibody‐stimulated NET formation contains autoantigens and anti‐microbial peptides. The current study sought to determine whether LAMP‐2, as a novel antigen of ANCA, was present on NETs in AAV patients, the influence of the anti‐LAMP‐2 antibody on the neutrophil apoptosis rate and the role of autophagy in anti‐LAMP‐2 antibody‐induced NET formation. NET formation was assessed using immunofluorescence microscopy, scanning electron microscopy or live cell imaging. The neutrophil apoptosis rate was analysed using fluorescence activated cell sorting (FACS). Autophagy was detected using LC3B accumulation and transmission electron microscopy. The results showed that enhanced NET formation, which contains LAMP‐2, was observed in kidney biopsies and neutrophils from AAV patients. The apoptosis rate decreased significantly in human neutrophils stimulated with anti‐LAMP‐2 antibody, and this effect was attenuated by the inhibitors of autophagy 3‐methyladenine (3MA) and 2‐morpholin‐4‐yl‐8‐phenylchromen‐4‐one (LY294002). The anti‐LAMP‐2 antibody‐stimulated NET formation was unaffected by benzyloxycarbonyl‐Val‐ Ala‐Asp (OMe)‐fluoromethylketone (zVAD‐fmk) and necrostatin‐1 (Nec‐1), which are inhibitors of apoptosis and necrosis, respectively, but was inhibited by 3MA and LY294002. Moreover, the proportion of LC3BI that was converted to LC3BII increased significantly (P = 0·0057), and massive vacuolizations that exhibited characteristics typical of autophagy were detected in neutrophils stimulated with anti‐LAMP‐2 antibody. Our results provide further evidence that autophagy is involved in ANCA‐induced NET formation in human neutrophils.