ANCA诱导中性粒细胞释放正五聚素蛋白3*

 目的：研究正五聚素蛋白3（PTX3）在中性粒细胞的表达及释放情况,为进一步探讨PTX3在抗中性粒细胞胞浆抗体（ANCA）相关性小血管炎（AAV）中的作用及机制奠定基础。方法：采用PolymorphprepTM进行密度梯度离心分离健康志愿者和AAV患者外周静脉血中性粒细胞,通过健康人血清、AAV患者血清、TNF-α和溶酶体膜蛋白2（LAMP-2）抗体分别刺激健康人外周血中性粒细胞,ELISA检测培养上清PTX3水平,免疫荧光观察中性粒细胞胞外捕网(NETs)的形成,激光共聚焦显微镜检测可溶性识别受体PTX3 的表达。结果：LAMP-2抗体及AAV患者血清均能促进中性粒细胞PTX3的释放。与正常中性粒细胞对照组相比,LAMP-2抗体刺激组中性粒细胞上清PTX3水平明显升高（P＜0.01）; AAV患者血清刺激组中性粒细胞中PTX3表达的荧光强度显著高于用健康人血清刺激的对照组（P＜0.01）,进一步通过激光共聚焦显微镜进行形态学观察,发现PTX3由中性粒细胞通过NETs形成释放。结论：PTX3可由ANCA诱导的NETs释放至胞外,参与血管炎的病理生理过程。     

PAD4在抗β2GP1/β2GP1复合物促进中性粒细胞胞外诱捕网形成中的作用

目的探讨肽酰基精氨酸脱亚氨酶4(PAD4)在抗β2GP1/β2GP1复合物诱导中性粒细胞胞外诱捕网(NETs)形成中的作用。方法分离健康人外周血中性粒细胞与抗β2GP1/β2GP1复合物(100μg/ml)共孵育一定时间,Western blot检测细胞PAD4表达;进一步采用PAD4抑制剂Cl-amidine(10μmol/L)预处理中性粒细胞,Western blot检测细胞瓜氨酸化组蛋白3(CitH3)蛋白质表达,ELISA检测细胞培养上清中髓过氧化物酶(MPO)-DNA相对含量。下腔静脉狭窄法建立APS小鼠血栓模型,并通过腹腔注射Cl-amidine(50 mg/kg)进行干预,Western blot检测血浆中CitH3蛋白质表达,荧光染色法检测血浆中循环游离DNA(cf-DNA)浓度,取下腔静脉血栓称其重量,观察Cl-amidine能否抑制APS-IgG诱导的NETs和血栓形成。组间差异采用t检验或单因素方差分析。结果抗β2GP1/β2GP1复合物能够显著下调细胞质中PAD4蛋白质表达水平[(3.67±0.32)vs(1.47±0.19),t=10.22,P<0.05],并使细胞核内PAD4蛋白质含量升高[(0.57±0.19)vs(2.97±0.31),t=11.49,P<0.05];Cl-amidine能显著抑制抗β2GP1/β2GP1复合物诱导的中性粒细胞CitH3蛋白质表达[(2.46±0.47)vs(0.46±0.13),t=12.24,P<0.01],明显减少培养上清中MPO-DNA含量[(4.09±0.94)vs(2.80±0.57),t=4.23,P<0.05]。在体内试验中,Cl-amidine能显著抑制APS小鼠血浆中CitH3蛋白质表达[(3.97±0.56)vs(1.09±0.45),t=11.83,P<0.01],明显降低APS小鼠血浆中cf-DNA浓度[(2685.0±735.8)vs(1784.0±577.0),t=3.93,P<0.05];与对照组EAPS小鼠相比,经Cl-amidine预处理的APS小鼠血栓形成明显减小[(8.22±3.06)vs(4.89±1.90),t=2.27,P<0.05]。结论PAD4参与了抗β2GP1/β2GP1复合物诱导的NETs形成,其可能在APS血栓形成中发挥重要作用。     

慢性华支睾吸虫感染对脂多糖刺激巨噬细胞反应的影响

 目的：了解慢性华支睾吸虫（Cs）感染的免疫状态及其对巨噬细胞表型和炎症反应的影响。方法：选择Sprague-Dawley雄性大鼠,按随机数字表法分组进行2部分实验。(1) 经口华支睾吸虫虫卵灌胃感染70 d建立慢性Cs感染模型,分为正常对照组和慢性Cs感染组,每组10只,用酶联免疫吸附法（ELISA）检测大鼠血清白细胞介素 4（IL-4)、IL-10、肿瘤坏死因子α（TNF-α）和干扰素γ（IFN-γ）水平,腹腔灌洗获取巨噬细胞,流式细胞术检测腹腔巨噬细胞亚型;(2)腹腔灌洗获取巨噬细胞,按照腹腔巨噬细胞的来源,分为空白对照组、正常组和慢性Cs感染组,以脂多糖（LPS,10 μg/L）刺激孵育,用ELISA法动态监测LPS刺激后0、2、12和24 h细胞培养上清液的TNF-α和IL-10的变化。结果：(1) 慢性Cs感染组大鼠血清促炎因子TNF-α［(77.64±3.25) ng/L］和IFN-γ［(212.69±12.60)  ng/L］水平较正常组TNF-α［(55.13±3.25) ng/L］和IFN-γ［(108.15±10.49)  ng/L］升高（均P＜0.05）,而抗炎因子IL-4［(248.24±8.99) ng/L］和IL-10［(223.56±5.60) ng/L］水平较正常组血清IL-4［(52.40±3.97) ng/L］和IL-10［(60.18±5.36) ng/L］也显著升高（均P＜0.01）,并可使腹腔巨噬细胞向替代活化型（M2型）巨噬细胞分化;(2) 2组腹腔巨噬细胞培养上清液TNF-α水平在LPS刺激后2 h即开始上升,至24 h达到高峰,慢性Cs感染组巨噬细胞在LPS刺激后2、12和24 h上清液的TNF-α水平均显著低于正常大鼠组［2 h： （88.20±1.91） ng/L vs（123.45±2.98） ng/L;12 h：（123.66±4.31） ng/L vs（161.11±7.38） ng/L;24 h：（154.52±4.83） ng/L vs（227.85±10.67） ng/L,均P＜0.05］,而IL-10的水平较正常组升高［2 h：（105.46±12.28） ng/L vs（80.86±2.28） ng/L;12 h：（194.19±8.62） ng/L vs（117.56±8.02） ng/L;24 h：（280.02±11.31） ng/L vs（168.14±8.97） ng/L,均P＜0.05］。结论：慢性Cs感染时宿主血清的促炎因子升高,而抗炎因子升高得更明显,使巨噬细胞向M2型极化;体外实验表明慢性Cs感染宿主的巨噬细胞对LPS刺激产生耐受。     

中性粒细胞胞外诱捕网在新生大鼠急性肺损伤中的作用

目的:探讨中性粒细胞胞外诱捕网(NETs)在新生大鼠急性肺损伤(ALI)中的作用。方法:取出生7 d的SD大鼠30只,按照随机数字表法分成生理盐水对照组、ALI组及ALI+脱氧核糖核酸酶(Dnase)组,每组10只。ALI组用脂多糖(LPS)以20 mg/kg的剂量腹腔注射,ALI+Dnase组则在注射LPS后即腹腔注射Dnase(5 mg/kg)。给药6 h后,水合氯醛麻醉大鼠,收集支气管肺泡灌洗液(BALF),荧光酶标仪检测BALF中游离DNA(cf-DNA)的含量;右肺组织固定于4%多聚甲醛中,HE染色观察各组大鼠肺组织形态结构;左肺组织制备肺组织匀浆,酶联免疫吸附测定(ELISA)法检测肺组织匀浆中白细胞介素6(IL-6)及肿瘤坏死因子α(TNF-α)的含量;使用免疫荧光法与Western blot检测各组大鼠肺组织中瓜氨酸化组蛋白H3(CitH3)及髓过氧化物酶(MPO)的生成情况。结果:与对照组相比,ALI组与ALI+Dnase组中cf-DNA、CitH3、MPO、IL-6及TNF-α水平均升高(P<0.05),肺组织中炎性细胞浸润严重;与ALI组相比,ALI+Dnase组新生大鼠肺组织中cf-DNA、Cith3、MPO、IL-6及TNF-α水平降低(P<0.05),ALI+Dnase组炎症浸润程度降低。结论:新生大鼠ALI中,NETs水平为反映肺组织损伤的重要指标,NETs可能为治疗新生儿ALI的新靶点。     

白蛋白对脂多糖诱导中性粒细胞胞外诱捕网生成的抑制作用

目的探讨白蛋白对脂多糖(LPS)诱导人外周血中性粒细胞胞外诱捕网(neutrophil extracellular traps,NETs)生成的抑制作用及机制。方法分离人外周血中性粒细胞,分别培养于无白蛋白和含生理浓度白蛋白的培养体系中,加入LPS刺激,同时使用钙离子(Ca²⁺)以及自噬调节剂干预,采用sytox green染色法检测NETs,采用Fluo-4 AM染色法检测胞内Ca²⁺水平,免疫荧光法检测NETs相关蛋白髓过氧化物酶(MPO)、弹性蛋白酶(NE)和瓜氨酸化组蛋白H3(cit-H3)以及自噬体相关蛋白LC3B的表达。结果 LPS可诱导中性粒细胞释放NETs,白蛋白可抑制NETs生成;白蛋白可降低LPS刺激下中性粒细胞胞内Ca²⁺浓度和自噬水平。Ca²⁺载体可增强中性粒细胞自噬水平并促进LPS诱导的NETs生成,Ca²⁺螯合剂可降低自噬水平并抑制NETs生成。自噬激动剂可显著增强NETs,自噬抑制剂则显著抑制NETs。结论白蛋白对LPS诱导中性粒细胞胞外诱捕网(N...     

分子伴侣性自噬参与LAMP-2抗体诱导中性粒细胞胞外捕网形成

目的探讨分子伴侣性自噬在LAMP-2抗体诱导中性粒细胞胞外捕网(NETs)形成的作用及机制。方法采用PolymorphprepTM方法分离健康志愿者和抗中性粒细胞胞浆抗体相关性血管炎(AAV)患者外周静脉血中的中性粒细胞,直接离体或LAMP-2抗体刺激健康人外周血中性粒细胞,通过自噬阻断剂3-甲基腺嘌呤(3-MA)和放线菌酮(CHX)进行干预,免疫荧光观测NETs的形成,免疫荧光法和免疫印迹法检测分子伴侣自噬相关蛋白LAMP-2A、Hsc70的表达。结果与正常中性粒细胞组相比,AAV患者中性粒细胞LAMP-2A表达增加(P=0.002 3);LAMP-2抗体可诱导中性粒细胞LAMP-2A、Hsc70蛋白表达明显上调(P<0.01),CHX能明显降低LAMP-2抗体引起的LAMP-2A、Hsc70蛋白表达(P<0.000 1);与3-MA组相比,CHX组能明显减少LAMP-2抗体诱导的NETs形成(P<0.000 1)。结论 LAMP-2抗体可诱导人中性粒细胞分子伴侣性自噬增强及NETs形成,放线菌酮可抑制此过程,提示分子伴侣性自噬可能参与了NETs的形成。     

烫伤后IL-6和IL-1α对大鼠外周血中性粒细胞凋亡的影响

目的:研究严重烫伤后血IL-6和IL-1α对中性粒细胞(PMN)凋亡的影响。方法:复制30%体表面积Ⅲ度烫伤大鼠模型;分离PMN,TUNEL荧光标记,流式细胞仪分析细胞凋亡;PMNcaspase3活性以荧光免疫吸附酶法测定;血清IL-6和IL-1α水平以酶联免疫法测定。结果:血清IL-6水平(μg/L)在伤后各组(3、6、12、24、48h依次分别为9.14±1.16、12.49±1.14、3.01±0.75、1.41±0.28和1.56±0.43)和IL-1α水平(ng/L)在伤后3、6、12h组(90.08±8.39、320.93±14.48和47.84±5.19)均分别显著高于伤前对照组IL-6(0.24±0.07)和IL-1α(27.65±4.86)水平(P<0.05);伤后各组PMN凋亡率(%)按时点依次为9.89±2.00、4.98±1.35、1.31±0.72、2.49±1.87和6.88±1.13显著少于伤前组13.66±3.88(P<0.05);PMNcaspase-3的活性测定结果与PMN的凋亡表现相一致。结论:大鼠烫伤后外周血PMN凋亡明显延迟;IL-6和IL-1α等细胞因子是重要的影响因素,减少细胞内caspase-3的激活可能是其机制之一。     

血清基质金属蛋白酶-9 在肺结核鉴别诊断中的价值分析

目的:分析血清基质金属蛋白酶-9(MMP 9)在肺结核鉴别诊断中的价值。方法:选取肺结核、肺炎、肺癌患者及健康志愿者各60 例分别作为肺结核组、肺炎组、肺癌组和对照组,对受试者血清MMP-9 水平检测分析。结果:对照组、肺结核组、肺炎组、肺癌组研究对象的血清MMP-9 水平分别为(1 976.36±907.44)ng/ ml、(4 350.45±2 574.75)ng/ ml、(2 135.68±1 263.56)ng/ ml 和(2 590.38±1 532.84)ng/ ml,差异有统计学意义(F =25.000,P<0.001),其中,肺结核组患者的血清MMP-9水平显著高于其他三组(P<0.001),肺癌组患者的血清MMP-9 水平显著高于对照组,差异有统计学意义(P<0.05)。血清MMP-9 在肺结核与健康人+肺炎+肺癌、健康人、肺炎、肺癌、肺炎+肺癌鉴别诊断中的受试者工作特征曲线下面积(AUC)分别为0.739、0.769、0.751、0.699、0.725(P 均<0.05)。结论:肺结核患者表现为血清MMP-9 水平显著升高,且幅度高于肺癌或肺炎患者,血清MMP-9 有助于肺结核鉴别诊断和筛查,但应注意适当提高诊断的灵敏度。     

鼠源性髓过氧化物酶特异性抗中性粒细胞胞质抗体的制备及鉴定

采用鼠源性髓过氧化物酶（myeloperoxidase, MPO）与弗氏佐剂混合注射的方式制备小鼠MPO特异性抗中性粒细胞胞质抗体（anti-neutrophil cytoplasmic antibody, ANCA）,并予以定性及定量检测。使用B6.129X1-Mpo^tm1Lus/J小鼠（即MPO敲除小鼠）,将mMPO与完全/不完全弗氏佐剂混合,通过腹腔注射方式诱导小鼠产生适应性免疫应答。采用定性ELISA以及间接免疫荧光法检测小鼠血清ANCA水平;采用肌酐检测试剂盒（肌氨酸氧化酶法）检测小鼠血清肌酐水平以评估其肾功能。ELISA检测结果显示,实验组小鼠血清MPO-ANCA的光密度D（450 nm）值较对照组显著升高（P<0.001）,约为对照组的5.6倍;间接免疫荧光法结果提示,实验组中性粒细胞胞质有较强的荧光信号,与MPO-ANCA的核周型特点相一致;H-E染色示部分肾小球囊壁层上皮细胞过度增殖;实验组与对照组小鼠血清肌酐水平检测结果差异不显著（P>0.05）。由此,注射MPO与弗氏佐剂混合液诱导MPO^-/-小鼠产生了抗MP...     

肺炎链球菌诱导中性粒细胞胞外捕获网形成

目的初步探究肺炎链球菌诱导中性粒细胞胞外捕获网(NETs)形成的作用及调节机制,为进一步研究奠定基础。方法采用免疫磁珠法分选C57BL/6小鼠骨髓中性粒细胞,肺炎链球菌刺激中性粒细胞,分别采用脱氧核糖核酸酶(DNase)降解NETs和NADPH氧化酶抑制剂二苯基氯化碘盐(DPI)预处理中性粒细胞阻断活性氧簇(ROS)生成,免疫荧光染色观察NETs结构,检测游离DNA定量观察NETs的生成。结果肺炎链球菌刺激中性粒细胞释放NETs,DNase降解NETs结构,阻断ROS生成后NETs形成受抑。结论肺炎链球菌能够诱导NETs形成,DNase直接降解NETs或DPI抑制NETs形成可以成为调节NETs生成的有效途径。     

Neutrophil extracellular traps can activate alternative complement pathways

The interaction between neutrophils and activation of alternative complement pathway plays a pivotal role in the pathogenesis of anti‐neutrophil cytoplasmic antibody (ANCA)‐associated vasculitis (AAV). ANCAs activate primed neutrophils to release neutrophil extracellular traps (NETs), which have recently gathered increasing attention in the development of AAV. The relationship between NETs and alternative complement pathway has not been elucidated. The current study aimed to investigate the relationship between NETs and alternative complement pathway. Detection of components of alternative complement pathway on NETs in vitro was assessed by immunostain and confocal microscopy. Complement deposition on NETs were detected after incubation with magnesium salt ethyleneglycol tetraacetic acid (Mg‐EGTA)‐treated human serum. After incubation of serum with supernatants enriched in ANCA‐induced NETs, levels of complement components in supernatants were measured by enzyme‐linked immunosorbent assay (ELISA). Complement factor B (Bb) and properdin deposited on NETs in vitro. The deposition of C3b and C5b‐9 on NETs incubated with heat‐inactivated normal human serum (Hi‐NHS) or EGTA‐treated Hi‐NHS (Mg‐EGTA‐Hi‐NHS) were significantly less than that on NETs incubated with NHS or EGTA‐treated NHS (Mg‐EGTA‐NHS). NETs induced by ANCA could activate the alternative complement cascade in the serum. In the presence of EGTA, C3a, C5a and SC5b‐9 concentration decreased from 800·42 ± 244·81 ng/ml, 7·68 ± 1·50 ng/ml, 382·15 ± 159·75 ng/ml in the supernatants enriched in ANCA induced NETs to 479·07 ± 156·2 ng/ml, 4·86 ± 1·26 ng/ml, 212·65 ± 44·40 ng/ml in the supernatants of DNase I‐degraded NETs (P < 0·001, P = 0·008, P < 0·001, respectively). NETs could activate the alternative complement pathway, and might thus participate in the pathogenesis of AAV .     

ANCA and associated diseases: immunodiagnostic and pathogenetic aspects

The past decade has seen an explosion of data on the new group of autoantibodies known collectively as ANCA (anti-neutrophil cytoplasmic antibodies). ANCA are specific for granule proteins of granulocytes and monocytes and induce distinct fluorescence patterns, e.g. the cytoplasmic (classic) cANCA and the perinuclear pANCA. cANCA is induced by antibodies directed against Proteinase 3 (PR3; PR3-ANCA) in about 90% of all ANCA-positive sera, and pANCA is induced by antibodies against myeloperoxidase (MPO; MPO-ANCA) in about 40%. A further staining pattern, which does not have a clear cut association with a distinct granule protein, is sometimes seen in chronic inflammatory bowel diseases. PR3-ANCA are serological markers for Wegener's granulomatosis (WG) and MPO-ANCA are associated with certain subtypes of primary vasculitides. Evidence exists that both the autoantigen and ANCA participate in the pathogenesis of at least the group of‘ANCA-associated vasculitides'.     

MPO-ANCA induces IL-17 production by activated neutrophils in vitro via classical complement pathway-dependent manner

The elevation of serum anti-neutrophil cytoplasmic autoantibodies (ANCA) is significantly associated with the progression of some patients with systemic vasculitis. Especially, myeloperoxidase-specific ANCA (MPO-ANCA) play a pivotal role in the progression of systemic vasculitis including crescentic glomerulonephritis. Here we demonstrated that MPO-ANCA-activated neutrophils allow the local environment to differentiate Th(17) cells through IL-6, IL-17A, and IL-23 production. We found a variety of elevated serum cytokines, especially IL-17A, in ANCA-mediated systemic vasculitis mice. Furthermore, activated peritoneal neutrophils in vitro also produced IL-17A and IL-23 in response to MPO-ANCA. Co-stimulation of fungal mannoprotein and complements significantly enhanced the MPO-ANCA-mediated IL-17A expression, but F(ab)'(2) fragments of MPO-ANCA diminished the cytokine response. These results suggest that the activated neutrophils produce IL-17A and IL-23 in response to MPO-ANCA via their Fc-region and classical complement pathway, which initiate the first steps of chronic autoimmune inflammation by allowing the local environment to develop Th(17)-mediated autoimmunity.     

Alternative complement pathway in the pathogenesis of disease mediated by anti-neutrophil cytoplasmic autoantibodies

Clinical and experimental data indicate that anti-neutrophil cytoplasmic autoantibodies (ANCAs) cause glomerulonephritis and vasculitis. Here we report the first evidence that complement is an important mediator of ANCA disease. Transfer of anti-myeloperoxidase (MPO) IgG into wild-type mice or anti-MPO splenocytes into immune-deficient mice caused crescentic glomerulonephritis that could be completely blocked by complement depletion. The role of specific complement activation pathways was investigated using mice with knockout of the common pathway component C5, classic and lectin binding pathway component C4, and alternative pathway component factor B. After injection of anti-MPO IgG, C4-/- mice developed disease comparable with wild-type disease; however, C5-/- and factor B-/- mice developed no disease. To substantiate a role for complement in human ANCA disease, IgG was isolated from patients with myeloperoxidase ANCA (MPO-ANCA) or proteinase 3 ANCA (PR3-ANCA) and from controls. Incubation of MPO-ANCA or PR3-ANCA IgG with human neutrophils caused release of factors that activated complement. IgG from healthy controls did not produce this effect. The findings suggest that stimulation of neutrophils by ANCA causes release of factors that activate complement via the alternative pathway, thus initiating an inflammatory amplification loop that mediates the severe necrotizing inflammation of ANCA disease.     

Anti-neutrophil cytoplasmic antibody--enzyme immunosorbent assay]

Enzyme immunosorbent assay(ELISA) is a very useful method to determine anti-neutrophil cytoplasmic antibody(ANCA), which is an important serological marker for pauci-immune type systemic vasculitis and necrotizing glomerulonephritis. A test was made using new myeloperoxidase(MPO)-ANCA ELISA(A), employing native MPO purified from the neutrophils in sputum as a liquid phase antigen. Furthermore, the ELISA(B) using MPO, composed of one large and one small subunit, was tested as solid phase antigen. The intra-assay and inter-assay CV of the new ELISA(A) were 3.92 to 6.75% and 5.0 to 8.1%, respectively. Close ANCA titer correlation was shown between the new MPO-ANCA ELISA(A) and the conventional ELISA, using native MPO from peripheral neutrophils as solid phase antigen. ELISA(B) showed low MPO-ANCA detection sensitivity compared to ELISA(A) and to conventional ELISA. ELISA using native MPO from neutrophils in sputum as liquid phase antigen is useful for MPO-ANCA detection. There might be an ANCA which recognizes only native form MPO.     

Regulation of histamine release from human bronchoalveolar lavage mast cells by stem cell factor in several respiratory diseases

We investigated the effects of stem cell factor (SCF) on histamine release (HR) from human bronchoalveolar lavage (BAL) mast cells. BAL cells were recovered from lavage performed in patients undergoing clinical bronchoscopy. SCF (0.02–20 ng/ml), which is by itself a poor secretagogue (mean ± SEM HR: 3.7 ± 0.9%; n = 27), strongly enhanced HR induced by anti-IgE in a concentration-related manner. Significant potentiation began at 0.2 ng/ml (30 ± 10°0; p <0.05; n = 12) and reached a plateau at 2 ng/ml (40 ± 10%; P <0.01 at 2 ng/ml and 45 ± 10%; P <0.01 at 20 ng/ml; n = 12). In contrast, SCF failed to enhance HR induced by calcium ionophore A23187. Among the BAL cell samples initially unresponsive to anti-IgE (55° of samples), 36% (10/28) were converted to responders if the cells were shortly preincubated with SCF. In 25% of samples (7/27), SCF (20 ng/ml) caused direct HR of 10 ± 2.1 %. The mast cells which released histamine when challenged with SCF also secreted higher levels of histamine in response to anti-IgE and calcium ionophore than those nonresponsive to SCF. While interleukin (IL)-3 and IL-5 (20 ng/ml) were unable to modulate immunologic HR. GM-CSF (20 ng/ml) produced significant potentiation ( P <0.05), which was, however, smaller than that observed with SCF. The rate of responders to anti-IgE in atopic asthma (47 %) was greater than that in control (9%) and intrinsic asthma (10%) but not different from that in some other respiratory diseases such as chronic bronchitis (44%), lung cancer (47%), or interstitial disease (68%,). The potentiation of HR afforded by SCF did not differ significantly among the several disease groups. We conclude that, whatever the underlying respiratory disease, SCF selectively enhances IgE-mediated HR from human BAL mast cells. Furthermore, this cytokine is sometimes necessary to render mast cells able to release histamine in response to anti-IgE.     

The diagnosis and classification of microscopic polyangiitis

Microscopic Polyangiitis (MPA) is a small vessel vasculitis. The disease is defined by the 2012 revised Chapel Hill Consensus Conference Nomenclature of Vasculitides [1] as necrotizing vasculitis, with few or no immune deposits, predominantly affecting small vessels (i.e. capillaries, venules, or arterioles). Necrotizing arteritis involving small and medium arteries may be present. Necrotizing glomerulonephritis is very common. Pulmonary capillaritis often occurs. Granulomatous inflammation is absent. MPA belongs to the ANCA-associated vasculitides (AAV). ANCA in MPA are predominantly directed against myeloperoxidase (MPO-ANCA) but may, in a minority of patients, be directed against proteinase 3 (PR3-ANCA). Not all patients, however, have ANCA. Microscopic polyangiitis (MPA) belongs to the anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides. MPA is clinically characterized by small-vessel vasculitis primarily affecting the kidneys and the lungs but other organs may be involved as well. Renal involvement, which can be the only manifestation, is clinically apparent as rapidly progressive glomerulonephritis and histopathologically as pauci-immune necrotizing and crescentic glomerulonephritis. ANCA in MPA are mainly directed to myeloperoxidase (MPO-ANCA). Besides their diagnostic significance, MPO-ANCA appear pathogenic in MPA. Rituximab with steroids is at least as effective as cyclophosphamide with steroids for induction of remission.