Vasculitis-ScreenisasolidphaseenzymeimmunoassayforthecombinedquantitativedetectionofantibodiesagainstPR3andMPOinhumanserum.Eachwelliscoatedwithnativehumanproteinase3(PR3)plusnativemyeloperoxidase(MPO),bothhighlypurifiedfromhumanperipheralbloodpolymorphnuclearcells.Anti-PR3andanti-MPOantibodiesrecognizespecificiallyconformationalepitopesonlyaccessIBLeonthenativetargetantigen.Theassayisanaidinthedifferentialdiagnosisofautoimmunevasculitis.Antibodiesagainstmyeloperoxidase(MPO)andproteinase3(PR3)belongtothegroupofanti-neutrophilcytoplasmicantibodies(ANCA)whicharedirectedagainstcytoplasmiccomponentsofneutrophilicgranulocytesandmonocytes.Indirectimmunofluorescencetestonethanol-fixedneutrophilshasbeentheestablishedmethodforthedetectionofANCAs.ItbecameapparentthatsomeANCAscreateacytoplasmicfluorescencepattern(thuscalledcANCA)whileotherscreateaperinuclearpattern(thepANCA).Asbothpatternsmaycovermultipleantigens,immunofluorescenceisnotsuitableforasatisfyingdifferentialdiagnosisofvasculitis;thuseachIFTshouldbeverifiedwithspecificELISAtests.Whileproteinase3isthemainantigenspecificforcANCAthemainantigenforpANCAhasbeenidentifiedasMPObutothercellularcomponents(lactoferrin,cathepsinG,elastasee.g.)maycauseperinuclearstaining.MPOisanenzymefromtheprimarygranulesofneutrophilswithamolecularweightofapproximately140kDa.ItshighlynegativchargemayberelevantforthelocationatpositivlychargedstructuressuchasthenuclearmembraneandDNAthusresponsiblefortheperinuclearstainingpatternofanti-MPOantibodiesinpatients`serainIFTusingethanol-fixedneutrophils.PR3isaserineproteasefromtheazurophilegranules(lysosomes)ofneutrophilswithamolecularweightof29kDa.Thecationicproteinhasaproteolyticactivitytoelastin,hemoglobinandcollagenVII.Inaddition,PR3promotestheactivationofplateletsbycathepsinGandinactivatestheC1-inhibitor.ANCAareimportantMarkersforthedifferentialdiagnosisofautoimmunevasculitis.Anti-PR3areaspecificSEROlogicalmarkerforWegener`sgranulomatosis(WG)andmayplayanactiveroleinthepathogenesisofWG.Anti-PR3titersarestronglyassociatedwithdiseaseactivityandinhibittheproteolyticactivityofPR3.Anti-MPOarecorrelatedwithidiopathicorvasculitisassociatednecrotizingcrescenticglomerulonephritisandarefoundfrequentlyin70%ofpatientswithmicroscopicpolyangiitis,and5-50%ofpatientswithChurg-Strausssyndrome.