Complement cascade (Homo sapiens)

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7, 14, 51, 76, 8448, 8733864211, 21, 6525, 31, 8012, 69, 74, 8148, 877617, 1957026, 52887446, 47, 54761, 5627, 36, 7716, 57, 888787657, 8858, 61, 835255446, 18, 20, 30, 35...3, 4, 23, 28, 39...6044, 7027, 36, 7744754, 23, 38, 45, 50...2, 21, 73767676, 838324, 40, 43, 49, 8532, 629, 1710, 74, 8276, 8373293448, 718, 29, 64, 82521517, 22, 6313, 6787C4b-binding protein MASP2 dimer MBL-IIActivated MASP-1 dimerActivated MASP-2 dimer complex deamidated-Q1013-C4B-derived C4b IgG Cell surfaceC4b C3b C4b Complement factor I C8 C4b C3b MBL-IIMASP-2 dimerMASP-1 dimer complex C3iC3b C4b Cell surfaceC4b MBLactivated MASPsmannose-based carbohydrates Cell surfaceC4b FCN1MASP2 dimerMASP1 dimer C3b C3C3b deamidated-Q1013-C4B-derived C4b FCN3MASP2 dimerMASP1 dimer C4b-binding protein C4 binding proteinC4bC2a Cell surfaceC3bFactor BbProperdin C3b Antigen-antibody complex C5b Ficolin-3 hexamer Cell surfaceC3b CD59C5b-C9 C5bC6C7C8 complex deamidated-Q1013-C4A-derived C4b VTNC5bC6C7C8C9 Cell surfaceC3b C4 binding proteinprotein S C3b Immunoglobulin Kappa Light Chain deamidated-Q1013-C4B-derived C4b MBL subunit MASP1 dimer Cell surfaceC3bFactor Bb deamidated-Q1013-C4A-derived C4b Ig Lamda Light Chain V Region Cell surfaceC3b FCN2MASP2 dimerMASP1 dimer MASP1 dimer Ficolin-3 hexamer FCN3MASPsCa2+FCN3 ligand Immunoglobulin Lambda Light Chain Ig Heavy Chain V Region deamidated-Q1013-C4A-derived C4b Immunoglobulin Kappa Light Chain Cell surfaceC3bFactor Bb Cell surfaceC4b deamidated-Q1013-C4B-derived C4b deamidated-Q1013-C4A-derived C4b thioester-C1010-Q1013- C4A-derived C4b MASP2 dimer Complement factor IFactor HC3b MASP2 dimer deamidated-Q1013-C4B-derived C4b Cell surfaceC3b Ig Kappa Light Chain V Region C5bC6C7 complex MASP1 dimer Cell surfaceFH,FHR3C3b IgG C region cytosolFCN2 subunit FCN2MASPsCa2+FCN2 ligand C5b C3b Cell surfaceFH,FHR3C3bBb Cell surfaceC4bC2a iC3b Ficolin-2 tetramer Cell surfaceC4b CR1C3b Ficolin-1 tetramer deamidated-Q1013-C4B-derived C4b IgG Heavy Chain MASP1 dimer C4b Ig Lambda C region Factor IMCP, CR1C4b, C3b complexes Complement factor ICell surfaceFH,FHR3C3b C3b Ig Heavy Chain V Region C4b C4b Cell surfaceC3b FCN1MASPsCa2+FCN1 ligand Cell surfaceC3bFactor Bb Cell surfaceFH,FHR3C3b MCPC4b FCN3 ligand CR1C4b C5b Activated C1R Cell surfaceC3bFactor BbProperdin DAFC3b C1Q subunit C3b MASP1 dimer FCN2 ligand MCPC3b IgG C5b Complement factor I deamidated-Q1013-C4B-derived C4b FCN3 subunit C5b C1Sactivated C1R tetramer C8 C3b MASP1 dimer MBL-II tetramer C4bC2aC3b C4-binding proteinC4b C3CR1C4b C-reactive protein homopentamer C3c C3b C8 C4-binding proteinC4b Cell surfaceC4b Cell surfaceC4b Cell surfaceC4bC2a Antigen antibody C1 complex MBL-II tetramer Cell surfaceC4b FCN2 subunit C1SC1R tetramer Cell surfaceC4bC2a MASP2 dimer thioester-C1010-Q1013-C4B-derived C4b FCN1 ligand MASP2 dimer thioester-C1010-Q1013-C4b FCN3MASP2 dimerMASP1 dimer MCPC4b C3b deamidated-Q1013-C4A-derived C4b MCP, CR1C4bC3b complexes Activated C1R CR1C3b Ig Lamda Light Chain V Region C5bC6 complex VTNC5bC6C7 C1Q subunit C5bC6C7 complex FCN1 subunit FCN2MASP2 dimerMASP1 dimer Antigen-antibody complex Ig Antibody Light Chain deamidated-Q1013-C4A-derived C4b C3b C3b Factor HC3b C3b C1Q C4b-binding protein C8 Ig Antibody Light Chain Complement factor 5 IgG C region C3b deamidated-Q1013-C4B-derived C4b Ig Kappa Light Chain V Region MASP1 dimer Host cell surface C5bC6C7C8 complex deamidated-Q1013-C4B-derived C4b C8 Antigen antibody C1 deamidated-Q1013-C4A-derived C4b C3b IgG C region C1Q subunit C4b C3b MASP2 dimer Complement factor 3 Antigen-antibody complex MBL subunit Ig Antibody Light Chain deamidated-Q1013-C4B-derived C4b C3b Factor HHost cell surface thioester-C1010-Q1013- C4A-derived C4b Ficolin-1 tetramer C4b-binding protein Ig Lamda Light Chain V Region Ig Lambda C region IgG Heavy Chain FCN1MASP2 dimerMASP1 dimer C1 complement factor thioester-C1010-Q1013-C4b C4b C1Q Ig Heavy Chain V Region deamidated-Q1013-C4A-derived C4b C3IgG Heavy Chain Cell surfaceC4b MBL-IIMASP-2 dimerMASP-1 dimer complex FCN1 subunit iC3b C3b deamidated-Q1013-C4A-derived C4b MBL bound to mannose-based carbohydrates on bacterial surfaces Ig Lambda C region Cell surfaceC4b C5bC6C7 complex Activated MASP-2 dimer Complement factor I C5b CR1iC3b MBL subunit C1Q C-reactive protein pentamerphosphocholineC1Q thioester-C1010-Q1013-C4B-derived C4b Ig Kappa Light Chain V Region C5b MBL-II tetramer C5b Activated C1S C3b FCN3 subunit MCPC3b C4b C4b-binding protein C3C1Q Membrane Attack Complex C4b-binding proteinFactor I DAFC4b MASP1 dimer Complement factor I Activated MASP-1 dimer VTNC5bC6C7 Ficolin-2 tetramer Immunoglobulin Kappa Light Chain Antigen antibody C1 C-reactive protein pentamerphosphocholine C3thioester-C1010-Q1013- C4A-derived C4b C5b C5bC6C7 complex Cell surfaceC3bFactor B complex Immunoglobulin Lambda Light Chain thioester-C1010-Q1013-C4B-derived C4b Activated C1Sactivated C1R tetramer thioester-C1010-Q1013-C4b C1 complement factor MASP2 dimer C1 complement factor Factor HC3b Complement factor I Host cell surface Cell surfaceC4bC2a C1Q subunit Cell surfaceC3b IgG MASP2 dimer Immunoglobulin Lambda Light Chain C4b C3bFactor BbC3bProperdin complex deamidated-Q1013-C4A-derived C4b C3bIg kappa chain V-III region B6 Ig lambda chain V-I region WAH C6 C4A gamma Cell surfaceC4bC2aC3 beta chain Ig heavy chain V-II region DAW Ig kappa chain V-III region Ti Ig lambda chain V-II region NIG-84 dNQ-C4BC4A gamma Ig kappa chain V-I region Rei Ig heavy chain V-I region SIE Ig lambda chain V-I region VOR Ig lambda chain V-IV region X C4A gamma C4B gamma C4A beta CR1 IgH heavy chain V-III region VH26 precursor Ig lambda chain V-VII region MOT MASP1Ig lambda chain V-II region TOG Ig lambda chain V-I region EPS IGLC1thioester-C1010-Q1013-C4bCell surfaceC3bFactor BbProperdinIg kappa chain V-II region MIL Ig kappa chain V-III region VH C6 C9Ig lambda chain V-II region NIG-84 C3 beta chain CFBIGLC3IGHG2Ig lambda chain V-I region EPS C4A beta Ig kappa chain V-I region OU Complement Factor 4Ca2+ C4B gamma Ig lambda chain V-VII region MOT Ig heavy chain V-III region HIL C3 beta chain IGHG3 Ig heavy chain V-I region EU C4B beta Ig lambda chain V-I region NEW MASP2-1 IGLC7IGKV4-1Heparins Ig heavy chain V-III region LAY Ig heavy chain V-I region WOL Ig kappa chain V-I region Kue IGHG1C5 beta Ig kappa chain V-III region VH Ig heavy chain V-III region BUR C4B gamma C4 binding proteinC4bC2aC4B beta C4A beta Ig kappa chain V-IV region JI C3 beta chain IGLV1-44C3c alpha' chain fragment 1 Ig lambda chain V-IV region Hil Ig lambda chain V-VI region AR MASP1Cell surfaceC4bIg kappa chain V-III region GOL C4A beta Cell surfaceFH,FHR3C3bVTNMBL-IIMASP-2 dimerMASP-1 dimer complexdNQ-C4BIg lambda chain V-VI region WLT Ig kappa chain V-I region DEE Ig heavy chain V-I region EU Ig lambda chain V-II region WIN Ig kappa chain V-I region Roy Ig heavy chain V-III region BRO IgH heavy chain V-III region VH26 precursor CFH IGLV4-3Ig lambda chain V-II region MGC H2OC4A beta dNQ-C4AIg heavy chain V-III region HIL IGLV3-22Ig heavy chain V-III region GA Ig heavy chain V-III region WEA Ig heavy chain V-I region HG3 Ig lambda chain V-III region LOI CFBIg kappa chain V-I region Daudi Ig kappa chain V-I region Bi Lipoteichoic acid 11xCbxE-PROS1 Ig kappa chain V-IV region STH Ig kappa chain V-III region VG Antigen antibody C1 FCN1 FCN2MASP2 dimerMASP1 dimerC8A Ig heavy chain V-III region GA C4B gamma dNQ-C4BC4B beta Ig kappa chain V-II region MIL Ig heavy chain V-II region DAW IGLVIg kappa chain V-I region Wes Ig lambda chain V-III region SH IGLV3-25IGLV3-16C3bC7Ig kappa chain V-II region Cum CFIC1QA Ig kappa chain V-I region Rei Cell surfaceC3bFactor B complexIGLV1-36C3 beta chain dNQ-C4BC5bC6C7C8 complexIg kappa chain V-IV region Len Ig kappa chain V-I region Scw C3 beta chain C4BPA IGLV3-12Ig kappa chain V-I region WAT C6 Ig heavy chain V-III region BRO IGLV3-12C1S N-terminal fragment Ig kappa chain V-I region HK101 C7Ig heavy chain V-II region HE C4B gamma Ig kappa chain V-I region Ka C3b alpha' Ig lambda chain V-V region DEL IGLV2-11Ig heavy chain V-I region SIE Ig kappa chain V-II region FR C1R N-terminal fragment IGKV1-5IGLV2-23IGLV4-69C2a C3c alpha' chain fragment 2 IGLV1-36C4B beta IGLV8-61Ig kappa chain V-II region GM607 Ig kappa chain V-III region HAH Properdin oligomerC4BPB Ig heavy chain V-I region EU Ig lambda chain V-VI region WLT C5 beta C4A beta FCN1MASP2 dimerMASP1 dimerC2aIg heavy chain V-I region SIE Ig kappa chain V-III region GOL Antigen antibody C1 complexC4A gamma dNQ-C4AIg kappa chain V-I region AG Ig kappa chain V-I region Hau CR1 Ig heavy chain V-III region BUT Ig kappa chain V-I region Bi C7Ig heavy chain V-I region Mot IGLV1-40C2a IGLV2-33MASP2-1 Ig lambda chain V-IV region MOL C3 beta chain Ig heavy chain V-III region DOB C4b-binding proteinFactor IVTNC5bC6C7C8G Ig kappa chain V-I region Lay Ig kappa chain V region EV15 CFIC5b alpha' MBL/FCNactivated MASPcarbohydrate patternsC3b alpha' C8B CRPC3b alpha' C3 beta chain CFIIg heavy chain V-III region DOB Ig heavy chain V-III region WAS Ig heavy chain V-II region ARH-77 N-acetyl-D-glucosamine Ig kappa chain V-I region CAR C4BPA Ig lambda chain V-II region TOG C4A alpha b C3 beta chain C5b alpha' Ig lambda chain V-I region BL2 C5 beta C4dIGLV3-22MASP1N-acetyl-D-glucosamine Ig lambda chain V-VI region AR Ig kappa chain V-II region GM607 CR1 Ig kappa chain V region EV15 C1QBCell surfaceFH,FHR3C3bBbIg kappa chain V-II region GM607 Ig kappa chain V-I region Bi Complement factor ICell surfaceFH,FHR3C3bC1RC3 beta chain C9CR1iC3bC3 beta chain Ig kappa chain V-III region SIE IGHG1IGLV5-37N-acetylgalactosamine Ig lambda chain V-II region TRO Ig kappa chain V-I region Ni C5b alpha' Ig heavy chain V-III region GAL Ig heavy chain V-III region NIE Ig kappa chain V-IV region Len Ig heavy chain V-III region BUR FCN3 Ig kappa chain V-III region CLL DAFC3bIGLV4-3Ca2+ D-fucose C5 beta Ig heavy chain V-III region BRO Ig lambda chain V-III region LOI Ig kappa chain V-I region Kue C2aIg kappa chain V-III region VH FCN3 ligandIGLV2-18IGKVA18Ig kappa chain V-III region Ti C3 beta chain Ig kappa chain V-I region Hau C3 beta chain Ig heavy chain V-III region GAL C3 beta chain IGLV1-44Ig heavy chain V-I region WOL IGLC6Ig heavy chain V-III region POM C5b alpha' Ig heavy chain V-II region COR C4A gamma CD55 Ig heavy chain V-III region CAM C3C8A Ig lambda chain V-II region MGC IGLV5-37Ig lambda chain V-II region BUR C3c alpha' chain fragment 2 C3b alpha' C1R C-terminal fragment IGLV3-12C4BPA C3 beta chain dNQ-C4AC8G C2a Ig kappa chain V-I region Rei Ig heavy chain V-II region COR Sialic acid Ig kappa chain V region EV15 Cell surfaceC4bC2aIg heavy chain V-III region WEA CFICFIIg lambda chain V-II region VIL C3 beta chain FCN2 Sialic acid C6 Ig kappa chain V-I region CAR Ig kappa chain V-I region AU Ig heavy chain V-I region WOL IGLC7Ig kappa chain V-III region IARC/BL41 C4B beta C3b alpha' C4A beta Ig lambda chain V-I region NIG-64 C1QC C3 beta chain Cell surfaceComplement factor IFactor HC3bdNQ-C4AC3 beta chain 11xCbxE-PROS1Ig heavy chain V-III region LAY Ig heavy chain V-II region WAH C3 beta chain Ig kappa chain V-II region TEW IGLV2-23CFIIg kappa chain V-II region MIL IGLV2-11Ig lambda chain V-V region DEL C4bC2a, C3bBbIg lambda chain V-VI region WLT IGLV7-43MASP1C3b alpha' dNQ-C4AC7C4A gamma Ig kappa chain V-III region Ti CD46 Ig lambda chain V-IV region Bau C2aIg kappa chain V-III region B6 C4BPB Ig lambda chain V-I region WAH FH, FHR-3Ig kappa chain V-I region BAN C3 beta chain C3 beta chain Ig kappa chain V-I region CAR Ig heavy chain V-III region DOB IGLV2-18CD46 Ig kappa chain V-II region RPMI 6410 C3fC8A Ig kappa chain V-III region HIC IGLV7-46IGLC2IGLC1C4BPA CFIC8G Ig heavy chain V-III region NIE C1QA IGLVIg kappa chain V-I region DEE IGLV2-23Ig kappa chain V-III region VG C3aIGLV4-60Ig kappa chain V-I region Gal CFHIGLV3-22C4B gamma C8B Ig lambda chain V-IV region MOL Ig heavy chain V-I region Mot IGKCC3b alpha' C1QC Ig kappa chain V-III region IARC/BL41 CFH Ig heavy chain V-III region BUT CR1C3bIGHV7-81Ig lambda chain V-II region BOH Ig kappa chain V-III region POM Ig heavy chain V-II region HE C7MASP2-1 Ig kappa chain V-III region GOL Ig lambda chain V-IV region Kern Ig kappa chain V-IV region Len C4B gamma Ca2+ FCN1 ligandIg lambda chain V-V region DEL IGLV5-45C4A beta Ig heavy chain V-III region HIL Ig kappa chain V-I region Daudi Ig heavy chain V-III region JON IGHV7-81IGLC6C4A alpha b CFIIGLV3-27IGLV10-54C4aC1QBIg kappa chain V-I region Scw Ig kappa chain V-IV region STH Ig kappa chain V-I region Walker FCN1MASPsCa2+FCN1 ligandC4A beta C3 beta chain IGLV3-25Factor IMCP, CR1C4b, C3b complexesIg lambda chain V-I region NEWM Ig lambda chain V-I region MEM C4B beta MASP1Ig kappa chain V-I region WAT Ig kappa chain V-I region OU IGLV4-60C4B beta IGLV3-27Ig heavy chain V-II region NEWM IGLV5-45C3b alpha' Cell surfaceC3bIGLV1-40Sialic acid IGLV2-33Ig lambda chain V-II region BO Ig heavy chain V-III region TUR MASP2-1Ig heavy chain V-III region TRO C4B gamma IGHVIg kappa chain V-I region WAT Ig kappa chain V-I region Walker IGLC7Ig lambda chain V region 4A C8B C1SIg lambda chain V-VI region AR Ig lambda chain V-I region VOR C5 alpha C4B beta IgH heavy chain V-III region VH26 precursor IGLC2IGLV5-45C1R C-terminal fragment Ig heavy chain V-II region OU Ig lambda chain V-II region TRO IGKV1-5C4b-binding proteinIg kappa chain V-III region SIE C1QC C4A gamma IGLV7-46Ca2+ Ig lambda chain V-I region NIG-64 IGHG4Ig heavy chain V-II region MCE IGHG3 Ig lambda chain V-II region TOG Host cell surfacedNQ-C4BIg heavy chain V-III region TEI Ig lambda chain V-II region VIL IGLVIg lambda chain V-II region NEI Ig lambda chain V-VI region NIG-48 MASP1Ig heavy chain V-III region WAS dNQ-C4BC6 IGLV10-54Ca2+ IGLV8-61Ig heavy chain V-III region WEA C4b with hydrolysed thioesterC3 beta chain CFH Ig lambda chain V-VII region MOT C6 C4A beta C5b alpha' CFBIg kappa chain V-III region CLL C4A gamma Ig heavy chain V-III region ZAP Ig kappa chain V-I region BAN Ig kappa chain V-II region FR Ig kappa chain V-III region WOL FCN3 Ig heavy chain V-III region TEI C1QBMCPC4bIg kappa chain V-I region EU C2aFCN2 IGLV1-40Ig kappa chain V-III region VG C3b alpha' C2aC4B beta MCPC3bC4B gamma Ig heavy chain V-III region TIL 1,3-beta-D-glucan IGLV2-11C5bC6 complexCell surfaceC3bIg kappa chain V-I region Mev IGKCIg kappa chain V-I region Kue C3c alpha' chain fragment 1 precursor Ig heavy chain V-III region WAS C4A gamma MASP2-1 Ig heavy chain V-III region KOL C8G Ig kappa chain V-III region B6 iC3bIGLV11-55Ig heavy chain V-III region TEI Ig lambda chain V-IV region MOL CFIC3b alpha' Ig lambda chain V-VI region SUT C3 beta chain Ig heavy chain V-II region NEWM C3b alpha' IGKV1-5Ig lambda chain V-II region WIN CR1C3bBb, C4bC2a complexesIg lambda chain V-VI region EB4 Ig lambda chain V-III region LOI Ig kappa chain V-I region Mev C5bC3cC9CD46 Ig kappa chain V-I region Gal IGLV3-27C3c alpha' chain fragment 2 Ig kappa chain V-III region NG9 CFIdNQ-C4BIg kappa chain V-I region Ka Ig lambda chain V-I region NEWM CR1Ig lambda chain V-VI region SUT C4B gamma Ig kappa chain V-IV region STH Ig heavy chain V-III region TRO Ig lambda chain V-I region NIG-64 CFBIg lambda chain V region 4A Ig lambda chain V-I region HA Ig kappa chain V-I region AG C4cH2OFCN2MASPsCa2+FCN2 ligandIg heavy chain V-III region LAY C4-binding proteinC4bCFBIg kappa chain V-II region FR Bacterial mannose-based carbohydrate surface patternIg kappa chain V-III region HAH PCho C3C6 Ig heavy chain V-II region MCE CR1C4bC1QA Ig heavy chain V-III region ZAP CD59C5b-C9C3c alpha' chain fragment 2 Ig kappa chain V-III region POM Ca2+Cell surfaceC3bFactor BbIg kappa chain V-I region Roy CFBC4BPB Ig kappa chain V-I region Lay C4B gamma Ig heavy chain V-III region NIE Ig heavy chain V-II region OU C3b alpha' Ig kappa chain V-II region Cum C6 Ig kappa chain V-III region NG9 Ig kappa chain V-I region Scw Ig heavy chain V-II region WAH Ig kappa chain V-I region Ni MBL bound to mannose-based carbohydrates on bacterial surfacesVTNIGLV3-25IGLV11-55Ig kappa chain V-I region Wes C4B alpha chain fragment b IGKCFactor HC3bIg lambda chain V-IV region Bau Ig kappa chain V-II region TEW Ig lambda chain V-IV region Kern MCP, CR1C4bC3b complexesMCP, CR1Ig heavy chain V-III region ZAP C4B beta Ig lambda chain V-I region HA C5 beta Ig kappa chain V-III region SIE Ig lambda chain V-II region BO C2a Ig kappa chain V-I region WEA Ig lambda chain V-III region SH C3 beta chain dNQ-C4AC5aC3b alpha' thioester-C1010-Q1013-C4bC3bC5bC6C7 complexMBL2 IGLC2C1QC Ig kappa chain V-III region HIC Complement factor IVTNIg heavy chain V-I region HG3 C4A beta Ig lambda chain V-IV region Hil Ig kappa chain V-I region EU C4BPA Ig kappa chain V-II region Cum IGLV7-46Ig lambda chain V-I region BL2 Ig lambda chain V-I region NEWM N-acetylgalactosamine dNQ-C4AFactor HHost cell surfaceC3 alpha chain IGLV7-43Ig heavy chain V-III region TUR Ig heavy chain V-III region BUR Ig lambda chain V-II region BUR C5 beta Ig heavy chain V-I region HG3 Ig heavy chain V-II region ARH-77 C1S C-terminal fragment Ig heavy chain V-II region HE Ig heavy chain V-III region JON IGLV4-3C4A alpha b Ig kappa chain V-III region HAH Ig lambda chain V-IV region Kern C2bIg kappa chain V-I region Ka C4B gamma VTNC5bC6C7C8C9Cell surfaceC4bCD59 IGKV4-1C3b alpha' Ca2+ C8C3c alpha' chain fragment 1 precursor dNQ-C4AC2MBLactivated MASPsmannose-based carbohydratesIg lambda chain V-I region WAH IGHG1IGLV7-43C3c alpha' chain fragment 1 precursor C3bC5b alpha' Ig heavy chain V-II region SESS Ig kappa chain V-IV region B17 Ig kappa chain V-III region HIC IGHG2Ig kappa chain V-I region BAN Ig lambda chain V-I region BL2 C4A gamma C5b alpha' C4BPB Ig kappa chain V-I region OU Ig kappa chain V-I region Ni C3b alpha' Ig kappa chain V-I region Lay Heparins IGLV10-54MASP2-1 Ig heavy chain V-I region Mot Ig kappa chain V-I region AU C1QBC8A Ig lambda chain V-II region WIN Complement factor 5C4B alpha chain fragment b IGLC1Ig kappa chain V-IV region JI Complement factor DC5 beta Ig heavy chain V-II region MCE IGLV1-36C5 beta C3 beta chain Ig lambda chain V-II region MGC C3aMASP2-1 Ig kappa chain V-I region HK101 Ig heavy chain V-II region OU C1R N-terminal fragment C4A gamma IGLV4-69Ig lambda chain V-II region BOH C3b alpha' IGLC3C4B gamma Ig heavy chain V-II region NEWM C4A gamma C1SdNQ-C3IGKVA18Ig kappa chain V-I region Gal Ig lambda chain V-I region MEM C4bC2aC3bIg kappa chain V-I region Daudi IGLV8-61dNQ-C4AIg lambda chain V-II region BO Ig kappa chain V-II region RPMI 6410 dNQ-C4AFCN1 C7IGLV4-60N-acetyl-D-glucosamine Ig kappa chain V-III region IARC/BL41 Ig lambda chain V-I region HA MASP2-1C3b alpha' C3b alpha' Ig lambda chain V-VI region NIG-48 CR1 MASP1C3b alpha' Ig kappa chain V-III region POM CD55 Ig lambda chain V-II region NIG-84 Cell surfaceIGLV4-69dNQ-C3Ig lambda chain V-I region VOR Ig lambda chain V-IV region Hil Membrane Attack ComplexC3 convertasesIg lambda chain V-VI region SUT C4c, C3fIg lambda chain V-II region NIG-58 CFBIg lambda chain V-II region VIL Ig kappa chain V-I region DEE C4d, iC3bIGHG4IGLV3-16CFBIGLV1-44IGHVC5 beta IGLV2-33FCN3MASPsCa2+FCN3 ligandC8B C4 activatorIg heavy chain V-II region SESS FCN3MASP2 dimerMASP1 dimerIg lambda chain V-II region TRO Ig kappa chain V-I region AG IGKV4-1C4A gamma C4BPB C3bFactor BbC3bProperdin complexCFBdNQ-C3Ig heavy chain V-II region COR C8B C3 beta chain Ig heavy chain V-II region DAW C7MASP1C8G IGHG4IGHVIg kappa chain V-III region CLL iC3bCFDC8A Ig lambda chain V-II region NIG-58 C9Ig lambda chain V-I region NEW CD55CD59DAFC4bIGLV3-16Ig heavy chain V-I region ND dNQ-C3Ig lambda chain V-III region SH Ig heavy chain V-III region JON C3Ig kappa chain V-I region AU Cell surfaceC3bFactor BbIg lambda chain V-I region MEM Ig lambda chain V-IV region Bau Ig heavy chain V-II region ARH-77 IGKVA18IGHG3 C3 beta chain CFIIGLV5-37Ig kappa chain V-I region EU Ig lambda chain V-II region NEI C6C4A beta C-reactive protein pentamerphosphocholineC1QCFIC3b alpha' MBL2 C5 beta Ig lambda chain V-I region NEW MASP2-1 C3 beta chain Ig heavy chain V-III region TUR Ig lambda chain V-II region NEI C4B beta Ig lambda chain V-VI region EB4 Ig heavy chain V-I region ND Ig heavy chain V-III region TIL C4A beta IGLV2-18C5b alpha' Ig heavy chain V-III region KOL DAFC3 convertase complexesIg lambda chain V-I region EPS Ig kappa chain V-I region Wes C5b alpha' FCN2 ligandAntigen antibody C1 C5 convertasesCFBC7IGLC3Ig heavy chain V-II region WAH Ig kappa chain V-IV region JI Ig kappa chain V-III region WOL dNQ-C4BIg lambda chain V-VI region EB4 MASP1MBL2 Ig kappa chain V-III region WOL C1QA Ig kappa chain V-I region HK101 Ig kappa chain V-II region RPMI 6410 Ig heavy chain V-III region TRO Ig lambda chain V-IV region X Ig kappa chain V-IV region B17 Ig kappa chain V-III region NG9 C3dgIg heavy chain V-III region CAM C4B beta Ig heavy chain V-III region TIL Ig kappa chain V-I region Hau Ig lambda chain V-II region BUR Ig heavy chain V-III region BUT IGLV11-55C4B beta C3b alpha' C9Ig kappa chain V-II region TEW IGHG2CD46IGLC6dNQ-C4BIg heavy chain V-II region SESS Complement factor 3C3 beta chain C5bC6C7 complexIg kappa chain V-IV region B17 Ig heavy chain V-III region GA Ig kappa chain V-I region Walker Ig heavy chain V-III region POM MASP1C4b, C3bIg heavy chain V-I region ND Ig kappa chain V-I region WEA Ig kappa chain V-I region WEA C4 binding proteinprotein SIg lambda chain V-II region BOH C3CFBdNQ-C4BIg heavy chain V-III region KOL Ig kappa chain V-I region Roy Ig heavy chain V-III region CAM Ig heavy chain V-III region POM Ig heavy chain V-III region GAL Ig lambda chain V-VI region NIG-48 C3 convertasesIg lambda chain V-II region NIG-58 Ig lambda chain V-IV region X C4B alpha chain fragment b MASP2-1 IGHV7-81Ig kappa chain V-I region Mev MBL/FicolinMASPs bound to carbohydrate patternsIg lambda chain V region 4A 1825, 805979414314, 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Wikipathways-description 
The complement system is a biochemical cascade, so named because it 'complements' the ability of antibodies to clear pathogens. It is part of the innate immune system. Complement system proteins circulate in the blood as inactive precursors (pro-proteins). When triggered by the presence of microbes, complement proteases cleave complement proteins, initiating a cascade of further cleavages. The end-result of this activation is the activation of the Membrane Attack Complex and cell lysis. The C3 and C5 components also lead to phagocytosis by leukocytes.

There are three branches that lead to activation of the complement system: the classical complement pathway, the alternative complement pathway, and the mannose-binding lectin pathway. Complement proteins are always present in the blood and a small percentage spontaneously activate. Innapropriate activation leads to host cell damage, so the activation process is tightly controlled by several regulatory mechanisms.


N.B. Originally the larger fragment of Complement Factor 2 (C2) was designated C2a. However, complement scientists decided that the smaller of all C fragments should be designated with an 'a', the larger with a 'b', changing the nomenclature for C2. Recent literature may use the updated nomenclature and refer to the larger C2 fragment as C2b, and refer to the classical C3 convertase as C4bC2b. Throughout this pathway Reactome adheres to the original convention to agree with the current (Feb 2012) Uniprot names for C2 fragments.
Original Pathway at Reactome: http://www.reactome.org/PathwayBrowser/#DB=gk_current&FOCUS_SPECIES_ID=48887&FOCUS_PATHWAY_ID=166658

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Bibliography

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  115. Arlaud GJ, Reboul A, Sim RB, Colomb MG.; ''Interaction of C1-inhibitor with the C1r and C1s subcomponents in human C1.''; PubMed Europe PMC Scholia

History

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CompareRevisionActionTimeUserComment
115062view17:00, 25 January 2021ReactomeTeamReactome version 75
113506view11:58, 2 November 2020ReactomeTeamReactome version 74
112706view16:10, 9 October 2020ReactomeTeamReactome version 73
101621view11:49, 1 November 2018ReactomeTeamreactome version 66
101157view21:35, 31 October 2018ReactomeTeamreactome version 65
100683view20:08, 31 October 2018ReactomeTeamreactome version 64
100233view16:53, 31 October 2018ReactomeTeamreactome version 63
99785view15:18, 31 October 2018ReactomeTeamreactome version 62 (2nd attempt)
99338view12:47, 31 October 2018ReactomeTeamreactome version 62
93740view13:33, 16 August 2017ReactomeTeamreactome version 61
93254view11:18, 9 August 2017ReactomeTeamreactome version 61
86332view09:15, 11 July 2016ReactomeTeamreactome version 56
83391view11:06, 18 November 2015ReactomeTeamVersion54
81582view13:07, 21 August 2015ReactomeTeamVersion53
77042view08:34, 17 July 2014ReactomeTeamFixed remaining interactions
76747view12:11, 16 July 2014ReactomeTeamFixed remaining interactions
76072view10:13, 11 June 2014ReactomeTeamRe-fixing comment source
75782view11:30, 10 June 2014ReactomeTeamReactome 48 Update
75419view10:07, 29 May 2014LifishModified description
75132view14:08, 8 May 2014AnweshaFixing comment source for displaying WikiPathways description
74779view08:52, 30 April 2014ReactomeTeamReactome46
44996view14:41, 6 October 2011MartijnVanIerselOntology Term : 'signaling pathway in the innate immune response' added !
42021view21:50, 4 March 2011MaintBotAutomatic update
39824view05:51, 21 January 2011MaintBotNew pathway

External references

DataNodes

View all...
NameTypeDatabase referenceComment
1,3-beta-D-glucan MetaboliteCHEBI:37671 (ChEBI)
11xCbxE-PROS1 ProteinP07225 (Uniprot-TrEMBL)
11xCbxE-PROS1ProteinP07225 (Uniprot-TrEMBL)
Antigen 
antibody
C1 		ComplexREACT_8066 (Reactome)
Antigen 
antibody
C1 		ComplexREACT_8973 (Reactome)
Antigen 
antibody
C1 complex		ComplexREACT_8034 (Reactome)
Bacterial mannose-based carbohydrate surface patternREACT_8923 (Reactome)
C-reactive protein pentamer

phosphocholine

C1Q		ComplexREACT_25403 (Reactome)
C1QA ProteinP02745 (Uniprot-TrEMBL)
C1QBProteinP02746 (Uniprot-TrEMBL)
C1QC ProteinP02747 (Uniprot-TrEMBL)
C1R C-terminal fragment ProteinP00736 (Uniprot-TrEMBL)
C1R N-terminal fragment ProteinP00736 (Uniprot-TrEMBL)
C1RProteinP00736 (Uniprot-TrEMBL)
C1S C-terminal fragment ProteinP09871 (Uniprot-TrEMBL)
C1S N-terminal fragment ProteinP09871 (Uniprot-TrEMBL)
C1SProteinP09871 (Uniprot-TrEMBL)
C2ProteinP06681 (Uniprot-TrEMBL)
C2a ProteinP06681 (Uniprot-TrEMBL)
C2aProteinP06681 (Uniprot-TrEMBL)
C2bProteinP06681 (Uniprot-TrEMBL)
C3 alpha chain ProteinP01024 (Uniprot-TrEMBL)
C3 beta chain ProteinP01024 (Uniprot-TrEMBL)
C3 convertasesREACT_8751 (Reactome)
C3ComplexREACT_8268 (Reactome)
C3ComplexREACT_8649 (Reactome)
C3ComplexREACT_8857 (Reactome)
C3aProteinP01024 (Uniprot-TrEMBL)
C3b

Factor Bb C3b

Properdin complex		ComplexREACT_8784 (Reactome)
C3b alpha' ProteinP01024 (Uniprot-TrEMBL)
C3bComplexREACT_8621 (Reactome) Linked by disulphide bond between positions 559 and 816.
C3c alpha' chain fragment 1 ProteinP01024 (Uniprot-TrEMBL)
C3c alpha' chain fragment 1 precursor ProteinP01024 (Uniprot-TrEMBL)
C3c alpha' chain fragment 2 ProteinP01024 (Uniprot-TrEMBL)
C3cComplexREACT_164188 (Reactome)
C3dgProteinP01024 (Uniprot-TrEMBL)
C3fProteinP01024 (Uniprot-TrEMBL)
C4 activatorREACT_8154 (Reactome)
C4 binding protein C4bC2aComplexREACT_120190 (Reactome)
C4 binding protein protein SComplexREACT_119894 (Reactome)
C4-binding protein C4bComplexREACT_118966 (Reactome)
C4A alpha b ProteinP0C0L4 (Uniprot-TrEMBL) C4 alpha chain has a thioester bond between Cys 1010 and Gln 1013
C4A beta ProteinP0C0L4 (Uniprot-TrEMBL)
C4A gamma ProteinP0C0L4 (Uniprot-TrEMBL)
C4B alpha chain fragment b ProteinP0C0L5 (Uniprot-TrEMBL)
C4B beta ProteinP0C0L5 (Uniprot-TrEMBL)
C4B gamma ProteinP0C0L5 (Uniprot-TrEMBL)
C4BPA ProteinP04003 (Uniprot-TrEMBL)
C4BPB ProteinP20851 (Uniprot-TrEMBL)
C4aProteinREACT_25991 (Reactome)
C4b

C2a

C3b		ComplexREACT_8556 (Reactome)
C4b with hydrolysed thioesterComplexREACT_164040 (Reactome)
C4b, C3bComplexREACT_119260 (Reactome)
C4b-binding protein Factor IComplexREACT_119445 (Reactome)
C4b-binding proteinComplexREACT_120080 (Reactome)
C4bC2a, C3bBbComplexREACT_119171 (Reactome)
C4c, C3fComplexREACT_119917 (Reactome)
C4cComplexREACT_119729 (Reactome)
C4d, iC3bProteinREACT_119732 (Reactome)
C4dProteinREACT_119059 (Reactome)
C5 alpha ProteinP01031 (Uniprot-TrEMBL)
C5 beta ProteinP01031 (Uniprot-TrEMBL)
C5 convertasesREACT_8864 (Reactome)
C5aProteinP01031 (Uniprot-TrEMBL)
C5b

C6 C7

C8 complex		ComplexREACT_8352 (Reactome)
C5b

C6

C7 complex		ComplexREACT_8333 (Reactome)
C5b

C6

C7 complex		ComplexREACT_8454 (Reactome)
C5b C6 complexComplexREACT_8500 (Reactome)
C5b alpha' ProteinP01031 (Uniprot-TrEMBL)
C5bComplexREACT_8814 (Reactome) Linked by disulphide bond between positions 559 and 816.
C6 ProteinP13671 (Uniprot-TrEMBL)
C6ProteinP13671 (Uniprot-TrEMBL)
C7ProteinP10643 (Uniprot-TrEMBL)
C8A ProteinP07357 (Uniprot-TrEMBL)
C8B ProteinP07358 (Uniprot-TrEMBL)
C8G ProteinP07360 (Uniprot-TrEMBL)
C8ComplexREACT_8563 (Reactome)
C9ProteinP02748 (Uniprot-TrEMBL)
CD46 ProteinP15529 (Uniprot-TrEMBL)
CD46ProteinP15529 (Uniprot-TrEMBL)
CD55 ProteinP08174 (Uniprot-TrEMBL)
CD55ProteinP08174 (Uniprot-TrEMBL)
CD59 C5b-C9ComplexREACT_164087 (Reactome)
CD59 ProteinP13987 (Uniprot-TrEMBL)
CD59ProteinP13987 (Uniprot-TrEMBL)
CFBProteinP00751 (Uniprot-TrEMBL)
CFDProteinP00746 (Uniprot-TrEMBL)
CFH ProteinP08603 (Uniprot-TrEMBL)
CFHProteinP08603 (Uniprot-TrEMBL)
CFIProteinP05156 (Uniprot-TrEMBL)
CR1 C3bBb, C4bC2a complexesComplexREACT_120030 (Reactome)
CR1 C3bComplexREACT_119014 (Reactome)
CR1 C4bComplexREACT_119535 (Reactome)
CR1 iC3bComplexREACT_164751 (Reactome)
CR1 ProteinP17927 (Uniprot-TrEMBL)
CR1ProteinP17927 (Uniprot-TrEMBL)
CRPProteinP02741 (Uniprot-TrEMBL)
Ca2+ MetaboliteCHEBI:29108 (ChEBI)
Ca2+MetaboliteCHEBI:29108 (ChEBI)
Cell surface

C3b

Factor B complex		ComplexREACT_8205 (Reactome)
Cell surface

C3b Factor Bb

Properdin		ComplexREACT_8531 (Reactome)
Cell surface

C3b

Factor Bb		ComplexREACT_8668 (Reactome)
Cell surface C3bComplexREACT_26114 (Reactome)
Cell surface

C4b

C2a		ComplexREACT_8917 (Reactome)
Cell surface C4bComplexREACT_25739 (Reactome)
Cell surface

FH,FHR3

C3bBb		ComplexREACT_118983 (Reactome)
Cell surface

FH,FHR3

C3b		ComplexREACT_119386 (Reactome)
Cell surfaceREACT_26575 (Reactome) This entity is intended to represent any molecule that might be at the outer cell surface of any cell, host or microbial.
Complement Factor 4ComplexREACT_26761 (Reactome)
Complement factor 3ComplexREACT_8213 (Reactome) Linked by disulphide bond between positions 559 and 816.
Complement factor 5ComplexREACT_8215 (Reactome)
Complement factor DProteinREACT_161511 (Reactome) This CandidateSet contains sequences identified by William Pearson's analysis of Reactome catalyst entities. Catalyst entity sequences were used to identify analagous sequences that shared overall homology and active site homology. Sequences in this Candidate set were identified in an April 24, 2012 analysis.
Complement factor I

Cell surface FH,FHR3

C3b		ComplexREACT_119579 (Reactome)
Complement factor I

Factor H

C3b		ComplexREACT_119450 (Reactome)
Complement factor IComplexREACT_119465 (Reactome)
D-fucose MetaboliteCHEBI:28847 (ChEBI)
DAF C3 convertase complexesComplexREACT_119393 (Reactome)
DAF C3bComplexREACT_119929 (Reactome)
DAF C4bComplexREACT_119228 (Reactome)
FCN1

MASP2 dimer

MASP1 dimer		ComplexREACT_164741 (Reactome)
FCN1

MASPs Ca2+

FCN1 ligand		ComplexREACT_165421 (Reactome)
FCN1 ProteinO00602 (Uniprot-TrEMBL)
FCN1 ligandMetaboliteREACT_165133 (Reactome)
FCN2

MASP2 dimer

MASP1 dimer		ComplexREACT_165253 (Reactome)
FCN2

MASPs Ca2+

FCN2 ligand		ComplexREACT_164948 (Reactome)
FCN2 ProteinQ15485 (Uniprot-TrEMBL)
FCN2 ligandMetaboliteREACT_164334 (Reactome)
FCN3

MASP2 dimer

MASP1 dimer		ComplexREACT_165152 (Reactome)
FCN3

MASPs Ca2+

FCN3 ligand		ComplexREACT_164302 (Reactome)
FCN3 ProteinO75636 (Uniprot-TrEMBL)
FCN3 ligandMetaboliteREACT_165296 (Reactome)
FH, FHR-3ProteinREACT_119141 (Reactome)
Factor H C3bComplexREACT_120113 (Reactome)
Factor H Host cell surfaceComplexREACT_119254 (Reactome)
Factor I

MCP, CR1

C4b, C3b complexes		ComplexREACT_120091 (Reactome)
H2OMetaboliteCHEBI:15377 (ChEBI)
Heparins MetaboliteCHEBI:24505 (ChEBI)
Host cell surfaceComplexREACT_119096 (Reactome)
IGHG1ProteinP01857 (Uniprot-TrEMBL)
IGHG2ProteinP01859 (Uniprot-TrEMBL)
IGHG3 ProteinP01860 (Uniprot-TrEMBL)
IGHG4ProteinP01861 (Uniprot-TrEMBL)
IGHV7-81ProteinQ6PIL0 (Uniprot-TrEMBL)
IGHVProteinA2KUC3 (Uniprot-TrEMBL)
IGKCProteinP01834 (Uniprot-TrEMBL)
IGKV1-5ProteinP01602 (Uniprot-TrEMBL)
IGKV4-1ProteinP06312 (Uniprot-TrEMBL)
IGKVA18ProteinA2NJV5 (Uniprot-TrEMBL)
IGLC1ProteinP0CG04 (Uniprot-TrEMBL)
IGLC2ProteinP0CG05 (Uniprot-TrEMBL)
IGLC3ProteinP0CG06 (Uniprot-TrEMBL)
IGLC6ProteinP0CF74 (Uniprot-TrEMBL)
IGLC7ProteinA0M8Q6 (Uniprot-TrEMBL)
IGLV1-36ProteinQ5NV67 (Uniprot-TrEMBL)
IGLV1-40ProteinQ5NV69 (Uniprot-TrEMBL)
IGLV1-44ProteinQ5NV81 (Uniprot-TrEMBL)
IGLV10-54ProteinQ5NV86 (Uniprot-TrEMBL)
IGLV11-55ProteinQ5NV87 (Uniprot-TrEMBL)
IGLV2-11ProteinQ5NV84 (Uniprot-TrEMBL)
IGLV2-18ProteinQ5NV65 (Uniprot-TrEMBL)
IGLV2-23ProteinQ5NV89 (Uniprot-TrEMBL)
IGLV2-33ProteinQ5NV66 (Uniprot-TrEMBL)
IGLV3-12ProteinQ5NV85 (Uniprot-TrEMBL)
IGLV3-16ProteinQ5NV64 (Uniprot-TrEMBL)
IGLV3-22ProteinQ5NV75 (Uniprot-TrEMBL)
IGLV3-25ProteinQ5NV90 (Uniprot-TrEMBL)
IGLV3-27ProteinQ5NV91 (Uniprot-TrEMBL)
IGLV4-3ProteinQ5NV61 (Uniprot-TrEMBL)
IGLV4-60ProteinQ5NV79 (Uniprot-TrEMBL)
IGLV4-69ProteinQ5NV92 (Uniprot-TrEMBL)
IGLV5-37ProteinQ5NV68 (Uniprot-TrEMBL)
IGLV5-45ProteinQ5NV82 (Uniprot-TrEMBL)
IGLV7-43ProteinQ5NV80 (Uniprot-TrEMBL)
IGLV7-46ProteinQ5NV83 (Uniprot-TrEMBL)
IGLV8-61ProteinQ5NV62 (Uniprot-TrEMBL)
IGLVProteinA2NXD2 (Uniprot-TrEMBL)
Ig heavy chain V-I region EU ProteinP01742 (Uniprot-TrEMBL)
Ig heavy chain V-I region HG3 ProteinP01743 (Uniprot-TrEMBL)
Ig heavy chain V-I region Mot ProteinP06326 (Uniprot-TrEMBL)
Ig heavy chain V-I region ND ProteinP01744 (Uniprot-TrEMBL)
Ig heavy chain V-I region SIE ProteinP01761 (Uniprot-TrEMBL)
Ig heavy chain V-I region WOL ProteinP01760 (Uniprot-TrEMBL)
Ig heavy chain V-II region ARH-77 ProteinP06331 (Uniprot-TrEMBL)
Ig heavy chain V-II region COR ProteinP01815 (Uniprot-TrEMBL)
Ig heavy chain V-II region DAW ProteinP01816 (Uniprot-TrEMBL)
Ig heavy chain V-II region HE ProteinP01818 (Uniprot-TrEMBL)
Ig heavy chain V-II region MCE ProteinP01817 (Uniprot-TrEMBL)
Ig heavy chain V-II region NEWM ProteinP01825 (Uniprot-TrEMBL)
Ig heavy chain V-II region OU ProteinP01814 (Uniprot-TrEMBL)
Ig heavy chain V-II region SESS ProteinP04438 (Uniprot-TrEMBL)
Ig heavy chain V-II region WAH ProteinP01824 (Uniprot-TrEMBL)
Ig heavy chain V-III region BRO ProteinP01766 (Uniprot-TrEMBL)
Ig heavy chain V-III region BUR ProteinP01773 (Uniprot-TrEMBL)
Ig heavy chain V-III region BUT ProteinP01767 (Uniprot-TrEMBL)
Ig heavy chain V-III region CAM ProteinP01768 (Uniprot-TrEMBL)
Ig heavy chain V-III region DOB ProteinP01782 (Uniprot-TrEMBL)
Ig heavy chain V-III region GA ProteinP01769 (Uniprot-TrEMBL)
Ig heavy chain V-III region GAL ProteinP01781 (Uniprot-TrEMBL)
Ig heavy chain V-III region HIL ProteinP01771 (Uniprot-TrEMBL)
Ig heavy chain V-III region JON ProteinP01780 (Uniprot-TrEMBL)
Ig heavy chain V-III region KOL ProteinP01772 (Uniprot-TrEMBL)
Ig heavy chain V-III region LAY ProteinP01775 (Uniprot-TrEMBL)
Ig heavy chain V-III region NIE ProteinP01770 (Uniprot-TrEMBL)
Ig heavy chain V-III region POM ProteinP01774 (Uniprot-TrEMBL)
Ig heavy chain V-III region TEI ProteinP01777 (Uniprot-TrEMBL)
Ig heavy chain V-III region TIL ProteinP01765 (Uniprot-TrEMBL)
Ig heavy chain V-III region TRO ProteinP01762 (Uniprot-TrEMBL)
Ig heavy chain V-III region TUR ProteinP01779 (Uniprot-TrEMBL)
Ig heavy chain V-III region WAS ProteinP01776 (Uniprot-TrEMBL)
Ig heavy chain V-III region WEA ProteinP01763 (Uniprot-TrEMBL)
Ig heavy chain V-III region ZAP ProteinP01778 (Uniprot-TrEMBL)
Ig kappa chain V region EV15 ProteinP06315 (Uniprot-TrEMBL)
Ig kappa chain V-I region AG ProteinP01593 (Uniprot-TrEMBL)
Ig kappa chain V-I region AU ProteinP01594 (Uniprot-TrEMBL)
Ig kappa chain V-I region BAN ProteinP04430 (Uniprot-TrEMBL)
Ig kappa chain V-I region Bi ProteinP01595 (Uniprot-TrEMBL)
Ig kappa chain V-I region CAR ProteinP01596 (Uniprot-TrEMBL)
Ig kappa chain V-I region DEE ProteinP01597 (Uniprot-TrEMBL)
Ig kappa chain V-I region Daudi ProteinP04432 (Uniprot-TrEMBL)
Ig kappa chain V-I region EU ProteinP01598 (Uniprot-TrEMBL)
Ig kappa chain V-I region Gal ProteinP01599 (Uniprot-TrEMBL)
Ig kappa chain V-I region HK101 ProteinP01601 (Uniprot-TrEMBL)
Ig kappa chain V-I region Hau ProteinP01600 (Uniprot-TrEMBL)
Ig kappa chain V-I region Ka ProteinP01603 (Uniprot-TrEMBL)
Ig kappa chain V-I region Kue ProteinP01604 (Uniprot-TrEMBL)
Ig kappa chain V-I region Lay ProteinP01605 (Uniprot-TrEMBL)
Ig kappa chain V-I region Mev ProteinP01612 (Uniprot-TrEMBL)
Ig kappa chain V-I region Ni ProteinP01613 (Uniprot-TrEMBL)
Ig kappa chain V-I region OU ProteinP01606 (Uniprot-TrEMBL)
Ig kappa chain V-I region Rei ProteinP01607 (Uniprot-TrEMBL)
Ig kappa chain V-I region Roy ProteinP01608 (Uniprot-TrEMBL)
Ig kappa chain V-I region Scw ProteinP01609 (Uniprot-TrEMBL)
Ig kappa chain V-I region WAT ProteinP80362 (Uniprot-TrEMBL)
Ig kappa chain V-I region WEA ProteinP01610 (Uniprot-TrEMBL)
Ig kappa chain V-I region Walker ProteinP04431 (Uniprot-TrEMBL)
Ig kappa chain V-I region Wes ProteinP01611 (Uniprot-TrEMBL)
Ig kappa chain V-II region Cum ProteinP01614 (Uniprot-TrEMBL)
Ig kappa chain V-II region FR ProteinP01615 (Uniprot-TrEMBL)
Ig kappa chain V-II region GM607 ProteinP06309 (Uniprot-TrEMBL)
Ig kappa chain V-II region MIL ProteinP01616 (Uniprot-TrEMBL)
Ig kappa chain V-II region RPMI 6410 ProteinP06310 (Uniprot-TrEMBL)
Ig kappa chain V-II region TEW ProteinP01617 (Uniprot-TrEMBL)
Ig kappa chain V-III region B6 ProteinP01619 (Uniprot-TrEMBL)
Ig kappa chain V-III region CLL ProteinP04207 (Uniprot-TrEMBL)
Ig kappa chain V-III region GOL ProteinP04206 (Uniprot-TrEMBL)
Ig kappa chain V-III region HAH ProteinP18135 (Uniprot-TrEMBL)
Ig kappa chain V-III region HIC ProteinP18136 (Uniprot-TrEMBL)
Ig kappa chain V-III region IARC/BL41 ProteinP06311 (Uniprot-TrEMBL)
Ig kappa chain V-III region NG9 ProteinP01621 (Uniprot-TrEMBL)
Ig kappa chain V-III region POM ProteinP01624 (Uniprot-TrEMBL)
Ig kappa chain V-III region SIE ProteinP01620 (Uniprot-TrEMBL)
Ig kappa chain V-III region Ti ProteinP01622 (Uniprot-TrEMBL)
Ig kappa chain V-III region VG ProteinP04433 (Uniprot-TrEMBL)
Ig kappa chain V-III region VH ProteinP04434 (Uniprot-TrEMBL)
Ig kappa chain V-III region WOL ProteinP01623 (Uniprot-TrEMBL)
Ig kappa chain V-IV region B17 ProteinP06314 (Uniprot-TrEMBL)
Ig kappa chain V-IV region JI ProteinP06313 (Uniprot-TrEMBL)
Ig kappa chain V-IV region Len ProteinP01625 (Uniprot-TrEMBL)
Ig kappa chain V-IV region STH ProteinP83593 (Uniprot-TrEMBL)
Ig lambda chain V region 4A ProteinP04211 (Uniprot-TrEMBL)
Ig lambda chain V-I region BL2 ProteinP06316 (Uniprot-TrEMBL)
Ig lambda chain V-I region EPS ProteinP06888 (Uniprot-TrEMBL)
Ig lambda chain V-I region HA ProteinP01700 (Uniprot-TrEMBL)
Ig lambda chain V-I region MEM ProteinP06887 (Uniprot-TrEMBL)
Ig lambda chain V-I region NEW ProteinP01701 (Uniprot-TrEMBL)
Ig lambda chain V-I region NEWM ProteinP01703 (Uniprot-TrEMBL)
Ig lambda chain V-I region NIG-64 ProteinP01702 (Uniprot-TrEMBL)
Ig lambda chain V-I region VOR ProteinP01699 (Uniprot-TrEMBL)
Ig lambda chain V-I region WAH ProteinP04208 (Uniprot-TrEMBL)
Ig lambda chain V-II region BO ProteinP01710 (Uniprot-TrEMBL)
Ig lambda chain V-II region BOH ProteinP01706 (Uniprot-TrEMBL)
Ig lambda chain V-II region BUR ProteinP01708 (Uniprot-TrEMBL)
Ig lambda chain V-II region MGC ProteinP01709 (Uniprot-TrEMBL)
Ig lambda chain V-II region NEI ProteinP01705 (Uniprot-TrEMBL)
Ig lambda chain V-II region NIG-58 ProteinP01713 (Uniprot-TrEMBL)
Ig lambda chain V-II region NIG-84 ProteinP04209 (Uniprot-TrEMBL)
Ig lambda chain V-II region TOG ProteinP01704 (Uniprot-TrEMBL)
Ig lambda chain V-II region TRO ProteinP01707 (Uniprot-TrEMBL)
Ig lambda chain V-II region VIL ProteinP01711 (Uniprot-TrEMBL)
Ig lambda chain V-II region WIN ProteinP01712 (Uniprot-TrEMBL)
Ig lambda chain V-III region LOI ProteinP80748 (Uniprot-TrEMBL)
Ig lambda chain V-III region SH ProteinP01714 (Uniprot-TrEMBL)
Ig lambda chain V-IV region Bau ProteinP01715 (Uniprot-TrEMBL)
Ig lambda chain V-IV region Hil ProteinP01717 (Uniprot-TrEMBL)
Ig lambda chain V-IV region Kern ProteinP01718 (Uniprot-TrEMBL)
Ig lambda chain V-IV region MOL ProteinP06889 (Uniprot-TrEMBL)
Ig lambda chain V-IV region X ProteinP01716 (Uniprot-TrEMBL)
Ig lambda chain V-V region DEL ProteinP01719 (Uniprot-TrEMBL)
Ig lambda chain V-VI region AR ProteinP01721 (Uniprot-TrEMBL)
Ig lambda chain V-VI region EB4 ProteinP06319 (Uniprot-TrEMBL)
Ig lambda chain V-VI region NIG-48 ProteinP01722 (Uniprot-TrEMBL)
Ig lambda chain V-VI region SUT ProteinP06317 (Uniprot-TrEMBL)
Ig lambda chain V-VI region WLT ProteinP06318 (Uniprot-TrEMBL)
Ig lambda chain V-VII region MOT ProteinP01720 (Uniprot-TrEMBL)
IgH heavy chain V-III region VH26 precursor ProteinP01764 (Uniprot-TrEMBL)
Lipoteichoic acid MetaboliteCHEBI:28640 (ChEBI)
MASP1ProteinP48740 (Uniprot-TrEMBL)
MASP2-1 ProteinO00187-1 (Uniprot-TrEMBL)
MASP2-1ProteinO00187-1 (Uniprot-TrEMBL)
MBL

activated MASPs

mannose-based carbohydrates		ComplexREACT_8515 (Reactome)
MBL bound to mannose-based carbohydrates on bacterial surfacesComplexREACT_8711 (Reactome)
MBL-II

MASP-2 dimer

MASP-1 dimer complex		ComplexREACT_8380 (Reactome)
MBL/FCN

activated MASP

carbohydrate patterns		ComplexREACT_165602 (Reactome)
MBL/Ficolin MASPs bound to carbohydrate patternsComplexREACT_165125 (Reactome)
MBL2 ProteinP11226 (Uniprot-TrEMBL)
MCP C3bComplexREACT_119903 (Reactome)
MCP C4bComplexREACT_119237 (Reactome)
MCP, CR1

C4b

C3b complexes		ComplexREACT_120251 (Reactome)
MCP, CR1ProteinREACT_119720 (Reactome) CR1 and MCP are widely distributed cell surface molecules that bind C4b and C3b, and act as cofactors for Complement factor I, thereby regulating the classical and alternative C3 convertases.
Membrane Attack ComplexComplexREACT_8325 (Reactome)
N-acetyl-D-glucosamine MetaboliteCHEBI:28009 (ChEBI)
N-acetylgalactosamine MetaboliteCHEBI:40356 (ChEBI)
PCho MetaboliteCHEBI:36700 (ChEBI)
Properdin oligomerREACT_8730 (Reactome)
Sialic acid MetaboliteCHEBI:28879 (ChEBI)
VTN

C5b C6 C7 C8

C9		ComplexREACT_164606 (Reactome)
VTN

C5b C6

C7		ComplexREACT_165289 (Reactome)
VTNProteinP04004 (Uniprot-TrEMBL)
dNQ-C3ProteinP01024 (Uniprot-TrEMBL)
dNQ-C4AProteinP0C0L4 (Uniprot-TrEMBL)
dNQ-C4BProteinP0C0L5 (Uniprot-TrEMBL)
iC3bComplexREACT_119218 (Reactome)
iC3bComplexREACT_120169 (Reactome)
thioester-C1010-Q1013-C4bComplexREACT_26471 (Reactome)

Annotated Interactions

View all...
SourceTargetTypeDatabase referenceComment
11xCbxE-PROS1REACT_118836 (Reactome)
Antigen 
antibody
C1 		REACT_7977 (Reactome)
Antigen 
antibody
C1 complex		REACT_7978 (Reactome)
Bacterial mannose-based carbohydrate surface patternREACT_7983 (Reactome)
C-reactive protein pentamer

phosphocholine

C1Q		ArrowREACT_7978 (Reactome)
C2aArrowREACT_118584 (Reactome)
C2aArrowREACT_118641 (Reactome)
C2aArrowREACT_118692 (Reactome)
C2aArrowREACT_118738 (Reactome)
C2aArrowREACT_7959 (Reactome)
C2aREACT_8014 (Reactome)
C2bArrowREACT_7959 (Reactome)
C3 convertasesREACT_7990 (Reactome)
C3ArrowREACT_118641 (Reactome)
C3ArrowREACT_7981 (Reactome)
C3REACT_7948 (Reactome)
C3REACT_8013 (Reactome)
C3aArrowREACT_7948 (Reactome)
C3aArrowREACT_7986 (Reactome)
C3aArrowREACT_7990 (Reactome)
C3b

Factor Bb C3b

Properdin complex		ArrowREACT_7986 (Reactome)
C3bArrowREACT_118641 (Reactome)
C3bArrowREACT_7948 (Reactome)
C3bArrowREACT_7990 (Reactome)
C3bREACT_118712 (Reactome)
C3bREACT_25075 (Reactome)
C3cArrowREACT_163860 (Reactome)
C3dgArrowREACT_163860 (Reactome)
C3fArrowREACT_118650 (Reactome)
C3fArrowREACT_118841 (Reactome)
C4 activatorREACT_7959 (Reactome)
C4 activatorREACT_8002 (Reactome)
C4-binding protein C4bArrowREACT_118738 (Reactome)
C4-binding protein C4bREACT_118647 (Reactome)
C4aArrowREACT_8002 (Reactome)
C4b, C3bREACT_118575 (Reactome)
C4b-binding proteinArrowREACT_118719 (Reactome)
C4b-binding proteinREACT_118752 (Reactome)
C4b-binding proteinREACT_118763 (Reactome)
C4b-binding proteinREACT_118836 (Reactome)
C4bC2a, C3bBbREACT_118580 (Reactome)
C4bC2a, C3bBbREACT_118782 (Reactome)
C4c, C3fArrowREACT_118673 (Reactome)
C4cArrowREACT_118719 (Reactome)
C4d, iC3bArrowREACT_118673 (Reactome)
C4dArrowREACT_118719 (Reactome)
C5 convertasesREACT_7989 (Reactome)
C5aArrowREACT_7989 (Reactome)
C5b

C6 C7

C8 complex		REACT_163829 (Reactome)
C5b

C6 C7

C8 complex		REACT_7988 (Reactome)
C5b

C6

C7 complex		REACT_163759 (Reactome)
C5b

C6

C7 complex		REACT_7946 (Reactome)
C5b C6 complexREACT_7950 (Reactome)
C5bArrowREACT_7989 (Reactome)
C5bREACT_7976 (Reactome)
C6REACT_7976 (Reactome)
C7REACT_7950 (Reactome)
C8REACT_163870 (Reactome)
C8REACT_7946 (Reactome)
C9REACT_163829 (Reactome)
C9REACT_163870 (Reactome)
C9REACT_7988 (Reactome)
CD46REACT_118575 (Reactome)
CD55REACT_118782 (Reactome)
CD59REACT_163829 (Reactome)
CFBArrowREACT_118584 (Reactome)
CFBArrowREACT_118641 (Reactome)
CFBArrowREACT_118692 (Reactome)
CFBArrowREACT_118727 (Reactome)
CFBArrowREACT_7981 (Reactome)
CFBArrowREACT_8026 (Reactome)
CFBREACT_7966 (Reactome)
CFBREACT_8013 (Reactome)
CFHArrowREACT_118650 (Reactome)
CFHREACT_118604 (Reactome)
CFHREACT_118712 (Reactome)
CFIREACT_118674 (Reactome)
CR1 C3bArrowREACT_118692 (Reactome)
CR1 C4bArrowREACT_118692 (Reactome)
CR1ArrowREACT_163860 (Reactome)
CR1REACT_118580 (Reactome)
Ca2+REACT_163715 (Reactome)
Ca2+REACT_163747 (Reactome)
Ca2+REACT_163758 (Reactome)
Ca2+REACT_7983 (Reactome)
Cell surface

C3b Factor Bb

Properdin		REACT_7986 (Reactome)
Cell surface

C3b

Factor Bb		ArrowREACT_8026 (Reactome)
Cell surface

C3b

Factor Bb		REACT_118710 (Reactome)
Cell surface

C3b

Factor Bb		REACT_8018 (Reactome)
Cell surface C3bREACT_118815 (Reactome)
Cell surface C3bREACT_7966 (Reactome)
Cell surface C3bREACT_8022 (Reactome)
Cell surface

C4b

C2a		ArrowREACT_118641 (Reactome)
Cell surface

C4b

C2a		REACT_118752 (Reactome)
Cell surface

C4b

C2a		REACT_8022 (Reactome)
Cell surface C4bArrowREACT_118641 (Reactome)
Cell surface C4bREACT_8014 (Reactome)
Cell surface

FH,FHR3

C3b		ArrowREACT_118727 (Reactome)
Cell surface

FH,FHR3

C3b		REACT_118844 (Reactome)
Cell surfaceREACT_25075 (Reactome)
Cell surfaceREACT_25166 (Reactome)
Complement factor 3REACT_7986 (Reactome)
Complement factor 3REACT_8007 (Reactome)
Complement factor DREACT_7981 (Reactome)
Complement factor DREACT_8026 (Reactome)
Complement factor I

Cell surface FH,FHR3

C3b		REACT_118841 (Reactome)
Complement factor I

Factor H

C3b		REACT_118650 (Reactome)
Complement factor IArrowREACT_118650 (Reactome)
Complement factor IArrowREACT_118673 (Reactome)
Complement factor IArrowREACT_118719 (Reactome)
Complement factor IArrowREACT_118841 (Reactome)
Complement factor IREACT_118583 (Reactome)
Complement factor IREACT_118631 (Reactome)
Complement factor IREACT_118647 (Reactome)
Complement factor IREACT_118844 (Reactome)
DAF C3bArrowREACT_118584 (Reactome)
DAF C4bArrowREACT_118584 (Reactome)
FCN1

MASP2 dimer

MASP1 dimer		REACT_163715 (Reactome)
FCN1 ligandREACT_163715 (Reactome)
FCN2

MASP2 dimer

MASP1 dimer		REACT_163747 (Reactome)
FCN2 ligandREACT_163747 (Reactome)
FCN3

MASP2 dimer

MASP1 dimer		REACT_163758 (Reactome)
FCN3 ligandREACT_163758 (Reactome)
FH, FHR-3ArrowREACT_118841 (Reactome)
FH, FHR-3REACT_118710 (Reactome)
FH, FHR-3REACT_118815 (Reactome)
Factor H C3bREACT_118583 (Reactome)
Factor H Host cell surfaceArrowREACT_118710 (Reactome)
Factor H Host cell surfaceArrowREACT_118815 (Reactome)
Factor I

MCP, CR1

C4b, C3b complexes		REACT_118673 (Reactome)
H2OREACT_163768 (Reactome)
H2OREACT_8007 (Reactome)
Host cell surfaceREACT_118604 (Reactome)
MBL-II

MASP-2 dimer

MASP-1 dimer complex		REACT_7983 (Reactome)
MCP C3bArrowREACT_118575 (Reactome)
MCP C4bArrowREACT_118575 (Reactome)
MCP, CR1

C4b

C3b complexes		REACT_118631 (Reactome)
MCP, CR1ArrowREACT_118673 (Reactome)
Properdin oligomerArrowREACT_118641 (Reactome)
Properdin oligomerREACT_8018 (Reactome)
REACT_118575 (Reactome) Membrane cofactor protein (MCP; CD46) is a widely distributed C3b/C4b-binding cell surface glycoprotein which is a cofactor for Complement factor I.
REACT_118580 (Reactome) Complement Receptor 1 (CR1) is a widely distributed cell surface protein that is a decay accelerating factor for the conventional (C4bC2a) and alternative (C3bBb) C3 convertases (Coico & Sunshine 2009).
REACT_118583 (Reactome) Complement factor I binds the factor H:C3b complex.
REACT_118584 (Reactome) Decay accelerating factor (DAF, CD55) is a widely distributed membrane protein. It accelerates the dissociation of C3bBb and C4C2a, thereby inhibiting the amplification of complement. DAF can bind C3b and Bb but must bind both for efficient decay acceleration. The regulatory function of DAF is believed to be inhibition of activated C3 convertase enzymes rather than binding of inactive proenzymes (Harris et al. 2007).
REACT_118604 (Reactome) Factor H preferentially binds to host cells and surfaces that have negatively charged cell surface polyanions such as heparin and sialic acid commonly found on host cells (Kazatchkine et al. 1979, Meri & Pangburn 1990). This mediates protection of plasma-exposed host structures.
REACT_118631 (Reactome) Membrane cofactor protein (MCP) and Complement Receptor 1 (CR1) act as cofactors for the protease activity of complement factor I which binds MCP or CR1 complexes with C3b or C4b, inactivating C3b/C4b.
REACT_118641 (Reactome) C3b:Bb is naturally labile with a half-life of ~90 s. unless bound to properdin on the cell surface (Medicus et al. 1976). C4bC2a is also unstable, lasting at best a few minutes (Kerr et al. 1980). Decay is associated with the release of the Bb or C2a fragments respectively into the fluid phase. The liberated C3b/C4b is able to re-bind Bb/C2a if Factor B/C2 are present.
REACT_118647 (Reactome) C4b-binding protein is a cofactor for Complement Factor I, allowing it to bind and thereby mediating C4b proteolysis.
REACT_118650 (Reactome) Complement factor I cleaves the alpha chain of C3b at two positions, generating inactivated C3b (iC3b) and a small fragment C3f which is released. The majority of the alpha chain is retained as two fragments which are tethered by disulphide bonds. iC3b is proteolytically inactive.
REACT_118673 (Reactome) Factor I cleaves the truncated alpha (a') chain of C4b between Arg-1336 and Asn-1337 and then again between Arg-956 and Thr-957, producing a 16 kDa fragment known as alpha4, derived from the C terminus of the a' chain, followed by a 27 kDa alpha3 fragment. The remaining alpha 2 (C4d) fragment stays covalently bound to the cell membrane while the complex of disulfide-linked alpha3, alpha4, beta chain and gamma chain are released (C4c) into the fluid phase (Fujita et al. 1978).
REACT_118674 (Reactome) Complement factor I (CFI) is a complex of one heavy and one light chain, both cleaved from the same precursor peptide. It inactivates complement subcomponents C3b, iC3b and C4b by proteolytic cleavage of the alpha chains of C4b and C3b in the presence of cofactors such as Factor H, C4b binding protein, Complement receptor 1 (CR1) or MCP (CD46).
REACT_118692 (Reactome) Complement Receptor 1 (CR1) displaces the activated enzyme components Bb and C2a from the conventional and alternative C3 convertases C4bC2a and C3bBb, respectivley.
REACT_118710 (Reactome) Factor H (FH) binds to C3bBb, leading to displacement of Bb. Complement factor H-related protein 3 (FHR-3) has also been reported to bind C3Bb leading to inhibition of C3Bb C3 convertase activity (Fritsche et al. 2010). FH also acts as a cofactor for the factor I-mediated proteolytic inactivation of C3b to iC3b.
REACT_118712 (Reactome) Factor H (FH) regulates the alternative pathway C3 convertase C3bBb and its C3b component both in plasma and at host cell surfaces. FH binds to plasma C3b, making it unavailable, and acts as a cofactor for the factor I-mediated proteolytic inactivation of C3b to iC3b.
REACT_118719 (Reactome) C4b-binding protein is a cofactor in Factor I mediated C4b proteolysis. C4b is cleaved, releasing C4c, leaving C4d bound to the cell surface.
REACT_118727 (Reactome) Factor H greatly accelerates the displacement (decay) of Complement factor Bb from C3b.
REACT_118738 (Reactome) C4 binding protein accelerates the decay of C4bC2a in a dose-dependent fashion. The mechanism of this is poorly understood, but is distinct from Factor I mediated degradation of C4b and believed to represent the displacement of C2a from specific binding sites on C4b (Gigli et al. 1979).
REACT_118752 (Reactome) C4 binding protein accelerates the decay of C4bC2a in a dose-dependent fashion, without causing degradation of C4b, and is presumed to bind to the convertase to mediate this effect.
REACT_118763 (Reactome) The most abundant form of C4b-binding protein (C4BP) consists of seven alpha-chains (70kDa) and one beta-chain (45kDa) all linked by disulphide bonds to form a native protein with a molecular weight of 570kDa (Hilarp et al. 1989). Each alpha chain can bind C4b; it is not known whether full occupancy is necessary for subsequent events. The beta chain binds and inactivates Protein S, a component of the coagulation system. C4BP down-regulates complement activity in several ways: It binds to C4b thus inhibiting the formation of the classical pathway C3 convertase C4bC2a; it acts as a decay accelerating factor for existing convertases, probably by promoting dissociation of C2a; it is a cofactor in Factor I mediated C4b proteolysis.
REACT_118782 (Reactome) Decay-accelerating-factor (DAF, CD55) is a membrane- bound complement regulatory protein that inhibits autologous complement cascade activation. It is expressed on all cells that are in close contact with serum complement proteins, but also on cells outside the vascular space and on tumour cells. DAF binds to C3bBb and C4bC2a on cell surfaces, accelerating their dissociation and thereby inhibiting the amplification of complement. DAF can bind C3b and Bb, and must bind both for efficient decay acceleration. Although it can bind the inactive proenzymes C3b and C4b, the regulatory function of DAF is believed to be inhibition of activated C3 convertase enzymes (Harris et al. 2007).
REACT_118815 (Reactome) Factor H (FH) regulates the alternative pathway C3 convertase C3bBb and its C3b component both in plasma and at host cell surfaces. FH binds to membrane-associated C3b, competing with Factor B and thereby preventing formation of the active C3 convertase C3bBb. In addition, it acts as a cofactor for the Factor I-mediated proteolytic inactivation of C3b to iC3b.
REACT_118836 (Reactome) The beta subunit of C4b binding protein binds and inactivates Protein S, a vitamin K dependent anticoagulation factor. This may represent part of a mechanism for fine-tuning the process of phagocytosis (Kask et al. 2004).
REACT_118841 (Reactome) Following the displacement of Bb from C3bBb, Factor I cleaves Factor H-bound C3b producing iC3b, which remains bound to the membrane. The majority of the C3b alpha chain is retained as two fragments which are tethered to the beta chain by disulphide bonds. iC3b is proteolytically inactive and cannot contribute to the complement cascade process, though it still contributes to opsonization.
REACT_118844 (Reactome) Complement factor I binds to the Factor H:C3b complex.
REACT_163715 (Reactome) Ficolin-1 (M-ficolin or FCN1) was shown to localize at the cell surface of circulating monocytes and granulocytes, despite lacking an obvious transmembrane domain, (Teh C et al. 2000; Honore C et al. 2010). Ficolin-1 has also been found in human plasma (Honore C et al. 2008; Wittenborn T et al. 2010; Kjaer TR et al. 2011). Monocytes and macrophages, but not immature dendritic cells were reported to secrete Ficolin-1 into the serum (Honore C et al. 2010). Moreover, early studies revealed its presence in secretory granules of peripheral blood monocytes and granulocytes (Liu Y et al. 2005). Soluble Ficolin-1 was found to form a complex with MASP2, while cell surface-bound Ficolin-1 did not associate with MASP (Honore C et al. 2010; Kjaer TR et al. 2011).

Ficolin-1 specifically recognizes sialic acid and can bind to acetylated compounds such as N-acetylglucosamine (GlcNAc) and N-acetylgalactosamine (GalNAc) (Garlatti V et al. 2007; Gout E et al. 2010; Kjaer TR et al. 2011).

REACT_163747 (Reactome) Human ficolin-2 (L-ficolin, P35 or FCN2) is synthesised in the liver and secreted into the bloodstream where it recognizes various capsulated bacteria and exhibits binding specificity for diverse ligands, such as lipoteichoic acid, 1,3-beta-d-glucan, and acetylated compounds [Lynch NJ et al. 2004; Aoyagi Y et al. 2008; Ma YG et al. 2004; Garlatti V et al. 2007; Gout E et al 2010]. Ficolin-2 also binds to apoptotic HL60, U937, and Jurkat cells [Kuraya M, et al. 2005].
REACT_163758 (Reactome) Ficolin-3 (H-ficolin, FCN3 or Hakata antigen) activates the lectin pathway of complement similar to mannose-binding lectin. Ficolin-3 is composed by a collagen-like strand and three C-terminal recognition domains which bind to carbohydrates on the target surface. Ficolin-3 circulates in plasma associated with mannan-binding lectin-associated serine proteases (MASPs). Upon ligand binding ficolin-3:MASPs complex triggers activation of the lectin pathway [Matsushita M et al. 2002; Teillet F et al. 2008; Zacho RM et al. 2012]. Ficolin-3 (FCN3 or H-ficolin) can specifically recognize Aerococcus viridans [Tsujimura M et al. 2002; Zacho RM et al. 2012]. Ficolin-3 has been shown to bind to patterns of bacterial polysaccharides such as d-fucose and galactose [Garlatti V et al. 2007]. In adition to pathogenic ligands ficolin-3 was reported to bind to apoptotic Jurkat cells [Kuraya M et al. 2005].
REACT_163759 (Reactome) Vitronectin interacts with C5b:C6:C7 complex preventing it from the binding with the cell membrane
REACT_163768 (Reactome) Cleavage of C4 exposes a highly reactive thioester bond on the C4b molecule. The thioester bond is rapidly inactivated by hydrolysis if C4b does not bind to the target cell surface [Sepp A et al 1993].
REACT_163829 (Reactome) CD59, the major inhibitor of the complement membrane attack complex, is an 18–20 kDa glycoprotein, linked to the membrane via a glycosylphosphatidylinositol (GPI)-anchor. It interacts with complement components C8 and C9 during assembly of the membrane attack complex (MAC) and inhibits C9 polymerization, thus preventing the formation of MAC [Lehto T and Meri S. 1993;Rollins SA et al 1991]
REACT_163860 (Reactome) Factor I (FI) inactivates C3 convertase activity by cleavage C3b producing iC3b, which remains bound to the membrane. A final proteolytic cleavage converts iC3b into two molecules, C3c, which is released into solution, and C3dg, which remains attached to the membrane. This cleavage requires CR1, which serves as a cofactor for cleavage of iC3b by factor I (Medof ME et al. 1982).

iC3b and C3dg are active molecules, that can bind CR2 (CD21) to enhance B-cell immunity (Tuveson DA et al.1991; Sarrias MR et al. 2001).

REACT_163870 (Reactome) Complement proteins C8 and C9 can bind to VTN:C5b:C6:C7 to form soluble C5b-C9 complex in plasma. The vitronectin binding to C5b-C9 complex prevents C9 polymerization by rendering it water-soluble and lytic inactive.
REACT_25075 (Reactome) Metastable C3b can bind a wide variety of proteins and carbohydrates expressed on biological surfaces (Coico & Sunshine, 2009; Kimball 2010). This is an essentially random event (Dodds & Law, 1998); binding may be to host or microorganism. However, certain surface sugars have greater C3b binding rates, perhaps explaining variations in microorganism suceptibility (Pangburn, M. in The Complement System, Ed. Rother et al. 1998).
REACT_25166 (Reactome) The cleavage of C4 into C4a and C4b releases an acyl group from the intrachain thioester bond, allowing C4b to bond covalently to any adjacent biological substrates (Dodds & Law 1998). C4 is encoded at two loci, C4A and C4B. The C4b proteins derived from these genes are not identical and have different binding preferences (Law et al 1984, Sepp et al. 1993); C4A-derived C4b binds more efficiently than C4B-derived C4b to amino groups, while C4B-derived C4b is more effective than C4A in binding to hydroxyl groups. The site of C4b deposition is not clearly established (Møller-Kristensen et al. 2003) but generally accepted to be the activating cell membrane surface, though it may be the activating complex itself.
REACT_7946 (Reactome)
REACT_7948 (Reactome) C3(H2O):Factor Bb is a C3 convertase, sometimes referred to as the initial C3 convertase (iC3). The Factor Bb component catalyzes the hydrolysis of C3 to produce C3b and C3a. This reaction is not known to be directly coupled to the association of C3b complexes with a cell surface. It is believed that a small proportion of C3b spontaneously associates with the cell surface, otherwise it is rapidly inactivated (Muller-Eberhard 1988).
REACT_7950 (Reactome)
REACT_7959 (Reactome) C2 is cleaved into the large C2a and the small C2b fragment. This irreversible, extracellular reaction can be catalyzed by activated MBL, generated through the lectin pathway of complement activation (Vorup-Jensen et al. 2000), and by activated C1, generated through the classical pathway (Nasagawa and Stroud 1977). N.B. Early literature refers to the larger fragment of C2 as C2a. However, complement scientists decided that the smaller of all C fragments should be designated with an 'a', the larger with a 'b', changing the nomenclature for C2. For this reason recent literature may refer to the larger C2 fragment as C2b, and the classical C3 convertase as C4bC2b. Throughout this pathway, Reactome uses the current (Feb 2012) Uniprot names which adhere to the original naming practice.
REACT_7965 (Reactome) MBL or ficolins binding to carbohydrates on the target surface results in conformational changes in the lectin:MASPs complex. It in turn promotes a cleavage of proenzyme form of MASP between the CCP2 and the serine protease domains, which results in the generation of the active form. The active form of MASP-2 is able to cleave C4 and C2 to generate the C3 convertase (Vorup-Jensen T et al. 2000; Chen CB and Wallis R 2004). The active form of MASP-1 was shown to facilitate the complement activation by either direct cleavage of complex-bound MASP-2 or cleavage of C2 bound to C4 (Matsushita M et al. 2000; Heja D et al. 2012).
REACT_7966 (Reactome) C3b on a surface binds Factor B from solution to form a complex (Schreiber et al. 1978; Muller-Eberhard 1988).
REACT_7976 (Reactome)
REACT_7977 (Reactome) In this irreversible reaction, the activated C1r subunit of the C1:antibody:antigen complex cleaves the C1s subunit of the complex, activating it in turn (Ziccardi and Cooper 1976). The resulting complex is a C4 activator.
REACT_7978 (Reactome) C1 activation requires interaction with two separate Fc domains, so pentavalent IgM antibody is far more efficient at complement activation than IgG antibody (Muller-Eberhard and Kunkel 1961). Antibody binding results in a conformational change in the C1r component of the C1 complex and a proteolytic cleavage of C1r, activating it (Ziccardi and Cooper 1976). This reaction is irreversible under physiological conditions.
REACT_7981 (Reactome) Factor D, a constitutively active serine protease found in trace amounts in the blood, cleaves a specific Arg-Lys bond in the Factor B component of the soluble C3(H2O):Factor B complex, yielding C3(H2O):Factor Bb and an inactive polypeptide, Factor Ba (Fearon and Austin 1975; Lesavre and Muller-Eberhard 1978; Lesavre et al. 1979; Schreiber et al. 1978).
REACT_7982 (Reactome)
REACT_7983 (Reactome) The MBL polypeptide chain consists of a short N-terminal cysteine-rich region, a collagen-like region comprising 19 Gly-X-Y triplets, a 34-residue hydrophobic stretch, and a C-terminal C-type lectin domain. MBL monomers associate via their cysteine-rich and collagen-like regions to form homotrimers, and these in turn associate into oligomers. The predominant oligomers found in human serum contain three (MBL-I) or four (MBL-II) homotrimers (Fujita et al. 2004; Teillet et al. 2005). Extracellular MBL oligomers circulate in plasma in complexes with MASP1/2. The carbohydrate recognition domain (CRD) of MBL binds carbohydrates with 3- and 4- OH groups in the pyranose ring, such as mannose and N-acetyl-D-glucosamine, in the presence of Ca2+. Such motifs occur on the surfaces of viruses, bacteria, fungi and protozoa. The affinity of any one MBL binding site for a carbohydrate ligand is low, but interaction between multiple binding sites on an MBL oligomer and a repetitive carbohydrate motif on a target surface allow high-avidity binding. The specificity of the MBL binding site (it does not bind glucose or sialic acid) and the requirement for a repeated target motif may account for the failure of MBL to bind human glycoproteins under normal conditions (Petersen et al. 2001). This reaction in particular represents the interaction of MBL with bacterial mannose repeats.
REACT_7986 (Reactome) The complex of C3b:Factor Bb, stabilized on the cell surface by properdin, catalyzes the cleavage of C3 to yield C3b and C3a. The C3b is recruited to the C3b:Factor B complex through its interaction with properdin (Daha et al. 1976; Medicus et al. 1976; Hourcade 2006), yielding the alternate C5 convertase.
REACT_7988 (Reactome) The membrane attack complex is composed of one C5:C6:C7:C8 complex and between 12-15 C9 molecules (Podack et al. 1982 - 12 represented in this reaction).
REACT_7989 (Reactome) The same complexes as for C3 activation are employed for the cleavage of C5. C3 convertases with an additional C3b molecule covalently deposited in the immediate vicinity form the C5 convertases C3bBbC3b and C4b2aC3b, respectively. The second C3b acts like an anvil for C5: it interacts with C5 and presents C5 in the correct conformation for cleavage by the C2a or Bb enzyme.
REACT_7990 (Reactome) C4b and C2a bind to form the classical pathway C3-convertase (C4b2a complex), C3b and the Bb fragment of Factor B form the alternative pathway C3 convertase. The C3(H2O):Bb C3 convertase is sometimes called the initiating convertase, and the C5 convertases also have C3 convertase activity (Rawal & Pangburn 2001).
REACT_8002 (Reactome) The alpha chain of C4 is cleaved, releasing an N-terminal portion of this chain as C4a. The beta and gamma chains are not cleaved and remain linked to the alpha chain by disulfide bonds (Nagasawa et al. 1976, 1980). The resulting C4b heterotrimer undergoes a gross conformational change; the internal thioester in C4b becomes exposed and able to form covalent bonds with surrounding molecules (Law and Dodds 1997). A large proportion of the bonds formed are with water, but some will attach C4b to biological surfaces (Rother et al. 1998). This irreversible reaction can be catalyzed by activated MBL, generated through the lectin pathway of complement activation (Fujita et al. 2004; Hajela et al. 2002), and by activated C1, generated through the classical pathway (Muller-Eberhard and Lepow 1965).

N.B. Humans have two highly polymorphic loci for Complement factor 4, C4A and C4B. C4A alleles carry the Rodgers (Rg) blood group antigens while the C4B alleles carry the Chido (Ch) blood group antigens. The two loci encode non identical C4 peptides; C4 derived from C4A reacts more rapidly with the amino groups of peptide antigens while C4B allotypes react more rapidly with the hydroxyl group of carbohydrate antigens. The names of the two loci are always represented in uppercase. C4a and C4b refer to the peptide products of Complement Factor 4 cleavage.
REACT_8007 (Reactome) The thioester linkage between cysteine residue 1010 and glutamine residue 1013 in the alpha chain of Complement factor 3 (C3) can spontaneously hydrolyze, yielding so-called C3(H2O) (Tack et al. 1980; Pangburn & Muller-Eberhard 1980; Pangburn et al. 1981). Thioester bond hydrolysis causes conformational rearrangements that give C3(H2O) the ability to bind Factor B. The spontaneous hydrolysis rate of C3 under physiological conditions and temperature is about l% per hour, thus the C3b-like properties of C3(H2O) provide a continuous low level initiation of the alternative pathway of complement activation (Pangburn & Muller-Eberhard 1983). If not bound by Factor B, C3(H2O) binds Factor H and is inactivated by Factor I
REACT_8013 (Reactome) Thioester bond hydrolysis causes conformational rearrangements that give C3(H2O) the ability to bind Factor B (Schreiber et al. 1978). The spontaneous hydrolysis rate of C3 under physiological conditions and temperature is about l% per hour, thus the C3b-like properties of C3(H2O) provide a continuous low level initiation of the alternative pathway of complement activation (Pangburn & Muller-Eberhard 1983).
REACT_8014 (Reactome) C4b and C2a form a complex termed the classical pathway C3 convertase (Muller-Eberhard et al. 1967). C2a that fails to bind C4b is rapidly inactivated.
REACT_8018 (Reactome) C3b:Bb is naturally labile with a half-life of ~90 s; association of the complex with properdin extends the half-life to ~30 min. (Medicus et al. 1976). Properdin is found in the blood as a mixture of multivalent oligomers: 30% dimers, 45% trimers, 10% tetramers, and 15% higher oligomers. Monomers associate with one another in a head-to-tail arrangement, producing closed circular structures (Smith et al. 1984). These features suggest that the properdin oligomer associated with a C3b:Bb complex on a surface such as a cell membrane can facilitate recruitment of additional C3b:Bb complexes to the site (Farries et al. 1988; Hourcade 2006).
REACT_8022 (Reactome) C5 convertases are serine proteases that cleave C5 with high efficiency; the C3 convertases can cleave C5 but have a poor affinity for C5, with a Km of 6-9 microM. The high affinity C5 convertases are generated when the low affinity C3/C5 convertases such as C4b:C2a deposit C3b by cleaving native C3. These C3b-containing C3/C5 convertases have Km values of 0.005 microM, well below the normal concentration of C5 in blood (0.37 microM). They have very low Vmax rates, just one C5 cleaved per 1–4 min per enzyme (Rawal & Pangburn 1998).
REACT_8026 (Reactome) Factor D, a constitutively active serine protease found in trace amounts in the blood, cleaves a specific Arg-Lys bond in the Factor B component of the cell surface-associated C3b:Factor B complex, yielding the alternate C3 convertase C3bBb on the surface and releasing an inactive polypeptide, Factor Ba (Lesavre and Muller-Eberhard 1978; Lesavre et al. 1979; Schreiber et al. 1978).
VTN

C5b C6

C7		REACT_163870 (Reactome)
VTNREACT_163759 (Reactome)
iC3bArrowREACT_118650 (Reactome)
iC3bArrowREACT_118841 (Reactome)
thioester-C1010-Q1013-C4bArrowREACT_8002 (Reactome)
thioester-C1010-Q1013-C4bREACT_118763 (Reactome)
thioester-C1010-Q1013-C4bREACT_163768 (Reactome)
thioester-C1010-Q1013-C4bREACT_25166 (Reactome)
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