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_Dr. Mohr's lectures_complement[1].lecture.04

_Dr. Mohr's lectures_complement[1].lecture.04 - Complement...

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Unformatted text preview: Complement Proteins and Receptors Immune Complexes IgM, IgG Carbohydrates Altered Surfaces Bacteria, LPS C3 Chemotaxins Opsonins Cell Lysis 1 Evolution of Complement • • • Ancient part innate immunity Complement proteins found in the Complement deuterostomes deuterostomes – Echinoderms—Sea urchins – Urochordates—Ascidians – Vertebrates—Jawless and jawed C3, C4, C5 derived from α2-macroglobulin by C3, 2-macroglobulin gene duplication gene 2 Biological Functions of Complement Cell act iv at io n Cell Ly sis Bridge between innate and acquired immunity C3 d CR2 Ag mI g Co m p l e m e n t Opso nizat io n B ly m p ho c y t e 3 General Features • • • • • • • Components synthesized in the liver Heat labile, serum components Reactions are proteolytic cleavages Internal thioester bond in C3 & C4 – ß-cysteinyl-γ -glutaminyl thioester – -Gly-Cys-Gly-Glu-Glu-AsnPathways produce separate C3 & C5 convertases C3 is a key molecule Amplifying and highly regulated 1 423 5678(9)n 4 Reactive thioester bond of C3 5 Classical pathway C2 b C4 C1 Ca2+ C4a C4 b C2 Mg 2 + C4 b 2 a C4 b C2 C3 C3 a C3 b ac t i v a t i n g su r f a c e C1 activated by IgM, IgG, LPS, MBL, C-Reactive protein 6 Structure of C1qrs 7 Activation of C1 C1 s C1 r C1 q C1 s C1 r C1 q Inactive C1q, r & s noncovalently associated One IgM; up to 1000 IgG C3b & C4b binding on surface loosen the C1 complex LPS: either direct binding to C1q or to anti-LPS antibody C1q binds to apoptotic buds and to phagocytic cells 8 C4 C4a C2b C2 Mg 2 + C4 b 2 a C3 C3 a C3 b C1 Ca2+ C4 b C4 b C2 a c t i v a t i n g su r f a c e Calcium very important for stability Activated C1 acts on C4 & C2 Single Activated C1 can generate over 200 C3b Alternative or Properidin Pathway • • • Discovered in early 1950’s by Dr. Louis Discovered Pillemer Pillemer – Isolated a protein that activated the Isolated complement cascade “in midstream” complement – C1, C4, C2 not needed Properidin— Pro-perdo [before loss of C3 Properidin— from consumption] from Validated by discovery of C4-deficient guinea Validated pigs pigs 10 Alternative Pathway • Two mechanisms for activation – C3 tickover pathway–spontaneous hydrolysis of C3 C3 – Amplification pathway—amplifies the classical pathway • • Microenvironment must favor binding of Factor B Initiated by – – – – – – – – – – Gm negative & positive bacteria LPS, pepidoglycans, teichoic acid Fungal cell walls Proteases Tumor cells Heterologous RBCs Anionic polymers (dextan) Pure carbohydrate Classical pathway (amplification loop) Lectin pathway (amplification loop) 11 Alternative pathway: C3 Tickover Pathway P H2O D [C3H2O] C3 C 3bBbP C3 C 3b H20 C3b B B Mg 2 + Ba C3 a C3 b 12 Alternative Pathway: C3 tickover & Amplification Loop 2 C3 P D C3 C3 2 HB 0 D P Mg 2 + B C 3 bBbP C3 b B Ba C3 a C3 b C3* BbP H0 Tickover Pathway a m pli f i ca t i o n l o o p ac t i v a t in g su r f ac e 13 Mannan­Binding­Lectin Pathway C2 b C4 M A SP C4a C2 Mg 2+ C4 b 2a C4 b C2 C3 C3 a C3 b C4 b Ca2+ MB L Mannose ac t iva t ing sur f ace 14 Mannan­Binding­Lectin Pathway P D C3 M A SP Mg 2 + B C 3 bBbP C3 b B Ba C3 a C3 b MBL a m p li f i ca t i o n l o o p ac t i v a t in g su r f ac e 15 Mannan­Binding­Lectin • • • Collectin family of proteins Different forms exist in some species Carbohydrate-recognition domain (CRD) – Binds carbohydrates (CBH) on bacteria, viruses, protozoa – Binds: mannose, glucans, lipophosphoglycans, glucose, Binds: fructose fructose – Distinguishes between self and non-self – Self-CBHs on membrane proteins terminate with sialic acid » Sialic acid not recognized by CRD of MBL • MBL structurally similar to C1q (can also bind to apoptotic buds) MASP • • Family of serine proteases and nonproteases Similar to C1r and C1s 16 Regulation of MBL/MASP • • • No selective regulator of MBL-MASP has No been described been α2-macroglobulin and C1 inhibitor form 2-macroglobulin complexes with MBL-MASP complexes Inhibitors of the classical and alternative Inhibitors pathway will have an effect on the MBL pathway pathway 17 Regulation up to C3 convertases • C1-Inhibitor (C1-INH) – SERPIN family – Covalently binds to activated C1r and C1s Covalently to inhibit activity to – C1-INH prevents spontaneous activation of C1-INH C1 in plasma C1 – Deficiency: Hereditary Angioneurotic Deficiency: Edema Edema – C1-INH also inactivates plasma kallekrein 18 Regulation of the pathway up to the C3 convertases • • C4b2a (classical C3 convertase) C4b2a spontaneous decays to C4b and a derivative of C2a of Decay accelerating factor (DAF) – Bound to membranes by a phosphatidyl inositol Bound glycan anchor glycan – Assembly of C3 convertase (Classical or Assembly Alternative) inhibited Alternative) – Deficiency: Paroxysmal Nocturnal Hemoglobinuria 19 Regulation (cont.) • Amplification loop control – C3bBb is unstable – Factor H binds to C3 & C5 convertases to accelerate decay – Self cell membranes contain regulatory molecules that Self promote the binding of Factor H instead of Factor B to C3b promote » High sialic acid content favors Factor H binding to C3b » Streptococcus (Group B) and Neisseria gonorhoeae put sialic Neisseria acid residues on their surface acid – On non-self structures Factor B has higher affinity for C3b On than Factor H than – C3bH is the substrate for Factor I with the resulting product C3bH P iC3b iC3b D C 3 b B bP B C3 b H H Ba 20 Degradation of C3b and C4b by Factor I B H X C3b CR1 Factor I MCP C3f C3c iC3b Factor I C3dg Membrane Cofactor Protein (MCP) Complement receptor 1 (CR1) MCP C4bBP C4c Factor I C4b H CR1 C4d Factor I deficiency: uncontrolled activation of alternative pathway increased turnover of C3 and consumption of B, H, P Consequence: recurrent bacterial infections 21 Regulation of Classical pathway DAF C1inh C2 b C4 C1 Ca2+ C4a C4 b C2 Mg 2 + C4 b 2 a C4 b C2 C3 C3 a C3 b ac t i v a t i n g su r f a c e spontaneous decay 22 Regulation of the Alternative Pathway: C3 tickover & Amplification Loop C3 CR1 MCP H20 P D DAF & H C3 C3 H20 Mg 2 + H Factor I C 3 bBbP B D P C3 b H Ba C3 a C3 b C3* BbP Tickover Pathway a m pli f i ca t i o n l o o p ac t i v a t in g su r f ac e 23 Membrane Attack Complex C5 C4 b 2a C5a C6 C5b C7 C6 C5b C6 C5b C7 C6 C5b C7 C8 C8 C9 C6 C5b C7 C8 Poly C9 C3 b 24 MAC 25 Membrane Attack Complex http://www.ultranet.com/~jkimball/BiologyPages/C/Complement.html26 Regulation of MAC • • • S-protein S-protein S-protein incorporates into the C5b67 complex at the S-protein stage when C7 is added stage – C8 and C9 can bind but C9 can’t polymerize Very low, low, and high density lipoproteins inhibit the Very formation of the C5b67 complex formation C5a C6 C5b C5 C4 b 2a C7 C6 C5b C6 C5b C7 C6 C5b C7 C8 C8 C9 C6 C5b C7 C8 Poly C9 C3 b 27 • Regulation of MAC Homologous restriction factor (HRF) in membranes of Homologous platelets, neutrophils, monocytes and lymphocytes, erythrocytes – GPI anchor – Binds to C8 & C9 Binds C8 – Becomes incorporated into the MAC – Paroxysmal Nocturnal Hemoglobinuria CD59 (membrane-bound on most nucleated cells CD59 limited amounts on erythrocytes) – GPI anchor – Binds to C8 when it incorporates into the C5b-7 Binds complex complex – Binds to C9 as it folds into the membrane – Paroxysmal Nocturnal Hemoglobinuria – Thrombosis 28 • Regulation of the Membrane Attack Complex HRF C5 C5a C6 C5b C7 S-protein C8 Factor H C4 b 2a C3 b CD59 C6 C5b C7 C6 C5b C7 C8 C6 C5b C7 C8 C6 C5b C9 Poly C9 29 MACs in nucleated cells • • Nucleated cells more resistant to attack – Ion pumps compensate for ionic disturbances – Shedding of MAC (ectocytosis) – Internalization and degradation – CD59 blocks pore assembly – Ectoproteases/ectokinases Killing requires increases in intracellular calcium – Entry through the pore – Release from intracellular stores 30 Other functions of MAC • Neutrophils & macrophages – Synthesis and release of inflam. mediators » Prostaglandins and superoxide anion readical • • – Signaling pathways involve—calcium fluxes, Signaling receptor tyrosine kinases, G-proteins leading to activation of MAPK, NK-κ B (TNFα ) activation Vascular smooth muscle cells, endothelial cells, Vascular mesangial cells mesangial – MAC-stimulated proliferation MAC modulation of apoptosis (promotes and inhibits) 31 Complement Deficiencies • Early component deficiency – C1, C4, C2 – Asymptomatic to pyogenic infections (especially if Asymptomatic there is also Factor B def.) there – Reduced clearance of soluble immune complexes » C3b binds to immune complexes; removed by CR1 • • C3 deficiency – Recurrent pyogenic infections Late component deficiency – C5, C6, C7, C8 – Increased frequency of infections with heavily Increased encapsulated bacteria encapsulated 32 Complement Receptors • CR1 (RBC, phagocytes, lymphocytes, NK cells, dendritic cells, phagocytes, CR1 glomerular cells) glomerular – Binds C3b & C4b – Factor I-induced C3b & C4b degradation » Blocks formation of alternative C3 convertase – Opsonization (immune adherence) – Clearing soluble immune complexes from circulation » CR1 on erythrocytes responsible • CR2 (B lymphocytes) – Binds C3dg, Cdg, iC3b – Part of B lymphocyte activation – Receptor for Epstein-Barr virus CR2 C3 d g Ag mI g B ly m p h o c y t e 33 Complement Receptors • • • CR3 (monocytes, macrophages, NK cells, CR3 neutrophils) neutrophils) – Same as CD11b/CD18—recognizes ICAM-1 – Binds iC3b (opsonic recognition) – Binds to several types of bacteria – Binds immune complexes & enhances their Binds phagocytosis phagocytosis – Binding to iC3b opsonized apoptotic buds Binding downregulates IL-12 and IFN-γ downregulates CR4 (monocytes, macrophages,NK cells) – iC3b – Enhances cell-adhesion & phagocytosis of Enhances immune complexes immune C3a/C4a receptor & C5a receptor 34 • • • • • • • • • References Nonaka, M. Evolution of the complement system. Curr. Opin. Immunol. 13:69Nonaka, Curr. 73, 2001 (on-line) Gadjeva, M. The mannan-binding-lectin pathway of the innate immune Gadjeva, response. Curr. Opin. Immunol. 13: 74-78, 2001 (on-line) Curr. Holers, V. M. Phenotypes of comlement knockouts. Immunopharmacol. 49: 125Holers, Immunopharmacol 131, 2000 (on-line) Zhang, B. The role of complement in inflammation and adaptive immunity. Zhang, Immunol. Rev. 180: 5-15, 2001 Immunol. Muller­Eberhard, H.J. Molecular organization and function of the complement system. Ann. Rev. Biochem. 57:321, 1988 Mold, C. et al. Regulation of complement activation by C­reactive protein. Immunopharmacology 42:23­30, 1999 (Internet Electronic Access) Matsushita, M. The lectin pathway of the complement system. Microbiol. Immunol. 40:887,1996 Liszewski, M. K., et al. Control of the complement system. Adv. Immunol. 61:201, 1996 Würzner, R. Evasion of pathogens by avoiding recognition or eradication by complement, in part via molecular mimicry. Immunopharmacology 42:249­260, 1999 (On­line) Morgan, B. P. Regulation of the complement membrane attack pathway. Crit. Rev. Immunol. 19:173­198, 1999 • 35 References • • • Cole, D. S. and B. P. Morgan. Beyond lysis: how complement Cole, influences cell fate. Clin. Sci. 104: 455-466, 2003 Clin. Turnberg, D, et al. The regulation of the complement system: insights Turnberg, et The from genetically-engineered mice. Mol. Immunol. 40: 145-153, 2003 Mol. Velasco-Velázquez, M. A., et al. Macrophage-Mycobacterium Velasco-Velázquez, et Macrophage-Mycobacterium tuberculosis interactions: role of complement receptor 3. Microbial Microbial Pathogenesis 35: 125-131, 2003 Pathogenesis 36 ...
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