Relevant bibliographies by topics / C3-convertase of alternative complement pathway

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  2. Dissertations / Theses
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Academic literature on the topic 'C3-convertase of alternative complement pathway'

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Published: 14 March 2023

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Journal articles on the topic "C3-convertase of alternative complement pathway"

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Hourcade, Dennis E., Lynne M. Mitchell, and M. Edward Medof. "Decay acceleration of the complement alternative pathway C3 convertase." Immunopharmacology 42, no. 1-3 (May 1999): 167–73. http://dx.doi.org/10.1016/s0162-3109(99)00005-3.

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Roumenina, Lubka T., Mathieu Jablonski, Christophe Hue, Jacques Blouin, Jordan D. Dimitrov, Marie-Agnes Dragon-Durey, Mathieu Cayla, et al. "Hyperfunctional C3 convertase leads to complement deposition on endothelial cells and contributes to atypical hemolytic uremic syndrome." Blood 114, no. 13 (September 24, 2009): 2837–45. http://dx.doi.org/10.1182/blood-2009-01-197640.

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Abstract Complement is a major innate immune defense against pathogens, tightly regulated to prevent host tissue damage. Atypical hemolytic uremic syndrome (aHUS) is characterized by endothelial damage leading to renal failure and is highly associated with abnormal alternative pathway regulation. We characterized the functional consequences of 2 aHUS-associated mutations (D254G and K325N) in factor B, a key participant in the alternative C3 convertase. Mutant proteins formed high-affinity C3-binding site, leading to a hyperfunctional C3 convertase, resistant to decay by factor H. This led to enhanced complement deposition on the surface of alternative pathway activator cells. In contrast to native factor B, the 2 mutants bound to inactivated C3 and induced formation of functional C3-convertase on iC3b-coated surface. We demonstrated for the first time that factor B mutations lead to enhanced C3-fragment deposition on quiescent and adherent human glomerular cells (GEnCs) and human umbilical vein endothelial cells (HUVECs), together with the formation of sC5b-9 complexes. These results could explain the occurrence of the disease, since excessive complement deposition on endothelial cells is a central event in the pathogenesis of aHUS. Therefore, risk factors for aHUS are not only mutations leading to loss of regulation, but also mutations, resulting in hyperactive C3 convertase.
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Mullick, Jayati, John Bernet, Yogesh Panse, Sharanabasava Hallihosur, Akhilesh K. Singh, and Arvind Sahu. "Identification of Complement Regulatory Domains in Vaccinia Virus Complement Control Protein." Journal of Virology 79, no. 19 (October 1, 2005): 12382–93. http://dx.doi.org/10.1128/jvi.79.19.12382-12393.2005.

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ABSTRACT Vaccinia virus encodes a homolog of the human complement regulators named vaccinia virus complement control protein (VCP). It is composed of four contiguous complement control protein (CCP) domains. Previously, VCP has been shown to bind to C3b and C4b and to inactivate the classical and alternative pathway C3 convertases by accelerating the decay of the classical pathway C3 convertase and (to a limited extent) the alternative pathway C3 convertase, as well as by supporting the factor I-mediated inactivation of C3b and C4b (the subunits of C3 convertases). In this study, we have mapped the CCP domains of VCP important for its cofactor activities, decay-accelerating activities, and binding to the target proteins by utilizing a series of deletion mutants. Our data indicate the following. (i) CCPs 1 to 3 are essential for cofactor activity for C3b and C4b; however, CCP 4 also contributes to the optimal activity. (ii) CCPs 1 to 2 are enough to mediate the classical pathway decay-accelerating activity but show very minimal activity, and all the four CCPs are necessary for its efficient activity. (iii) CCPs 2 to 4 mediate the alternative pathway decay-accelerating activity. (iv) CCPs 1 to 3 are required for binding to C3b and C4b, but the presence of CCP 4 enhances the affinity for both the target proteins. These results together demonstrate that the entire length of the protein is required for VCP's various functional activities and suggests why the four-domain structure of viral CCP is conserved in poxviruses.
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Schwendinger, M. G., M. Spruth, J. Schoch, M. P. Dierich, and W. M. Prodinger. "A novel mechanism of alternative pathway complement activation accounts for the deposition of C3 fragments on CR2-expressing homologous cells." Journal of Immunology 158, no. 11 (June 1, 1997): 5455–63. http://dx.doi.org/10.4049/jimmunol.158.11.5455.

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Abstract Complement receptor type 2 (CD21, CR2), the receptor for the C3 fragment C3dg, activates complement via the alternative pathway and also serves as a preferential acceptor site for C3 fragments. The molecular basis for this phenomenon, which has recently been demonstrated for B lymphocytes in vivo, is currently not understood. Here we present a model for this CR2-dependent complement activation. The inactive C3 (iC3), which forms spontaneously in serum in low amounts by reaction of native C3 with H2O, binds noncovalently to the N-terminal part of CR2. Subsequent association of properdin and factor B, and cleavage of factor B by factor D lead to formation of a C3 convertase associated with CR2, thus focussing covalent C3 deposition to CR2 itself. This model is supported by the following experimental findings. 1) By FACS analysis and radioreceptor assays we showed that iC3, properdin, and factor B bound to CR2 on Raji B cells, MT2 T cells, and peripheral blood B cells. 2) Both binding of these proteins and complement activation by CR2-expressing cells were reduced in parallel by Abs against CR2. 3) 125I-labeled C3b was covalently deposited on CR2, when hemolytically active 125I-labeled C3 was added to Raji cells preincubated with iC3, factor B, properdin, and factor D, thus proving functionality of CR2-bound C3 convertase. This model of C3 convertase activity formed on CR2 domains inaccessible for decay-accelerating factor offers an explanation for the deposition of C3 found on CR2-expressing cells.
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Chauvet, Sophie, Romain Berthaud, Magali Devriese, Morgane Mignotet, Paula Vieira Martins, Tania Robe-Rybkine, Maria A. Miteva, et al. "Anti-Factor B Antibodies and Acute Postinfectious GN in Children." Journal of the American Society of Nephrology 31, no. 4 (February 7, 2020): 829–40. http://dx.doi.org/10.1681/asn.2019080851.

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BackgroundThe pathophysiology of the leading cause of pediatric acute nephritis, acute postinfectious GN, including mechanisms of the pathognomonic transient complement activation, remains uncertain. It shares clinicopathologic features with C3 glomerulopathy, a complement-mediated glomerulopathy that, unlike acute postinfectious GN, has a poor prognosis.MethodsThis retrospective study investigated mechanisms of complement activation in 34 children with acute postinfectious GN and low C3 level at onset. We screened a panel of anticomplement protein autoantibodies, carried out related functional characterization, and compared results with those of 60 children from the National French Registry who had C3 glomerulopathy and persistent hypocomplementemia.ResultsAll children with acute postinfectious GN had activation of the alternative pathway of the complement system. At onset, autoantibodies targeting factor B (a component of the alternative pathway C3 convertase) were found in a significantly higher proportion of children with the disorder versus children with hypocomplementemic C3 glomerulopathy (31 of 34 [91%] versus 4 of 28 [14%], respectively). In acute postinfectious GN, anti-factor B autoantibodies were transient and correlated with plasma C3 and soluble C5b-9 levels. We demonstrated that anti-factor B antibodies enhance alternative pathway convertase activity in vitro, confirming their pathogenic effect. We also identified crucial antibody binding sites on factor B, including one correlated to disease severity.ConclusionsThese findings elucidate the pathophysiologic mechanisms underlying acute postinfectious GN by identifying anti-factor B autoantibodies as contributing factors in alternative complement pathway activation. At onset of a nephritic syndrome with low C3 level, screening for anti-factor B antibodies might help guide indications for kidney biopsy to avoid misdiagnosed chronic glomerulopathy, such as C3 glomerulopathy, and to help determine therapy.
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Weiler, J. M., R. E. Edens, and G. J. Gleich. "Eosinophil granule cationic proteins regulate complement. I. Activity on the alternative pathway." Journal of Immunology 149, no. 2 (July 15, 1992): 643–48. http://dx.doi.org/10.4049/jimmunol.149.2.643.

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Abstract Eosinophil granules contain several cationic proteins that mediate tissue damage in allergic disease. The present study examined the capacity and mechanisms by which these cationic proteins regulate activity of the alternative pathway of C. Eosinophil peroxidase and eosinophil cationic protein inhibited formation of cell-bound alternative pathway C3 convertase, causing 50% inhibition of lysis at about 0.19 and 0.75 microgram/10(7) cellular intermediates, respectively. Major basic protein inhibited alternative pathway C3 activity by only 19% at 1.5 micrograms/10(7) cellular intermediates. Eosinophil-derived neurotoxin had no activity on the alternative pathway. The eosinophil granule proteins were examined for the mechanism by which they inhibited alternative pathway activity. Eosinophil peroxidase and major basic protein inhibited fluid phase factor B consumption in a reaction mixture that also contained factors D and C3b, eosinophil-derived neurotoxin had no activity on factor B consumption, and eosinophil cationic protein consumed factor B in the absence of C3b and factor D. Both eosinophil cationic protein and eosinophil peroxidase enhanced the decay of preformed alternative pathway convertase. Lysis of EAC4b,3b cellular intermediates formed to contain a low surface amount of C3b was more inhibited than was lysis of cells formed with a standard amount of C3b on the surface. This suggests that these eosinophil proteins acted predominantly on C3b to regulate alternative pathway activity. We also found that none of the eosinophil granule cationic proteins had any effect on later events after the formation of the C3 convertase. We conclude that although eosinophil-derived neurotoxin (isoelectric pH value (pI) = 8.9) does not regulate alternative pathway activity, the more highly charged eosinophil granule cationic proteins--major basic protein (pI = 10.9), eosinophil cationic protein (pI = 10.8), and eosinophil peroxidase (pI = 10.8)--do share the capacity to regulate C activity and may exert this activity in vivo.
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Irmscher, Sarah, Nadia Döring, Luke D. Halder, Emeraldo A. H. Jo, Isabell Kopka, Christine Dunker, Ilse D. Jacobsen, et al. "Kallikrein Cleaves C3 and Activates Complement." Journal of Innate Immunity 10, no. 2 (December 14, 2017): 94–105. http://dx.doi.org/10.1159/000484257.

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The human plasma contact system is an immune surveillance system activated by the negatively charged surfaces of bacteria and fungi and includes the kallikrein-kinin, the coagulation, and the fibrinolytic systems. Previous work shows that the contact system also activates complement, and that plasma enzymes like kallikrein, plasmin, thrombin, and FXII are involved in the activation process. Here, we show for the first time that kallikrein cleaves the central complement component C3 directly to yield active components C3b and C3a. The cleavage site within C3 is identical to that recognized by the C3 convertase. Also, kallikrein-generated C3b forms C3 convertases, which trigger the C3 amplification loop. Since kallikrein also cleaves factor B to yield Bb and Ba, kallikrein alone can trigger complement activation. Kallikrein-generated C3 convertases are inhibited by factor H; thus, the kallikrein activation pathway merges with the amplification loop of the alternative pathway. Taken together, these data suggest that activation of the contact system locally enhances complement activation on cell surfaces. The human pathogenic microbe Candida albicans activates the contact system in normal human serum. However, C. albicans immediately recruits factor H to the surface, thereby evading the alternative and likely kallikrein-mediated complement pathways.
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Pangburn, M. K., and H. J. Müller-Eberhard. "The C3 convertase of the alternative pathway of human complement. Enzymic properties of the bimolecular proteinase." Biochemical Journal 235, no. 3 (May 1, 1986): 723–30. http://dx.doi.org/10.1042/bj2350723.

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The association of Factor B with C3b (the major fragment of complement component C3) in the presence of Mg2+ results in the formation of a bimolecular zymogen, C3b,B, which is activated by the serine proteinase Factor D, generating the C3 convertase, C3b,Bb (EC 3.4.21.47). Cleavage of native C3 by the C3 convertase was monitored by recording the increase in fluorescence associated with C3b formation in the presence of the fluorescent probe 8-anilinonaphthalene-1-sulphonate. Measurements of initial rates of C3b formation at various C3 concentrations were analysed in accordance with the Michaelis-Menten equation, yielding kcat. = 1.78 +/- 0.08 s-1, Km = 5.86 × 10(-6) M and turnover number = 107 min-1. The assay was used to measure the Ki values of a variety of proteinase inhibitors. The C3 convertase has a short half-life, owing to spontaneous dissociation of the complex. The t1/2 and kcat./Km of the enzyme were determined by fitting an equation modelling both the kinetic reaction and enzyme decay to the fluorimetrically measured progress curve. The enzyme, C3b,Bb, exhibited a t1/2 of 90 +/- 2 s and a kcat./Km of 31.1 × 10(4) +/- 0.8 × 10(4) M-1 × s-1 at physiological pH, ionic strength and temperature. The enzyme that initiates activation of the alternative pathway, C3(H2O),Bb, was also examined. It was slightly less stable (t1/2 = 77 +/- 3 s) and exhibited only half the activity of C3b,Bb (kcat./Km = 16.3 × 10(4) +/- 1.0 × 10(4) M-1 × s-1).
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Sahu, Arvind, Stuart N. Isaacs, Athena M. Soulika, and John D. Lambris. "Interaction of Vaccinia Virus Complement Control Protein with Human Complement Proteins: Factor I-Mediated Degradation of C3b to iC3b1 Inactivates the Alternative Complement Pathway." Journal of Immunology 160, no. 11 (June 1, 1998): 5596–604. http://dx.doi.org/10.4049/jimmunol.160.11.5596.

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Abstract Vaccinia virus complement control protein (VCP) is a virulence determinant of vaccinia virus that helps protect the virus from the complement attack of the host. To characterize the interaction of VCP with C3 and C4 and understand the mechanism by which VCP inactivates complement, we have expressed VCP in a yeast expression system and compared the biologic activity of the purified protein to that of human factor H and complement receptor 1 (CR1). Recombinant VCP bound to C3 and the proteolytically cleaved form of C3 (C3b), but not to the 135,300-m.w. fragment of C3 generated using elastase (C3c) and the 35,000-m.w. fragment of C3 generated using elastase (C3d) and inhibited both the classical and alternative pathways of complement activation. Although rVCP was less effective at inhibiting the alternative pathway than factor H or CR1, it was more effective than factor H at inhibiting the classical pathway. Unlike factor H, rVCP was unable discriminate between alternative pathway-mediated lysis of rabbit and sheep E. A comparison of the cofactor activity in factor I-mediated cleavage of C3b suggested that in contrast to factor H and CR1, which displayed cofactor activity for the three sites, rVCP displayed cofactor activity primarily for the first site, leading to generation of C3b cleaved by factor I between Arg1281-Ser1282 (iC3b1). Its cofactor activity for C4b cleavages was similar to that of soluble complement receptor type 1. Purification and functional analysis of iC3b1 showed that it was unable to interact with factor B to form the alternative pathway C3 convertase, C3b,Bb. These results suggest that the interaction of VCP with C3 is different from that of factor H and CR1 and that VCP-supported first cleavage of C3b by factor I is sufficient to render C3b nonfunctional.
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Jiang, Haixiang, Eric Wagner, Huamei Zhang, and Michael M. Frank. "Complement 1 Inhibitor Is a Regulator of the Alternative Complement Pathway." Journal of Experimental Medicine 194, no. 11 (December 3, 2001): 1609–16. http://dx.doi.org/10.1084/jem.194.11.1609.

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We studied complement 1 inhibitor (C1-INH) as an inhibitor of the alternative complement pathway. C1-INH prevented lysis, induced by the alternative complement pathway, of paroxysmal nocturnal hemoglobinuria (PNH) erythrocytes in human serum. It inhibited the binding of both factors B and C3 to PNH and rabbit erythrocytes and blocked the ability of factor B to restore alternative-pathway function in factor B–depleted serum. C1-INH did not bind to factors B or D but did bind to immobilized C3b and cobra venom factor (CVF), a C3b analogue. C1-INH prevented factor B from binding to CVF-coated beads and dissociated bound factor B from such beads. Factor B and C1-INH showed cross competition in binding to CVF-coated beads. Factor D cleaved factor B into Bb and Ba in the presence of C3b. Cleavage was markedly inhibited when C3b was preincubated with C1-INH. C1-INH inhibited the formation of CVFBb and decreased the C3 cleavage. Removal of C1-INH from serum, in the presence of Mg-EGTA with an anti–C1-INH immunoabsorbant, markedly increased alternative-pathway lysis. C1-INH interacts with C3b to inhibit binding of factor B to C3b. At physiologic concentrations, it is a downregulator of the alternative pathway convertase.
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Dissertations / Theses on the topic "C3-convertase of alternative complement pathway"

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Marinozzi, Maria Chiara. "Characterization of the complement hereditary and acquired abnormalities in atypical Hemolytic Uremic Syndrome and C3 Glomerulopathy." Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCB037/document.

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Harris, Claire Louise. "Analysis of covalent binding reactions between human complement component C3 and other proteins of the alternative pathway." Thesis, University of Cambridge, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309802.

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DI, FEDE MARTINA. "Dissecting the role of Neisseria Heparin Binding Antigen cleavage during adaptation of Neisseria meningitidis to mucosal surface." Doctoral thesis, Università di Siena, 2017. http://hdl.handle.net/11365/1009815.

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Neisserial Heparin Binding Antigen (NHBA) is a surface-exposed lipoprotein specific for Neisseria and is one of the three main protein antigens of the Bexsero vaccine. Meningococcal and human proteases, including lactoferrin and kallikrein, cleave NHBA protein upstream or downstream a conserved Arg-rich motif, respectively. The cleavage results in the release of the C-terminal portion of the protein. C-terminal fragment originating from the processing of meningococcal proteases, referred as C2 fragment, exerts a toxic effect on endothelial cells altering their permeability. In this work, we reported that recombinant C2 fragment has no influence on the integrity of human airway epithelial cell monolayers, consistently with previous findings showing that N. meningitidis traverses the epithelial barrier without disrupting the junctional structures. Unexpectedly, epithelial cells constantly secreted proteases responsible for a rapid processing of C2 fragment, generating a new fragment that does not contain the Arg-rich motif. This cleavage might inactivate the toxic effect of C2 fragment by eliminating its docking domain. Epithelial cell proteases processed also the NHBA full-length protein, and we demonstrated it on live bacteria. Moreover, looking for the epithelial cell protease responsible for this processing, we identified the C3-convertase of alternative complement pathway as a novel human protease able to cleave NHBA during meningococcal infection. Overall, our data provide new insights on the cleavage of NHBA protein during meningococcal infection. This cleavage occurs at different stages of the infection, and it likely has a different role depending on the environment the bacterium is interacting with.
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Praz, Françoise. "Effets de l'activation du systeme du complement sur differentes populations lymphocytaires." Paris 6, 1987. http://www.theses.fr/1987PA066589.

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Garnier, Gérard. "Le facteur B du complément humain : bases structurales et biosynthétiques de sa microhétérogénéité, mises en évidence par les techniques électrophorétiques." Rouen, 1988. http://www.theses.fr/1988ROUES026.

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Iferroudjene, Djedjiga. "Complément et réponse immune : effet comitogénique du composant C3 et du facteur H sur les lymphocytes T." Rouen, 1988. http://www.theses.fr/1988ROUES011.

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Books on the topic "C3-convertase of alternative complement pathway"

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Medjeral-Thomas, Nicholas, Anna Richards, and Matthew C. Pickering. Molecular basis of complement-mediated renal disease. Edited by Neil Turner. Oxford University Press, 2015. http://dx.doi.org/10.1093/med/9780199592548.003.0333.

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Abnormal regulation of complement is intimately associated with C3 glomerulopathy and atypical haemolytic uraemic syndrome. Atypical haemolytic uraemic syndrome is characterized by renal thrombotic microangiopathy due to an inability to regulate complement activation along the renal endothelium. The development of thrombosis is critically dependent on the ability to activate C5. Eculizumab, a monoclonal anti-C5 antibody, is an effective therapy for this condition. C3 glomerulopathy refers to glomerular lesions characterized by accumulation of C3 in the absence of immunoglobulin. The prototypic example is dense deposit disease. This condition is associated with impaired regulation of the alternative pathway in plasma. In other subtypes of C3 glomerulopathy, familial studies have identified mutations within the complement factor H-related protein family. Polymorphic variation within this protein family also influences susceptibility to IgA nephropathy. The mechanism underlying these associations remains unknown and is the subject of ongoing research efforts.
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Book chapters on the topic "C3-convertase of alternative complement pathway"

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Michels, Marloes A. H. M., Nicole C. A. J. van de Kar, Elena B. Volokhina, and Bert(L) P. W. J. van den Heuvel. "Functional Hemolytic Test for Complement Alternative Pathway Convertase Activity." In The Complement System, 83–96. New York, NY: Springer US, 2021. http://dx.doi.org/10.1007/978-1-0716-1016-9_8.

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Densen, P., C. McRill, and S. C. Ross. "The contribution of the alternative and classical complement pathways to gonococcal killing and C3 fixation." In Gonococci and Meningococci, 693–97. Dordrecht: Springer Netherlands, 1988. http://dx.doi.org/10.1007/978-94-009-1383-7_108.

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Turner-Stokes, Tabitha, and Mark A. Little. "Membranoproliferative glomerulonephritis." In Oxford Textbook of Medicine, edited by John D. Firth, 4937–43. Oxford University Press, 2020. http://dx.doi.org/10.1093/med/9780198746690.003.0487.

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The key histological features of membranoproliferative glomerulonephritis (MPGN) are mesangial hypercellularity, endocapillary proliferation, and capillary wall remodelling. There are two main types: (1) immune complex-mediated disease—caused by chronic infection causing persistent antigenaemia (notably hepatitis C), autoimmune disease, or monoclonal immunoglobulin production by plasma cell dyscrasia, and a few ‘idiopathic’ cases; and (2) complement-mediated disease—caused by dysregulation of the alternative pathway of complement, including by C3 nephritic factor (C3Nef), an autoantibody that stabilizes the alternative pathway C3 convertase. Clinical presentation is varied, including nephrotic syndrome, episodic visible haematuria, hypertension/rapidly progressive glomerulonephritis, asymptomatic nonvisible haematuria, and chronic kidney disease. Treatment depends on the underlying disease. All patients should receive appropriate conservative measures (blood pressure control, angiotensin-converting enzyme inhibitor/angiotensin II receptor blocker). Underlying infection or monoclonal gammopathy should be treated, when possible, in those with immune complex-mediated MPGN. Eculizumab may have a role in treatment of some patients with complement-mediated MPGN. Steroids and cyclophosphamide or mycophenolate mofetil are used in patients with severe idiopathic MPGN.
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Vuković Brinar, Ivana, and Matija Matošević. "Complement-Mediated Kidney Disease." In Novel Topics in the Diagnosis, Treatment, and Follow-Up of Nephritis, Nephrotic Syndrome, and Nephrosis [Working Title]. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.108555.

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From very discovery of the complement cascade, it had an intriguing role in pathophysiology of kidney disease. The hallmark of complement cascade involvement in kidney diseases comprises of immune-complexes deposits in the glomeruli, acting as activation for the classical pathway. However, additional mechanisms of complement activation, namely alternative and lectin pathways are extremely important and prominent in complement-mediated kidney disease. Disease prototype of activation of complement is an atypical hemolytic uremic syndrome with solid activation of complement and C3 glomerulopathy is a hallmark of fluid phase activation of alternative complement pathway. Further research has shown that alternative pathway also plays a role in pathogenesis and progression of other kidney diseases including anti-neutrophil cytoplasmic antibody-associated vasculitis and immune complex-mediated glomerulonephritis as well as IgA nephropathy. A better understanding of complement system’s role in kidney disease has also brought forth novel therapeutic approaches in form of complement cascade inhibitors, revolutionizing the treatment of patients that were faced with unfavorable outcomes. Through this chapter, we bring to you an overview of most prevalent complement-mediated kidney diseases with emphasis on the role of complement in their pathogenesis and the potential for treatment targeting the complement cascade.
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Kerr, Michael A. "Factor B and the Alternative Pathway C3/C5 Convertase." In Handbook of Proteolytic Enzymes, 2869–75. Elsevier, 2013. http://dx.doi.org/10.1016/b978-0-12-382219-2.00635-9.

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Conference papers on the topic "C3-convertase of alternative complement pathway"

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Devine, D. V., and W. F. Rosse. "PLATELET FACTOR H REGULATES THE ACTIVITY OF THE ALTERNATIVE PATHWAY OF COMPLEMENT ON THE SURFACE OF NORMAL AND PAROXYSMAL NOCTURNAL HEMOGLOBINURIA PLATELETS." In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1643979.

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Paroxysmal nocturnal hemoglobinuria (PNH)-is frequently complicated by thrombosis. It has been suggested that the abnormal interactions of PNH platelets with complement contribute to thrombosis. Using purified complement proteins, we have previously demonstrated that the platelets from some patients with PNH do not demonstrate elevated activity of C3bBb, the alternative pathway C3 amplification enzyme complex, even though they lack the C3bBb regulatory protein, decay accelerating factor (DAF). As measured by fluorescence flow cytometry, washed platelets from both normal donors and PNH patients released the fluid phase C3bBb regulatory protein, factor H, in response to the deposition of purified complement proteins. Platelet factor H was localized to the alpha granules by immunocytochemical techniques. A quantitative radioimmunoassay demonstrated that normal platelets released 54 ± 6 ng factor H/108 platelets in response to thrombin stimulation. PNH platelets contained less factor H (22 ±7 ng/108 platelets) than normal platelets. Thrombin stimulated platelets from patients with elevated C3bBb activity released less than half of the factor H measured in detergent extracts. However, thrombin stimulated platelets from PNH patients exhibiting normal C3bBb activity released nearly all their factor H. The release of factor H from normal platelets was blocked by treating the platelets with metabolic inhibitors. In the absence of factor H release, the activity of the C3bBb complex increased three-fold. In addition, the number of molecules of 1251-factor B bound per C3b increased from 0.40 to 0.92 when factor H release was blocked. The inhibition of DAF by anti-DAF had no effect on the activity of C3bBb if factor H could be released from the platelets. However, when factor H release was blocked by treatment with metabolic inhibitors, the inhibition of DAF by anti-DAF increased the activity of C3bBb by 40%. Therefore, in the absence of DAF, platelets can regulate complement activation by the alternative pathway via the release of platelet factor H. Since factor H is an alpha granule protein, platelet release in the presence of activated complement may contribute to the occurrence of thrombosis.
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Naji, Foziyeh Esmaiel, Mohammed Ehlayel, Nader Al-Dewik, and Ahmed Malki. "Clinical Utility and Cost Effectiveness of Complement 3 and Complement 4 in different Clinical Subspecialties in Hamad Medical Corporation." In Qatar University Annual Research Forum & Exhibition. Qatar University Press, 2020. http://dx.doi.org/10.29117/quarfe.2020.0161.

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Background: Complement system is one of ancient innate immune systems in our body fighting against pathogens and foreign bodies. Either one of its three pathways, classical, alternative or lectin activates it. Because of its role and importance in combating against different pathological conditions, it works through defined proteins including regulators and inhibitors. However, over or under stimulation of complement system can lead to various diseases. A number of analytical assays are used to measure complement proteins and its activation states considering complement 3 (C3), complement 4 (C4) as the most common test used. Objectives: Our aims are to study the clinical utility and cost effectiveness of C3 and C4 among different clinical subspecialties in Hamad Medical Corporation (HMC), Doha-Qatar. Design and methods: A retrospective study was conducted using electronic medical records to generate patient’s list from clinical immunology laboratory at HMC. Data on 326 patients were collected from 1st January till 31st March, 2017 and used as pilot study after omitting duplications. The data was studied for its demographical, disease categories, C3 and C4 test results. C3 and C4 test cost were calculated inside HMC and compared to other healthcare providers in country and abroad. Results: A total of 326 patients, 148 males and 178 females (M/F ratio:0.8:1), of age (mean age ±SD) of 36 ± 17.6 years. 289(86%) were >15 years and 47(14%) were 15 or less. Kidney diseases (34%), autoimmune diseases (25%), and allergic diseases (18%) were the top 3 diseases, and constituted 77% of all diseases. 45/336 (13.4%) showed low C3, C4, or both. Mean levels of C3 (±SD) was 120.8 ±36.3 mg/dl, and C4 was27.85±11.9 mg/dl. High C3 and C4 levels were observed in 53 (15.7%) of patients. The cost of performing one test either C3 or C4 in HMC is 22 QR ($6), while other healthcare providers inside the country costed 150-300 QR ($41.2-$82.4). Conclusion: Autoimmune diseases, renal diseases and joist diseases were the most common diseases with low C3 and C4 levels. Although the cost of a single test of C3 or C4 is low, the total annual cost is huge. The treating physician is recommended to exercise judicious clinical wisdom when ordering C3 or C4 tests as diagnostic tools
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