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The Chemistry and Biology of Lipooligosaccharides: The Endotoxins of Bacteria of the Respiratory and Genital Mucosae
Published in Helmut Brade, Steven M. Opal, Stefanie N. Vogel, David C. Morrison, Endotoxin in Health and Disease, 2020
J. McLeod Griffiss, Herman Schneider
Properdin (P), a regulatory protein of the alternative complement pathway (ACP) that stabilizes the ACP C3 convertase and thereby augments the density of C3b deposited following CP activation, binds to a gonococcal outer membrane protein that is variously surface exposed (31). Strains of N. gonorrhoeae bind various amounts of P, depending on their expression of the P-binding protein, and therefore variously support ACP augmentation of the C3b that is deposited following binding of gangliosyl IgM (31). Sers strains that bind equivalent amounts of gangliosyl IgM are therefore lysed at different titers (31).
Herpes Simplex Virus Vaccines and the Viral Strategies Used to Evade Host Immunity
Published in Marie Studahl, Paola Cinque, Tomas Bergström, Herpes Simplex Viruses, 2017
Lauren M. Hook, Harvey M. Friedman
gC is expressed on both the virion envelope, as well as on the surface of virus-infected cells. gC of both HSV-1 and HSV-2 binds C3b when in a purified form and when expressed on the surface of transfected cells (48,49). Regions of the gC proteins that are involved in C3b binding are well conserved in both proteins. Four regions on gC-1 and three regions on gC-2 are known to be important (50,51). Binding of gC-1 to C3b inhibits activation of the classical pathway on the HSV-1 virion, and may function in a similar manner for gC-2 (49,52). Differences do exist however, as gC-1, but not gC-2, is able to accelerate the decay of the alternative pathway C3 convertase, C3bBb, preventing lysis of HSV-infected cells (49,53). Properdin extends the lifetime of C3bBb three- or four-fold by binding to and stabilizing the C3bBb complex. This extended lifetime should increase the amount of C3b functioning as a component of the alternative C3 convertase, thereby amplifying the complement cascade, as well as the amount of C3b coating the cell surface. gC-1 destabilizes the C3 convertase by inhibiting the binding of properdin to C3b, which limits the effectiveness of the alternative complement pathway in lysing HSV-infected cells (43,50). gC-1 has also been shown to inhibit the interaction of C5 with C3b, leading to the disruption of both the classical and alternative complement activation pathways at the level of the C5 convertase (53). Expression of gC-1 may therefore limit the assembly of the MAC on membranes of HSV virions and infected cells.
Clinical Toxicology of Snakebite In Africa and The Middle East / Arabian Peninsula
Published in Jürg Meier, Julian White, Handbook of: Clinical Toxicology of Animal Venoms and Poisons, 2017
The venoms of the dangerous African colubrids, D. typus and Thelotornis sp., have low intravenous mouse median lethal doses (LD50) of 0.07 and 1.23 mg/kg respectively. Both venoms contain enzymes which activate prothrombin and possibly Factor X which explains the disseminated intravascular coagulation with deposition of microthrombi observed in human victims of envenoming. A human victim of D. typus showed activation of the alternative complement pathway. The venoms of a number of other African colubrid snakes such as the Natal green snake (Philothamnus natalensis) demonstrate powerful procoagulant activity which, in unusual circumstances, might prove clinically significant. Nothing is known about the venoms of Malpolon species.
Avacopan for the treatment of ANCA-associated vasculitis: an update
Published in Expert Review of Clinical Immunology, 2023
Mohammed Osman, Jan Willem Cohen Tervaert, Christian Pagnoux
The complement protein network includes three different pathways: the classical, lectin, and alternative pathways (Figure 1) [20–22]. The previous version of this article, published in 2021, detailed more extensively all these three pathways [23]. Evidence for a role of alternative complement pathway in AAV is the strongest. This pathway is activated following C3 cleavage, promoted by properdin binding to myeloperoxidase (MPO) [24], and/or after C3 binds to bacterial surfaces [20,25,26]. C3 can also be cleaved spontaneously and then stabilized through its association with Factor B (and its co-activator, Factor D) to a C3 convertase ternary complex (C3bBb) [27]. Factor H competes with Factor B for binding to Bb, thereby reducing its activation and that of the alternative complement pathway [27]. Factor H provides other immunoregulatory roles, particularly in AAV as it can directly inhibit ANCA-mediated neutrophil activation [28]. It can also reduce T cell activation by dendritic cells [29] and promote regulatory T cell expansion. Polymorphisms in Factor H are more common in patients with AAV, particularly those with crescentic glomerulonephritis [14].
Circulating immune-complexes and complement activation through the classical pathway in myeloperoxidase-ANCA-associated glomerulonephritis
Published in Renal Failure, 2022
Tadasu Kojima, Dan Inoue, Takeaki Wajima, Takahiro Uchida, Muneharu Yamada, Isao Ohsawa, Takashi Oda
Previous studies on mice demonstrated that ANCA does not cause RPGN in C5 or complement factor B knockout mice, but does so in C4 knockout mice [4]. Gou et al. reported that the renal deposition of factor Bb and urinary factor Bb levels are associated with the severity of renal injury [17]. Several studies have shown that low serum C3 levels, but not C4 levels, can estimate severe ANCA-associated vasculitis (AAV), and can predict poor renal outcome at diagnosis [5,18–22]. Furthermore, Sethi et al. evaluated the glomerular deposited protein by laser microdissection and mass spectrometry-based proteomic analysis, and found accumulation of complement factors, predominantly of the alternative pathway in MPO and PR3-ANCA positive as well as ANCA negative AAGN [7]. These studies suggest the important roles of the alternative complement pathway in the disease process of AAGN.
Retinal findings in glomerulonephritis
Published in Clinical and Experimental Optometry, 2022
Heather G Mack, Deborah J Colville, Phillip Harraka, Judith Anne Savige, Alessandro Invernizzi, Samantha Fraser-Bell
Membranoproliferative glomerulonephritis was previously classified into three patterns based on immunopathology and ultrastructural location of electron dense deposits in the glomerular basement membrane. Membranoproliferative glomerulonephropathy is now classified as C3 complement-mediated disease recognising the key role of Complement 3 in its pathogenesis. When the alternative complement pathway is activated two subtypes are recognised 1) with renal dense deposits, the previous type II membranoproliferative glomerulonephritis, and 2) without dense deposits, known as C3 glomerulonephritis. C3 complement mediated glomerulonephritis may also involve the classical complement pathway (membranoproliferative glomerulonephritis type I) and both alternative and classical pathways (membranoproliferative glomerulonephritis type III).27 C3 glomerulonephropathy is associated with mutations in Complement 3, Complement factor H, complement factor B, and complement factor H-related 1, 2 and 5, as well as a circulating auto-antibody C3 nephritic factor in many individuals, and autoantibodies to factor H, C3 and factor B in some individuals.