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Dermal filler complications and management
Published in Michael Parker, Charlie James, Fundamentals for Cosmetic Practice, 2022
The cascading nature of complement protein activation allows for rapid amplification of a signal, and therefore a trace amount of pathogenic material can result in a large and coordinated immune response. There are three main ways in which the complement cascade can be activated: The classical pathway occurs when IgG or IgM antibodies bind to and form a complex with microbial antigens with resultant phagocytosis, cytolysis and inflammation.The alternative pathway does not rely on antibodies but instead is triggered by interactions between lipid-carbohydrate complexes on the surface of microbes.The lectin pathway is initiated when macrophages digest microbes and release chemicals which stimulate the liver to produce proteins called lec-tins which bind to carbohydrates on the surface of microbes. All three of the preceding pathways can initiate the complement cascade; however, they are not independent entities and all three may be activated independently of one another at various stages of the immune response to infection.
Immune system and Innate Immunity
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
The three ways by which the complement system may be activated are: The classical pathway that is activated by immune complexes, initiated by the binding of C1q to the Fc portion of immunoglobulin.The alternative pathway that occurs in the fluid phase or on contact with foreign surfaces and is initiated by C3 activation.The lectin pathway initiated by mannose-binding lectin (MBL) which binds to carbohydrate (sugar) on bacteria and activates C4 and the classical pathway.
Secretory immunoglobulins and their transport
Published in Phillip D. Smith, Richard S. Blumberg, Thomas T. MacDonald, Principles of Mucosal Immunology, 2020
Charlotte S. Kaetzel, Jiri Mestecky, Jenny M. Woof
Analyses of IgA-associated glycans indicate that 6%–10% of total molecular mass is contributed by N- and O-linked side chains that display a remarkable heterogeneity in their number and composition (see Figure 11.1c and d). The most striking difference is the presence of three to five short O-linked glycans in the IgA1 hinge region composed of N-acetylgalactosamine (GalNAc), galactose (Gal), and sialic acid. The total glycan content of SIgA is even higher than that of serum monomeric IgA due to the presence of glycans on J chain and especially on secretory component, which is particularly rich in N-linked glycans (approximately 22% of the total molecular mass). Glycans appear to play an important role in IgA catabolism, the ability to activate the lectin pathway of complement, and binding to bacteria with consequent inhibition of their adherence to epithelial cells (see later).
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
The classical pathway is typically ‘antibody-dependent’ and activated by IgM-IgG clusters. The lectin pathway primarily recognises carbohydrate patterns on microbial surfaces. The alternative pathway is activated by bacteria and bacterial toxins, but in contrast to the classical and lectin pathways, has a low basal rate of turnover (‘tick over’) that is thought to monitor for pathogen invasion. In further contrast to the classical and lectin pathways, the activated alternative pathway can also bind host cells, but this is usually controlled by an army of membrane-expressed or fluid phase-recruited complement regulators. The common terminal pathway, shared by all three pathways, comprises factors C5 to C9. When C5b associates with C6 and C7, the complex is inserted into the cell membranes and interacts with C8, inducing binding of C9 to form a lytic pore (membrane attack complex, or terminal complement complex), the hallmark of complement attack.1,2
Understanding the genetic basis of immune responses to fungal infection
Published in Expert Review of Anti-infective Therapy, 2022
Samuel M. Gonçalves, Cristina Cunha, Agostinho Carvalho
Besides PRRs, several soluble mediators interact with and bind to microbial polysaccharides without transducing intracellular signals and function as opsonins to facilitate phagocytosis [15]. Among these, mannose-binding lectin (MBL) binds carbohydrate patterns from pathogens and activates the lectin pathway of the complement system. Several studies have disclosed common genetic variation in MBL to regulate its expression levels, functional activity, or both [47]. Except for cryptococcosis in HIV-uninfected patients [48], the contribution of genetic variation in MBL to invasive disease has not been addressed, although the levels of circulating protein were found to vary significantly during IPA [49], invasive candidiasis [50], and pneumonia by Pneumocystis jirovecii [51]. Likewise, SNPs in the triggering receptor expressed on myeloid cells 1 (TREM1) were found to influence the levels of soluble TREM1 as well as TREM1-mediated cytokine production in response to stimulation with A. fumigatus [52], despite no evidence for a direct association with human infection has been reported thus far.
Activation of Complement System in Henoch-Schönlein Purpura Nephritis
Published in Fetal and Pediatric Pathology, 2022
Hea Min Jang, Heesun Baek, Man Hoon Han, Yong Jin Kim, Chan-Duck Kim, Yong-Lim Kim, Sun-Hee Park, Min Hyun Cho
Many reports have suggested that the pathophysiology of IgAN is associated with complement activation [8,9,17]. Complement activation is initiated by mesangial IgA-immune complex (IgA-IC) deposition. In early studies, IgAN was associated with alternative pathways, but recently Roos et al. suggested that the lectin pathway plays an important role. The lectin pathway of complement is activated by the interaction of the plasma lectins, mannose-binding lectin (MBL), L-ficolin, or H-ficolin, with their carbohydrate ligands. It induces the activation of MBL-associated serine proteases (MASPs), and activated MASP-2 produces C4b2a and induces C3 cleavage [9]. Investigators found that, among 60 IgAN patients, 25% of renal biopsy had positive glomerular staining for MBL, and L-ficolin was positive for all MBL-positive patients [9]. With or without MBL staining, C3 deposition was positive in most biopsies, but C1q was negative. This suggests that the alternative pathway was activated in 75% of patients with IgAN, and the glomerular lectin pathway was involved in 25% of IgAN in that study.