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Inherited Defects in Immune Defenses Leading to Pulmonary Disease
Published in Stephen D. Litwin, Genetic Determinants of Pulmonary Disease, 2020
Hereditary C3 deficiencies result in an increased susceptibility to pyogenic infectious agents [43]. Three different types of C3 deficiency are known. Homozygous C3 deficiency was described in a patient with low total serum complement, a C3 concentration less than 2.5 μg/ml (normal 1000-2000 μg/ml), and normal concentrations of other complement components. The C3 concentration in the proband's parents and five of six sibs was close to half of normal, while total hemolytic complement was only slightly reduced. The proband's parents were first cousins. Type I essential hypercatabolism of C3 was noted in one puzzling patient who had 300 μg/ml of C3, most of which was an inactive conversion product, C3b. Other complement components were normal. The proband has been found to be deficient in a C3 inactivator [120]. A type II essential hypercatabolism of C3, differing from the above, has also been documented.
The Acute Phase Complement Proteins
Published in Andrzej Mackiewicz, Irving Kushner, Heinz Baumann, Acute Phase Proteins, 2020
The C3 protein is a principle source of biologically active cleavage products that mediate inflammation, solubilize and clear immune complexes, and further propogate the complement cascade, resulting in assembly of the terminal complement protein complex (the membrane attack complex, MAC) and cytolysis via the generation of discrete membrane channels. The complement effector proteins are controlled by an elaborate network of regulatory proteins, some of which also serve as cell-surface receptors for complement activation products. A detailed account of the complement effector and regulatory genes and gene products is beyond the scope of this chapter. The reader should consult relatively recent reviews.9-11
Phagocytosis By Human Neutrophils
Published in Hans H. Gadebusch, Phagocytes and Cellular Immunity, 2020
Both the classical pathway and the alternate pathway converge at the point of C3 activation. Since C5-deficient serum shows normal opsonic activity,141,145 it is apparent that the heat-labile opsonic activity of serum lies in the activated C3 molecule. Several patients have been described with either a genetic or functional deficiency of C3.146,147 The sera from these patients had no opsonic activity for antibody-coated pneumococci, Candida albicans, or paraffin oil emulsion coated with endotoxin. In one case, addition of purified C3 in vitro restored the opsonic activity of the deficient serum. The nature of the opsonic component derived from C3 has been investigated by Stossel et al.148 They employed a paraffin oil emulsion coated with endotoxin which constitutes a very stable system for phagocytic assay. Once particles were opsonized with normal serum, they remained opsonized even when subjected to some very stringent chemical and physical manipulations. The preparation was not affected by boiling in 8 M urea or 2% deoxycholic acid, but the bound C3 could be removed by treatment with sodium dodecyl sulfate, suggesting a strong hydrophobic type of binding. The opsonic fragment was somewhat smaller than the C3b fragment, containing two chains of about 70,000 daltons each, but appeared to be derived from the C3b fragment by further proteolytic attack.
Clinical features of children with anti-CFH autoantibody-associated hemolytic uremic syndrome: a report of 8 cases
Published in Renal Failure, 2022
Qian Li, Xinxin Kong, Minle Tian, Jing Wang, Zhenle Yang, Lichun Yu, Suwen Liu, Cong Wang, Xiaoyuan Wang, Shuzhen Sun
In this study, all 8 patients presented with severe hemolytic anemia, thrombocytopenia, acute kidney injury, hematuria and gross proteinuria. Extrarenal symptoms such as pancreatitis, pulmonary hemorrhage, gastrointestinal hemorrhage, and hypertension encephalopathy were also observed in these patients. Serum positivity for anti-CFH Ab was present in these 8 children, and 6 patients showed reduced serum CFH levels. Reduced serum C3 levels were shown in 8 patients. Aditi Sinha reported complement C3 levels lower than 70 mg/dl in 62.0% of aHUS children [17]. These results suggest abnormalities of the alternative complement pathway in the pathogenesis of anti-CFH Ab-associated HUS. CFH is a central regulator of the alternative pathway C3 convertase, both in the fluid phase and on cell surfaces. Nozal and Lopez-Trascasa reported that anti-CFH antibodies in aHUS can recognize the C-terminus end of factor H, prevent factor H from binding to endothelial cells, and help in the regulation of the alternative pathway [18].
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.
A Differential Immune Modulating Role of Vitamin D in Urinary Tract Infection.
Published in Immunological Investigations, 2022
The complement activation is also essential to cooperate in the efficient elimination of microbial intruders. In the patient groups, the C3 and AP50 levels were increased significantly without showing any significant difference in the levels of C4 and CH50. Among those, the C3 was just associated with 25(OH)D levels. Since bacteria alone did increase the alternative pathway without considering vitamin D status, this probably implies a possible contribution of increased C3 levels to substantial bacterial opsonization, and also maintenance of supportive function of the complement system through the alternative pathway. It appears that TLR-mediated signaling and the VDR activation might synergistically enhance the innate effector functions. The C3 protein is known as acute-phase reactants, and it could be hypothesized that its upregulation is related to inflammatory conditions. It also seems possible that the neutralization capacity of antibodies can be enhanced in the presence of complement which remains to be examined. However, evidence supports the detrimental role of C3 in bacteria ascending to the kidneys and enhanced bacterial internalization and pathogenicity, proposing adverse effects of the complement system on the infection (Li et al. 2006, 2008; Springall et al. 2001).