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PubMed1988

A sensitive method to assay blood complement C1- inhibitor activity.

Hereditary angioneurotic edema results from deficiency of complement protein C1- inhibitor. Using a new spectrophotometric assay for C1-s esterase activity on the N-alpha-benzoyl-L-arginine ethyl ester, we describe a routinely available method for quantifying low C1- Inhibitor functional activities in EDTA-treated plasma of hereditary angioneurotic edema patients. C1- Inhibitor activity is deduced from the residual esterase activity of C1-s incubated with 20-80 microliters plasma samples. Arbitrary units (volume of sample inhibiting 50% of C1-s activity) were used to express C1- Inhibitor normal activity which was estimated as 22,500 +/- 5,000 (SD) U/l in 45 healthy individuals. The correlation with C1- Inhibitor antigen in these healthy individuals and 89 patients with varying concentrations of C1 Inhibitor ranging from 0.05-1.05 g/l was r = 0.91. Levels down to 2,000 U/l could be estimated. Specific inhibitory activity is an absolute requirement to distinguish between type I and type II hereditary angioneurotic edema.

Complement C1 Inactivator Proteins↗

PubMed1998

The role of complement and gp120-specific antibodies in virus lysis and CD4+ T cell depletion in HIV-1-infected patients.

The substantial virus lysis was induced by HIV-1-infected patient serum and normal human complement serum in the presence of purified patient IgG. Non-infected CD4+ T cells coated with the whole virus or with a recombinant HIV-1 envelope gp120 and sensitised with patient IgG were also shown to be susceptible to complement-dependent lysis. The serum level of complement regulatory protein in a fluid phase, the C1-esterase inhibitor, was significantly correlated with serum concentration of C1q-circulating immune complexes (P=0.0062), but inversely with CD4+ T cell count (P < 0.0001). Accordingly, the disease progression in HIV-1-infected patients was significantly correlated with the level of complement activation as determined by serum level of C1-esterase inhibitor (P=0.0001), and inversely correlated with CD4+ cell count (P < 0. 0001) and gp120-specific antibody titre (P=0.0086). These results strongly suggest that the complement activation by gp120-specific antibodies play a very important role in virus clearance, but also in depletion of infected as well as gp120-coated non-infected CD4+ bystander T cells during the course of HIV-1 infection.

Animals↗

PubMed1980

A kinetic test for the assay of the C1 esterase-inhibitor.

The most satisfactory diagnostic procedure for hereditary angioneurotic oedema is the demonstration of low serum levels of C1 esterase-inhibitor. A modified method for the assay of this protein is described. It is based on the kinetic measurement of the C1 esterase-inhibitor when it inhibits the hydrolysis of N-acetyl-L-tyrosine-ethyl ester by C1 esterase. The relative C1 esterase-inhibitor concentration is based on the initial hydrolytic velocity, which can be evaluated from the pH change in a short time and within a small range. High reproducibility, cheap instrumentation and short time of analysis are some of the favorable aspects of this method in comparison with the 'end point titrimetric' method. Furthermore, this paper describes the mechanism of inhibition of C1 esterase by C1 esterase-inhibitor. The results are indicative of a non-competitive mechanism. The value of the Michaelis-Menten constant, Km, is 0.017 +/- 0.001 mol/l at 37 degrees C, in the optimum pH range 7.2-7.4. An estimate of KI in arbitrary units is also given.

Angioedema↗

PubMed1998

Regulation of C1 inhibitor synthesis.

The primary biologic roles of C1 inhibitor (C1-INH) are the regulation of activation of the classical complement pathway and of the contact system of kinin formation. Heterozygosity for deficiency or dysfunction of C1-INH results in hereditary angioedema (HAE). This deficiency results in loss of homeostasis with unregulated complement and contact system activation. Due to the consequent C1-INH consumption, plasma levels of C1-INH in patients with HAE are decreased below 50% of normal. In addition, diminished synthesis contributes to the lowered levels in some patients. The hepatocyte is the primary source of C1-INH, although a number of other cell types, including peripheral blood monocytes, microglial cells, fibroblasts, endothelial cells, the placenta, and megakaryocytes also synthesize and secrete the protein both in vivo and in vitro. Interferon-gamma and alpha (IFN), colony stimulating factor-1, interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) all induce C1-INH synthesis in a variety of cell types. The IFN-response elements in the 5'-flanking region and in the first intron have been partially characterized, as have several of the promoter elements that direct basal transcription of the gene. However, although androgen therapy, in vivo, results in an increase in C1-INH plasma levels, a direct effect of androgens on C1-INH synthesis has not been convincingly demonstrated. Although the C1-INH gene contains a potential glucocorticoid/androgen response element, this element does not appear to respond to androgen. Continued analysis of the transcriptional regulation of the C1-INH gene may lead to new approaches to therapy of HAE.

Acute-Phase Reaction↗

PubMed1986

Demonstration of modified inactive first component of complement (C1) inhibitor in the plasmas of C1 inhibitor-deficient patients.

The first component of complement (C1) inhibitor plays a critical role in the regulation of the classical complement pathway and the contact system, and the deficiency of C1 inhibitor protein or function is associated with recurrent angioedema. In this study we evaluated the size of the C1 inhibitor antigens present in the plasmas of C1 inhibitor-deficient patients. We found that the C1 inhibitor in the plasmas existed in three forms: high molecular weight forms in complex with proteases, native 110-kD C1 inhibitor, and a modified inactive 94-kD form. The proportion of the total C1 inhibitor in the 94-kD form was 28% in nine hereditary angioedema patients, 92% in five acquired C1 inhibitor-deficiency patients, and 1.2% in five normal controls. In vitro activation of normal plasma with kaolin, but not heat-aggregated gamma-globulin generated 94-kD C1 inhibitor from 110-kD C1 inhibitor. Neither kaolin activation nor heat-aggregated gamma-globulin activation generated 94-kD C1 inhibitor in Hageman factor-deficient plasma. These results suggest that 94-kD C1 inhibitor is generated in vitro by activation of the contact system. The in vivo mechanism of 94-kD C1 inhibitor generation in C1 inhibitor-deficient patients is not known.

Angioedema↗

PubMed1988

Hereditary angioedema. Undersuspected, underdiagnosed.

Although hereditary angioedema accounts for only a small fraction of all angioedema, it is relatively common among inherited deficiencies of plasma proteins. The occurrences of upper respiratory obstruction, of attacks following trauma, and of episodes of abdominal pain are clues to the diagnosis, and the absence of a family history is no reassurance against it. Measurement of C4 concentration is a useful screening test: Normal values exclude the diagnosis, while subnormal values mandate measurement of C1 INH by immunoassay or functional assay. The functional assay is required to detect the genetic variant form. The importance of making the diagnosis is threefold. It facilitates prevention of life-threatening complications, such as upper airway obstruction and needless abdominal surgery. It leads to use of short-term prophylactic measures to prevent complications associated with trauma. In patients with disability due to frequent attacks, suppression or elimination of all symptoms can be achieved by chronic treatment with impeded androgens.

Adult↗

PubMed2001

C1 inhibitor: analysis of the role of amino acid residues within the reactive center loop in target protease recognition.

Previous analysis of a naturally occurring C1 inhibitor P2 mutant (Ala(443)-->Val) indicated a role for P2 in specificity determination. To define this role and that of other reactive center loop residues, a number of different amino acids were introduced at P2, as well as at P6 (Ala(439)) and P8'/9' (Gln(452)Gln(453)). Ala(439)-->Val is a naturally occurring mutant observed in a patient with hereditary angioedema. Previous data suggested that Gln(452)Gln(453) might be a contact site for C1s. Reactivity of the inhibitors toward target (C1s, C1r, kallikrein, beta factor XIIa, and plasmin) and nontarget proteases (alpha-thrombin and trypsin) were studied. Substitution of P2 with bulky or charged residues resulted in decreased reactivity with all target proteases. Substitution with residues with hydrophobic or polar side chains resulted in decreased reactivity with some proteases, but in unaltered or increased reactivity with others. Second order rate constants for the reaction with C1s were determined for the mutants with activities most similar to the wild-type protein. The three P2 mutants showed reductions in rate from 3.35 x 10(5) M(-1)s(-1) for the wild type to 1.61, 1.29, and 0.63 x 10(5) for the Ser, Thr, and Val mutants, respectively. In contrast, the Ala(439)-->Val and the Gln(452)Gln(453)-->Ala mutants showed little difference in association rates with C1s, in comparison with the wild-type inhibitor. The data confirm the importance of P2 in specificity determination. However, the P6 position appears to be of little, if any, importance. Furthermore, it appears unlikely that Gln(452)Gln(453) comprise a portion of a protease contact site within the inhibitor.

Amino Acid Substitution↗

PubMed1997

C1Q synthesis by tissue mononuclear phagocytes from normal and from damaged rat liver: up-regulation by dexamethasone, down-regulation by interferon gamma, and lipopolysaccharide.

The subcomponent of complement C1, C1q, mediates complement activation via the classical pathway, and therefore may play an important role in the inflammatory processes in which complement activation is involved. The aim of our study was to investigate C1q synthesis by macrophages of normal and of acutely damaged livers. The localization of C1q in liver tissue was studied by immunohistochemistry. Rat liver tissue macrophages were isolated from normal as well as from acutely damaged (carbon tetrachloride model) liver, and were separated into small, monocyte-like phagocytes and large, mature tissue macrophages, as revealed by immunocytochemistry. C1q gene expression was studied by endogeneous labeling of newly synthesized proteins, immunoprecipitation, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and by reverse-transcription polymerase chain reaction (RT-PCR) of C1qB messenger RNA (mRNA). Semiquantitative analysis was performed by Northern blotting of total RNA and hybridization with the radioactively labeled RT-PCR product. C1 esterase inhibitor synthesis was studied in parallel. For comparison, C1q and C1-inhibitor synthesis were also investigated in blood monocytes and peritoneal macrophages. C1q was weakly detectable in sinusoidal cells of the normal liver. C1qB mRNA, as well as constitutive synthesis and secretion of C1q, was clearly detected in freshly isolated and cultured Kupffer cells from normal rat liver. In comparison, newly recruited "inflammatory" macrophages from damaged rat liver synthesized considerably lower amounts of the protein, similar to what was found in the monocyte-like macrophages of normal liver and in peritoneal macrophages. Monocyte C1qB mRNA was not detected even by RT-PCR, and remained undetectable during the time in culture. Similar behavior was observed for C1-inhibitor synthesis. Treatment of the cultures with interferon gamma (IFN-gamma) or lipopolysaccharide (LPS) strongly decreased, whereas treatment with dexamethasone strongly increased C1q gene expression in the macrophage populations, and induced C1qB mRNA in cultured monocytes, as revealed by RT-PCR. Kupffer cells of normal liver may produce considerable amounts of C1q, whereas the inflammatory macrophages of the acutely damaged liver may not be so important for the synthesis of C1q.

Animals↗

PubMed1991

Modulation of complement gene expression by glucocorticoids.

The addition of dexamethasone, prednisolone or cortisol (in order of efficacy) to human monocytes in culture produced dose-related increases in the synthesis rates of the complement components C1 inhibitor (C1-inh), factor B (B) and C2. In contrast, concentrations of C3 and lysozyme in the culture supernatants were decreased. Indomethacin stimulated synthesis of C1-inh, C2 and B, but had little effect on synthesis of C3 or lysozyme. The simultaneous addition of cycloheximide (2.5 micrograms/ml) abrogated the effects of dexamethasone on synthesis of C2, B and C1-inh, but the effect of indomethacin on the synthesis of these components was unchanged. These data suggest that protein synthesis is required for the effects of glucocorticoids on the synthesis of C2, B and C1-inh to occur. Dexamethasone and indomethacin increased the abundances of C1-inh mRNA, B mRNA and C2 mRNA in parallel with changes in the synthesis rates of these proteins. The changes in mRNA abundance were not transcriptional, but were shown to be due to increased mRNA stability. In contrast, dexamethasone decreased the expression of C3 and lysozyme by decreasing the rate of transcription of these genes. Indomethacin had no effect on transcription of the C3 and lysozyme genes. The half-lives of C3 mRNA, lysozyme mRNA and actin mRNA were not altered by dexamethasone or indomethacin. It is concluded that the effects of glucocorticoids on monocyte synthesis of C2, B and C1-inh are due to increased mRNA stability and may be related to inhibition of prostaglandin synthesis, as these effects are similar to those produced by indomethacin. The effects of dexamethasone on the synthesis of C3 and lysozyme differ from those on C2, B and C1-inh as they depend upon a decrease in gene transcription, which is not affected by indomethacin.

Cells, Cultured↗

PubMed1993

Prevention of complement-mediated activation of xenogeneic endothelial cells in an in vitro model of xenograft hyperacute rejection by C1 inhibitor.

The complement system plays a major role in hyperacute rejection of discordant xenografts. In an immediately vascularized xenograft of a porcine organ to a primate, natural antibodies bind to the vascular endothelium of the graft, triggering activation of complement via the classical pathway. One consequence of antibody binding and complement activation is the activation of endothelial cells leading to the loss from the cells of heparan sulfate. We explored to what extent the classical pathway regulatory protein C1 inhibitor (C1 inh) would inhibit complement-mediated cytotoxicity and activation of endothelial cells. Cultured porcine aortic endothelial cells were used as a model for a xenogeneic organ and human serum as a source of xenoreactive natural antibody and complement. Addition of purified human C1 inh to human serum inhibited deposition of C4b and iC3b and cytotoxicity after the serum was reacted with the cultured cells. C1 inh prevented, in a dose-dependent manner, activation of the endothelial cells, as manifested by release of heparan sulfate. These observations demonstrate that C1 inh added in sufficient amounts to human serum can effectively inhibit C1 activation in an antigen-antibody system. These studies extend our previous findings consistent with the concept that complement activation occurs via the classical pathway in models of hyperacute rejection in which porcine vascular endothelial cells are in contact with human serum containing xenogeneic natural antibodies against the endothelial cells. Thus, our results suggest a potential clinical use of C1 inh in conjunction with other therapies to prevent hyperacute rejection in xenogeneic combinations mediated by complement activation via the classical pathway.

Animals↗

PubMed2002

Continuous 48-h C1-inhibitor treatment, following reperfusion therapy, in patients with acute myocardial infarction.

AIMS: Complement inhibition by C1-inhibitor has been shown to reduce myocardial ischaemia-reperfusion injury in animal models. We therefore studied the effects of intravenous C1-inhibitor, following reperfusion therapy, in patients with acute myocardial infarction. METHODS AND RESULTS: C1-inhibitor therapy was started not earlier than 6h after acute myocardial infarction, in order to prevent interference with thrombolytic therapy. A loading dose of C1-inhibitor was followed by a continuous infusion for 48 h, using three escalating dosage schemes. Efficacy of complement inhibition was estimated from C4 activation fragments. Plasma concentrations of myocardial proteins were compared to values measured in matched control patients. In 22 patients, C1-inhibitor was well tolerated and drug-related adverse events were not observed. Target plasma levels of C1-inhibitor were reached, with values of 48.2 ml.kg(-1) for distribution space and 35.5h for the half-life time of C1-inhibitor. A dose-dependent reduction of C4 fragments was found P=0.005). In 13 patients who received early thrombolytic therapy, release of troponin T and creatine kinase-MB(mass) was reduced by 36% and 57%P =0.001), compared to 18 controls. CONCLUSION: Continuous 48-h treatment with C1-inhibitor provides safe and effective inhibition of complement activation after reperfused acute myocardial infarction and may reduce myocardial injury.

Adult↗

PubMed2002

In vivo pharmacokinetics of calreticulin S-domain, an inhibitor of the classical complement pathway.

Inhibition of the complement system is potentially therapeutic in diseases where uncontrolled or overshooting complement activation plays a significant role in the pathogenesis of the disorder. Calreticulin (CRT) is a multifunctional protein whose cell-surface form (ectocalreticulin) is reported to be a C1q receptor. A 124-residue domain within CRT, the S-domain, binds to C1q, prevents the formation of C1 and so inhibits activation of the classical pathway. To assess the usefulness of CRT S-domain as a complement inhibitor, recombinant S-domain was expressed, radiolabeled, and the fate of the radiolabeled peptide followed in vivo. In rats, CRT-S-domain shows a half-life of 1.21 +/- 0.34 and 40.5 +/- 2.7 min in the distribution and elimination phases from plasma, respectively. The peptide remains largely intact, and is cleared from the circulation by the kidneys, where it accumulates in the proximal convoluted tubules, but is not excreted. Much smaller amounts of the peptide accumulate in other tissues, and essentially none crosses the blood-brain barrier.

Animals↗

PubMed2005

C1 inhibitor deficiency: consensus document.

We present a consensus document on the diagnosis and management of C1 inhibitor deficiency, a syndrome characterized clinically by recurrent episodes of angio-oedema. In hereditary angio-oedema, a rare autosomal dominant condition, C1 inhibitor function is reduced due to impaired transcription or production of non-functional protein. The diagnosis is confirmed by the presence of a low serum C4 and absent or greatly reduced C1 inhibitor level or function. The condition can cause fatal laryngeal oedema and features indistinguishable from gastrointestinal tract obstruction. Attacks can be precipitated by trauma, infection and other stimulants. Treatment is graded according to response and the clinical site of swelling. Acute treatment for severe attack is by infusion of C1 inhibitor concentrate and for minor attack attenuated androgens and/or tranexamic acid. Prophylactic treatment is by attenuated androgens and/or tranexamic acid. There are a number of new products in trial, including genetically engineered C1 esterase inhibitor, kallikrein inhibitor and bradykinin B2 receptor antagonist. Individual sections provide special advice with respect to diagnosis, management (prophylaxis and emergency care), special situations (childhood, pregnancy, contraception, travel and dental care) and service specification.

Adolescent↗

PubMed1988

Functional and structural similarities between protease nexin I and C1 inhibitor.

Protease nexin I is a proteinase inhibitor that is secreted by human fibroblasts and forms stable complexes with certain serine proteinases; the complexes then bind to the fibroblasts and are rapidly internalized and degraded. In this report, we show that this inhibitor, which is present in very low concentrations in plasma, has functional and structural similarities to C1 inhibitor, an abundant proteinase inhibitor in plasma. Both inhibitors complex and inactivate certain proteinases that previously were known to rapidly react only with C1 inhibitor. Kinetic inhibition studies show that protease nexin I inhibits Factor XIIa and plasma kallikrein with second-order rate constants of 2.3 x 10(3) and 2.5 x 10(5) M-1 s-1, respectively, which are similar to the rate constants for inhibition of these proteinases by C1 inhibitor. Protease nexin I inhibits C1s about one-tenth as rapidly as does C1 inhibitor. Alignment of the amino acid sequences of protease nexin I and C1 inhibitor shows that these proteins have similarity at their reactive centers (from sites P7 to P1). The remaining regions of the two proteins share much less similarity. In contrast to protease nexin I, C1 inhibitor is not secreted by human fibroblasts. Although 125I-C1s-protease nexin I complexes readily bind to human fibroblasts, binding of 125I-C1s-C1 inhibitor complexes or other 125I-proteinase-C1-inhibitor complexes to these cells is not detectable. Thus, protease nexin I and C1 inhibitor may control some common regulatory proteinases in the extravascular and vascular compartments, respectively.

Amino Acid Sequence↗

PubMed1991

[Angioedema due to acquired complement-C1-inhibitor deficiency in a female patient with non-Hodgkin lymphoma and autoimmune hemolytic anemia].

A case of angioedema due to acquired deficiency of the regulatory protein C1-esterase-inhibitor (C1-INH) is reported. The edematous attack occurred 3 1/2 weeks after initiation of successful therapy for autoimmune-hemolytic anemia in the course of long-standing non-Hodgkin's lymphoma. At the time of acute edema the complement profile was typical: virtual absence of C1-INH function was associated with diminished concentrations of the components of the classical pathway of complement (C1q, C1r, C1s, C2, C4) and reduced complement hemolytic activity (CH50). Anti-C1-INH-autoantibodies were not detected. The angioedema lasted for about one week, and no further attacks occurred during the five-months follow-up period. Although there was only a minor adjustment to the therapy, the C1q, C2, C4 and CH50 values gradually increased to levels close to the lower limit of the normal range, while C1r and C1s showed normal values. In contrast to most other reports, this case was characterized by angioedema which was precipitated only after initiation of appropriate treatment for the underlying disease rather than before therapy or even diagnosis of the underlying disease.

Aged↗

PubMed1994

Factor J, a human inhibitor of complement C1, is a cationic, highly glycosylated protein.

Factor J (FJ) is a new inhibitor of the complement system. This work supports the fact that FJ is a cationic molecule (pI > or = 9.6 in native conditions, or pI = 8.1 in denaturing conditions) with a high sugar content (40%) that is able to interact with different lectins, suggesting a complex glycosylation. SDS impaired FJ migration in polyacrylamide gel electrophoresis. In Triton-acid-urea-polyacrylamide gel electrophoresis FJ migrated as a complex, dispersed molecule. In contrast, FJ after Smith degradation (dFJ) gave a single, smeared band of M(r) = 23.4 kDa in reducing SDS-PAGE. dFJ retained only 60% of the initial inhibitory activity of intact FJ. When digestions with different proteinases were performed, no modification of activity was observed. After beta-glucuronidase digestion, FJ lost 80% of its initial activity. Consequently, glycosylation plays an important role in the inhibitory activity of FJ.

Carbohydrate Sequence↗

PubMed2003

Complete sequencing and expression of three complement components, C1r, C4 and C1 inhibitor, of the classical activation pathway of the complement system in rainbow trout Oncorhynchus mykiss.

Three complement components, C1r, C4 and C1 inhibitor, of the classical activation pathway have been fully sequenced and their expression investigated in rainbow trout (Oncorhynchus mykiss). Trout C1r cDNA encodes a 707-amino-acid (aa) protein with a theoretical M(r) of 77,200. The trout translation shows highest homology with carp C1r/s, and lower, equal homologies to mammalian C1r and C1s, and MASPs from other vertebrate species. However, phylogenetic analysis and structural features suggest that the trout sequence, together with the two carp sequences, are the orthologues of mammalian C1r. The trout C4 cDNA encodes a 1,724-aa protein with a theoretical M(r) of 192,600. The trout translation shows higher homologies to the carp C4B and medaka C4, but lower homologies to C4 from other species and the carp C4A. It has a predicted signal peptide of 22 aa, a alpha-chain of 773 aa, a beta-chain of 635 aa and a lambda-chain of 288 aa. Trout C1 inhibitor cDNA encodes a 611-aa protein with a theoretical M(r) of 68,700. The trout translation has a C-terminal serpin domain with high homologies with mammalian counterparts (~37% identities), and a longer N-terminus, with no significant homology to other serpins, which contains two Ig-like domains. A molecule containing two Ig-like domains followed by a serpin domain, has also been found in an EST clone from another bony fish, the Japanese flounder. This suggests a unique structural feature of C1 inhibitor in fish. The functional significance of the Ig domains is discussed. The liver is the major site of expression of the three trout complement components, C1r, C4 and C1 inhibitor, although their expression is also detectable in other tissues. The extra-hepatic expression of complement genes may be important for local protection and inflammatory responses. Low-level constitutive expression of the three components was also detectable in a trout monocyte/macrophage cell line RTS-11, but only the expression of C4 could be upregulated by LPS.

Amino Acid Sequence↗

PubMed1992

Activation of complement in normal serum by hydrogen peroxide and hydrogen peroxide-related oxygen radicals produced by activated neutrophils.

Neutrophils activated by soluble particulate stimuli generate superoxide anion and subsequently form hydrogen peroxide and other oxygen radicals. The effect of hydrogen peroxide on the complement system in normal serum was investigated. Treatment of normal serum with hydrogen peroxide resulted in a diminution of the haemolytic activity of the total and alternative complement pathways and the haemolytic titres of C3 and C5 but not of C2, in normal serum. These decreases in complement activity depended on the concentration of hydrogen peroxide added to the serum. Immunoelectrophoretic analysis of hydrogen peroxide-treated serum showed that C3 and C5 proteins were activated. Complement degradation products C3a and C5a were produced in normal serum treated with hydrogen peroxide, and 20 mM EDTA abolished C3a and C5a production in hydrogen peroxide-treated serum but 20 mM Mg-EGTA did not. Catalase completely abolished and dimethylsulphoxide and D-mannitol, hydroxyl radical scavengers, partially inhibited the hydrogen peroxide-mediated complement activation. Hypochlorite, incubated with normal serum, significantly inhibited serum haemolytic activity, and sodium thiosulphate, a reducing agent, abolished the effect of hypochlorite. Normal serum incubated with activated neutrophils showed neutrophil chemotactic activity and decreased serum haemolytic activity, and the addition of catalase or methionine (5 mM) completely abolished the effects of activated neutrophils. These results suggest that hydrogen peroxide activates complement via an alternative pathway of complement activation and that hydroxyl radicals and other hydrogen peroxide-related species such as hypochlorite are most likely involved in hydrogen peroxide-mediated complement activation. Complement activation by oxygen radicals produced by activated neutrophils may be one of the mechanisms by which complement is activated in human immune complex diseases.

Complement Activation↗