Genetic polymorphism of human complement proteins.
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Blood Proteins↗
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[Acquired C1-esterase inhibitor deficiencies during lymphoid syndromes].
Very marked abnormalities of the complement system were discovered in two patients suffering from a lymphoid syndrome and an IgM 7S dysglobulinaemia. The abnormalities in the complement system were related to a deficiency in C1-estérase (C1 INH). Several findings suggest that such a deficiency is acquired, in particular the absence of any family history of angio-neurotic oedema and, above all, the detection of a marked fall in levels of the C1 fraction which does not exist in the congenital form of deficiency of the inhibitor. The IgM 7S immunoglobulins found in the serum of both patients are probably responsible for the abnormalities in the complement system observed. Such acquired deficiencies in C1 INH are extremely rare since only a few cases have been reported in the literaute, in particular two cases in patients with lymphosarcoma with a serum IgM 7S.
Aged↗
Effect of interferon-gamma on complement gene expression in different cell types.
We have studied the expression of the complement components C2, C3, factor B, C1 inhibitor (C1-inh), C4-binding protein (C4-bp) and factor H in human peripheral blood monocytes, skin fibroblasts, umbilical vein endothelial cells (HUVEC) and the human hepatoma cell line G2 (Hep G2) in the absence and the presence of interferon-gamma (IFN-gamma). E.l.i.s.a. performed on culture fluids, run-on transcription assays, Northern blot and double-dilution dot-blot techniques confirmed that monocytes expressed all six components, whereas fibroblasts, HUVEC and HepG2 each expressed five of the six components. Fibroblasts and HUVEC did not synthesize C4-bp, and Hep G2 did not produce factor H. In addition to these differences, the synthesis rates of C3, C1-inh and factor H were not the same in all cell types. However, the synthesis rates of C2 and factor B were similar in all four cell types. The half-lives of the mRNAs were shorter in monocytes than in other cell types. Monocyte factor H mRNA had a half-life of 12 min in monocytes, compared with over 3 h in fibroblasts and HUVEC. The instability of factor H mRNA in monocytes may contribute to their low factor H secretion rate. IFN-gamma produced dose-dependent stimulation of C2, factor B, C1-inh, C4-bp and factor H synthesis by all cell types expressing these proteins, but decreased C3 synthesis in all four cell types. Cell-specific differences in the response to IFN-gamma were observed. The increased rates of transcription of the C1-inh and factor H genes in HUVEC were greater than in other cell types, while the increased rate of transcription of the C2, factor B and C1-inh genes in Hep G2 cells was less than in other cell types. IFN-gamma did not affect the stability of C3, factor H or C4 bp mRNAs, but increased the stability of factor B and C1-inh mRNAs and decreased the stability of C2 mRNA. Although these changes occurred in all four cell types studied, the half-life of C1-inh mRNA in monocytes was increased almost 4-fold, whereas the increases in the other cell types were less than 30%. These data show that the constitutive synthesis rates of complement components may vary in the different cell types. They also show that the degree of change in synthesis rates in response to IFN-gamma in each of the cell types often varies due to differences in transcriptional response, sometimes in association with changes in mRNA stability.
Carrier Proteins↗
Evidence for glomerular modulation of complement activation.
Using indirect immunofluorescence, three regulatory proteins of the complement system, C1-inhibitor (C1-INH), C3b inactivator (C3bINA) and beta 1H globulin have been detected in the glomeruli of patients with glomerulonephritis associated with complement activation. C1-INH and beta 1H were found frequently but C3bINA was rarely detected (only 14 biopsies). beta 1H globulin and C3b inactivator which modulate C3b activity were never found in the absence of C3, but C1-INH was sometimes found in the absence of C1s. The patterns for staining for C1s and C1-INH, C3 and beta 1H were almost identical suggesting that the regulatory proteins are binding to the proteins they regulate, as has been demonstrated in vitro. Thus, in tissues undergoing complement-mediated tissue damage, the extent of complement activation is controlled by the normal regulatory mechanisms.
Complement Activation↗
Regulation of the hepatic synthesis of C1 inhibitor by the hepatocyte stimulating factors interleukin 6 and interferon gamma.
C1 inhibitor (C1INH), the major plasma inhibitor of activated C1, kallikrein, and activated Hageman factor, may be an important factor in limiting inflammatory injury mediated by the complement and contact systems. C1INH is thought to be synthesized primarily in the liver; however, the regulators of hepatic C1 inhibitor synthesis are completely unknown. In this report, we analyze the regulation of C1INH synthesis by hepatocyte stimulating factors in human hepatoma cell lines and primary hepatocytes. Interleukin-6 and interferon gamma increase C1INH production in both hepatoma cells and hepatocytes. These cytokines stimulate de novo synthesis of functional C1INH, acting at a pretranslational level as assessed by Northern blotting. The stimulatory effects of interleukin-6 and interferon gamma on C1INH synthesis are separate and are differentially modulated by interleukin-1. These results establish that hepatic C1INH synthesis is regulated by hepatocyte stimulating factors and reveal novel interactions between these factors.
Acute-Phase Proteins↗
Human recombinant macrophage colony-stimulating factor (M-CSF) increases Cl-esterase inhibitor (Cl-INH) synthesis by human monocytes.
The ability of macrophage colony-stimulating factor (M-CSF) to influence production of complement proteins by cultured human monocytes was studied. Three-day-old cultures of human monocytes were treated with 250-1000 U/ml recombinant human M-CSF (Cetus Corporation, Emeryville, CA). After 3 days the M-CSF containing medium was replaced by the same medium without M-CSF, and the cells were cultured for 3 more days. Samples taken at the removal of M-CSF and 3 days later were tested for the concentration of factor B and Cl-esterase inhibitor (Cl-INH) using ELISA methods, and C2 by using an immunohaemolytic assay. M-CSF induced a marked dose-dependent increase in the synthesis of Cl-INH, but did not significantly change Bf and C2 production. The findings suggest that M-CSF is able to influence selectively the complement protein-producing ability of cultured human monocytes.
Cells, Cultured↗
Modulation by interferons of the expression of monocyte complement genes.
Interferons-alpha, -beta and -gamma (IFNs-alpha, -beta and -gamma) stimulated the synthesis of the second complement component (C2), Factor B (B) and C1 inhibitor (C1-inh) by human monocytes in vitro. The degree of increase of the secretion rates of C2, B and C1-inh was dose-dependent and proportional to increases in the abundances of their respective mRNAs. IFN-gamma was the most effective at stimulating monocyte C1-inh synthesis, whereas IFN-alpha and IFN-beta were marginally more effective at stimulating monocyte C2 and B synthesis. Kinetic studies showed that the effect of the IFNs was rapid, with maximum stimulation occurring within 1-2 h for all three proteins. After the removal of IFNs from cultures the C1-inh mRNA abundance remained elevated for over 24 h in IFN-gamma-treated monocytes but returned to control levels within 8 h in IFN-alpha-treated and IFN-beta-treated monocytes. The abundances of C2 mRNA and B mRNA also returned to basal values within 8 h after removal of any of the three cytokines from the cultures. Both IFN-alpha and IFN-beta acted synergistically with IFN-gamma to stimulate synthesis of C1-inh and B. This synergistic effect only occurred when the cytokines were present in the cultures simultaneously. The effects of IFN-gamma plus IFN-alpha or IFN-beta on C2 synthesis appeared to be additive rather than synergistic. IFN-gamma inhibited synthesis of C3 by monocytes, but IFN-alpha and IFN-beta had no effect on the synthesis of this protein. Furthermore, none of the three cytokines had any effect on the expression of actin mRNA in monocytes.
Cells, Cultured↗
The proteoglycan decorin binds C1q and inhibits the activity of the C1 complex.
Decorin, a small collagen-binding dermatan sulfate proteoglycan, is widely distributed as a component of extracellular matrices. Using a solid phase binding assay, we showed that decorin bound C1q at physiologic pH and ionic strength. The interaction did not require divalent cations and was time and temperature dependent reaching equilibrium in 4 h at 37 degrees C. Binding was specific and saturable with an apparent dissociation constant of 7.6 x 10(-9) M. Decorin was shown to bind pepsin-derived fragments containing the collagenous domain of C1q and collagenase-derived fragments containing the globular domain of C1q. Because these fragments share a short sequence of amino acids, this finding suggests that decorin binds to a region of C1q located near the junction of the two domains. Competition studies using purified preparations of the decorin core protein and the glycosaminoglycan chains showed that only the former inhibited binding of decorin to C1q indicating that the interaction is mediated by the decorin core protein. Decorin was shown to inhibit the hemolytic activity of purified C1 as well as C1 in normal human serum. Approximately 50% inhibition was observed at a decorin concentration of 2 micrograms/ml. Inhibition was not observed if C1 was bound to Ag-complexed antibody. Furthermore, neither the core protein nor the glycosaminoglycan chain of decorin inhibited C1, indicating that the intact proteoglycan is necessary for functional activity.
Animals↗
Hereditary angioneurotic oedema.
Three families with hereditary angioneurotic oedema (HANE) are described. Serum CI-INH and C4 immunochemical determinations were performed on 23 members of the families: in 6 persons low CI-INH and C4 levels were found with typical symptoms of HANE, and in one asymptomatic subject. Normal ranges of both proteins for adults, children and newborns are given for comparative purposes. The importance of the early diagnosis and treatment is emphasized.
Adolescent↗
Hereditary angio-oedema and C3 nephritic factor--HL-A study.
In one family of twenty-four members hereditary angio-oedema was present in the family for six generations. The protein C1 esterase inactivator found in nine patients proved to be non-active in a functional test. Another anomaly found in the complementary system was labelled C3 nephritic factor without any renal, or other clinical symptoms. Study of HL-A haplotypes did not show any linkage with the loci A, B and C. Hereditary angio-oedema is a disease arising from a specific defect in the inactivator of the C1 esterase (C1 INA) which is a regulating component of the complement system (Donaldson & Evans, 1963). This system is of current interest because of its interaction with other mechanisms of inflammation. Moreover, some links have been discovered recently between HL-A and hereditary defects of complement. This paper reports new findings in a family with hereditary angio-oedema.
Angioedema↗
C1-inhibitor prevents PEG fractionation-induced, EDTA-resistant activation of mouse complement.
Fractionation of mouse serum by precipitation with a critical amount of polyethylene glycol 6000 (PEG; 11% w/v) results in a classical and alternative pathway-independent activation of the terminal complement route. The activation can take place after the separation of an activating principle together with the terminal route components from a natural regulator. The isolation and identification of the regulatory component preventing this activation in serum, is subject of this paper. The regulator was purified by fractionated PEG-precipitation (15-25%), followed by heparin-Sepharose affinity, Mono Q anion-exchange, and Superose 12 gel filtration chromatography. The regulator appeared to be a single-chain protein with a Mr of 96 k. A protein with similar activity purified from human serum had a Mr of 104 k and was functionally and antigenically indistinguishable from C1-INH. The mouse 96 k protein inhibited C1-esterase activity indicating that this protein is indeed C1-INH. Mouse C1-INH regulates the PEG fractionation-induced bypass activation of complement, but does not interfere with the assembly or the lytic activity of membrane attack complexes. alpha 2-Macroglobulin appeared also to be capable of inhibiting the PEG-precipitation-induced activation process, but with lower efficiency.
Animals↗
Cold-dependent activation of complement: recognition, assessment, and mechanism.
Cold-dependent activation of complement (CDAC) is a phenomenon characterized by low hemolytic complement activity in chilled serum. Complement component levels are normal when measured immunologically, and there is normal hemolytic activity in EDTA plasma or serum maintained at 37 degrees C. Little attention has been paid to CDAC except in Japan, and current unfamiliarity with it, even by clinical immunologists, can lead to confusion and unnecessary laboratory tests. A 66-year-old patient with a complex medical history is described whose complement tests showed abnormalities characteristic of CDAC. Evidence for classical complement pathway activation in the cold was obtained by CH50 measurements, by hemolytic C4 determinations, by C4a, C3a, and C4d generation, and by quantitating C1s-C1r-(C1 inhibitor)2 complexes. A good correlation was observed among these parameters. Cryoprecipitates were absent. CDAC activity has persisted for over 5 years and is greater at 13 than at 4 degrees C. Activation is ablated by heating at 56 degrees C and restored by the addition of C1 to the heated serum. Adsorption by streptococcal protein G-Sepharose and precipitation by 2.5% polyethylene glycol support the hypothesis that CDAC is caused by aggregated IgG. The CDAC factor(s) also induces complement activation in normal serum but has not interfered with Raji cell or C1q binding tests or with FACS analysis. More limited studies of a second individual experiencing CDAC yielded similar results.
Adult↗
A familial case of hereditary angioneurotic edema in Japan.
A 53-year-old man was admitted with impairment of breathing following laryngeal edema. Serum levels of CH50 (22 U/ml), C4 (3 mg/dl), C1-INH protein (10.6 mg/dl) and C1-INH activity (LT 25%) were low. Complement study of the patient's family members revealed that he was one of 5 patients in 3 generations with hereditary angioneurotic edema (HANE). Administration of the androgen derivatives Danazol (600 mg/day) and Oxymetholone (30 mg/day) effectively increased serum levels of C1-INH activity and C4. Though eruption and hepatic dysfunction attributable to administration of the drugs appeared, these side effects improved after withdrawal of the drugs. Subsequently, the treatment with Danazol at a low dose (100 mg/day) was resumed, and the patient has had no episodes of edema for the past 3 years. Regarding the familial cases of HANE, fewer than 20 have been reported in Japan.
Angioedema↗
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↗
[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↗
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↗
C1 inhibitor hinge region mutations produce dysfunction by different mechanisms.
Heterozygosity for a mutant dysfunctional C1 inhibitor protein, a member of the serine proteinase inhibitor (serpin) superfamily, results in type II hereditary angioneurotic oedema. We identified a "hinge" region mutation in C1 inhibitor with a Val to Glu replacement at P14 Val-432. Recombinant C1 inhibitors P10 Ala-->Thr and P14Val-->Glu did not form stable complexes with fluid phase C1s or kallikrein. The P14 Val-->Glu mutant, however, was cleaved to a 96K form by C1s, while the P10 Ala-->Thr mutant was not. The recombinant P10 mutant also did not complex with C1s, kallikrein or beta-factor Xlla-Sepharose. The two mutations, therefore, result in dysfunction by different mechanisms: in one (P14 Val-->Glu), the inhibitor is converted to a substrate, while in the other (P10 Ala-->Thr), interaction with target protease is blocked.
Alanine↗
C1-INH defect as an example of deficiency disease.
Primary defect of C1-inhibitor (C1-INH), the regulatory protein of the initial classical pathway of complement, is the cause of hereditary angioedema. Clinical symptoms involve potentially fatal obstruction of the upper respiratory tract, abdominal pains, and subcutaneous edemas. Since the description of functional tests for C1-INH two types of hereditary defect have been known: type I and type II. Sixteen patients with the type I of hereditary angioedema were diagnosed and treated in our hospital. The onset of the disease occurred between 1.5-12 y. of age. Clinical symptoms were observed in skin, gastrointestinal and respiratory tracts. Mean concentration of C1-INH in sera of 16 patients was 3.25 mg/dl, below 8.75 mg/dl that is the critical for well-functioning C1-INH. Inhibitory activity of C1-INH for C1 esterase in plasma was zero in most of the patients, while it was 0.94 +/- 0.20 U/ml in plasma samples of 91 healthy blood donors. Three modalities of treatment are available: substitution with C1-INH concentrate in acute attacks and antifibrinolytic and/or anabolic drugs for prophylaxis. We have obtained good therapeutic results with epsilon-aminocaproic acid (antifibrinolytic), 2g daily during 3 months, with 6 months intervals.
Adolescent↗