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PubMed1981

Membrane attack complex of complement: distribution of subunits between the hydrocarbon phase of target membranes and water.

Membrane destruction by complement is effected by the membrane attack complex (MAC) which is the dimer of a fusion product of the complement proteins C5b, C6, C7, C8, and C9. Phospholipid bilayer vesicles were used as target membranes for the MAC and its intermediate complexes. The subunits of these membrane-bound complexes were explored as to their relative exposure to the hydrocarbon phase of the lipid bilayer and to water surrounding the lipid vesicles. Protein exposed to the aqueous phase was labeled with 125I; protein exposed to the hydrocarbon phase was labeled by using tritiated azido phospholipids and irradiation. Analysis of the membrane-bound MAC showed that subunits C5b, C8 beta, and C9 were exposed to the aqueous phase. The subunits C8 alpha-gamma and C9 were primarily in contact with the hydrocarbon phase. C6 and C7 were little exposed to either phase, suggesting that these proteins are inaccessible within the MAC. Analysis of the intermediate complexes showed that C5b was the subunit most exposed to water in membrane-bound C5b-7, and C5b and C8 beta were the water-exposed subunits in C5b-8. Subunit exposure to the hydrocarbon phase of the lipid bilayer changed during MAC assembly. Whereas all three subunits of C5b-7 carried the phospholipid photolabel; most of the label was bound to the C8 subunit in C5b-8 and to C9 in the MAC. It is proposed that contact with the hydrocarbon core of membranes is established by C5b-7 through each of its subunits, by C5b-8 through C8, and by the MAC through C8 and, particularly, C9.

Affinity Labels↗
PubMed1981

Human complement in the arachidonic acid transformation pathway in platelets.

Arachidonate-mediated release of 14C serotonin and thromboxane B2 (TXB2) is significantly enhanced in the presence of complement. Only purified complement components C5, C6, C7, C8, and C9 are required for this reactivity. No known activating mechanism of the classical or alternative pathway is required, nor is C3. In the absence of exogenously added complement, platelet membrane-bound complement components play an essential role in modulating arachidonate-mediated serotonin release. Incubation of platelet membranes with arachidonate and C5--C9 led to the production of dimers of the membrane attack complex (C5b--9) on the platelet surface. These macromolecular complexes were eluted from the platelet membrane and were identified physicochemically and morphologically. The possibility arises that C3 in association with C5--C9 is required for mobilization of the arachidonic acid from the phospholipid of the platelet membrane. Once the arachidonic acid is mobilized, C3 is no longer required, C5--C9 being sufficient to modulate this pathway leading to enhanced production of TXB2.

Animals↗
PubMed1997

Molecular, genetic, and functional analysis of homozygous C8 beta-chain deficiency in two siblings.

UNLABELLED: C8 deficiency is associated with an increased susceptibility to neisserial infections. We present a case of an 11 year old boy who suffered from infection with Neisseria meningitidis. Medical history of the patient and his family (n = 5) did not indicate any previous immunodeficiency symptoms. Results from the analysis of phagocyte and lymphocyte functions were within the normal range. No hemolytic activities of the classical (CH50) and the alternative (APH50) pathways of complement were measurable, and SC5b-9 protein complexes could not be detected in the patient's plasma. Further analysis by highly sensitive ELISA and functional assays revealed a complete deficiency of C8. Upon the reconstitution with purified C8 total hemolytic activity could be restored. SDS-PAGE and Western blot analysis established a deficiency of the C8 beta chain. Genetic analysis at the genomic DNA level demonstrated the common C-T mutation in exon 9 of the C8B gene. Family analysis presented the older sister with non-detectable function of C8 in serum, both parents with about half-normal C8 titres, and the younger sister with normal C8 function. The parents and both sisters were asymptomatic, although the older of the sisters presented with the same complete C8 beta-chain deficiency as the patient described. IN CONCLUSION: the common C-T mutation in the C8B genes is the genetic basis of C8 beta-chain deficiency in two members of this Bosnian family.

Alleles↗
PubMed1990

Synthesis of complement by alveolar macrophages from patients with sarcoidosis.

Sarcoidosis is a granulomatous disorder of unknown aetiology. Alveolar macrophages (AM) in sarcoidosis release a variety of mediators important to the pathogenesis of the disease. Complement is essential for the inflammatory response and we investigated whether there were any major defects in the potential for sarcoidosis AM to synthesize complement in vitro. AM from 11 patients with active sarcoidosis and three healthy controls were cultured under serum-free conditions. There was a significant binding of polyclonal (anti-C5, -C6, -C7, -C8) and monoclonal anti-complement antibodies (anti-C3c and anti-C9 neoepitope (aE11] to agarose beads incubated with unstimulated AM for 24, 48, or 72 h. A significant and inhibitable production of soluble C3c, C5, C9, and S-protein was found in the harvested medium as detected by enzyme immunoassays. Activated C3 and C9 were also detected based on neoepitope expression. Presence of co-cultured agarose beads reduced the amount of soluble S-protein due to deposition on the agarose. We argue that the C9 neoepitope is an integral part of the terminal complement complex (TCC), both in the fluid and solid phase when bound to the agarose. In the fluid phase, SC5b-9 was generated, whereas the agarose-bound S-protein is assumed not to be associated with TCC on the beads. The results demonstrate for the first time that AM from sarcoidosis patients synthesize the functional alternative and terminal pathway of complement.

Adult↗
PubMed1987

Bactericidal capacity against Neisseria meningitidis of normal human serum and sera with functional deficiencies of the third and eight complement factor.

The bactericidal capacity of serum with C3 deficiency secondary to circulating C3 nephritic factor, serum with C8 deficiency and normal human serum were assessed in vitro against Neisseria meningitidis groups A-C. Normal human serum and C8-deficient serum, originating from a 28-year-old male with two episodes of meningococcal meningitis, showed significant bactericidal capacity against meningococci groups A and B. Against group C meningococci the C8-deficient serum revealed significant bactericidal capacity, whereas normal human serum showed no bactericidal effect. Serum with C3 deficiency, obtained from a 16-year-old female with two episodes of meningococaemia, showed no bactericial effect against meningococci groups A-C. Incubation of normal human serum and C8-deficient serum with isolated nephritic factor resulted in C3 depletion and abolished the bactericidal effect.

Adolescent↗
PubMed1996

Detection of heterozygous C8 beta deficiency by PCR in a healthy Italian population.

In Italy a rather high number of homozygotes with late complement component defects has been found among patients with meningococcal disease. It seems that clinical manifestations of meningococcal disease are less severe in patients with complement deficiency than in normal individuals. This situation could even be more evident in the heterozygous carriers for whom a selective advantage is discussed. In this study we have screened a cohort of 527 Italian blood donors from western Sicily for the presence of C8B mutated allele. Heterozygotes for C8 beta deficiency were identified using a specific PCR assay to detect a C-->T transition in exon 9 of the C8B gene. This mutation represents the most frequent genetic mechanism for C8 beta deficiency in Caucasians. A rapid PCR screening test was performed on DNA extracted from pooled blood samples of up to 8 individuals. A single male individual with heterozygous C8 beta deficiency was detected. In the family studies it was shown that his two brothers and the mother were heterozygous carriers too. Functional activity of the classical and alternative complement pathways were normal. No neisserial infections or inflammatory diseases were found in the family history. It was shown that the allele-specific PCR is a sensitive and rapid method to examine large numbers of DNA samples. It permitted to assess the real prevalence of the C8B mutated null allele in the general population free of ascertainment bias.

Alleles↗
PubMed2001

Interaction of poly(2-acrylamido 2-methylpropane sulfonate)-grafted polystyrene beads with cationic complement proteins.

Influence of various biomaterials on the complement system in serum has been intensively studied by many research groups, since activation of the complement pathway in vivo has been known to give rise to some pathological conditions, such as inflammation and anaphylaxis. Much effort has been devoted to develop new materials that do not activate or deteriorate the complement system. The present work is aimed at revealing the mode of reactions of anionic poly(2-acrylamido 2-methylpropane sulfonate) grafted on polystyrene bead (PAMPS-g-bead) with serum complement. Complement activity assay, determination of complement proteins levels, and immunoblot analysis were carried out for sera pretreated with PAMPS-g-beads. The results clearly showed that, when PAMPS-g-beads were incubated with serum, those beads adsorbed several complement proteins, i.e. C1q, factor D, factor P, C6, and C8, but the generation of activation fragments of complement components was not observed. Especially, factor D was most effectively removed from serum, resulting in potential inhibition of the alternative pathway. A larger amount of PAMPS-g-beads was needed to decrease the serum CH50 level. That may be caused by removal of C6. Although some polyanions, such as dextran sulfate, were reported to activate the complement system, the obtained results indicate that the PAMPS-g-bead is not an activator of the complement pathway, but acts as an adsorbent of complement components. One possible clinical application of the PAMPS-g-beads is adsorption of serum factor D by extracorporeal treatment of patients with renal failure with a high level of factor D, because the increased quantity of factor D in serum may cause consistent activation of the alternative pathway.

Biocompatible Materials↗
PubMed1993

[The complement system].

The complement system represents a multitude of activating factors, associated with the cellular membrane and providing for cell lysis. The system is composed of 21 serum proteins and 8 receptors and may be found in cells of various types. The major function of the system consists in its activation which entails a cascade of events terminated by cell lysis. Two complement system activation mechanisms are generally distinguished, one of which is classical and one is alternative. These two mechanisms converge after the activation of the third component (C3) or as a result of interaction between the terminal components (C5, C6, C7, C8 and C9) of the complement cascade. The complement system is linked with the fibrinolytic, blood coagulating and kinin systems.

Complement Activation↗
PubMed1992

Bullous pemphigoid autoantibodies reactive with intracellular basal keratinocyte antigens: studies of subclass distribution and complement activation.

Using immunofluorescence (IF) and monoclonal antibodies (MoAbs) to IgG subclasses, terminal complement components, and S-protein/vitronectin, we have extended recent observations concerning reactivity of bullous pemphigoid autoantibodies with intracellular antigens located on the polar tips of basal human keratinocytes (HuK). Using three purified bullous pemphigoid IgG fractions, autoantibody reactivity with these intracellular antigens was present in all four IgG subclasses. When skin sections were used as substrate, an identical IgG subclass distribution of autoantibodies for each bullous pemphigoid IgG fraction was observed, but reactive with the basement membrane zone. All three bullous pemphigoid IgG preparations contained IgG subclass autoantibodies capable of complement fixation. Each IgG fraction resulted in fixation of all of the terminal complement components (C5, C6, C7, C8, and C9) and assembly of the membrane attack complex (MAC) on the polar tips of basal HuK. S-protein/vitronectin was not bound in a similar fashion. Normal IgG fractions yielded consistently negative reactions. Thus, bullous pemphigoid autoantibodies, fixed to polar tips of basal HuK, are found in all four IgG subclasses and will activate complement resulting in generation of MAC.

Antibodies, Monoclonal↗
PubMed1989

Comparison of isolates of Neisseria gonorrhoeae causing meningitis and report of gonococcal meningitis in a patient with C8 deficiency.

We studied a previously healthy 20-year-old woman who presented with gonococcal meningitis. The gonococcal isolate, HT-1, was prototrophic by auxotyping, was protein I serovar IB-1, and agglutinated with wheat germ lectin. This isolate differed from the proline-requiring, serovar IA-1 and IB-4, wheat germ-agglutination-negative gonococcal isolates recovered from three patients during a recent outbreak of gonococcal meningitis in Philadelphia. HT-1 was killed by normal pooled human sera (greater than or equal to 98% at 30 min) but not effectively killed by the convalescent-phase sera of the patient (greater than 30% survival at 30 min). Similar results were obtained when mucosal and cerebrospinal fluid isolates from a Philadelphia patient were exposed to these sera, but mucosal and blood isolates from another Philadelphia case showed increased resistance to killing by normal pooled human sera. Further characterization revealed multiple differences in outer membrane and cellular proteins and lipopolysaccharide between case isolates. Absence of the L8 lipopolysaccharide epitope was noted for all isolates. Sera of our patient were found to have low total hemolytic complement (CH100 = 21 U/ml; normal = 55 to 100 U/ml) due to deficiency of C8 (C8 less than 1,000 CH50 U/ml; normal = greater than or equal to 16,000 CH50 U/ml). This is the first reported case of gonococcal meningitis occurring in a patient with a terminal-complement deficiency. Gonococcal meningitis is a rare complication of gonococcal bacteremia. Both defects in host defenses (e.g., terminal-complement deficiency) and organisms with unusual virulence appear to contribute to the pathogenesis of this complication of gonococcal bacteremia.

Adult↗
PubMed1990

Persistent low C3 levels associated with meningococcal meningitis and membranoproliferative glomerulonephritis.

Recurrent meningococcal meningitis is usually related to terminal complement factor deficiencies (C5-C8); however it is not frequent with isolated primary C3 deficiency. Similarly, membranoproliferative glomerulonephritis has been described in association with primary C3 deficiencies and the presence of C3 nephritic factor. We present a case of an 18-year-old woman with relapsing meningococcal meningitis in whom membranoproliferative glomerulonephritis and persistent low serum C3 levels were found. A detailed immunological study was performed, but no other abnormalities in the complement components were found. C3 Nef was also negative. Moreover, the familiar complement studies showed an asymptomatic C4 deficiency in her mother and borderline C3 levels in her sister. The presence of persistent low serum C3 levels in the absence of other immunological abnormalities suggests that this is the cause of the relapsing meningococcal infections and the glomerular disease of this patient. We suggest that a complement deficiency, including isolated C3 deficiency, should be ruled out in all cases of relapsing meningitis. Further, the possibility of glomerular disease should be carefully considered in these patients.

Adolescent↗
PubMed1992

Serum SC5b-9 (terminal complement complex) level, a sensitive indicator of disease activity in patients with Henoch-Schönlein purpura.

The concentration of the terminal complement complex (TCC), SC5b-9, was determined by enzyme immunoassay using 95 serum samples from 30 patients with Henoch-Schönlein purpura (HSP), 27 with other forms of inflammatory skin disease and 20 normal healthy donors. Twenty-five patients with HSP showed significantly increased TCC concentration in the active phase of the disease, during which newly formed urticarial or purpuric macules/papules could be seen. Skin biopsy specimens of skin lesions from patients with elevated TCC levels in nearly all cases contained the membrane attack complex of complement and consisted of C5b, C6, C7, C8, C9 without S protein on the vessel walls. Systemic and local activation of complement may thus possibly occur in HSP. Three patients with various manifestations of the disease were followed over a period of several years during which the active and inactive phases were scanned. TCC elevation in all cases was correlated with exacerbation of the disease. In contrast, C3, C4 and CH50 levels either remained normal or increased and thus were not reliable indicators of disease activity. Measurement of TCC should thus prove quite useful for monitoring the activity of HSP in patients in whom there is complement activation and also serve to facilitate clarification of the functions of complement in the pathogenesis of the disease.

Acute Disease↗
PubMed1994

The membrane attack complex of complement. Assembly, structure and cytotoxic activity.

The membrane attack complex of complement is formed by the molecular fusion of the five terminal complement proteins, C5, C6, C7, C8, and C9. While the assembly process on a target membrane and its modulation by restriction factors present on host cells is now quite well understood the molecular details of the architecture of the complex still need much further clarification. This is especially true for the interaction of the last acting protein C9, which provides the cytotoxic action of the complex, with the precursor C5b-8 complex. Because of this lack of structural details the molecular mechanisms that lead to complement-mediated cell death remain cryptic, however, it is hoped that recent advances in controlling the assembly process and in site-specific modification of the terminal complement proteins by recombinant DNA techniques should change this predicament quickly.

Bacteria↗
PubMed1979

Genetic control of the eighth component of complement.

Using isoelectric focusing in polyacrylamide gel and a hemolytic assay for development of patterns, extensive, structural polymorphism in human C8 has been delineated. Two alleles, C8A and C8B, have been identified in orientals, with gene frequencies of 0.655 and 0.345. In blacks, what appears to be a third common allele was found, so that frequencies were 0.692, 0.259, and 0.049 for C8A, C8B, and C8A1. In whites, C8A1 was rare with a frequency of 0.003, and frequencies for C8A and C8B were 0.649 and 0.349. Inheritance was autosomal codominant in family studies and the distribution of types in random unrelated populations fit the Hardy-Weinberg equilibrium in all groups. C8 allotypes have been determined for two previously studied families, each with a homozygous C8-deficient propositus. This study suggests that C8 deficiency is a silent or null allele of the C8 structural locus, and that half normal levels of C8 cannot be used as a single criterion for the establishment of heterozygous C8 deficiency. C8 allotypes, as well as 18 other autosomal markers, were also determined for 24 families. The C8 structural locus is not closely linked to these markers, including the human histocompatibility loci complex.

Alleles↗
PubMed1994

[Homozygote CB deficiency revealed by recurrent Neisseria meningitidis infections in an adolescent].

BACKGROUND: Meningococcal infections associated with late complement component deficiency are rarely severe and usually occur during adolescence and adulthood. We report severe manifestations in a boy in whom the first episode appeared early. CASE REPORT: A 14 year-old gypsy boy was admitted because of a febrile meningococcal meningitis that was complicated by a rapidly extensive and necrotic purpura, obnubilation and clotting abnormalities without hemodynamic anomalies. The patient was given symptomatic therapy and a 12-day course of antibiotics that resulted in rapid and complete recovery. Medical history of this patient showed that he had been admitted at the age of 3 years for a severe febrile purpura with septic shock and clotting abnormalities followed by rapid and complete recovery after symptomatic and antibiotic therapy. No germ had been then isolated. The complement system was studied 3 weeks after the second hospitalization: total hemolytic complement activity could not be detected and C2, C3 and C4 were normal. Examination of the terminal pathway-revealed total C8 deficiency. The patient received meningococcal vaccine and was discharged on oral penicillin prophylaxis. He remained healthy during the ensuing 4 years. CONCLUSIONS: Meningococcal infections associated with late complement component deficiency are generally uncomplicated but they remain potentially severe. Early screening for this late complement component deficiency should be considered after severe clinical manifestations.

Adolescent↗
PubMed1973

The complement system in bullous pemphigoid. I. Complement and component levels in sera and blister fluids.

Compared with other serum and blister fluid proteins, total hemolytic complement was reduced in the blister fluid of six serologically positive bullous pemphigold patients while four serologically negative cases had blister fluid complement levels closely approaching the serum levels. Except for pemphigus vulgaris blisters. blister fluids from most patients with other bullous diseases and experimentally induced blisters had blister fluid complement levels more closely approaching the serum levels. With the exception of the two terminal components. C8 and C9, individual components of the complement sequence were also reduced in the blister fluids of the six bullous pemphigold patients with circulating basement membrane zone antibodies. On the other hand, transferrin and IgG levels of these same six serologically positive blister fluids closely approached the corresponding serum levels. Conversion of C3 proactivator was also demonstrable in the serologically positive bullous pemphigoid blister fluids, but not in the corresponding sera. Our studies, therefore, are suggestive of local activation of the complement sequence, by both the classical and alternate pathways, in blisters of serologically positive bullous pemphigold patients.

Basement Membrane↗
PubMed1985

Enhanced complement-mediated lysis of type III paroxysmal nocturnal hemoglobinuria erythrocytes involves increased C9 binding and polymerization.

The interaction of terminal complement proteins (C5-C9) with normal erythrocytes and type III paroxysmal nocturnal hemoglobinuria erythrocytes (PNH-E) has been compared in terms of binding of the C5-9 complex, C9 polymerization, and C9 insertion into membranes. Complement components C5, C7, and C8 bind equally well to both types of erythrocytes, whereas the binding of C9 to PNH-E is 5-6 times greater than that to normal erythrocytes. The kinetics of C9 binding was compared with the kinetics of lysis for both types of cells under conditions leading to 100% lysis. There was a noticeable lag time between C9 binding and lysis of normal erythrocytes, but the lysis of PNH-E proceeded without a lag and the kinetics of lysis more closely paralleled C9 binding. The efficiency of C9 insertion was similar for both types of cells, but C9 polymerization was significantly enhanced on PNH-E. These data indicate that the enhanced susceptibility of type III PNH-E toward lysis by C5-9 can be correlated with abnormally high C9 binding and increased formation of poly(C9).

Carrier Proteins↗
PubMed1983

Interaction of human beta-endorphin with nonopiate binding sites on the terminal SC5b-9 complex of human complement. Significance of COOH-terminal beta H-endorphin fragments.

We have characterized the binding of 125I-labeled human beta-endorphin (125I-beta H-endorphin) to sites present on the terminal fluid-phase complex of human complement, consisting of complement components C5b, C6, C7, C8, C9, and the S-protein (SC5b-9 complex). Specific binding exhibited saturability, reversibility, structural specificity, temperature dependence, and absence of negative cooperative effects. Binding was maximal at 4 degrees C and pH 7.0; it was diminished by monovalent and divalent cations as well as by increasing concentrations of urea and Triton X-100 and apparently required intact disulfide groups. Binding was not inhibited by a number of opioid peptides sharing common sequences with the NH2 terminus of beta H-endorphin. In contrast, binding was inhibited by beta H-endorphin, N-acetyl-beta H-endorphin, and a series of COOH-terminal beta H-endorphin fragments, where of the COOH-terminal dipeptide Gly-Glu represented the minimal effective structure. Stepwise extension towards the NH2 terminus led to an increased binding affinity of the respective fragment. Computer resolution of competition curves yielded one binding component for several shorter COOH-terminal beta H-endorphin fragments and for beta H-endorphin (1-5) + (16-31), whereas two distinct binding components were obtained when beta H-endorphin (27-31), beta H-endorphin (6-31), N-acetyl-beta H-endorphin or beta H-endorphin were used as inhibitors. This study presents detailed data on the binding of COOH-terminal beta H-endorphin fragments to specific nonopiate binding sites present on the terminal SC5b-9 complex of human complement. We suggest that through this interaction, beta H-endorphin may modulate certain functions within the immune system.

Binding Sites↗