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PubMed1983

Molecular composition of the terminal membrane and fluid-phase C5b-9 complexes of rabbit complement. Absence of disulphide-bonded C9 dimers in the membrane complex.

The terminal membrane C5b-9(m) and fluid-phase SC5b-9 complexes of rabbit complement were isolated from target sheep erythrocyte membranes and from inulin-activated rabbit serum respectively. In the electron microscope, rabbit C5b-9(m) was observed as a hollow protein cylinder, a structure identical with that of human C5b-9(m). Monodispersed rabbit C5b-9(m) exhibited an apparent sedimentation coefficient of 29 S in deoxycholate-containing sucrose density gradients, corresponding to a composite protein-detergent molecular-weight of approx. 1.4 X 10(6). Protein subunits corresponding to human C5b-C9 were found on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. By densitometry, there were consistently six molecules of monomeric C9 present for each monomeric C5b-8 complex. Fluid-phase rabbit SC5b-9 was a hydrophilic 23 S ma macromolecule that differed in subunit composition from its membrane counterpart in that it contained S-protein and only two to three molecules of C9 per monomer complex. The data are in accord with the previous report on human C5b-9 that C5b-9(m) contains more C9 molecules than SC5b-9 [Ware & Kolb (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 6426-6430]. They corroborate the previous molecular-weight estimate of approx. 10(6) for C5b-9(m) and thus support the concept that the fully assembled, unit lesion of complement is a C5b-9 monomer [Bhakdi & Tranum-Jensen (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 1818-1822]. They also show that C9 dimer formation is not required for assembly of the rabbit C5b-9(m) protein cylinder, or for expression of its membrane-damaging function.

Animals↗
PubMed1996

Complement proteins are present in developing endochondral bone and may mediate cartilage cell death and vascularization.

Normal endochondral bone formation follows a temporal sequence: immature or resting chondrocytes move away from the resting zone, proliferate, flatten, become arranged into columns, and finally become hypertrophic, disintegrate, and are replaced by bone. The mechanisms that guide this process are incompletely understood, but they include programmed cell death, a stage important in development and some disease processes. Using immunofluorescence we have studied the distribution of various complement proteins to examine the hypothesis that this sequence of events, particularly cell disintegration and matrix dissolution, are complement mediated. The results of these studies show that complement proteins C3 and Factor B are distributed uniformly in the resting and proliferating zones. Properdin is localized in the resting and hypertrophic zone but not in the proliferating zone. Complement proteins C5 and C9 are localized exclusively in the hypertrophic zones. This anatomically segregated pattern of distribution suggests that complement proteins may be important in cartilage-bone transformation and that the alternate pathway is involved.

Animals↗
PubMed1985

The membrane attack complex of complement: C5b-8 complex as accelerator of C9 polymerization.

Polymerization of C9 occurs spontaneously or can be induced by the tetramolecular complex C5b-8. Spontaneous C9 (0.15 mg/ml) polymerization required more than 3 days at 37 degrees C. In the presence of C5b-8, C9 polymerization was complete within 10 min. The molar C9:C5b-8 ratio determined the extent of tubular poly C9 formation by C5b-8-bearing phospholipid vesicles. When this ratio was 9:1 or 12:1, 72% of complex-bound C9 was present as SDS resistant tubular poly C9 (Mr = 1.1 X 10(6]. At lower C9:C5b-8 ratios, poly C9 was bound primarily in nontubular form. Tubular poly C9, as part of C5b-9, could also be generated on rabbit erythrocytes by using whole human serum as a complement source. At limiting serum concentration (molar C9 to C8 ratio approximately 2), no SDS-resistant tubular poly C9 was detected. At high serum concentration or when using serum that was supplemented with C9, up to 40% of the C9 was SDS-resistant tubular poly C9, and the rest was poly C9, which was incompletely polymerized. It is suggested that the C5b-8 complex acts as an accelerator of C9 polymerization, and that its relative concentration to C9 determines the ultrastructure of the C5b-9 complex.

Animals↗
PubMed1990

Synthesis of C3, C5, C6, C7, C8, and C9 by human fibroblasts.

We investigated the ability of human fibroblasts to produce the components of the final common pathway (C3-C9) of complement in vitro by co-culturing an alternative complement activator (agarose beads) with the cells. The test system involved incubation of beads with anti-complement antibodies followed by radioactive-labelled anti-Ig detection antibodies. Subsequently, the beads were examined in a radioimmunoassay. Our results indicate that human fibroblasts produce C3, C5, C6, C7, C8, and C9. A neoepitope selectively expressed on activated C9 was detected, indicating assembly of the terminal complement complex and thus formation of a functional terminal complement pathway by the fibroblasts.

Antibodies, Monoclonal↗
PubMed1990

Deposition of C3, C9 neoantigen and vitronectin (S-protein of complement) in lichen planus pemphigoides.

We have compared the distribution of C3, C9 neoantigen (C9n) and vitronectin at the dermoepidermal junction in lichen planus pemphigoides with that in bullous pemphigoid. Eight out of 30 biopsies from patients with lichenoid lesions had linear C3 deposition at the basement membrane zone (BMZ); four of these patients had bullae and fulfilled the criteria for lichen planus pemphigoides. C9n immunoreactivity was detected as a linear or an intermittent linear/granular band at the BMZ only in these four patients, suggesting a role for the membrane attack complex of complement (MAC) in the pathogenesis of blister formation in lichen planus pemphigoides. Faint linear deposition of vitronectin, in addition to C9n, at the BMZ was seen in two of the four cases of lichen planus pemphigoides and three of six cases of bullous pemphigoid. This suggests that vitronectin may be deposited in association with C9n not only as part of the non-lytic SC5b-9 complex, but also as a regulatory step following the lytic action of MAC. A regulatory function for vitronectin in limiting tissue damage following activation of MAC is supported by our finding of a heavy deposition of vitronectin in association with C9n in a lichen planus pemphigoides patient in whom bulla formation had ceased.

Adult↗
PubMed1984

Complement channels in membranes: inhibition with a monoclonal antibody to a neoantigen of polymerized C9.

The channels produced by complement in red cell membranes are heterogeneous, with diameters of approximately 0.5 to approximately 12.0 nm. We investigated the relationship of the components of the membrane attack complex, C5b through C9, to the functional transmembrane channels greater than 3 nm in diameter. Radiolabelled macromolecules were incorporated into resealed red cell membrane ghosts which were then treated with complement. A monoclonal antibody to a neoantigen in polymerized C9 inhibited macromolecule diffusion through the complement channels. There was also inhibition with polyclonal antisera to C9 but not with antisera to any of the other components of the membrane attack complex. The results demonstrate a functional correlation of the larger complement lesions with the previously described poly C9 tubular structures.

Animals↗
PubMedDate not supplied

Immunocytochemical localization of the terminal complement complex in multiple sclerosis.

Granular deposits of C9 and the terminal complement complex, measuring 0.3-1.2 microns, have been demonstrated immunocytochemically in association with capillary endothelial cells, predominantly within plaques and adjacent white matter, in tissue obtained at autopsy from 5/7 patients with multiple sclerosis (MS) and one individual with subacute sclerosing panencephalitis but not from 7/7 controls. This finding suggests that the evolution of focal tissue damage in MS may involve complement activation associated with passage of humoral and cellular mediators of the immune system through the blood-brain barrier.

Adolescent↗
PubMed1984

Ultrastructure of the membrane attack complex of complement. Heterogeneity of the complex caused by different degree of C9 polymerization.

The membrane attack complex (MAC) of complement and its precursors, i.e. C5b-7 and C5b-8, were examined by electron microscopy. C5b-7 bound to lipid vesicles exhibits an extended structure of 25 nm connected to the lipid membrane via a 10-nm long, 3-nm wide stalk. Binding of C8 to vesicle-bound C5b-7 results in the disappearance of this stalk, whereas the overall length remains unchanged. Addition of 12 C9 molecules per C5b-8 induces C9 polymerization which is accompanied by the formation of C9 tubules and membrane lesions. By using biotinyl precursors and streptavidin -coated colloidal gold particles, C5b-6, C7, and C8 was found to be in the club-like part of the MAC; C9 was identified in the tubular moiety. Only one C5b-8 moiety was detected in an individual MAC complex thus excluding the proposed "dimeric" structure of the MAC. A membrane channel of 10 nm was formed by the MAC at a C9 to C5b-8 ratio equal or larger than 12 to 1, as suggested by the penetration of negative stain into the vesicle. In contrast, binding of an average of three C9 per C5b-8 caused formation of incomplete C9 tubules with apparent membrane channels of less than 10 nm diameter. The MAC isolated from red blood cells was ultrastructurally heterogenous . Although an excess of serum was used for the formation of the complexes, mostly incomplete poly C9 tubules were formed. It is proposed that the MAC is an ultrastructurally heterogenous complex that induces the formation of membrane channels of different sizes.

Animals↗
PubMed1982

Studies on the mechanism of bacterial resistance to complement-mediated killing. II. C8 and C9 release C5b67 from the surface of Salmonella minnesota S218 because the terminal complex does not insert into the bacterial outer membrane.

The mechanism for consumption of terminal complement components and release of bound components from the surface of serum-resistant salmonella minnesota S218 was studied. Consumption of C8 and C9 by S218 occurred through interaction with C5b67 on the bacterial surface because C8 and C9 were consumed when added to S218 organisms previously incubated in C8-deficient serum and washed to remove all C5b67 on the bacterial surface because C8 and C9 were consumed when added to S218 organisms previously incubated in C8- deficient serum and washed to remove al but cell bound C5b67. Rapid release of (125)I C5 and (125)I C7 from the membrane of S218 was dependent on binding of C8 because (125)I C5 and (125)I C7 deposition in C8D serum was stable and was twofold higher in C8D than in PNHA, and addition of purified C8 or C8 and C9 to S218 previously incubated in C8D serum caused rapid release of (125)I C5 and (125)I C7 from the organism. Analysis by sucrose density gradient ultracentrifugation of the fluid phase from the reaction of S218 and 10 percent PNHS revealed a peak consistent with SC5b-9, in which the C9:C7 ratio was 3.3:1, but the NaDOC extracted bound C5b-9 complex sedimented as a broad peak with C9:C7 of less than 1.2:1. Progressive elution of C5b67 and C5b-9 from S218 but not serum-sensitive S. minnesota Re595 was observed with incubation in buffers of increasing ionic strength. Greater than 90 percent of the bound counts of (125)I C5 or (125)I C9 were released from S218 by incubation in 0.1 percent trypsin, but only 57 percent of (125)I C9 were released by treatment of Re595 with trypsin. These results are consistent with the concept that C5b-9 forms on the surface of the serum-sensitive S. minnesota S218 in normal human serum, but the formed complex is released and is not bactericidal for S218 because it fails to insert into hydrophobic outer membrane domains.

Blood Bactericidal Activity↗
PubMed1998

A novel ELISA for the evaluation of the classical pathway of complement.

Assessment of the overall function of the classical pathway of complement is traditionally performed by the hemolytic titration assay CH50. In the present study, we established a novel method for the quantitation of complement activity by measuring the deposition of C1q, C4, C3 and C9 on solid-phase IgM by an enzyme-linked immunosorbent assay (ELISA). Using the CH50 method as the reference, C9 deposition values displayed a sensitivity of 96.3% and a specificity of 99.4% in sera from patients with a variety of diseases. For C3, the sensitivity was 91.3% and the specificity 100%, for C4, the values were 95% and 100%, and for C1q the corresponding values were 52.9% and 98.9%. A close correlation was found between CH50 values below 30 U/ml and the deposition of C9 (r = 0.92), C3 (r = 0.91) and C4 (r = 0.92). In two patients with postinfectious glomerulonephritis normal C4 and C1q deposition was accompanied by decreased C3 and C9 deposition reflecting complement activation predominantly through the alternative pathway. In contrast, in two patients with complete C2 deficiency the deposition of C3 and C9 was undetectable together with normal C4 deposition values. Furthermore, in two patients with hereditary C1-inhibitor deficiency distinctly increased C1q deposition was accompanied by decreased C4 deposition values. In conclusion, the determination of complement deposition by ELISA represents a novel, quantitative method for the evaluation of complement activity. The measurement of C9 deposition alone or in combination with further complement proteins makes this ELISA a valuable tool for assessing the degree and level of complement consumption as well as localizing the missing protein in the case of complement deficiencies.

Complement C1q↗
PubMed1975

Immunochemical analyses of membrane-bound complement. Detection of the terminal complement complex and its similarity to "intrinsic" erythrocyte membrane proteins.

(1) Membranes of sheep erythrocytes lysed with antibody and human or rabbit complement were solubilized in non-ionic detergents (Triton X-100 or Berol EMU-043) and analysed immunochemically using antisera directed against individual complement components. The precipitation behaviour of membrane-bound C3, C5, C6 and C9 components of complement was examined by immuno-double diffusion, rocket- and crossed immunoelectrophoresis performed in agarose gels containing 1% non-ionic detergent. (2) Membrane-bound C5, C6 and C9 are antigenically altered compared with the native (serum) components. (3) Immuno-double diffusion in the presence of non-ionic detergents reveals formation of C5-C6-C9 complexes on the membranes; these complexes are stable in non-ionic detergent. No complex formation was detected in serum between native C5, C6 and C9 components. There was also no evidence for complexing between membrane-bound C3, C4 or membrane proteins and the "late-reacting" complement components. (4) The extractability of complement components by various manipulations has been studied by use of quantitative rocket immunoelectrophoresis. Up to 65% of membrane-bound C3 is readily extracted by dialysis of membranes against 1mM EDTA, pH 8.0, 100 mM EDTA, pH 8.0, 1.2 NaCl plus or minus EDTA, by extraction in isotonic buffers at 37 degrees C, by heating at 45 degrees C over several hours, or by treating membranes with 1 mM p-chloromercuribenzoate sulfonate. In contrast, less than 6% of the terminal complement complex can be eluted by any of the described methods or combination of methods. (5) Our data suggest that the terminal complement complex associates with membrane "core" components through apolar interactions.

Animals↗
PubMed1989

Inhibition of immune haemolysis by a serum factor found in C3-deficient subjects.

A serum factor, which inhibits haemolysis of the buffer control used in a C3 haemolytic assay, was found in a C3-deficient subject (C3D). Since the buffer control consisted of EAC142, C5 and C6-9 reagent (C6-9R, prepared by treatment of guinea-pig serum with KSCN and hydrazine hydrate), the factor seems to be an inhibitor of C3-independent immune haemolysis. Gel filtration and CM cellulose column chromatography of C3D serum suggested that the inhibitor may be C8. The inhibition was not observed in C8-depleted C3D serum. Furthermore, isolated C8 was found to inhibit haemolysis of EAC142 by C5 and C6-9R in a dose-dependent fashion. Thus, C8 was found to be an inhibitor of C3-independent immune haemolysis in the assay. Further studies revealed that C8 also inhibits haemolysis of EAC142 by C3, C5 and C6-9R (C3 assay system) or that of EAC1423 by C5 and C6-9R (C5 assay system), indicating that C3 or C5 haemolytic activity can be underestimated by the presence of C8 in a sample. C8 did not inhibit haemolysis in the assay system when isolated C6-C9 of human origin were used, but did inhibit haemolysis when isolated C6-C9 of guinea-pig origin was used instead of C6-9R. Thus, it was suggested that the incompatibility of human C8 with guinea-pig C6-C9 might be responsible for this phenomenon. Additional experiments for the mechanism clearly showed that human C8 inhibits the haemolysis of EAC1-7 (EA bearing human C1-C5 and guinea-pig C6 and C7) by guinea-pig C8 and C9 by binding to EAC1-7 prior to guinea-pig C8.

Animals↗