Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Complement C5b”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMed1996

Evaluation of tissue trauma after laparoscopic and abdominal hysterectomy: measurements of neutrophil activation and release of interleukin-6, cortisol, and C-reactive protein.

BACKGROUND: Trauma and major surgery stimulate a cascade of events that mediate the inflammatory response. The aim of our study was to determine whether or not hysterectomy leads to release of cytokines, cortisol, and C-reactive protein (CRP), activation of neutrophils, and activation of the complement cascade. A further aim was to compare laparoscopic and abdominal hysterectomy with regard to the same parameters. STUDY DESIGN: Twenty-four consecutive patients were randomized to either abdominal (n = 12) or laparoscopic hysterectomy (n = 12). Blood samples were drawn preoperatively, intraoperatively, and then at one minute, 24 hours, and seven days postoperatively. Interleukin-6 (IL-6) levels were used to evaluate cytokine release, cortisol and CRP to evaluate the inflammatory response, and polymorphonuclear (PMN) elastase to detect neutrophil activation. To evaluate complement activation, the terminal C5b-9 complement complex (TCC) was determined. RESULTS: Interleukin-6 concentrations were significantly elevated one minute and 24 hours postoperatively in both groups. Independent of the surgical technique or operative time, the highest IL-6 concentration was reached four hours after beginning the operation. Cortisol levels were significantly elevated during and after the operation in both groups. C-reactive peptide levels were significantly elevated in both groups 24 hours and seven days after the operation. Polymorphonuclear elastase was elevated 24 hours postoperatively in both groups. There were no signs of complement activation during the operative period or postoperatively in either patient group. CONCLUSIONS: Our results indicate serious tissue trauma during both laparoscopic and abdominal hysterectomy. The extent of surgical trauma did not differ between the two operative methods.

C-Reactive Protein↗
PubMed1999

Control of C3b and C5b deposition by CD46 (membrane cofactor protein) after alternative but not classical complement activation.

C3b and C5b deposition following complement activation, and its regulation by CD46 were studied using xenogenic Chinese hamster ovary (CHO) cells as targets and cytofluorometry. Following activation of the alternative pathway, an initial low level of C3b deposition was observed on CHO cell surfaces after a lag time of approximately 4 min. This was followed by a secondary high level of C3b deposition with a slower rate. C3b deposition was maximal within 15 min. When CD46 was expressed (B2 isoform), the kinetics of C3b deposition were essentially unchanged, but the onset of the secondary high C3b deposition was fully prevented. C5b deposition was also observed on CHO but not on CHO.CD46 cells following activation of the alternative pathway. Activation of the classical pathway on CHO and CHO.CD46 cells, using factor B-depleted human serum and anti-CHO antibodies, resulted in almost identical single-peak C3b deposition profiles. Accordingly, no regulation of C5b deposition by CD46 was evident following activation of the classical pathway. These data indicate that CD46 prevents the C3b deposition amplification loop mediated by the alternative C3 convertase and, consequently, inhibits the formation of the alternative C5 convertase. But CD46 prevents neither the spontaneous tick-over C3b deposition leading to the formation of the alternative C3 convertase nor the formation of the functional classical C3 and C5 convertases.

Animals↗
PubMed1982

Complement activation in muscle fiber necrosis: demonstration of the membrane attack complex of complement in necrotic fibers.

The membranolytic C5b-9 complement membrane attach complex (MAC) is assembled after activation of either the classic or the alternative complement pathway. The quaternary configuration of the MAC macromolecule presents neoantigenic determinants not present on precursor molecules. Consequently, antibodies specific for these neoantigen(s) do not detect nonspecifically bound native complement precursors of MAC. By means of antibodies rendered specific for MAC neoantigen(s), MAC was localized by the immunoperoxidase reaction in cryostat sections of human muscle. In 66 biopsy specimens containing necrotic muscle fibers (Duchenne dystrophy, 13; other dystrophies, 15; inflammatory myopathies, 31; miscellaneous myopathies, 7) all of the necrotic fibers reacted for MAC neoantigen(s). C3 and C9 were also consistently localized in necrotic fibers, but localization of C1q, C4, and IgG was variable and often did not exceed background staining. None of the nonnecrotic fibers reacted for immunoglobulin or complement. Detection of MAC neoantigen(s) in necrotic fibers in a wide variety of muscle disease unambiguously shows that (1) the lytic complement pathway is consistently activated and participates in muscles fiber necrosis in vivo, and (2) complement reaction products are generated than can stimulate cellular infiltration and phagocytosis of the necrotic fiber. The findings also suggest that cell necrosis in general may involve participation of complement.

Antigens↗
PubMed1987

Activation of the human terminal complement pathway in atherosclerosis.

The presence of the terminal C5b-9 complement complex in tissues indicates that complement activation has occurred in situ with subsequent membrane damage, tissue injury, and inflammatory response mediation. The terminal C5b-9 neoantigens of the complement system, S protein C3c, C3d, and apolipoprotein B deposits were localized in 20 aortic fibrous plaques, 12 aortic intimal thickenings, 8 aortic fatty streak intimae, 14 coronary fibrous plaques, 5 coronary intimal thickenings, and 8 femoral fibrous plaques, using an indirect and double-staining immunoperoxidase technique. The specific granular deposits were present from the early to the advanced stages of atherosclerosis in relation to the degree of fibrosis and necrosis. The different double-staining localization of C5b-9 and S protein may suggest local assembly of the complex as a consequence of complement activation and may sustain its role in the chronic progression of atherosclerosis.

Aorta↗
PubMed1992

Persistent complement activation on tumor cells in breast cancer.

The neoantigens of the C5b-9 complement complex, IgG, C3, C4, S-protein/vitronectin, fibronectin, and macrophages were localized on 17 samples of breast cancer and on 6 samples of benign breast tumors using polyclonal or monoclonal antibodies and the streptavidin-biotin-peroxidase technique. All the tissue samples with carcinoma in each the TNM stages presented C5b-9 deposits on the membranes of tumor cells, thin granules on cell remnants, and diffuse deposits in the necrotic areas. When chemotherapy and radiation therapy preceded surgery, C5b-9 deposits were more intense and extended. The C5b-9 deposits were absent in all the samples with benign lesions. S-protein/vitronectin was present as fibrillar deposits in the connective tissue matrix and as diffuse deposits around the tumor cells, less intense and extended than fibronectin. IgG, C3, and C4 deposits were present only in carcinoma samples. The presence of C5b-9 deposits is indicative of complement activation and its subsequent pathogenetic effects in breast cancer.

Blood Proteins↗
PubMed1981

Effect of agents that produce membrane disorder on lysis of erythrocytes by complement.

To evaluate the effect of membrane lipid acyl-chain packing on the efficiency of cell lysis by complement, we have studied membrane modulation by 2-(2-methoxy)-ethoxyethyl-8-(cis-2-n-octylcyclopropyl)-octanoate (A2C) and by myristoleyl alcohol, the cis isomer of a C14:1 aliphatic alcohol. These substances are known to increase the membrane lipid disorder by virtue of the bend in their acyl chains, which is believed to loosen the phospholipid acyl-chain packing. We have found that both of these compounds markedly enhance the lysis of erythrocytes by the terminal complement proteins C5b-9. The enhancing effect by A2C is operative in the formation of erythrocytes carrying complement components C5b, C6, and C7, as well as in the subsequent reactions with complement components C8 and C9. We have also found that A2C-treated erythrocytes bind C5b6 to a measurable extent, whereas untreated erythrocytes do not. We attribute this to a shift in the partition equilibrium of C5b6 toward membrane association, which would improve lytic efficiency. The increase of membrane lipid disorder by these agents would also be expected to increase insertion of hydrophobic peptides from C7, C8, and C9, with consequent gain in lytic efficiency. Treatment of erythrocytes with sublytic doses of NaDodSO4, or Triton X-100 did not enhance lysis by C5b-9 appreciably, suggesting that enhancement of lysis by C5b-9 is not a general property of amphiphiles.

Complement C5↗
PubMed1996

S-protein/vitronectin interaction with the C5b and the C8 of the complement membrane attack complex.

S-protein/vitronectin participates in the regulation of complement-mediated lysis by incorporating into the membrane attack complex C5b-9. Subsequently, soluble SC5b-7 and SC5b-9 macromolecules are not inserted into the membrane lipid bilayer nor induce lytic pore formation. Using a dot blot binding assay, it was determined that soluble S-protein/vitronectin interacted with immobilized C5b and C8 among the five separately immobilized components (C5b, C6, C7, C8, C9) of the membrane attack complex. Those interactions imply a new model of the formation of the complement membrane attack complex and its regulation by S-protein/vitronectin.

Animals↗
PubMed1982

Terminal membrane C5b-9 complex of human complement: transition from an amphiphilic to a hydrophilic state through binding of the S protein from serum.

The membrane-damaging C5b-9(m) complex of complement is a cylindrically structured, amphiphilic molecule that is generated on a target membrane during complement attack. Isolated C5b-9(m) complexes are shown here to possess the capacity of binding a protein, termed "S"-protein, that is present in human plasma. Binding of this protein apparently shields the apolar surfaces of C5b-9(m), since the resulting "SC5b-9(m)" complex is hydrophilic and no longer aggregates in detergentfree solution. Dispersed SC5b-9(m) complexes exhibit an apparent sedimentation coefficient of 29S in sucrose density gradients, corresponding to a molecular weight of approximately 1.4 million. SDS PAGE analyses indicate binding of 3-4 molecules of S-protein per C5b-9(m) complex. These data are consistent with a monomer nature and molecular weight of 1-1.1 million of the C5b-9(m) complex. Ultrastructural analysis of SC5b-9(m) shows preservation of the hollow cylindrical C5b-9(m) structure. Additional material, probably representing the S-protein itself, can be visualized attached to the originally membrane-embedded portion of the macromolecule. The topography of apolar surfaces on a molecule thus appears directly probed and visualized through the binding of a serum protein.

Complement System Proteins↗
PubMed1990

H19, a surface membrane molecule involved in T-cell activation, inhibits channel formation by human complement.

Here we compare the properties of leukocyte antigens H19 and CD59 with those of the PI-linked 18,000-20,000 Mr molecules which inhibit lysis of human cells by the autologous terminal complement components C5b-9. H19, a 19,000 Mr protein found on human erythrocytes, monocytes, neutrophils, T-lymphocytes and other cells, is one of the ligands involved in the spontaneous rosette formation between human T-lymphocytes and erythrocytes. Recent evidence indicates that H19 also participates in T-cell activation. CD59 is a widely distributed 18,000-25,000 Mr protein anchored to the cell membrane by phosphatidylinositol (PI). The function of CD59 is unknown. Affinity-purified H19 incorporates into cell membranes and inhibits channel formation by human C5b-9 on guinea pig erythrocytes. Significant inhibition is achieved with picogram quantities of H19, corresponding to approximately 600 molecules per erythrocyte. H19 is most effective when C9 is limiting but quite active when C5b-7 or C8 are limiting, indicating that it may interact with several of the structurally related terminal complement components. The inhibitory activity is blocked by mAbs to either CD59 or to H19. H19 is PI-anchored: it is released from the cell membrane by treatment with PI-specific phospholipase C, and it is absent from cells from a patient with paroxysmal nocturnal hemoglobinuria (PNH). Analysis of PNH erythrocytes after treatment with terminal complement proteins shows that the H19-negative erythrocytes are more susceptible to C5b-9-mediated lysis. Treatment of normal human erythrocytes with either anti-H19 or anti-CD59 renders them more susceptible to lysis by human C5b-9. We conclude that H19 and CD59 are probably the same molecule and are identical or closely related to the recently described inhibitors of C5b-9 channel formation.

Antibodies, Monoclonal↗
PubMed1988

The structure of human complement component C7 and the C5b-7 complex.

The molecular architecture of human complement component C7 was elucidated at several structural levels. The complete primary structure of C7 was derived from the cDNA sequence of clones isolated from a human liver library. C7 is a mosaic protein that consists of 821 amino acids. The amino-terminal two-thirds of C7 has 23-30% homology with complement components C8 and C9. In addition, the carboxyl-terminal third contains four cysteine-rich segments that have overlapping internal homology. The protein is a single polypeptide chain with 28 disulfide bonds and is glycosylated at two sites. Virtually all the cysteines are found in small units of 35-77 amino acids that exhibit homology with those of various proteins including the low density lipoprotein receptor, epidermal growth factor precursor, thrombospondin, and blood coagulation factors IX and X. The secondary structural analysis, estimated by circular dichroism, suggested a high content of beta-sheet (38%) and beta-turns (24%). The tertiary structure, visualized by transmission electron microscopy, indicated a flexible elongated molecule with dimensions of 151 X 59 X 43 A. The quaternary structure of the C5b-7 complex bound to lipid vesicles was observed to be in the form of monomers or dimers. The monomer C5b-7 consists of a leaflet and a long flexible stalk, and the dimer has two leaflets linked through a supercoiled stalk. Membrane binding is mediated by the stalk part of the complexes. Using a radioiodinated photoreactive cross-linking reagent bound to the polar head group of phosphatidylethanolamine, the stalk part of the C5b-7 complex could be labeled preferentially, and it was found to consist mainly of C6 and C7. Thus, C7 plays a major role in bringing about the hydrophilic-amphiphilic transition during the formation of the membrane attack complex, and it serves as a membrane anchor for the C5b-7 complex.

Amino Acid Sequence↗
PubMed1999

Increased susceptibility to erythrocyte C5b-9 deposition and complement-mediated lysis in chronic renal failure.

BACKGROUND: Decreased red blood cell survival contributes to the anemia of chronic renal failure patients. Because patients on chronic dialysis therapy are frequently exposed to excessive complement activation, we investigated the susceptibility of this patient population to erythrocyte C5b-9 deposition, complement-mediated lysis, and ghost formation. METHODS: We developed a flow cytometric assay using antibodies to both glycophorin and the C5b-9 complex to detect C5b-9 deposition on intact erythrocytes and erythrocyte ghosts. Serum C5b-9 levels and C5b-9 deposition on erythrocyte ghosts were measured by enzyme-linked immunosorbent assay. RESULTS: A significant increase in C5b-9 deposition on intact erythrocytes was demonstrated in patients with advanced chronic renal failure (2.2 +/- 0.5%) and in patients on chronic maintenance hemodialysis (2.3 +/- 0.4%) compared with normal volunteers (0.9 +/- 0.1%, P = 0.005 vs. chronic renal failure, P < 0.001 vs. chronic hemodialysis patients). There was also a significantly higher percentage of C5b-9-positive erythrocyte ghosts in patients with advanced chronic renal failure (20.6 +/- 5%) and in chronic hemodialysis patients (15.5 +/- 3.1%) compared with normal controls (2.6 +/- 0.9%, P < or = 0.001 vs. advanced chronic renal failure and chronic hemodialysis patients). Treatment of erythrocyte preparations with cobra venom factor, which activates the complement cascade, resulted in dramatic increases in the percentages of C5b-9-positive erythrocyte ghosts in patients with chronic renal failure (49.9 +/- 6.9%) and in chronic hemodialysis patients (45.0 +/- 4.2%) compared with normal volunteers (22.3 +/- 2.7%, P < 0.001 vs. chronic renal failure and chronic hemodialysis patients). Erythrocyte membrane expression of the complement regulatory proteins CD59 and CD55 did not significantly differ between normal controls and hemodialysis patients. Plasma C5b-9 levels after cobra venom factor stimulation were higher in chronic renal failure patients (538 micrograms/ml) compared with normal controls (345 micrograms/ml, P < 0.001). CONCLUSIONS: Patients with chronic renal failure and on hemodialysis therapy are susceptible to erythrocyte C5b-9 deposition with subsequent lysis and ghost formation. Susceptibility to complement-mediated erythrocyte injury may contribute to the anemia of chronic renal disease.

Cell Survival↗
PubMed1984

Mechanism of bacterial resistance to complement-mediated killing: inserted C5b-9 correlates with killing for Escherichia coli O111B4 varying in O-antigen capsule and O-polysaccharide coverage of lipid A core oligosaccharide.

The interaction of C3 and terminal complement components with three isogenic strains of Escherichia coli O111B4 varying in outer membrane and capsule composition was examined. Strains CL99 and 1-1, which possess O-antigen capsule and 74 to 77% coverage of lipid A core oligosaccharide, were sensitive to killing in pooled normal human serum (PNHS) or magnesium ethylene glycoltetraacetic acid PNHS in the presence but not the absence of antibody, although 1-1 contained 35% more lipopolysaccharide than CL99 and was slightly less sensitive to alternative pathway killing. In contrast, strain 1-2 lacks O-antigen capsule but contains 84% coverage and resists serum killing in the presence and absence of antibody in both PNHS and magnesium ethylene glycoltetraacetic acid PNHS. All three strains consumed C3 and C9 when incubated in PNHS, but consumption was most rapid with 1-2, which also bound the largest number of C3 molecules per CFU. Between 15 X 10(3) and 24 X 10(3) molecules of C9 per CFU bound to CL99 and 1-1 during incubation in 10% PNHS or 10% magnesium ethylene glycoltetraacetic acid PNHS, and binding was relatively stable. Binding and release of 3 X 10(3) to 8 X 10(3) molecules of C9 per CFU was observed for strain 1-2. The majority of C9 bound to CL99 and 1-1 in the presence of antibody distributed with the outer membrane after lysis of the organisms in a French press, whereas only 16.1 to 20.1% of C9 was deposited on these organisms in the absence of antibody, and 31.5 to 39.8% of C9 on strain 1-2 with or without antibody sedimented with the outer membrane. Between 4.6 X 10(3) and 5.5 X 10(3) molecules of C9 per CFU remained bound in a salt- and trypsin-resistant form to the outer membrane of organisms that were killed, whereas fewer than 1.4 X 10(3) molecules of C9 per CFU were bound to the outer membrane of organisms not killed by serum. These results indicate that C5b-9 that is bound to the outer membrane of E. coli O111B4 in a form resistant to salt or protease elution correlates with bacterial killing.

Antigens, Bacterial↗
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↗
PubMed1983

Studies on the mechanism of bacterial resistance to complement-mediated killing. III. C5b-9 deposits stably on rough and type 7 S. pneumoniae without causing bacterial killing.

Gram-positive cocci resist direct killing by serum. The mechanism of resistance was studied by measuring consumption of terminal complement components from serum and uptake of purified, radiolabeled C7 and C9 on rough and encapsulated type 7 Streptococcus pneumoniae. Extensive consumption of C5, C7, and C9 occurred when 5 X 10(8) rough or type 7 pneumococci were incubated for 1 hr in 10% pooled normal human serum (PNHS). Approximately 10,000 molecules of C7 and C9 bound per organism during the same period of incubation. Twenty to 30% of C7 and C9 was released from rough organisms. Release was not due to autolysis since it occurred with glutaraldehyde-fixed organisms as well as in S. pneumoniae that were rendered resistant to autolysis by growth in ethanolamine. Between 10 and 30% of bound 125IC9 counts were eluted from the rough and type 7 organisms by incubation in 1 M NaCl or 0.01 M EDTA, which suggests that bound C5b-9 was not attached by predominantly ionic interactions. Elution of 44 to 74% of 125IC9 from live and glutaraldehyde-fixed organisms by 1% sodium deoxycholate suggests that hydrophobic bonds are involved in C5b-9 attachment. Trypsin cleaved 67 and 55% of 125IC9 counts from live rough and type 7 S. pneumoniae, respectively which indicates that the bound complex is not protected by the cell wall from proteolytic attack. Serum resistance in S. pneumoniae does not represent a failure to form C5b-9 on the bacterial cell wall but apparently reflects a failure of the bound complex to penetrate the thick peptidoglycan layer.

Blood Bactericidal Activity↗
PubMed1994

Complement system activation during orthotopic liver transplantation in man. Indications of peroperative complement system activation in the gut.

Sixteen patients with acute and chronic liver disease undergoing OLT were studied regarding the role of the liver and the gut in complement activation. Also, the relation between complement activation and clinical manifestations during the liver transplantation reperfusion period was investigated. Blood samples for measurement of complement anaphylatoxin C3a (C3a), complement anaphylatoxin C5a (C5a), and terminal C5b-9 complement complex (TCC) were taken simultaneously from the central venous catheter and the radial arterial line before starting the operative procedure, 1 min before declamping, and 1-2 min, 5 min, 30 min and 6-12 hr after declamping. Simultaneous blood sampling from the radial arterial line, central venous catheter, portal vein, and hepatic vein was performed 1-2 min and 5 min after completed unclamping. Elevated plasma levels of C3a and TCC were found upon reperfusion, while C5a levels remained unchanged throughout the operation compared with the preoperative levels. The levels of C3a in the portal vein were higher compared with the levels in the simultaneously obtained samples from the radial artery. The results indicate complement cascade activation located to the gut during the reperfusion phase of OLT. Seventy-five percent of the patient studied suffered from the postreperfusion syndrome, indicated by profound hypotension upon reperfusion of the transplanted liver. There was a significant correlation between high concentration of C3a anaphylatoxin and development of profound hypotension.

Adult↗
PubMed1991

Formation of ion-conducting channels by the membrane attack complex proteins of complement.

The effects of sequential additions of purified human complement proteins C5b-6, C7, C8, and C9 to assemble the C5b-9 membrane attack complex (MAC) of complement on electrical properties of planar lipid bilayers have been analyzed. The high resistance state of such membranes was impaired after assembly of large numbers of C5b-8 complexes as indicated by the appearance of rapidly fluctuating membrane currents. The C5b-8 induced conductance was voltage dependent and rectifying at higher voltages. Addition of C9 to membranes with very few C5b-8 complexes caused appearance of few discrete single channels of low conductance (5-25 pS) but after some time very large (greater than 0.5 nS) jumps in conductance could be monitored. This high macroscopic conductance state was dominated by 125-pS channels having a lifetime of approximately 1 s. The high conductance state was not stable and declined again after a period of 1-3 h. Incorporation of MAC extracted from complement-lysed erythrocytes into liposomes and subsequent transformation of such complexes into planar bilayers via an intermediate monolayer state resulted in channels with characteristics similar to the ones produced by sequential assembly of C5b-9. Comparison of the high-conductance C5b-9 channel characteristics (lifetime, ion preference, ionic-strength dependence) with those produced by poly(C9) (the circular or tubular aggregation product of C9) as published by Young, J.D.-E., Z.A. Cohn, and E.R. Podack. (1986. Science [Wash. DC]. 233:184-190.) indicates that the two are significantly different.

Animals↗
PubMed1996

Influence of the terminal complement-complex on reperfusion injury, no-reflow and arrhythmias: a comparison between C6-competent and C6-deficient rabbits.

OBJECTIVE: The complement system has been suggested to play a role in reperfusion injury which may result from an enhanced destruction of myocardial tissue or from an impairment of reflow. We investigated the influence of the C5b-9 complement complex on infarct size, reflow and arrhythmogenesis. METHODS: Twenty-eight C6-competent rabbits and 18 rabbits with congenital C6 deficiency were subjected to either 30 min or 2 h of coronary artery occlusion followed by reperfusion. C6 deficiency was confirmed by the complement titration test and immunohistology. The triphenyl tetrazolium chloride method was used to delineate infarct size. Reflow into infarcted areas was evaluated histologically after an in vivo injection of propidium iodide which served as an early fluorescence microscopic marker of damaged myocardium subjected to reflow. Continuous ECG monitoring allowed the recording of arrhythmias. RESULTS: After 30 min of coronary artery occlusion infarct size was significantly smaller in C6-deficient rabbits (5.0 +/- 2% of the risk region) as compared to C6-competent rabbits (28.4 +/- 8.5%, P = 0.0371). The extent of reflow into damaged myocardium was nearly the same in both animal groups at this time (38 +/- 9 vs. 39 +/- 7% of the risk region). After 2 h of coronary artery occlusion, infarct size was not different between both animal groups, but the extent of reflow into damaged myocardium was significantly smaller in C6-competent rabbits than in C6-deficient rabbits (25 +/- 4 vs. 40 +/- 4%; P = 0.0185). Two of the 18 C6-deficient rabbits had ventricular arrhythmias (Lown II-IV), none of which was fatal. Eleven of the 28 C6-competent animals had major ventricular arrhythmias which were fatal in 6 rabbits. CONCLUSIONS: These results suggest that the lytic C5b-9 complement complex leads to reperfusion injury in the early phase (30 min) of ischaemia, resulting in a larger infarct. After 2 h of ischaemia, complement activation enhances the no-reflow phenomenon but does not affect infarct size. Finally, the C6 status seems to influence the susceptibility to ventricular arrhythmias after coronary artery occlusion, independent of reperfusion.

Animals↗
PubMed1986

Functional C8 associated with human platelets.

Haemolytic assay for C8 revealed its association in functionally active form with washed human platelets. Platelet-bound C8 haemolytic activity was inhibited by F(ab')2 anti-C8 and was undetectable in the platelet suspension obtained from three C8 deficient patients. Incubation of platelets from C8 deficient individuals in normal plasma did not restore C8 haemolytic activity, indicating that platelets do not absorb C8 from plasma in vitro during platelet preparation. Thrombin, a mediator of the platelet release reaction, did not induce the release of C8 from normal platelets. Conversely, lysis of EAC1-7.9 by platelet bound C8 was not accompanied by release of beta-thromboglobulin or serotonin from the platelets. C8 was detected in a homogenate prepared from platelets as well as in the supernatant collected after high speed centrifugation of the homogenate. The association of C8 with platelets as an individual component rather than as part of the C5b-9 membrane-attack complex was supported by the following evidence: platelet bound C8 eluted from a Sephacryl S-200 column at the same volume as C8 from normal human serum; F(ab')2 anti-C8, but not F(ab')2 anti-C5, inhibited platelet C8 activity; the platelet homogenate, which lysed EAC1-7.9, had no effect on EAC43 which are susceptible to the lytic activity of the C5b-9 complex.

Blood Platelets↗