Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Complement Membrane Attack Complex”

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 1,531 records · Page 85Linked to original sources
PubMed1991

Activation of human complement by IgG antisperm antibody and the demonstration of C3 and C5b-9-mediated immune injury to human sperm.

To investigate the role of C in the pathogenesis of antisperm antibody (ASA)-mediated infertility, we evaluated the binding and biologic effects of antisperm IgG and autologous C on human sperm. A flow cytometric assay using motile sperm as a target for IgG ASA+ (n = 30) and ASA- (n = 5) sera was developed for the concomitant detection of sperm-bound IgG and the initial (C3d) and terminal (C5b-9) C components on the surface of human sperm. Of the 30 IgG ASA+ sera evaluated by flow cytometry, 15 (50%) and 22 (73.3%) sera were also positive for sperm-bound C3d and C5b-9, respectively. Monomeric IgG purified from C-fixing ASA+ serum was able to bind to sperm and induced deposition of C3 on the sperm surface in the presence of human C. Incubation of motile sperm with C-fixing immune sera resulted in a significant loss (43 to 87%) of motility associated with characteristic C5b-9-induced alterations in sperm morphology leading ultimately to sperm lysis. When motile sperm were cocultured with purified polymorphonuclear leukocytes (PMN) in the presence of C-fixing immune sera, the binding of sperm heads to the PMN resulted in the formation of sperm rosettes, whereas non C-fixing or control sera had no such effect. Transmission electron microscopy of thin sections of the rosettes revealed ingestion of the sperm by the human PMN. These data suggested that 1) antibody bound to sperm is capable of activating autologous C by the classical pathway; 2) binding of both IgG and C proteins initiates C3-mediated sperm binding to PMN and sperm inactivation by deposition of membrane attack complex (MC5b-9) of C; and 3) concomitant detection of sperm-bound IgG, C3d, and C5b-9 may serve as an indicator of C-fixing cytotoxic ASA in the sera of infertile couples.

Autoantibodies↗
PubMed1996

Determinants of activation by complement of group II phospholipase A2 acting against Escherichia coli.

Prompt killing of many strains of Escherichia coli during phagocytosis in vitro by isolated polymorphonuclear leukocytes (PMN) requires the presence of nonlethal doses of nonimmune serum (B. A. Mannion, J. Weiss, and P. Elsbach, J. Clin. Invest. 86:631-641, 1990). Because this requirement is bypassed in a phospholipase A (PLA)-rich mutant (pldA ) of E. coli, we have examined the effect of serum on bacteria] phospholipid (PL) degradation during phagocytosis of wild-type (pldA+) and PLA-deficient (pldA) E. coli. In parallel with increased killing, nonlethal doses of serum increased the degradation of prelabeled bacterial PL during phagocytosis by two- to fivefold, to nearly the same levels (ca. 50 to 60%) as those produced during phagocytosis of E. coli pldA in the absence of serum. The effects on the E. coli pldA mutant imply that there is a serum-mediated enhancement of granule-associated group II PMN PLA2 activity. At the same doses, serum promoted action against E. coli in the presence of purified rabbit and human group II PLA2 but did not activate bacterial PLA. Related PLA2s that lack specific structural determinants needed for optimal activity against E. coli treated with the bactericidal/permeability-increasing protein (BPI) of PMN are also less active than wild-type group II PLA2 against serum-treated E. coli. Treatment of E. coli with C7- or C9-depleted serum did not enhance bacterial killing or PL degradation during phagocytosis or the action of purified PLA2. In summary, these findings suggest that (i) nonlethal assemblies of the membrane attack complex promote intracellular killing and destruction of E. coli ingested by PMN, in part by promoting the action of granule-associated PLA2 against ingested bacteria, and (ii) structural determinants first implicated in PLA2 action against BPI-treated E. coli are also important in PLA2 action in concert with other host defense systems, such as complement.

Animals↗
PubMed2002

Molecular bases for human complement C7 polymorphisms, C7*3 and C7*4.

Complement C7 is one of the components of membrane attack complex (MAC) generated by the terminal complement cascade. C7 protein is polymorphic and most of its polymorphisms have been identified using isoelectric focusing (IEF), which detects protein charge differences. To date, the molecular bases of the polymorphisms detected by IEF have not been determined. In this paper, we describe the structural bases of two C7 IEF-detected polymorphisms, C7*3 and C7*4, both of which are common in Asian populations. C7*3 resulted from substitution of cysteine (Cys) at amino acid residue 106 by charged arginine (Arg; C106R), while charged lysine (Lys) at amino acid residue 398 was replaced by neutral glutamine (Gln; K398Q) in C7*4. As C7*3 is hypomorphic, it is important to study its possible associations with diseases such as immunological disorders and infections. We present genetic bases for this C7 polymorphism, which we determined using polymerase chain reaction (PCR)-based genotyping, a simple and accurate method suitable for large-scale studies.

Base Sequence↗
PubMed2005

Activation/inactivation of the classical pathway of complement in non-lesional skin of patients with systemic lupus erythematosus.

BACKGROUND: The link between the lupus band and pathogenesis remains controversial, because immunoglobulins and complement components, including the membrane attack complex, can be found in both lesional and non-lesional skin of patients with systemic lupus erythematosus (SLE). The expression of proteins that regulate complement has not been previously investigated in the skin of patients with SLE. AIM: The aim of this study is to compare the expression of protectin (CD59), which demonstrates the activation of the classical pathway of complement, in non-lesional skin obtained from patients with SLE with its expression in normal skin. This may help us explain the link between the lupus band and pathogenesis of cutaneous lupus erythematosus. METHODS: An indirect immunofluorescence technique was performed in order to provide unequivocal evidence for the activation of complement via the classical pathway and to compare the expression of CD59 in non-lesional skin from patients with SLE with normal skin samples obtained from healthy people. RESULTS: The activation of the classical pathway of complement was demonstrated in non-lesional skin in more than 90% of SLE patients investigated in this study. Staining intensity of the complement regulatory protein CD59 was markedly increased in the majority of non-lesional skin samples obtained from patients with SLE, compared to that from normals. CONCLUSIONS: CD59 is overexpressed in non-lesional skin in which complement activation has occurred. It seems likely that an increased and continuous CD59 expression may be important for maintaining the integrity of the skin BMZ during inflammatory responses involving complement activation in SLE skin. Alahlafi A, Wordsworth P, Wojnarowska F. Activation/inactivation of the classical pathway of complement in non-lesional skin of patients with systemic lupus erythematosus.

CD59 Antigens↗
PubMed2001

The supportive role of complement in HIV pathogenesis.

This review focuses on interactions of HIV with the first-line defence of native immunity, the complement system. In all body compartments tested so far, HIV meets complement. Activation of the complement system results in deposition of C3 fragments on the viral surface, but in contrast to other pathogens, most of HIV is not or is only poorly lysed by membrane attack complexes. To survive complement-mediated lysis, HIV has not only developed resistance mechanisms, but uses opsonisation with complement fragments for its own advantage. Opsonised virions interact with complement receptor-expressing cells, which are either subsequently infected with high efficiency or retain viral particles on their surface, which promotes transmission of virus to other permissive cells. Our knowledge of these mechanisms has increased enormously over the past few years. A complete understanding of these complex interactions of HIV with the complement system opens new perspectives for development of alternative therapeutic strategies.

AIDS Dementia Complex↗
PubMed1994

Assessment of soluble adhesion molecules (sICAM-1, sVCAM-1, sELAM-1) and complement cleavage products (sC4d, sC5b-9) in urine. Clinical monitoring of renal allograft recipients.

Increasing evidence exists that inducible adhesion molecules are involved in cell-mediated allograft rejection. In addition, complement activation during rejection has been described. This study investigated, whether specific molecules derived from either pathway are excreted into urine during rejection and whether they can provide useful diagnostic tools for the monitoring of renal transplant recipients. Urinary concentrations of soluble adhesion molecules (sICAM-1, sVCAM-1, sE-selectin) and of complement cleavage products (sC4d and sC5b-9), were determined by standardized ELISA in 30 normal controls and 80 samples from 49 recipients of renal allografts. In contrast to the low amounts of adhesion molecules and complement components uniformly excreted by healthy persons (group 0), marked differences were observed among allograft recipients. To prove the clinical relevance of these differences in excretion, patient samples were assigned to 5 categories according to clinical and histopathological criteria: group I--acute steroid-resistant rejection (n = 10); group II--acute steroid-sensitive rejection (n = 10); group III--chronic rejection (n = 23); group IV--stable graft function (n = 27); and group V--miscellaneous disorders (n = 10), including infections, CsA overdoses, and glomerulonephritis. Urinary levels of sICAM-1, sVCAM-1, and sC4d were significantly higher in group I compared with all other groups (P < 0.01). The difference in sICAM-1 excretion between groups III and IV also reached statistical significance (P < 0.05). Urinary concentrations of sICAM-1, sVCAM-1, and sC4d were reflective of their histological distribution in corresponding graft biopsies. None of the patients excreted E-selectin in detectable amounts. Excretion of the terminal membrane attack complex C5b-9 was not significantly associated with any diagnosis. It is concluded that for clinical purposes the combined evaluation of sICAM-1, sVCAM-1, and sC4d is most useful and can provide valuable information with regard to the severity and the type of allograft rejection.

Cell Adhesion Molecules↗
PubMed1996

Complement-binding proteins are strongly expressed by human preimplantation blastocysts and cumulus cells as well as gametes.

Human preimplantation embryos, gametes and cumulus cells were studied for expression of the complement-binding proteins CD46 (membrane cofactor protein), CD55 (decay accelerating factor) and CD59 (membrane attack complex inhibitory factor) as well as complement receptors type 1 (CRI), type 2 (CR2) and type 3 (CR3). Both the CD55 and CD59 glycosyl phosphatidylinositol (GPI)-anchored proteins were expressed by the plasma membrane and zona pellucida of oocytes, early embryos and expanded preimplantation blastocysts; in contrast, CD46 was expressed only on the plasma membrane. Cumulus cells consistently expressed CD46 and, most strongly, CD59 whereas CD55 expression was variable. Monoclonal antibodies (mAbs) to CRI, CR2 and CR3 epitopes gave only occasional reactivity on oocytes and were unreactive with blastocysts, spermatozoa and cumulus cells. CD46 is expressed only on the spermatozoal inner acrosomal membrane, and CD59 on the plasma membrane; CD55 expression was confirmed on the plasma membrane as well as the inner acrosomal membrane. Control mAbs specific for factor H were usually unreactive with gametes, blastocysts and cumulus cells. These data support the concept that gametes and early embryonic cells are protected from complement-mediated attack by expression of CD46, CD55 and CD59, although these complement-binding proteins may have additional roles in reproductive events.

Acrosome↗
PubMed2002

Marked activation of complement and leukocytes and an increase in the concentrations of soluble endothelial adhesion molecules during cardiopulmonary resuscitation and early reperfusion after cardiac arrest in humans.

OBJECTIVE: Animal studies have demonstrated that reperfusion disorders occurring after cardiac arrest affect outcome. Reperfusion injury can be caused by activation of complement, polymorphonuclear leukocytes (PMN), and PMN-endothelial interaction. We studied different specific markers of these processes during and after cardiopulmonary resuscitation in humans. DESIGN: Prospective clinical trial. SETTING: University hospital. PATIENTS: A total of 55 patients who underwent out-of-hospital cardiopulmonary resuscitation for nontraumatic causes. INTERVENTIONS: Blood samples were drawn immediately, 15 mins, and 30 mins after initiation of cardiopulmonary resuscitation. In the case of restoration of spontaneous circulation, additional blood samples were taken at serial time points until 7 days after cardiac arrest. MEASUREMENTS AND MAIN RESULTS: A marked activation of complement and PMN was found in all patients investigated. Serum concentrations of specific activation markers of the complement system, anaphylatoxin C3a and the soluble membrane attack complex SC5b-9, and PMN elastase were increased during cardiopulmonary resuscitation and for </=48 hrs after restoration of spontaneous circulation. Compared with controls at 30 mins after initiation of cardiac massage, concentrations of C3a, SC5b-9, and PMN elastase were increased in patients without and in those with restoration of spontaneous circulation. PMN elastase concentrations were significantly greater in patients without restoration of spontaneous circulation than in those who could be stabilized. In addition, the plasma concentrations of the soluble P-selectin were significantly increased between 15 mins and 24 hrs after the start of cardiopulmonary resuscitation. The concentrations of soluble intercellular adhesion molecule-1 were increased between 2 hrs and 72 hrs. CONCLUSIONS: Our data clearly demonstrate a marked activation of complement and PMN and an increased PMN-endothelial interaction during cardiopulmonary resuscitation and early reperfusion after cardiac arrest in humans. These changes are known to induce reperfusion disorders and tissue injury and point to new therapeutic options to improve outcome after cardiac arrest.

Aged↗
PubMed2005

The pathology of multiple sclerosis is location-dependent: no significant complement activation is detected in purely cortical lesions.

Complement activation is known to occur in white matter multiple sclerosis (MS) lesions. It is thought to mediate oligodendrocyte/myelin damage and to be a marker of pathologic heterogeneity among individuals. Less is known about complement deposition in the gray matter in MS. The aim of this study was to characterize the presence and distribution of complement activation products in cortical MS lesions. Immunohistochemical staining was performed on cryostat sections from the brains of 22 MS patients and 5 nonneurologic control patients obtained at autopsy. Deposition of the complement activation products C1q, C3d, and C5b-9 (membrane attack complex) was detected on and within macrophages/microglia and astrocytes and in blood vessel walls in white matter MS lesions. C3d and C4d were detected along myelin sheaths at the edge of the lesions. In the gray matter part of combined gray matter/white matter lesions complement activation was less frequent, but increased immunopositivity was detected for C3d on blood vessels, and for C3d and C4d on myelin at the border of lesions, when compared with control areas. In contrast, in the purely cortical lesions, the extent of complement deposition in general was low. In conclusion, the role of complement in MS pathogenesis seems lesion location-dependent.

Adult↗
PubMed1989

Deposition of complement activation products on plastic-adsorbed immunoglobulins. A simple ELISA technique for the detection of defined complement deficiencies.

The activation of complement components in human serum has been studied using immunoglobulins adsorbed to microtiter plates. The sequential deposition of complement fragments was detected by a series of mono- and polyclonal antibodies in an indirect enzyme-linked immunosorbent assay (ELISA). Antibodies against C1q, C1s, C4b/d, C3b/d, factor B, C5b-9 membrane attack complex (MAC), the regulatory complement proteins C4 binding protein (C4bp) and properdin were reactive. Several lines of evidence suggest that complement activation was via the classical pathway: (1) complement activation was highly isotype-restricted with regard to the adsorbed Igs (human IgG1 and IgG3 as well as mouse IgM, IgG2a and IgG2b isotypes are strong activators in contrast to human IgG2, IgG4, IgA and mouse IgG1); (2) Ca2+ depletion, heat treatment (56 degrees C for 45 min), incubation with 0.5 M KSCN or heat-aggregated immunoglobulins (aggIgG) abrogated serum activity; (3) complement deficient sera (C1q def', C2 def', C6 def' human sera; C2 def', C4 def' guinea pig sera) showed impaired deposition of the complement components that follow the missing component in the cascade of activation. In a clinical study sera from patients with systemic lupus erythematosus (SLE) were investigated in order to measure the effect of hypocomplementemia due to complement consumption. The results obtained suggest that this new and simple assay is well suited for (1) the detection of various inherited complement deficiencies, (2) the semiquantitative evaluation of sera with decreased complement levels, (3) a more detailed study of complement components bound to a solid phase.

Adsorption↗
PubMed2000

Complement activation products in the urine from proteinuric patients.

The presence of plasma proteins in the tubular lumen has variety of adverse effects on the tubular cells. Among various plasma proteins filtered through glomerular barrier, complement has been proven as the possible candidate inducing tubulointerstitial injury. To study the role of intratubular complement activation in proteinuric patients, complement activation products (CAP) at C3 level (iC3b and Bb) and C9 level (membrane attack complex) were measured in both plasma and urine of patients with minimal change nephrotic syndrome (MCNS), focal glomerular sclerosis, IgA nephropathy, membranous nephropathy, and diabetic nephropathy. For evaluation of the effect of metabolic acidosis on the intratubular complement activation, urinary CAP were measured before and after sodium bicarbonate administration in patients with renal insufficiency. The following results were obtained: (1) Patients with focal glomerular sclerosis and diabetic nephropathy showed the highest level of urinary CAP excretion rate (unit/creatinine), while MCNS revealed no increase. (2) Patients with membranous nephropathy showed a unique finding, i.e., isolated increase of membrane attack complex excretion. (3) There was no significant correlation between urine and plasma levels of CAP. (4) Except for MCNS patients, the urinary excretion rate of CAP significantly increased when the level of proteinuria exceeded the nephrotic range, and it was significantly correlated with the serum creatinine level. (5) Urinary CAP excretion rate significantly decreased 2 wk after sodium bicarbonate administration without affecting the level of proteinuria or plasma CAP. These results suggest that the degree of intratubular complement activation correlates with the level of proteinuria, type of glomerular disease, impairment of renal function, and metabolic acidosis.

Adolescent↗
PubMed2006

Complement component C3 transcription in Atlantic halibut (Hippoglossus hippoglossus L.) larvae.

The complement systems of fish are well developed and play an important role in the innate immune response. Complement C3 is the central protein of all three activation pathways and is the major opsonin of the complement system and essential for the generation of the membrane attack complex. A 1548 bp part of complement component C3 was isolated from a halibut liver cDNA library by immunoscreening. The deduced amino acid sequence showed that this part of halibut C3 contained key amino acids for factor H, I and properdin binding as well as two N-glycosylation sites. Digoxigenine labelled mRNA probes were synthesised and the transcription of C3 was monitored in three larval stages at 206, 430 and 1000 degrees d (30, 50 and 99 days post hatching), by in situ hybridisation. C3 mRNA was detected in muscle, liver, brain, chondrocytes, spinal cord, eye, intestines, oesophagus and kidney. These findings are in accordance with a former immunohistochemical study on halibut C3 protein ontogeny, indicating that C3 is indeed locally expressed in many organs from the youngest stages on. Complement may thus be linked to the formation and generation of different organs during development and play an important role in the early immune response of halibut larvae.

Amino Acid Sequence↗
PubMed1996

Characterization of the human C6 promoter: requirement of the CCAAT enhancer binding protein binding site for C6 gene promoter activity.

The sixth complement component (C6) is a late-acting complement protein that participates in the assembly of the membrane attack complex. C6 and most of the complement proteins are mainly synthesized in the liver. However, the human hepatoma-derived cell line Hep-G2, which produces the majority of complement proteins, synthesizes traces of C6. Here, we have isolated and characterized the human C6 promoter. Approximately 1 kb of C6 upstream sequence is shown to be sufficient to achieve tissue-specific expression of a luciferase reporter gene in two hepatic (Hep-G2 and Hep-3B) and two extrahepatic cell lines (fibroblast M1 and HeLa) in a manner similar to endogenous C6. There are wide differences in C6 mRNA expression among the four cell lines, whereas Hep-3B expresses high levels of C6, Hep-G2 and M1 poorly synthesize C6, and HeLa completely lacks C6 expression. Deletional and mutational analysis demonstrates that a C/EBP (CCAAT/enhancer binding protein) site located at -67 is required for C6 expression in Hep-3B cells, but it has little effect in M1 and Hep-G2 cells. Electrophoretic mobility shift assays show that this sequence binds to a C/EBP alpha using Hep-3B nuclear extract, but a negligible activity is detected using a Hep-G2 extract. To further investigate whether C/EBP alpha is the limiting factor for C6 expression, we have transfected a C/EBP alpha expression vector into Hep-G2 and Ml cells. C/EBP alpha expression vector dramatically trans-activates the luciferase reporter gene controlled by the C6 promoter, and it partially restores C6 mRNA expression in Hep-G2 cells.

Animals↗
PubMed2005

Insights into the human CD59 complement binding interface toward engineering new therapeutics.

CD59 is a 77-amino acid membrane glycoprotein that plays an important role in regulating the terminal pathway of complement by inhibiting formation of the cytolytic membrane attack complex (MAC or C5b-9). The MAC is formed by the self assembly of C5b, C6, C7, C8, and multiple C9 molecules, with CD59 functioning by binding C5b-8 and C5b-9 in the assembling complex. We performed a scanning alanine mutagenesis screen of residues 16-57, a region previously identified to contain the C8/C9 binding interface. We have also created an improved NMR model from previously published data for structural understanding of CD59. Based on the scanning mutagenesis data, refined models, and additional site-specific mutations, we identified a binding interface that is much broader than previously thought. In addition to identifying substitutions that decreased CD59 activity, a surprising number of substitutions significantly enhanced CD59 activity. Because CD59 has significant therapeutic potential for the treatment of various inflammatory conditions, we investigated further the ability to enhance CD59 activity by additional mutagenesis studies. Based on the enhanced activity of membrane-bound mutant CD59 molecules, clinically relevant soluble mutant CD59-based proteins were prepared and shown to have up to a 3-fold increase in complement inhibitory activity.

Alanine↗
PubMed2000

Complement activation in heart diseases. Role of oxidants.

Increasing evidence demonstrated that atherosclerosis is an immunologically mediated disease. Myocardial ischemia/reperfusion injury is accompanied by an inflammatory response contributing to reversible and irreversible changes in tissue viability and organ function. Three major components are recognized as the major contributing factors in reperfusion injury. These are: (1) molecular oxygen; (2) cellular blood elements (especially the neutrophils); and (3) components of the activated complement system. The latter two often act in concert. Endothelial and leukocyte responses are involved in tissue injury, orchestrated primarily by the complement cascade. Anaphylatoxins and assembly of the membrane attack complex contribute directly and indirectly to further tissue damage. Tissue damage mediated by neutrophils can be initiated by complement fragments, notably C5a, which are potent stimulators of neutrophil superoxide production and adherence to coronary artery endothelium. The complement cascade, particularly the alternative pathway, is activated during myocardial ischemia/reperfusion. Complement fragments such as the anaphylatoxins C3a and C5a, are produced both locally and systematically, and the membrane attack complex is deposited on cell membranes and subsequent release of mediators such as histamine and platelet activating factor (PAF), thereby causing an increase in vascular permeability with concomitant manifestation of cellular edema. Complement increases the expression of CD18 on the neutrophils and increases P-selectin expression on the surface of the endothelium. Mitochondria may be a source of molecules that activate complements during ischemia/reperfusion injury to myocardium, providing therewith a stimulus for infiltration of polymorphonuclear leukocytes. Tissue salvage can be achieved by depletion of complement components, thus making evident a contributory role for the complement cascade in ischemia/reperfusion injury. The complexities of the complement cascade provide numerous sites as potential targets for therapeutic interventions designed to modulate the complement response to injury. The latter is exemplified by the ability of soluble form of complement receptor 1 (sCR1) to decrease infarct size in in vitro models of ischemia/reperfusion injury. The mechanism(s) that initiates complement activation is not clearly known, although loss of CD59 (protectin) from cells compromised by ischemia/reperfusion may contribute to direct damage of the coronary vascular bed by the terminal complement complex. Therapeutic approaches to ischemia/reperfusion injury in general, and especially those involving complements, are at the very beginning and their potential benefits have still to be adequately evaluated. It may be noted that complement activation has both positive and negative effects and, therefore, might be modulated rather than abruptly blunted.

Animals↗
PubMed1996

Complement-induced release of monocyte chemotactic protein-1 from human smooth muscle cells. A possible initiating event in atherosclerotic lesion formation.

Increasing evidence suggests that complement activation might represent an important mechanism in early atherogenesis. Thus, complement components, in particular the membrane attack complex (MAC) C5b-9(m), have been isolated from human atherosclerotic lesions. Furthermore, complement activation is known to occur in atherosclerotic lesions induced in experimental animals, and the severity of cholesterol-induced plaques is markedly reduced in complement-deficient animals. During atherogenesis monocytes are recruited into the arterial wall, and a potent chemoattractant for monocytes, monocyte chemotactic protein-1 (MCP-1), is expressed by vascular smooth muscle cells (SMCs). We hypothesized that generation of MACs on SMCs during the activation of complement might lead to the release of MCP-1 and hence to monocyte recruitment. In this study, MACs were generated on human SMCs in vitro by sequential addition of the purified complement components C5b6, C7, C8, and C9. This supernatant of the culture was chemotactic for freshly isolated peripheral blood monocytes in a modified Boyden chamber. The chemotactic activity of the supernatant was abolished by anti-MCP-1 blocking antibodies but not by an isotype-matched antibody against an irrelevant antigen. The release of chemotactic activity was dependent on the dose of MAC formed on SMCs and was demonstrated within 10 minutes of exposure of the cells. The data support the hypothesis that complement-mediated release of MCP-1 from SMCs might be important in the recruitment of monocytes into the developing atherosclerotic lesion and could be an important initiating event in atherogenesis.

Arteriosclerosis↗
PubMed1992

Effects of complement activation in the isolated heart. Role of the terminal complement components.

The mechanisms of the complement-mediated myocardial injury associated with ischemia and reperfusion have not been elucidated fully. Complement activation may directly mediate injury through actions of the anaphylatoxins C3a and C5a or generation of the membrane attack complex C5b-9. A model was developed to examine the direct effects of complement activation on heart function, assess myocardial tissue damage, and determine which complement components mediate tissue injury. Isolated rabbit hearts were perfused with Krebs-Henseleit buffer by using a modified Langendorff apparatus. Human plasma was added to the perfusate as a source of complement. Rabbit tissue activates human complement. Treatment with 6% normal plasma resulted in complement activation as assessed by the generation of Bb, C3a, C5a, and SC5b-9. Functional changes in cardiac performance became apparent 7-15 minutes after plasma addition and developed fully over the next 20-30 minutes. The effects were dependent on the complement titer and included 1) an increase in the end-diastolic pressure, 2) a decrease in the developed pressure, 3) an increase in the coronary perfusion pressure, and 4) an increase in lymphatic fluid formation. These effects were not elicited when an inhibitor of complement activation (FUT-175) was present or when heat-inactivated plasma was used. The effects of complement activation on myocardial function could not be reproduced by treatment with recombinant human C5a, zymosan-activated plasma, or plasma selectively depleted of C8. Myocardial tissue accumulated sodium and calcium and lost potassium as a result of complement activation. Activation caused the release of creatine kinase from myocytes and an increase in the radiolabeled albumin space of the hearts. The data demonstrate that complement activation caused decrements in myocardial function and increased the coronary perfusion pressure and lymphatic fluid flow rate. The effects were not mediated by the anaphylatoxins but were dependent on the distal complement component C8, suggesting that C5b-9 was responsible for the physiological changes. Complement activation directly mediated tissue injury in a manner consistent with plasmalemmal disruption as a result of C5b-9 formation. The data suggest that the C5b-9 complex, which is known to form under conditions of ischemia, may contribute directly to myocardial cell injury.

Animals↗
PubMedDate not supplied

Monoclonal antibodies demonstrate protection of polymorphonuclear leukocytes against complement attack.

Studies on erythrocytes have shown that the formation of the membrane attack complex on a cell surface inevitably results in lysis. However, it is known that nucleated cells are much more difficult to kill with complement, although the molecular basis of this resistance has never been established. We have shown that a very early intracellular event, occurring within seconds of formation of the attack complex in the membrane, is a rise in cytoplasmic Ca2+, which can activate cell responses without cell death 5,6. Here we report the use of a monoclonal antibody to the terminal complement component C9, quantified by 125I and visualized by fluorescein, to demonstrate a protection mechanism in polymorphonuclear leukocytes (PMNs) attacked by complement, involving removal of the attack complex by vesiculation. Concomitantly, there is a Ca2+-dependent activation of reactive oxygen metabolite production without cell lysis. These findings have important implications in the evolutionary and pathological significance of the terminal components of the complement pathway.

Animals↗